SM2.1 | Fibre-optic point and distributed sensing: theory, instrumentation, observations and modelling
EDI
Fibre-optic point and distributed sensing: theory, instrumentation, observations and modelling
Co-organized by ERE1/OS4/TS2
Convener: Philippe Jousset | Co-conveners: Gilda Currenti, Zack Spica, Stefanie Donner, Shane Murphy, Yara Rossi, Marc-Andre Gutscher
Orals
| Tue, 25 Apr, 08:30–12:30 (CEST), 14:00–15:45 (CEST)
 
Room D3
Posters on site
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
Hall X2
Orals |
Tue, 08:30
Tue, 16:15
Fibre optic based techniques allow probing highly precise direct point and distributed sensing of the full ground motion wave-field including translation, rotation and strain, and environmental parameters such as temperature and even chemicals at a scale and to an extent previously unattainable with conventional geophysical methods. Considerable improvements in optical and atom interferometry enable new concepts for inertial rotation, translational displacement and acceleration sensing. Laser reflectometry using both fit-to-purpose and commercial fibre optic cables have successfully detected a variety of signals including microseism, local and teleseismic earthquakes, volcanic events, ocean dynamics, etc. Significant breakthrough in the use of fibre optic sensing techniques came from the new ability to interrogate telecommunication cables at high precision both on land and at sea, as well as in boreholes and at the surface. Applications of the resulting new type of data are manifold: they include seismic source and wave-field characterization with single point observations in harsh environments like active volcanoes, the ocean bottom, the correction of tilt effects, e.g. for high performance seismic isolation facilities, as well as seismic ambient noise interferometry and seismic building monitoring.

We welcome contributions on developments in instrumental and theoretical advances, applications and processing with fibre optic point and/or distributed multi-sensing techniques, light polarization and transmission analyses, using standard telecommunication and/or engineered fibre cables. We seek studies on theoretical, observation and advanced processing in fields, including seismology, volcanology, glaciology, geodesy, geophysics, natural hazards, oceanography, urban environment, geothermal applications, laboratory studies, large-scale field tests, planetary exploration, gravitational wave detection, fundamental physics. We encourage contributions on data analysis techniques, machine learning, data management, instrumental performance and comparison as well as new experimental, field, laboratory, modeling studies in fibre optic sensing studies.

We are happy to announce Prof. Martin Landrø, Prof. Kuo-Fong Ma and Dr. David Sollberger as invited speakers!

Orals: Tue, 25 Apr | Room D3

Chairpersons: Stefanie Donner, Philippe Jousset
Fibres, rotation, 6C and DAS
08:30–08:50
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EGU23-9312
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solicited
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On-site presentation
David Sollberger, Nicholas Bradley, Pascal Edme, and Johan O. A. Robertsson

We present a technique to automatically classify the wave type of seismic phases that are recorded on a single six-component recording station (measuring both three components of translational and rotational ground motion) at the earth's surface. We make use of the fact that each wave type leaves a unique 'fingerprint' in the six-component motion of the sensor. This fingerprint can be extracted by performing an eigenanalysis of the data covariance matrix, similar to conventional three-component polarization analysis. To assign a wave type to the fingerprint extracted from the data, we compare it to analytically derived six-component polarization models that are valid for pure-state plane wave arrivals. For efficient classification, we make use of the supervised machine learning method of support vector machines that is trained using data-independent, analytically-derived six-component polarization models. This enables the rapid classification of seismic phases in a fully automated fashion, even for large data volumes, such as encountered in land-seismic exploration or ambient noise seismology. Once the wave-type is known, additional wave parameters (velocity, directionality, and ellipticity) can be directly extracted from the six-component polarization states without the need to resort to expensive optimization algorithms.

We illustrate the benefits of our approach on various real and synthetic data examples for applications such as automated phase picking, aliased ground-roll suppression in land-seismic exploration, and the rapid close-to real time extraction of surface wave dispersion curves from single-station recordings of ambient noise. Additionally, we argue that an initial step of wave type classification is necessary in order to successfully apply the common technique of extracting phase velocities from combined measurements of rotational and translational motion.

How to cite: Sollberger, D., Bradley, N., Edme, P., and Robertsson, J. O. A.: Six-component wave type fingerprinting and filtering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9312, https://doi.org/10.5194/egusphere-egu23-9312, 2023.

08:50–09:00
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EGU23-1069
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ECS
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On-site presentation
Le Tang, Heiner Igel, and Jean-Paul Montagner

A new approach is proposed for measuring the local dispersion curves of surface waves in weakly anisotropic media using a single, multi-component station, which consists of translation and rotation or strain. We directly extract the local azimuth-dependent phase velocity of the Rayleigh wave from the 6C amplitude ratio using seismic arrays deployed in Southern California. The extracted dispersion curves match well with the theoretical 2φ azimuthal anisotropy term. And the estimated fast wave direction is also consistent well with results calculated from SKS and beamforming methods which demonstrates the feasibility of studying local seismic anisotropy directly from 6C amplitude observations.

How to cite: Tang, L., Igel, H., and Montagner, J.-P.: Seismic Anisotropy from 6C Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1069, https://doi.org/10.5194/egusphere-egu23-1069, 2023.

09:00–09:10
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EGU23-8851
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ECS
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On-site presentation
Anjali Dhabu, Felix Bernauer, Chun-Man Liao, Celine Hadziioannou, Heiner Igel, and Ernst Niederleithinger

The increasing evidence of rotational motions due to earthquakes is now motivating civil engineers to investigate the effects of rotational ground motions on structures. With the advancement in instrumentation techniques, rotational sensors have been developed in the past few years, which can measure three components of rotational waves in addition to the translational waves. Conventionally, buildings are designed to withstand horizontal and vertical translational ground motions to minimize the damage to human life and financial losses during an earthquake. Damage to the structure is identified at two levels; (i) structural and (ii) material. The structural damage in reinforced concrete buildings is visible in the form of cracks and spalling concrete, which reduces the overall load-carrying capacity of the building. The damage at the material level is not visible to the human eye. This damage can be identified using coda wave interferometry techniques. In this method, a high cross-correlation between the coda of two waves passing a point on different days of experiment indicates a negligible change in the shear wave velocity of the material. In comparison, a lower cross-correlation signifies considerable change in the material properties.    

In order to understand how rotational motions affect reinforced concrete structures and how these can be simulated, the present work makes a novel attempt to use the newly developed rotation measuring sensors, BlueSeis 3A and IMU50, to understand the damage in a model concrete bridge structure (BLEIB). We employ advanced sensors in addition to conventional broadband and ultrasonic sensors on the 24m long two-span continuous reinforced concrete bridge equipped with various non-destructive sensing techniques and subjected to a variable pre-tension force of up to 450kN and various static loads. As an initial analysis, we first identify the bridge's first three fundamental frequencies and mode shapes from both recorded translational and rotational data. The analysis shows that the same fundamental frequencies are obtained from the recorded translational and rotational data. However, we expect to see a difference in the mode shapes. Theoretically, rotations are maximum at the bridge support and minimum at the centre of the bridge span. This behaviour is the reverse of what we observe from translational motions, where maximum translations are observed at the centre of the span while minimum at the supports. As the study plans to simulate rotational motions for reinforced concrete structures, a finite element model of the prototype bridge is also developed, and the fundamental frequencies and mode shapes of the model are validated with those obtained from the recorded data. This work shall be extended to applying coda wave interferometry to the rotational data recorded on the bridge to understanding the change observed in material properties when the bridge is subjected to active and passive forces.

How to cite: Dhabu, A., Bernauer, F., Liao, C.-M., Hadziioannou, C., Igel, H., and Niederleithinger, E.: Using Rotational Motions to understand material damage in Civil Engineering structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8851, https://doi.org/10.5194/egusphere-egu23-8851, 2023.

09:10–09:20
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EGU23-13600
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On-site presentation
Frédéric Guattari, Guillaume Lenogue, Kevin Gautier, Arnaud Frenois, and André Couderette

First announced at EGU2021, and said to be “released soon”, the 1C rotation seismometer which complements the blueSeis product line on the high performance segment, will be finally disclosed at EGU2023.

2019 and 2020 results have been shared about large mockup of giant Fiber-Optic Gyroscope from iXblue, having diameter as large as 1.2 meters, and the development road to reach an industrial product had been drawn. But several critical additional issues raised on the track.

Keeping in mind all the requirement of the instrument, the need for a transportable, and easily deployable instrument, the calibration capability, the possibility to push the performance pilling up the sensors, and the need for an optional orthogonal structure, we finally come to an instrumental solution with high versatility at expected performances.

The full development story will be shared, and the tests results of first production units of blueSeis-1C will be disclosed. Explanation about the various way to use it will be offered too.

Perspectives and applications using this long-awaited sensor will be presented, from ocean-bottom system tilt denoising to improved inversion of the seismic source.

How to cite: Guattari, F., Lenogue, G., Gautier, K., Frenois, A., and Couderette, A.: Long-awaited and delayed Transportable Highest grade of Fiber Optic Gyroscope for Seismology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13600, https://doi.org/10.5194/egusphere-egu23-13600, 2023.

09:20–09:30
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EGU23-3061
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On-site presentation
Simon Pevec and Denis Donlagic

A work describes a deeply etched, long active length, high sensitivity short Fabry-Perot cavity nano-strain resolution sensor. The presented sensors exhibit high spectral sensitivity, low intrinsic temperature sensitivity which is for about 40 times lower than in case of FBG, small size and mounting comparable to conventional Fiber Bragg gratings. The sensor high potential is not only high sensitivity and low temperature intrinsic sensitivity, but also in short cavity length and its tunability, which can be simply accomplished in one production step. This brings versatility in interrogation with different general purpose and cost-efficient VIS-NIR widely available linear detector array-based spectrometers, while still providing strain sensing resolution within the range of few 10 nε. A strain resolution of 20 to 70 nε was demonstrated when using a cost-efficient VIS spectrometer. Furthermore, the sensor structure can be combined with multimode telecom lead-in fibers and low-cost broadband LEDs intended for automotive/lightning applications, which allow production of cost efficient solutions.

How to cite: Pevec, S. and Donlagic, D.: Nano-strain resolution fiber-optic Fabry-Perot sensors based measuring systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3061, https://doi.org/10.5194/egusphere-egu23-3061, 2023.

09:30–09:40
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EGU23-6998
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ECS
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Virtual presentation
Emanuele Virgillito, Stefano Straullu, Rudi Bratovich, Fransisco M. Rodriguez, Hasan Awad, Andrea Castoldi, Roberto Proietti, Andrea D'Amico, Francesco Aquilino, Rosanna Pastorelli, and Vittorio Curri

Optical networks for data transmission have become a pervasive infrastructure in the last years in order to cope with the increasing bandwidth request, thus there is a huge potential to be employed as a wide fiber optic sensing network. In the terrestrial scenario such networks are usually arranged on meshed topologies densely covering large areas of hundreths or thousands of kilometers. On the network's nodes, dedicated hardware is used to routed the data traffic between the connections' endpoints. Such nodes are interconnected by optical fiber links of hundreds of kilometers long, repeated every tenths of kilometers using optical amplifiers.

To fulfill the modern traffic requirements, optical networks are evolving towards multi-service autonomous, flexible, software defined entities based on a centralized intelligence orchestrating the networking functions and communicating with the network elements using standardized interfaces. This trend opens the perspective of using the optical network for evironmental sensing, such as earthquake detection or anthropic activities monitoring. 

Indeed, distributed acoustic sensing (DAS) systems based on Rayleigh scattering have demonstrated that optical fibers are excellent sensors of mechanical stress. However, such systems are expensive and pose some limitations on the maximum reach, so they cannot be deployed extensively. In this context, re-using the already deployed optical data infrastructure to support and integrate dedicated system sensing may be highly beneficial. In this work, we propose an optical data network architecture exposing sensing functionalities with minimum or no additional hardware simply by exploiting the pervasiveness of the telecommunication infrastructure and getting data from the physical quantities already monitored for data transmission purposes. Such architecture on a typical terrestrial optical data network is outlined in figure.

Modern coherent transceivers based on digital signal processing already track the evolution of the transmitted optical signal phase and polarization to recover the transmitted data at the receiver side. As those quantities are strongly affected by external strain, they already contain environmental information. Furthermore, some polarization-based processing can be implemented on cheaper non-coherent transceivers available at each amplifier site as data-service channel, providing several sensing sources.

In addition, further optical devices such as add-drop multiplexer or optical amplifiers typically have several other sensors already embedded (power monitors, temperature sensors) or they can be equipped with some others which can provide environmental data from other physical quantities.

The set of all such environmental data streams produced by the network elements constitutes the streaming telemetry fed to a network controller. A post-process agent may be implemented by exploiting the computational power available in typical network elements to perform local data analysis and reduce the amount of data sent to the sensing controller. By cross-processing the data coming from the network elements, a sensing controller is able to detect and localize events making the network act as a smart grid by continuously monitoring large areas and providing early warning signals.

To support our proposal, in this work we show the results of an experimental activity aimed at detecting and localizing anthropic activities in the city of Turin using a deployed fiber ring.

 

How to cite: Virgillito, E., Straullu, S., Bratovich, R., M. Rodriguez, F., Awad, H., Castoldi, A., Proietti, R., D'Amico, A., Aquilino, F., Pastorelli, R., and Curri, V.: Exploiting Terrestrial Meshed Optical Data Networks as Environmental Sensing Smart Grids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6998, https://doi.org/10.5194/egusphere-egu23-6998, 2023.

09:40–09:50
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EGU23-15050
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On-site presentation
Paul-Eric Pottie, Mads Tonnes, Maxime Mazouth-Laurol, Hendrix Montlavan-Leyva, Etienne Cantin, Benjamin Pointard, Hector Alvarez-Martinez, Rodolphe Le Targat, Olivier Lopez, Christian Chardonnet, and Anne Amy-Klein

Optical fiber networks are being implemented in several countries aiming at dissemination of ultra-stable time and frequency references. This enables the comparison of optical clocks, which is a key part of the roadmap towards the future redefinition of the International System of Units (SI) second. Furthermore, this enables uses in chronometric geodesy, where the sensitivity of the optical clocks to the gravitation field enables measurements of height differences as low as 1 cm [1].
The frequency signals in the optical fibers are sensitive to acoustic vibrations which are present in the ground, which is the main source of noise to the disseminated signals.
In recent years, this has enabled studies in the use of optical fiber links for the detection of earthquakes [2]. In such an approach, the measurement is the integrated noise over the fiber path. This typically allows for one to several orders of magnitudes longer range as compare to DAS techniques, but with the loss of localization along the fiber. Such integrated approaches include measurements of the total polarization change of the light along the fiber [3], or the total phase change of a coherent ultra-stable laser signal, potentially including distributed sensing techniques in submarine fibers [2,4].

Here, we will present the first quantitative studies on the use of coherent optical fiber links for seismic detection. Using a the fiber network REFIMEVE in France (see Fig. 1), we present studies on the sensitivity of coherent optical fiber links to seismic events. We describe the dependence of the sensitivity to a number of parameters like incident angle, magnitude and distance, and compare the sensitivity of a fiber link with that of conventional seismometers. We show, for a first time to our knowledge, the detection of seismic waves by a coherent optical fiber network, and we study the prospects of using such a network for the localization of earthquakes. Lastly, we discuss the principles and results of a machine learning algorithm, which enables automatic detection of earthquakes in a coherent optical fiber link.

Bibliography:
1. M. Takamoto et al., Test of general relativity by a pair of transportable optical lattice clocks, Nat. Phot., 14 (7), 411–415. doi:30210.1038/s41566-020-0619-8
2. G. Marra et al. , Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458. doi: 10.1126/science.aat4458279
3. J.C. Castellanos et al. ,Optical polarization-based sensing and localization of submarine earthquakes. In Optical fiber communication conference (OFC) 2022, doi:26210.1364/OFC.2022.M1H.4
4. G. Marra et al., Optical interferometry–based array of seafloor environmental sensors using a transoceanic submarine cable. Science, doi: 10.1126/science.abo193

Figure 1 : Map of the French REFIMEVE fiber network, shown in red lines. Dotted lines indicates indicate the full scale of the planned network, and continuous red lines indicate links used in these studies. Blue lines indicates the linear approximations of the links. All seismometers of the RESIF network is shown by small green triangles, and seismometers used in theses studies are shown by larger, turquoise triangles.

How to cite: Pottie, P.-E., Tonnes, M., Mazouth-Laurol, M., Montlavan-Leyva, H., Cantin, E., Pointard, B., Alvarez-Martinez, H., Le Targat, R., Lopez, O., Chardonnet, C., and Amy-Klein, A.: Low-frequency seismic wave sensing using coherent optical fiber networks for metrology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15050, https://doi.org/10.5194/egusphere-egu23-15050, 2023.

09:50–10:00
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EGU23-4769
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ECS
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Virtual presentation
Xiang Wang, Honghui Wang, Yuhang Wang, Shangkun Zeng, and Yiru Wang

In recent years, fiber-optic distributed acoustic sensing (DAS) has been gradually applied to seismology because of its long-distance and dense observation capability. It is a great challenge to effectively process the massive seismic data recorded by DAS. At present, the seismic data processing methods based on deep learning have achieved great success, especially in the tasks of seismic detection and arrival-time picking. However, due to the differences between DAS and geophone, such as sensing principles, spatial and temporal sampling rates, and noise intensity. The seismic arrival time picking model based on deep learning, which is trained by geophone seismic data with low spatial and temporal sampling rates and low noise intensity, severely degrades in performance on DAS seismic data with high spatial and temporal sampling rates and high noise intensity. In addition, a new seismic arrival time picking model is trained by fully supervised learning, which usually requires a large number of seismic data with accurate labels. However, the huge cost of manual picking and the lack of effective automatic picking models make it very difficult to build large-scale DAS seismic data sets with accurate labels. Therefore, it is very difficult to build an arrival time picking model based on fully supervised learning for DAS seismic data.

In this study, we propose a DAS seismic arrival time picking method based on fractional lower order statistics. Based on the difference of probability density function between noise and seismic signal, the proposed method uses alpha-stable distribution modeling noise (generally follow a Gaussian distribution) and seismic signal (generally follow a non-Gaussian distribution), and uses fractional lower order statistics under the assumption of alpha-stable distribution as the characteristic function to pick the arrival time.

Synthetic and actual DAS data tests show that the proposed method has better performance and robustness to random noise than other methods based on characteristic functions, such as STA/LTA, AR-AIC and kurtosis. Since the actual DAS seismic data has no ground truth of arrival time, we have further the performance of the proposed method on the geophone seismic data set. The proposed method provides better results on geophone seismic data and the data after up-sampling them to the typical time sampling rate of DAS.

How to cite: Wang, X., Wang, H., Wang, Y., Zeng, S., and Wang, Y.: Arrival Picking for Distributed Acoustic Sensing seismic based on fractional lower order statistics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4769, https://doi.org/10.5194/egusphere-egu23-4769, 2023.

10:00–10:10
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EGU23-5955
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ECS
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Virtual presentation
Jianhui Sun, Yuyao Wang, Jialei Zhang, Anchi Wan, Shibo Zhang, Zhenyu Ye, Fulie Liu, Gulan Zhang, and Zinan Wang

Seismic monitoring requires high temporal-spatial resolution and low deployment cost. Distributed acoustic sensing (DAS), as an emerging sensing technology for recording seismic data in recent years, can leverage communication cables for seismic monitoring, providing strong support for more intensive and real-time observation of geological activity. However, the traditional DAS phase unwrapping algorithms (PUAs) derived from Itoh requires the phase difference of adjacent pixels to be less than π, and thus make mistakes in the case of severe noise or large disturbance. In this paper, to the best of our knowledge, two-dimensional (2D) PUA is used to obtain seismograms in DAS for the first time. Satisfactory phase unwrapping is achieved by the 2D PUA method based on the transport of intensity equation (TIE), due to its robustness and noise immunity. Dynamic strain measurements in 80 m straight fiber-optic cable using homemade high-performance DAS, combined with TIE-based 2D PUA produce high-quality seismograms. Time Difference of Arrival (TDOA) Algorithm is applied based on the sensing signal of reliable channels in the seismograms, realizing the high-precision localization of the source. 2D PUAs apply to all phase-demodulation-based sensing techniques and are suitable for recovering spatially correlated objects such as seismic waves, thus having great potential in the field of seismic monitoring.

How to cite: Sun, J., Wang, Y., Zhang, J., Wan, A., Zhang, S., Ye, Z., Liu, F., Zhang, G., and Wang, Z.: Two-dimensional phase unwrapping algorithm aided high-precision source positioning with DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5955, https://doi.org/10.5194/egusphere-egu23-5955, 2023.

10:10–10:15
Ocean, Moon, Earthquakes and Volcanoes
Coffee break
Chairpersons: Gilda Currenti, Marc-Andre Gutscher
10:45–11:05
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EGU23-2091
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solicited
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Highlight
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On-site presentation
Martin Landrø

We have used two seabed fibre optic cables connecting Ny Ålesund and Longyearbyen at Svalbard, North of Norway, to track several whales for several weeks. Exploiting that we have access to two fibres we demonstrate that it is possible to track several whales in a fairly large region. It is possible to create sound records of whales that can be used for identification and discrimination between various species. The localization method has also been tested by using a small air gun to confirm the localization method used for whales. Examples of earthquake recordings, ship traffic monitoring and distant storms will be shown.

Based on the rapid and promising developments within DAS technology, there is a growing interest for using fibre optic cables at the moon. Some challenges and possibilities related to Lunar DAS applications will be discussed.

How to cite: Landrø, M.: Using DAS-fibres at ocean floor and lunar surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2091, https://doi.org/10.5194/egusphere-egu23-2091, 2023.

11:05–11:15
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EGU23-16640
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ECS
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On-site presentation
Gauthier Guerin and Diane Rivet

In this study we use distributed acoustic sensing (DAS) on a 41-km-long submarine optical fibre (OF) cable located offshore Toulon, France. We record both the amplitude and frequency of seafloor strains induced by ocean surface gravity waves, as well as secondary microseisms. Combining the analysis of the two types of waves, we identify and localize local sources of secondary microseisms that manifest as Scholte waves generated by the reflection of oceanic gravity waves on the coastline. During the experiment, these local sources represent the most energetic contribution to the seismic noise recorded along the OF and by an onshore broad-band station located near the DAS interrogator. As a result, the characteristics of this noise are closely related to local wave conditions. One major challenge in performing seismic imaging using ambient seismic noise correlations using DAS data is that we cannot solve for the true seismic velocity because the noise wave field is dominated by local sources. To address this, we measure the incident angle of the dominant local noise sources, correct the apparent velocity using the incident angle retrieve from beamforming analysis and generate a 2D model. We then quantify the errors that arise from picking the dispersion curves of the most energetic velocities without correcting from the incident angle. Our results show that there are significant differences in velocities, with differences reaching up to several hundred meters per second. This highlights the importance of correcting these velocities before generating a tomography. Finally we evaluate an alternative strategy for a linear DAS fiber that cannot be use to localized the dominant noise source. We measure the dispersion curve of the slowest Scholte waves recorded and compare it to the corrected dispersion curves of the dominant source. Although this strategy suffers from limitation, it minimizes the error in the velocity model.

How to cite: Guerin, G. and Rivet, D.: Using localized microseismic noise sources to perform high-resolution seismic Imaging of seafloor using Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16640, https://doi.org/10.5194/egusphere-egu23-16640, 2023.

11:15–11:25
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EGU23-16307
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On-site presentation
Nasim Karamzadeh Toularoud, Ya-Jian Gao, Jérôme Azzola, Thomas Forbriger, Rudolf Widmer-Schnidrig, Emmanuel Gaucher, and Andreas Rietbrock

The application of distributed acoustic sensing (DAS) in seismology is rapidly expanding due to its ability to perform a large number of high-density measurements, i.e., distributed sensing, without using many point sensors, which is cost-effective. DAS application includes vertical seismic profiling, microseismic measurements, and hydraulic fracturing monitoring and mainly focuses on the event detection capability of  DAS data. 

Febus optics DAS interrogator (A1-R) is continuously running at German Black Forest Observatory (BFO) since May 2021, recording RAW data (selectively stored) or strain-rate data (continuously stored). Our study is in the experimental phase and focuses on testing basic concepts of DAS data, i.e., the effect of gauge-length on the amplitude of measurement and comparing the amplitude of DAS with other seismological sensors such as strain-meter array and a STS2 broadband sensor as well as synthetic simulations. Such comparison is performed using background noise characteristics (power spectral density) and examples of local and regional events that are detectable at the BFO site. 

In this study, we show examples of strain rate measurements related to local earthquakes recorded by horizontal fiber optic cables, employing two different DAS interrogators, cable types and coupling of the cables to the ground. We compared simultaneous recordings using Febus A1 DAS interrogator and OptoDAS by Febus optic and Alcatel Submarine Networks (ASN), respectively, and, concluded about the frequency and gauge-length dependent sensitivity of recordings in two cases. In addition, we compare the amplitude of DAS recordings, for example of local earthquakes, with the synthetic strain simulated  at lower frequency bands using the spectral-element method (Salvus) based on 3D media and analytic approach (Qseis) for 1D model. 

 

How to cite: Karamzadeh Toularoud, N., Gao, Y.-J., Azzola, J., Forbriger, T., Widmer-Schnidrig, R., Gaucher, E., and Rietbrock, A.: Local earthquake recordings using Distributed Acoustic Sensing (DAS) at BFO, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16307, https://doi.org/10.5194/egusphere-egu23-16307, 2023.

11:25–11:35
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EGU23-9314
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ECS
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On-site presentation
Verónica Rodríguez Tribaldos, Chet Hopp, Florian Soom, Yves Guglielmi, Paul Cook, Tanner Shadoan, Jonathan Ajo-Franklin, Michelle Robertson, Todd Wood, and Jens Birkholzer

Identifying and monitoring the reactivation of faults and opening of fractures affecting low permeability, sealing formations in natural underground storage complexes such as Carbon Capture and Storage projects and Nuclear Waste repositories is essential to ensure storage integrity and containment. Although passive seismic monitoring can be effective for detecting induced failure, stress accumulation and fault reactivation can occur aseismically in clay-rich formations, preventing early failure to be recognized. Here, we investigate the potential of applying strain monitoring with fiber-optics sensing technologies to assess in-situ changing stress conditions at high spatial and temporal resolution.

We present results of fiber-optic sensing monitoring during the FS-B experiment, a controlled activation of a fault zone affecting the Opalinus Clay Formation in the Mont Terri underground Laboratory (Switzerland). Six constant flowrate water injections induced the hydraulic opening of the fault. A hydraulic connection between the injector and a monitoring borehole occurred, developing a flow path sub-parallel to the fault strike. A 2 km long fiber-optic cable looped through 10 monitoring boreholes surrounding and crossing the fault zone was used for distributed acoustic and strain sensing (DAS and DSS) before, during and after injection. Continuous low-frequency (< 1 Hz) DAS data reveals mechanical strain associated with fault reactivation. Increasing extensional strain is recorded near the point of injection and near the newly formed hydraulic flow path, reaching a value of ~150 μɛ. Post-activation residual strain of ~60 μɛ suggests irreversible fault zone deformation. Smaller strain changes are recorded above and below the high pressure flow path, suggesting a mechanically disturbed zone larger than the leakage zone. Low-frequency DAS data are consistent with co-located DSS strain data, local, 3D displacement measurements of fault movements and P-wave velocity anomalies derived from Continuous Active Source Seismic Monitoring (CASSM). Our results are promising and demonstrate the potential of fiber-optic sensing as a powerful tool for monitoring spatio-temporal evolution of fault reactivation processes and leakage in clay formations induced by fluid pressurization.

How to cite: Rodríguez Tribaldos, V., Hopp, C., Soom, F., Guglielmi, Y., Cook, P., Shadoan, T., Ajo-Franklin, J., Robertson, M., Wood, T., and Birkholzer, J.: Using Distributed Fiber-optic Sensing for Tracking Caprock Fault Activation Processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9314, https://doi.org/10.5194/egusphere-egu23-9314, 2023.

11:35–11:45
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EGU23-13803
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ECS
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Virtual presentation
Itzhak Lior, Diane Rivet, Jean-Paul Ampuero, Anthony Sladen, Sergio Barrientos, Rodrigo Sánchez-Olavarría, German Alberto Villarroel Opazo, and Jose Antonio Bustamante Prado

Earthquake Early Warning (EEW) systems provide seconds to tens of seconds of warning time before potentially-damaging ground motions are felt. For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismological stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work, we harness available optical fiber infrastructure for EEW using the novel approach of Distributed Acoustic Sensing (DAS). DAS strain measurements of earthquakes from different regions are converted to ground motions using a real-time slant-stack approach, magnitudes are estimated using a theoretical earthquake source model, and ground shaking intensities are predicted via ground motion prediction equations. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes.

How to cite: Lior, I., Rivet, D., Ampuero, J.-P., Sladen, A., Barrientos, S., Sánchez-Olavarría, R., Villarroel Opazo, G. A., and Bustamante Prado, J. A.: Magnitude Estimation and Ground Motion Prediction to Harness Fiber Optic Distributed Acoustic Sensing for Earthquake Early Warning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13803, https://doi.org/10.5194/egusphere-egu23-13803, 2023.

11:45–11:55
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EGU23-3955
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ECS
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On-site presentation
Francesco Biagioli, Jean-Philippe Métaxian, Eléonore Stutzmann, Maurizio Ripepe, Alister Trabattoni, Pascal Bernard, Roberto Longo, Gianluca Diana, Lorenzo Innocenti, Yann Capdeville, Marie-Paul Bouin, and Giorgio Lacanna

Volcano seismology is essential for understanding, monitoring, and forecasting eruptive events. The use of distributed acoustic sensing (DAS) technology can be particularly useful for this purpose because of its high temporal and spatial resolution, which may help to overcome the challenges of deploying and maintaining seismic arrays on volcanoes.

Between 2020 and 2022, we installed 4 km of optical fibre on Stromboli volcano, Italy, whose persistent activity is well-suited for investigating the related dynamic strain rate. The cable was buried at a depth of 30 cm and the layout geometry was designed to provide wide coverage while being constrained by natural obstacles and topographical features. Seismometers were also installed along the fibre. DAS data were collected using a Febus A1-R interrogator, and the acquisition period increased from one week in 2020 to over four months in 2022. We recorded volcanic tremor, ordinary explosions (several per hour), two major explosions in 2021 and 2022, and the entire sequence of a pyroclastic flow in 2022. 

DAS and seismic data show good agreement in both time and frequency domains after converting strain rate to velocity and vice versa using different methodologies. Beamforming of DAS data shows a dominant signal in the 3-5 Hz frequency band coming from the active craters. We will also present preliminary results of major explosions and pyroclastic flow. This experiment demonstrates that DAS can be used for monitoring volcanic activity.

How to cite: Biagioli, F., Métaxian, J.-P., Stutzmann, E., Ripepe, M., Trabattoni, A., Bernard, P., Longo, R., Diana, G., Innocenti, L., Capdeville, Y., Bouin, M.-P., and Lacanna, G.: Using Distributed Acoustic Sensing to Monitor and Investigate Eruptive Events at Stromboli Volcano, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3955, https://doi.org/10.5194/egusphere-egu23-3955, 2023.

11:55–12:05
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EGU23-9089
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ECS
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On-site presentation
Julius Grimm, Piero Poli, and Philippe Jousset

Distributed Acoustic Sensing (DAS) has been successfully employed to monitor volcanic seismicity and to infer volcanic subsurface structures. Here, we analyse data recorded in September 2018 at Mount Etna by the 9N seismic network. The multi-instrument network includes a 1.3 km long fibre-optic cable that was buried 2-2.5 km away from the main craters. Additionally, 15 geophones were installed along the trajectory of the DAS cable, allowing for a comparison of strain-rate and ground velocity data.
During the acquisition period, tiny seismic events, likely caused by fluid movement and degassing, are visible with inter-event times in the range of 1 min. Volcanic explosions and volcano-tectonic earthquakes also occur frequently. We detect events over all frequency ranges by calculating the coherence matrix for very short time windows (stacking 15 windows of 5 seconds length). An eigendecomposition of the coherence matrices allows to extract the first eigenvectors, corresponding to the dominant source in the time window. The principal eigenvectors can be clustered to find groups of events with similar source properties. We also use the principal eigenvector of already known events as a matched filter to scan the whole dataset. The results of the DAS cable are compared to the observations of the geophone array. While largely obtaining similar findings, the DAS cable seems to better capture high-frequency features of certain events. We also explore the effects of stacking and downsampling of the DAS data prior to detection, which influences both resolution and computational efficiency of the algorithm.

How to cite: Grimm, J., Poli, P., and Jousset, P.: Detecting seismo-volcanic events based on inter-channel coherency of a DAS cable, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9089, https://doi.org/10.5194/egusphere-egu23-9089, 2023.

12:05–12:15
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EGU23-15265
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ECS
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On-site presentation
Sergio Diaz-Meza, Philippe Jousset, Gilda Currenti, Air David, Andy Clarke, Anna Stork, Athena Chalari, and Charlotte Krawzcyk

Distributed Dynamic Strain Sensing (DDSS), also known as Distributed Acoustic Sensing (DAS), is becoming a popular tool for volcano monitoring. The sensing method relies on sending coherent light pulses into an optical fibre and measuring the phase-shift of Rayleigh back-scattered light due to strain on the fibre. This provides distributed strain rate measurements at high temporal and spatial sampling rates. Standard telecom fibres have been conventionally used for this purpose, however engineered fibres are being developed to enhance the back-scattered light, providing up to 100 times improved sensitivity in contrast to the conventional standard fibre. Despite the technical advantages of engineered fibres, standard fibres already have extensive coverage around the Earth surface, and so there is an interest in using the existing telecommunication infrastructure. In this study we compare stack DDSS data from a fibre loops made of several fibres within the same optical fibre cable, with DDSS data measured on an engineered fibre. We analyse how stacking can improve the signal quality of the recorded DDSS data. In an area located 2.5 km NE from the craters of Mt. Etna, we spliced 9 standard fibres together from a 1.5 km long cable to create a single optical path and interrogated using an iDAS unit. At the same time, we interrogated with a Carina unit a 0.5 km engineered fibre installed parallel to the standard multi-fibre cable. Both fibres were interrogated in a common period of 5 days. We use a spatial cross-correlation function to find the channel equivalences between each fibre and then stack them to evaluate the changes in the DDSS data and compare with the engineered fibre data. Our results show that, despite engineered fibres have lower noise, a stack of 5 fibres can achieve a maximum noise reduction of 20% outside of the optical noise band, in comparison to the engineered fibre. We achieved this noise reduction for our specific configuration, and so we show how the stack improvement is dependent on the type of configuration in terms of fibres stacked and length of the fibres. Our findings motivate the exploitation of multi-fibre cables in existing infrastructures, so-called dark fibres, for monitoring volcano and applications to other environments.

How to cite: Diaz-Meza, S., Jousset, P., Currenti, G., David, A., Clarke, A., Stork, A., Chalari, A., and Krawzcyk, C.: Towards exploiting the advantages of a Standard telecom multi-fibre cable for volcano monitoring: an example from Mt. Etna, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15265, https://doi.org/10.5194/egusphere-egu23-15265, 2023.

12:15–12:25
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EGU23-16459
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ECS
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On-site presentation
Martina Allegra, Gilda Currenti, Flavio Cannavò, Philippe Jousset, Michele Prestifilippo, Rosalba Napoli, Mariangela Sciotto, Giuseppe Di Grazia, Eugenio Privitera, Simone Palazzo, and Charlotte Krawczyk3

Since September 2021, signs of unrest at Vulcano Island have been noticed after four years of quiescence, along with CO2 degassing and the occurrence of long-period and very long-period events. With the intention of improving the monitoring activities, a submarine fiber optic telecommunications cable linking Vulcano Island to Sicily was interrogated from 15 January to 14 February 2022. Of particular interest has been the recording of 1488 events with wide range of waveforms made up of two main frequency bands (from 3 to 5 Hz and from 0.1 to 0.2 Hz).

With the aim of the automatic detection of seismic-volcanic events, different approaches were explored, particularly investigating whether the application of machine learning could provide the same performance as conventional techniques. Unlike many traditional algorithms, deep learning manages to guarantee a generalized approach by automatically and hierarchically extracting the relevant features from the raw data. Due to their spatio-temporal density, the data acquired by the DAS can be assimilated to a sequence of images; this property has been exploited by re-designing deep learning techniques for image processing, specifically employing Convolutional Neural Networks.

The results demonstrate that deep learning not only achives good performance but that it even outperforms classical algorithms. Despite providing a generalized approach, Convolutional Neural Networks have been shown to be more effective than traditional tecniques in expoiting the high spatial and temporal sampling of the acquired data. 

How to cite: Allegra, M., Currenti, G., Cannavò, F., Jousset, P., Prestifilippo, M., Napoli, R., Sciotto, M., Di Grazia, G., Privitera, E., Palazzo, S., and Krawczyk3, C.: Deep learning approach for detecting low frequency events on DAS data at Vulcano Island, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16459, https://doi.org/10.5194/egusphere-egu23-16459, 2023.

12:25–12:30
Theory, methods - Urban and boreholes
Lunch break
Chairpersons: Yara Rossi, Philippe Jousset
14:00–14:10
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EGU23-14444
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ECS
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On-site presentation
Nicolas Luca Celli, Christopher J. Bean, Gareth O'Brien, and Nima Nooshiri

Since its first applications in the past decade, the use of fiber optic cables as ground motion sensors has become a central topic for seismologists, with successful applications of Distributed Acoustic Sensing (DAS) in various key fields such as seismic monitoring, structural imaging and source characterisation.

The instrument response of DAS cables however is largely unknown. Instrument response is a combination of instrument design, local site effects and ground coupling, and for DAS, the latter ones are believed to have a strong, spatially variable, but yet largely unquantified effect. This limits the application of a large number of staple seismological techniques (e.g. earthquake magnitude estimation, waveform tomography) that can require accurate knowledge of a signal’s amplitude and frequency content.

Here we present a method for accurately simulating a DAS cable and its response. The scheme is based on molecular dynamic-like particle-based numerical modelling, allowing the investigation of the effect of varying DAS-ground coupling scenarios. At first, we compute the full strain field directly, for each pair of neighbouring particles in the model. We then define a virtual DAS cable, embedded within the model and formed by a single string of interconnected particles. This allows us to control all aspects of the cable-ground coupling and their properties at an effective granular level through changing the bond strengths and bond types (e.g. nonlinearity) for both the cable and the surrounding medium. Arbitrary cable geometries and heterogeneous materials can be accommodated at the desired scale of investigation.

We observe that at the meter scale, realistic DAS materials, cable-ground coupling and the presence of unconsolidated trench materials around it dramatically affect wave propagation, each change affecting the synthetic DAS record, with differences exceeding at times the magnitude of the recorded signal. These differences show that cable coupling and local site effects have to be considered both when designing a DAS deployment and analysing its data when either true or along-cable relative amplitudes are considered.

How to cite: Celli, N. L., Bean, C. J., O'Brien, G., and Nooshiri, N.: Modelling of DAS cable and ground coupling response using Discrete Particle Schemes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14444, https://doi.org/10.5194/egusphere-egu23-14444, 2023.

14:10–14:20
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EGU23-11842
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On-site presentation
Alister Trabattoni, Francesco Biagioli, Claudio Strumia, Gaetano Festa, Martijn van den Ende, Diane Rivet, Anthony Sladen, Jean-Paul Ampuero, Jean-Philippe Metexian, and Éléonore Stutzmann

Distributed Acoustic Sensing (DAS) is becoming a well-established technology in seismology. For historical and practical reasons, DAS manufacturers usually provide instruments that natively record strain (rate) as the principal measurement. While at first glance strain recordings appear similar to particle motion (displacement, velocity, acceleration) waveforms, not all of the seismological tools developed over the past century (e.g., magnitude estimation, seismic beamforming, etc.) can be readily applied to strain data. Notably, the directional sensitivity of DAS differs from conventional particle motion sensors, and DAS experiences an increased sensitivity to slow waves, often composed of highly scattered waves that are challenging to analyze. To address these issues, several strategies have been already proposed to convert strain rate measurements to particle velocity.

Based on a previously proposed mathematical formalism, we stress some fundamental differences between path-integrated strain and conventional displacement measurements. DAS inherently records arc length variation of the cable which is a relative motion measurement along a curvilinear path. We show that if the geometry of the DAS deployment is adapted to the wavefield of interest, path-integrated strain can be used to closely approximate the displacement wavefield without the need of additional instruments. We validate this theoretical result using collocated seismometers, discuss the limitations of this approach, and show two benefits: enhancing direct P-wave arrivals and simplifying the magnitude estimation of seismic events. While using path integrated strain is in some aspects more challenging, it achieves flat (hence lower) noise levels both in frequency and wavenumber. It also provides better sensitivity to high velocity phases, and permits the direct application of conventional seismological tools that are less effective when applied to the original strain data.

How to cite: Trabattoni, A., Biagioli, F., Strumia, C., Festa, G., van den Ende, M., Rivet, D., Sladen, A., Ampuero, J.-P., Metexian, J.-P., and Stutzmann, É.: Using path-integrated strain in Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11842, https://doi.org/10.5194/egusphere-egu23-11842, 2023.

14:20–14:30
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EGU23-6189
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ECS
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On-site presentation
Camille Huynh, Clément Hibert, Camille Jestin, Jean-Philippe Malet, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) is an acoustic sensor instrument that turns a single optical fiber into a dense array of thousands of equally spaced seismometers. Geoscientists and companies have an interest in investing in DAS technologies for better understanding the Earth by observing natural and anthropogenic seismic events or assisting in large infrastructure monitoring with low installation and maintenance costs. However, this type of instrument generates a significantly larger amount of data than conventional seismometers, data that can be complex to store, exploit and interpret.

Several strategies for classifying seismic events from fiber-optics DAS data exist in the scientific literature. Conventional approaches rely on the use of features that describe the waveforms and frequency content of signals recorded individually at virtual stations along the fiber; they do not integrate the spatial density of information permitted by DAS. Several studies on dense seismological arrays have introduced similarity measures between the different time series data such as cross-correlations, dynamic time warping (DTW) or compression-based dissimilarity.

This study aims to quantify the contribution of spatial features for DAS data streams classification. We have chosen to explore spatial features related to both standard statistical measures (e.g., spatial mean, median, skewness, kurtosis), and advanced signal processing measures (e.g., auto-correlations, cross-correlations, DTW). This set of measures allows enriching a list of already used time series features which includes waveform, spectrum and spectrogram. A Random Forest (RF) classifier is then trained, and a Random Markov Field (RMF) algorithm is used after classification to account for redundant spatial and temporal information.

The evaluation of the spatial feature contribution is based on the output of the RF-RMF processing chain. Anthropogenically-triggered seismic data were acquired at the FEBUS Optics test bench. We consider five seismic sources: footsteps, impacts, excavators, compactor and fluid leaks. A class of noise is added as the RF-RMF algorithm is developed for processing DAS streams inherently affected by  noise.  Accurate  classification results can be obtained using only time features, and ongoing tests show a 2% increase in the correct classification rate with the use of both time and spatial features. The improvement allowed by the addition of spatial features is tangible but limited on our test dataset, but we think it should have a much greater impact on natural sources and we will discuss this perspective.

How to cite: Huynh, C., Hibert, C., Jestin, C., Malet, J.-P., and Lanticq, V.: Contribution of spatial features for classifying seismic events from Distributed Acoustic Sensing (DAS) data streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6189, https://doi.org/10.5194/egusphere-egu23-6189, 2023.

14:30–14:40
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EGU23-7309
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ECS
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On-site presentation
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Emanuele Bozzi, Nicola Piana Agostinetti, Alan F. Baird, Carlos Becerril, Biondo Biondi, Andreas Fichtner, Sara Klaasen, Nate Lindsey, Takeshi Nishimura, Patrick Paitz, Junzhu Shen, Arantza Ugalde, Fabian Walter, Siyuan Yuan, Tieyuan Zhu, and Gilberto Saccorotti

The Distributed Acoustic Sensing (DAS) method re-purposes fiber optic cables into a very-dense array of strain/strain-rate sensors, capable of detecting different types of seismic events. However, DAS data are characterized by lower SNRs compared with standard seismic sensors, mainly because of a) strong directivity effects, 2) ground coupling inhomogeneities, and 3) site effects. Hence, beyond the array geometry, specific noise sources may reduce the potential of DAS for seismic monitoring. Previous research has already shown successful case-studies for event detection/location. Nevertheless, a coherent test on the performances of various arrays of different sizes and geometries is still lacking.

In this study, an extensive DAS database is organized for such a goal, including 15 DAS arrays that recorded at least one seismic event (located at a range of distances from the arrays). P wave arrival times are exploited to estimate the epicentral parameters with a Markov Chain Monte Carlo method. Then, to analyze the effects of cable geometry and potential sources of noise/ambiguity on the location uncertainties, a series of synthetic tests are performed, where synthetic traveltimes are modified as follows: a) adding noise with equal variance to all the DAS channels (SYNTH-01), b) adding noise characterized by an increasing variance with the distance from the event (SYNTH-02), c) simulating the mis-pick between P and S phases (SYNTH-03) and d) adding noise with a variance influenced by cable coupling inhomogeneities (SYNTH-04). Results show that the epicentral locations with automatic P wave arrival times have different degrees of uncertainty, given the geometrical relation between the event and the DAS arrays. This behavior is confirmed by the SYNTH-01 test, indicating that specific geometries provide a lower constraint on event location. Moreover, SYNTH-04 shows that simulating cable coupling inhomogeneities primarily reproduces the observed location uncertainties. Finally, some cases are not explained by any of the synthetic tests, stressing the possible presence of more complex noise sources contaminating the signals.

How to cite: Bozzi, E., Piana Agostinetti, N., F. Baird, A., Becerril, C., Biondi, B., Fichtner, A., Klaasen, S., Lindsey, N., Nishimura, T., Paitz, P., Shen, J., Ugalde, A., Walter, F., Yuan, S., Zhu, T., and Saccorotti, G.: Effects of cable geometry and specific noise sources on DAS monitoring potential, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7309, https://doi.org/10.5194/egusphere-egu23-7309, 2023.

14:40–14:50
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EGU23-2814
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On-site presentation
Pascal Edme, David Sollberger, Tjeerd Kiers, Cedric Schmelzbach, Felix Bernauer, and Johan Robertsson

We present a novel seismic acquisition and processing technique to efficiently evaluate the local dispersion curves of Rayleigh waves for subsequent inversion of shear velocities and near-surface characterization.

The proposed approach consists of computing the ratio between the (time derivated) horizontal spectra H(f)=(∂tVx(f)2+∂tVy(f)2)1/2  and the pseudo-divergence spectra D(f), with D being the sum of the horizontal gradients of the horizontal components (i.e. D=∂xVx+∂yVy).

The processing method itself is comparable to the commonly used H/V approach, except that the H/D spectral ratio provides a direct estimate of the frequency-dependent phase velocities cR(f)  instead of the site frequency amplification(s). This is demonstrated using synthetic data.

We describe how the D component can be obtained in practice, i.e. by finite-differencing closely spaced horizontal phones or potentially using Distributed-Acoustic-Sensing (DAS) and fibre-optic deployed at the surface. Some limitations about wavelength dependency and impact of Love waves are discussed, as well as potential mitigation measures.

A field test on several hours of ambient noise data collected in Germany with multi-component geophones results in realistic values of Rayleigh wave velocities ranging from ~770 m/s at 10 Hz to ~500 m/ at 30 Hz. Thanks to the local and omni-directional nature of the estimation, the minimal number of required channels and the applicability to ambient noise, we believe that the proposed H/D method can be an attractive alternative to expensive array-based techniques.

How to cite: Edme, P., Sollberger, D., Kiers, T., Schmelzbach, C., Bernauer, F., and Robertsson, J.: Divergence-based estimation of Rayleigh wave dispersion curves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2814, https://doi.org/10.5194/egusphere-egu23-2814, 2023.

14:50–15:00
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EGU23-15841
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On-site presentation
CharLotte M. Krawczyk, Martin P. Lipus, Johannes Hart, Christopher Wollin, Christian Cunow, and Philippe Jousset

Maintenance of infrastructure is costly and difficult to implement systematically when it spreads over wide areas, such as road or pipeline networks. In the monitoring of road ways, conventional methods to control the road integrity rely on discrete measurements in space and time. There is a large demand for innovative technologies that are able to assess the structural integrity as a whole and in regular intervals or even continuously. Distributed fiber-optic sensing opens the opportunity to measure numerous physical quantities such as temperature and strain with high spatial and temporal resolution over tens of kilometers. In addition, it is easily deployable at reasonable cost.

In order to address the issue of asphalt aging due to exposure to heavy traffic loads, we installed a fiber-optic cable into a reworked road interval and recorded fiber-optic data in a controlled experiment with numerous test vehicles of different sizes and weights. The recorded data suggests that elastic properties of the asphalt can be retrieved from the bypassing traffic. Vehicles can be characterized by the number of axes and load on the asphalt composite. In the next phase, we will monitor the aging of the test field to deduce how varying matrial properties can be better identified for geotechnical and geoscience applications.

How to cite: Krawczyk, C. M., Lipus, M. P., Hart, J., Wollin, C., Cunow, C., and Jousset, P.: Monitoring of elastic properties using DAS and DTS in a controlled experiment during road construction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15841, https://doi.org/10.5194/egusphere-egu23-15841, 2023.

15:00–15:10
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EGU23-12740
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ECS
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On-site presentation
Leila Ehsaninezhad, Christopher Wollin, Benjamin Schwarz, and Charlotte Krawczyk

At a local scale, e.g. in urban settlements, seismic subsurface characterization requires implementing experiments at high spatial resolution. Distributed acoustic sensing (DAS) provides the opportunity of using pre-existing fiber optic cables as dense receiver arrays, thus potentially reducing the effort for active seismic surveying in urban areas. Due to their small footprint, passive experiments appear particularly appealing. However, extracting coherent signals in an urban environment, i.e. in the presence of anthropogenic activity in the receivers' vicinity, remains a challenge.

 

In this study, we present results from combining the well known technique of Multichannel Analysis of Surface Waves (MASW) with the coherency-based enhancement of wavefields. The investigation is based on a DAS dataset acquired along a major road in Berlin, Germany. We analyse a 4.5 km long straight subsegment of a dark fiber that was sampled at 8 m intervals with 1000 Hz over a period of 15 days. After temporal decimation and the interferometric analysis, clear causal and a-causal branches of Rayleigh-surface waves emerge in the virtual shot gathers.

 

In the further processing, we employ coherence-based enhancement of wavefields to amplify the Signal to Noise Ratio of the virtual shot gathers. Compared to the traditional workflow of ambient-noise tomography the modified one yields improved dispersion curves particularly in the low-frequency part of the signal. This leads to an increased investigation depth along with lower uncertainties in the inversion result. The final velocity model reaches depths down to 300 m. We show that the application of coherence-based enhancement of the virtual shot gathers in the MASW-workflow may significantly relax the necessity of collecting long baselines for passive tomography in urban environments.

How to cite: Ehsaninezhad, L., Wollin, C., Schwarz, B., and Krawczyk, C.: Coherence-based Amplification of Rayleigh Waves from Urban Anthropogenic Noise recorded with Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12740, https://doi.org/10.5194/egusphere-egu23-12740, 2023.

15:10–15:20
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EGU23-15291
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ECS
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On-site presentation
Johannes Hart, Martin Peter Lipus, Christopher Wollin, and Charlotte Krawzcyk

Efficient, safe and sustainable utilization of geothermal reservoirs depends on reliable well completion and monitoring technologies. Conventional borehole measurement methods can only be used after the completion process and usually show snapshots of the borehole conditions at discrete points in time. Therefore, the successful borehole completion is a risky process and mainly relies on the experience of the driller. By using distributed fiber-optic sensing technologies, it is possible to monitor all along the cable with dense spatial sampling and continuous in real-time.

In this presentation, we give insights into our newest case study in Berlin. A 450 m deep exploration well for an Aquifer Thermal Energy Storage was completed. We installed a fiber optic sensor cable along the whole production tubing, that contained several single-mode and multi-mode fibers in loose tube and tight buffered configuration. This cable allows to simultaneously measure distributed temperature (DTS), distributed acoustics (DAS) and distributed strain (DSS/DTSS) for the entire completion process.

Particularly with a combined analysis and interpretation of the different fiber-optic technologies, conventionally untraceable processes can be visualized. We are able to show changes of subsurface flow paths due to blockages. Processes to be prevented, like caving or bridging can be detected and the proper rise of gravel or cement can be surveyed. Provided to the driller in real time, subsurface uncertainties can be significantly reduced.

Monitoring geothermal wells with a fiber-optic sensing infrastructure is not only a powerful tool to reduce risks during well completion, which can lead to compromised well integrity. The installed equipment and technology can also be used to assess the well integrity over the whole cycle of the well, to ensure a longest possible lifespan.

How to cite: Hart, J., Lipus, M. P., Wollin, C., and Krawzcyk, C.: Supporting the completion process of boreholes using combined fiber-optic monitoring technologies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15291, https://doi.org/10.5194/egusphere-egu23-15291, 2023.

15:20–15:40
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EGU23-17585
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solicited
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Highlight
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On-site presentation
Kuo-Fong Ma, Li-Wei Kuo, Hsin-Hua Huang, Sebastian von Specht, Chin-Jen Lin, Jing-Shan Ku, Chen-Ray Lin, En-Shi Wu, Chien-Yin Wang, and Wen-Yen Chang

Understanding fault zone dynamics in multi-scale is important to embrace the complexity of the earthquake behavior and its natural system. However, the opportunity to map and observe the fault zone behavior at depth with high spatial resolution are rare as also the challenge itself on targeting and identifying the fault zone at depth. We placed a 3D cross-fault fiber array with a downhole loop from surface to depth of 700m for Hole-A (Hanging wall site, crossing fault at depth), after drilling and coring to a frequent slip fault, Milun fault in a plate boundary zone, which ruptured during the 6 February 2018 Mw6.4 Hualien earthquake, and resulted in severe damage to several tall buildings with tens of casualties and injuries. Then, the surface segment crosses the surface fault rupture zone using commercial fiber, and to another downhole loop of 500m fiber for Hole-B (Footwall site). The high spatial resolution from distributed acoustic sensing (DAS) allows us to characterize the fault zone feature together with the retrieved core and geophysical logs after drilling through this frequent slip zone. This 3D route includes the experiment of using commercial fiber to the future application of surface rupture zone identification for seismic hazard mitigation. The project successfully retrieved the fault core associated with Milun fault zone, which could be also seen in geophysical logs with low velocity and resistivity, and mapped using Optical Fiber Sensing technique of the downhole fiber. Within the Milun fault zone, while a 20m thick fault core with grey and black gouge was discovered, a distinct seismic feature associated with this 20m fault gouge was found by its amplification of the strain records from DAS. This amplification ratio is about 2.5-3 when compared to the channels at deeper depth related to a consolidated rock material.  This amplification factor was frequency and azimuth independently, as genuinely observed from all events (e.g. local, and teleseismic earthquakes) with similar amplification factor. Our study shows that the amplification from this 20m fault gouge zone is mainly from the nature of the heterogeneous medium in elastic constant while crossing the fault zone, especially the fault core. Similar feature at surface but with wider surface rupture zone (~ 200m) was found in DAS data as well although less evidence using commercial fiber, while could be validated from the densely deployed geophones crossing the surface rupture of the 2018 Hualien earthquake. Through the depth, a high-resolution asymmetric feature of this active fault was evidenced from the downhole optical fiber and cores. This fault zone behavior would be hardly seen or confirmed without continuous viewing of the wavefields to this high spatial resolution to meter scale. Although the narrow fault gouge, the nature of its amplification in strain due to its strong material contrast from fault gouge was intriguing, and requires intensive attention to consider the contribution of the fault zone heterogeneity in the medium. This might give hints on the understanding of the observation of earthquake dynamics triggering reported worldwide after the occurrence of a mega-earthquake.

How to cite: Ma, K.-F., Kuo, L.-W., Huang, H.-H., von Specht, S., Lin, C.-J., Ku, J.-S., Lin, C.-R., Wu, E.-S., Wang, C.-Y., and Chang, W.-Y.: Why high spatial resolution matters: narrow fault zone, but big effects observed by Taiwan Milun-fault Drilling and All-inclusive Sensing (Taiwan MiDAS) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17585, https://doi.org/10.5194/egusphere-egu23-17585, 2023.

15:40–15:45

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X2

Chairpersons: Gilda Currenti, Stefanie Donner, Marc-Andre Gutscher
X2.97
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EGU23-1292
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ECS
|
Jérôme Azzola and Emmanuel Gaucher

Distributed Acoustic Sensing (DAS) in geothermal wells is a particularly attractive technology to implement as part of routine seismic monitoring of geothermal plant operations. It brings a large network of sensors close to the monitoring target – the operated reservoir – increasing the sensitivity towards low magnitude events and allows the application of processing procedures inspired by large network or array processing. However, the technical management of the large flow of produced data and the suitability of the strain-rate acquisitions to monitor locally induced seismicity was yet to be fully assessed.

We present the results of a continuous 6-month monitoring period that aimed at testing an integrated system designed to manage the acquisition, the processing and the saving of DAS data collected from behind casing at the Schäftlarnstraße (SLS) geothermal project (Munich, Germany). The data management system links the existing on-site infrastructure to a cloud Internet-of-Things (IoT) platform integrated into the company’s IT infrastructure. The cloud platform has been designed to deliver both a secure storage environment for the DAS records and optimized computing resources for their continuous processing.

With a special focus on seismic risk mitigation, we investigate the potential of the monitoring concept to provide sensitive detection capabilities, despite operational conditions, while ensuring efficient data processing in order to strive for real-time monitoring. Further analysis of the records confirm additional logging capabilities of borehole DAS. We also evaluate the ability of DAS to provide reliable seismic source description, in particular in terms of location, moment magnitude, and stress drop.

Using two detected local seismic events, we demonstrate the relevance of the system for monitoring the SLS-site in an urban environment, while complementing advantageously the surface seismometer-based monitoring network.

How to cite: Azzola, J. and Gaucher, E.: Continuous seismic monitoring of a geothermal project using Distributed Acoustic Sensing (DAS): a case study in the German Molasse Basin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1292, https://doi.org/10.5194/egusphere-egu23-1292, 2023.

X2.98
|
EGU23-6915
|
ECS
Davide Pecci, Juan Porras, Michele De Solda, Francesco Grigoli, Eusebio Stucchi, and Renato Iannelli

DAS technology is particularly suitable for microseismic monitoring application in geothermal environments. This instrumentation can resist to high temperatures (up to about 100°C or more) higher than the operational temperature of standard acquisition instruments (e.g., geophones), allowing the fiber to be located very close to the reservoir. For this reason, DAS is particularly useful for induced seismicity monitoring of Enhanced Geothermal System (EGS). Being of recent development, this acquisition technology still lacks appropriate modeling and analysis tools able to handle such a large amount of data without losing efficiency. Furthermore, open-access DAS datasets are still a rarity, if compared to other geophysical datasets (e.g., seismological data). Therefore, we aim to generate an open-access synthetic (but realistic) DAS dataset that may help the geophysical community to develop “ad hoc” data analysis methods suitable for this kind of data. In the presented work we make use of the spectral element modeling software 'Salvus', developed by Mondaic, which also allows the simulation of DAS data. In particular, it outputs a strain measurement between all points defined as receivers in the simulation. Using the repositories of DAS data collected at the geothermal test site Frontier Observatory for Research in Geothermal Energy (FORGE) located in Utah (USA), we tried to simulate realistic DAS acquisition conditions of seismic events related to low-magnitude natural seismic activity from the nearby Mineral Mountains and microseismic events related to hydraulic stimulation operations for the generation of an EGS.

In order to obtain realistic synthetic data, we first analyze the spectral properties of real noise waveforms by using the Power Spectral Density (PSD) Analysis. Starting from observed PSDs we model the synthetic noise waveforms using a stochastic approach. Then we add it to the synthetic event traces and compare them with the observed ones. We finally test a semblance-based event detector on a 1-hour continuous waveforms of synthetic data to evaluate the performance of the detector in different operational conditions (e.g., different noise levels and inter-event times).

How to cite: Pecci, D., Porras, J., De Solda, M., Grigoli, F., Stucchi, E., and Iannelli, R.: Modeling and analysis of Distributed Acoustic Sensing (DAS) data in Geothermal environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6915, https://doi.org/10.5194/egusphere-egu23-6915, 2023.

X2.99
|
EGU23-4256
|
ECS
Destin Nziengui Bâ, Olivier Coutant, and Camille Jestin

Water resource management is a crucial socio-economic issue that requires developing high-resolution monitoring techniques, including non-invasive geophysical methods. Among them, passive seismic interferometry takes advantage of natural ambient seismic noise to recover the slight variations of the seismic wave velocity induced by changes in the groundwater level. In this study, we present the time and space monitoring of groundwater changes artificially generated by infiltration ponds at the exploitation field of Crépieux-Charmy (Lyon, France).  We deployed 3km of optical fibre and a dense array of fifty 3C geophones around infiltration basins. We recorded several cycles of filling-emptying with a DAS using a 2m spatial sampling (i.e., 1500 fibre sensors). The recorded signals are mainly associated with local anthropogenic noise (highways, trains, pumping, etc.). We could track seismic velocity variations with high temporal and spatial resolutions using ambient noise interferometry techniques. These variations are associated with the interaction between the water diffused from the basins and water table variations. This dynamic information helps understand and model water exchanges on the ground. The study confirms the possibility of groundwater monitoring using DAS records of ambient noise for seismic interferometry in a highly urbanized zone.

How to cite: Nziengui Bâ, D., Coutant, O., and Jestin, C.: Groundwater monitoring using fibre-optics and DAS: Application to the Lyon water catchment area., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4256, https://doi.org/10.5194/egusphere-egu23-4256, 2023.

X2.100
|
EGU23-5455
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ECS
|
Katinka Tuinstra, Antonio Pio Rinaldi, Federica Lanza, Alba Zappone, Andreas Fichtner, and Stefan Wiemer

Underground laboratories have become indispensable in the understanding of physical processes during e.g., hydraulic stimulation and seismic monitoring of deep geothermal reservoirs or CO2 storage target reservoirs. They provide a test bench and constitute the bridge between small-scale laboratory studies and full-scale pilot sites. Here, we present results from multiple active source seismic campaigns in one of the Swiss underground laboratories: the Mont Terri Rock Laboratory. Here, DAS fibres are cemented behind the casing of multiple monitoring boreholes and active shots are taken with a P-wave sparker. This dense array of active seismic measurements enables us to obtain a baseline characterisation of the P-wave velocity of the rock before any activity (e.g., injection) takes place. During stimulations, dynamic measurements with an active sparker source are recorded, followed by a time-lapse monitoring approach where seismic measurements are collected through active seismic campaigns in set time intervals in the months after stimulations. In this way we can create high-resolution, four-dimensional monitoring and characterisations of the rock body and potential earthquakes during the full monitoring period. We show different configurations and measurements settings with their effect on the DAS recordings of active signals.

How to cite: Tuinstra, K., Rinaldi, A. P., Lanza, F., Zappone, A., Fichtner, A., and Wiemer, S.: Active-source seismic experiments with DAS for monitoring reservoir rock in underground laboratories, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5455, https://doi.org/10.5194/egusphere-egu23-5455, 2023.

X2.101
|
EGU23-15325
Olivier Sèbe, Camille Jestin, Amaury Vallage, Stéphane Gaffet, Daniel Boyer, Alain Cavaillou, Jean-Baptiste Decitre, Charly Lallemand, Vincent Lanticq, and Olivier Rousseau

Thanks to its ability to provide dense strain rate measurements along Optical Fiber (OF) cable, the Distributed Acoustic Sensing (DAS) technique spreads over different seismic and geophysical domains. They range from exploration geophysics (Mestayer et al. 2011, Daley et al. 2013), to underground structure imaging (e.g. Ajo-Franklin et al. 2019, Cheng et al. 2021) or seismic activity and background noise monitoring (Jousset et al 2018, Nayak et al. 2021). Beyond the advantage of its dense spatial sampling and given a better understanding of its instrument response (e.g. Lindsey et al. 2020), the detection performance of these new DAS measurements also depends on its ability to precisely characterize the amplitude and phase of the seismic background noise in different environments. According to recent offshore seismic noise studies (Ugalde et al. 2021, Lior et al. 2021, Guerin et al 2022), we propose a study based on DAS recordings of the seismic background noise in an on-land quiet environment.

In 2020, a temporary seismic experiment PREMISE (PREliminary MIga Seismic Experiment) was carried out on the site of the underground low noise Laboratory (LSBB, Laboratoire Souterrain Bas Bruit) at Rustrel, France, in order to study the 3D seismic wave field properties in a pretty well-known underground geological structure. During this experiment, we deployed several kilometers of different OF in the LSBB galleries in order to create a multidirectional DAS array with a total fiber length of 10.5km and several ground-coupling conditions. We reprocessed two hours of “raw” DAS data, recorded with a FEBUS A1-R instrument, with different acquisition parameters to find the best configuration for enhancing the DAS measurement Signal to Noise Ratio. The power spectral density (PSD) of these reprocessed strain time-series reveals a peak in the background noise frequency range [0.08-0.25Hz] for gauge lengths of 90m and 150m. Independently, an estimation of the local strain field has been derived by a geodetic analysis (Spudich et al 1995) of the records from the LSBB broadband seismometers antenna. The comparison of the DAS and seismometers array-derived strain PSD shows a very good agreement with the secondary microseism peak in terms of frequency band, amplitude, and the wave field polarization, especially for DAS strain records processed with gauge-length of several tens of meters.

How to cite: Sèbe, O., Jestin, C., Vallage, A., Gaffet, S., Boyer, D., Cavaillou, A., Decitre, J.-B., Lallemand, C., Lanticq, V., and Rousseau, O.: Observation of the microseismic peak from Distributed Acoustic Sensing (DAS) measurements at the LSBB underground Laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15325, https://doi.org/10.5194/egusphere-egu23-15325, 2023.

X2.102
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EGU23-12213
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ECS
Giuseppe Maggio, Andrew Trafford, and Shane Donohue

The behaviour of geological slopes during seasonal weather patterns represents one of the challenges for assessing the geotechnical state of health of the ageing infrastructures. In the presence of man-made soil infrastructure slopes, rainfall and prolonged dry periods can cause cycles of swelling and shrinking of the ground that could potentially compromise their structural integrity. Recent research has found that time-lapse velocity monitoring, has the potential to provide information on climate-related deterioration of geotechnical infrastructure. Variations of the ground conditions could manifest as changes in seismic velocity, detectable through the seasons and after extreme weather events.

In this work, we perform seismic imaging and velocity-monitoring of a critical railway embankment in the United Kingdom using fibre optic distributed sensing (DAS). The study area is a 6 m tall, and 350 m long embankment slope built more than 100 years ago in the outskirts of London (Surrey). The railway is currently utilised mostly by commuter trains. Since August 2022, a passive DAS dataset rich in train signals has been acquired. data acquisition will continue until July 2023. Furthermore, periodic active surveys have been conducted along the slope.

Firstly, to validate the seismic response of the fibre (i.e., maximum usable frequencies based on the gauge length), we calculate and compare surface wave dispersion curves derived from both DAS and geophones using passive ambient noise, train signals and active sledgehammer shots. As a result, we obtain consistent and comparable dispersion curves ranging from ~200 m/s at 10 Hz to ~140m/s at 40 Hz. 

Secondly, we invert, using global search algorithms, DAS-derived dispersion curves for 1D depth-velocity models to identify and clarify the trend of the near-surface (top 10 m) seismic structures. 

Thirdly, we apply seismic interferometry and moving window cross-spectral techniques to measure changes in seismic velocity at the embankment using the 6-month passive DAS data acquired so far. 

The ultimate goal of this project is to develop a geophysical tool diagnostic of geotechnical deterioration of critical infrastructures by linking together DAS-based seismic observations, temporal seismic velocity changes, weather data and laboratory-based soil sample tests.

How to cite: Maggio, G., Trafford, A., and Donohue, S.: Near-surface seismic characterisation of a railway embankment slope using fibre-optic distributed acoustic sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12213, https://doi.org/10.5194/egusphere-egu23-12213, 2023.

X2.103
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EGU23-10767
|
ECS
Marco Dominguez-Bureos, Celine Hadziioannou, Niklas Epple, Camila Sanchez Trujillo, and Ernst Niederleithinger

It has been shown that non-destructive tests (NDTs) based on nonlinear wave propagation are more sensitive to detecting very small damages in concrete structures than linear techniques. With the aim of exploring the nonlinear effects in civil structures as a damage indicator, we perform a 1-day multiscale vibration monitoring of a test bridge equipped with a pretension system.

We used the pretension system to subject the specimen to eight compression states in its longitudinal direction (400kN at the highest, and 280kN at the lowest). At every compression state, we struck the structure in the vertical direction three times at two locations on the bridge with an impulse source. Throughout the whole experiment, we recorded seismic ambient noise at different frequency bands with a 14-IMU50-sensor array to measure the acceleration and rotation rate, a 14-geophone array with a 4.5 Hz natural frequency, a DAS system, and 4 pairs of ultrasound transducers; the internal temperature of the concrete was also recorded.

At the structural scale (from 1 to 40 Hz) we were able to observe different responses of the structure to pre-tension changes, depending on where the measurement took place in relation to the vertical support pillars by estimating relative velocity changes using the Coda Wave Interferometry stretching processing technique.

At the material scale (ultrasound regime) we can observe temperature-dependent slow dynamics features related to changes in the seismic velocity of the concrete as a consequence of vertical strikes, and its recovery process that returns its physical properties to a steady state after the action of the impulse source.

With this work, we work towards the development of new NDTs that are increasingly sensitive to small cracks and imperfections using conventional and non-conventional seismic instruments to measure linear and nonlinear wave propagation.

How to cite: Dominguez-Bureos, M., Hadziioannou, C., Epple, N., Sanchez Trujillo, C., and Niederleithinger, E.: Exploring multiscale nonlinear NDTs for damage detection in concrete structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10767, https://doi.org/10.5194/egusphere-egu23-10767, 2023.

X2.104
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EGU23-9641
Christopher Wollin, Leila Ehsaninezhad, Johannes Hart, Martin Lipus, and Charlotte Krawczyk

Seismic microzonation and ambient noise tomography via Distributed Acoustic Sensing (DAS) may contribute to the seismic hazard assessment and the exploration or monitoring of utilizable and utilised subsurface volumes at favorable costs. However, numerous technical aspects remain under investigation to further maturate this innovative seismological approach – particularly when applied to dark telecommunication fibers. For instance unknown coupling of the fiber to the ground or presence of loops of slack fiber may disturb the regular measuring of the stringed virtual sensors.

 

In this study, we investigate how loops of slack fiber affect the results of passive ambient tomography, a particularly appealing exploration approach due to its low footprint. We present results obtained with DAS recordings on purposefully installed as well as dark telecommunication optic fiber. Sledgehammer blows were recorded on an optic fiber laid out in an urban heating tunnel before and after introducing several loops of slack. The loops coiled up fractions and multiples of the utilized gauge length and were spaced in sufficient distance to independently analyze the surrounding wavefield. Discontinuous wavefronts can be observed once the coiled fiber exceeds the gauge length. Similar observations were made on the virtual shot gathers calculated along a 4.5 km long segment of dark fiber along a major road in the city of Berlin, Germany. We show how the loops of slack affect the further processing with respect to ambient noise tomography. On average, the removal of virtual sensors identified to be located in coiled fiber reduces the shear-wave velocities in the resulting model.

 

We conclude that the careful removal of virtual sensors within loops of slack is a mandatory processing step towards ambient noise tomography with linear DAS arrays. However, the calculation of virtual shot gathers can help to reveal the affected fiber segments.

How to cite: Wollin, C., Ehsaninezhad, L., Hart, J., Lipus, M., and Krawczyk, C.: Loops of slack in dark fiber and their effect on interferometric analysis of ambient noise – symptoms, consequences and remedies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9641, https://doi.org/10.5194/egusphere-egu23-9641, 2023.

X2.105
|
EGU23-8569
Marc-Andre Gutscher, Lionel Quetel, Giuseppe Cappelli, Jean-Gabriel Quillin, Christophe Nativelle, Jean-Frederic Lebrun, and Melody Philippon

Submarine telecom cables criss-cross the oceans, connecting islands to continents and providing internet, financial and media services to consumers all around the world. Laser reflectometry as well as other optical techniques can potentially transform the optical fibers in these cables into sensors which can detect vibrations and ground motion from earthquakes, ocean waves, currents as well as permanent deformation of the seafloor. The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study movements at the seafloor.

 

Within the framework of the FOCUS project, and in collaboration with the “Conseil Regional” of Guadeloupe, in 2022 we began long-term monitoring of a network of submarine telecom cables that link the islands of the Guadeloupe archipelago. These cables connect the larger island of Basse Terre and Grande Terre to the smaller southern islands of Les Saintes, Marie Galante and La Desirade, with segment lengths ranging from 30 to 70 km. This network was deployed recently (in 2019) and is the property of the Conseil Regional of Guadeloupe, operated with the assistance of Orange. All cables contain twelve fiber pairs, of which three pairs are in use by mobile phone operators and thus unused fibers were available for this scientific monitoring project. In June 2022, we established BOTDR baselines on 8 optical fiber segments, in several cases in both directions. In December 2022, we repeated the measurements of the same fiber segments, allowing us to detect any strain along the cable over this period.

 

Here, we report that using the BOTDR technique, we detect significant strain signals  (50 micro-strain and more) in several locations along the cable network. These signals, which can be positive (elongation) or negative (shortening) occur typically in areas of steep seafloor slopes or in submarine valleys/canyons. Our tentative interpretation is that stretching and shortening of the cable (representing about 1 cm over a few hundred meters) is occurring, most likely due to sea-bottom currents. These currents may be related to the late summer/early autumn hurricane season, with the passage of tropical storm Fiona in Sept. 2022 dropping heavy rains, causing torrential floods and debris flows in some of the larger rivers with possible impacts further offshore. A longer time-series and more detailed analysis are necessary to test this preliminary hypothesis.

How to cite: Gutscher, M.-A., Quetel, L., Cappelli, G., Quillin, J.-G., Nativelle, C., Lebrun, J.-F., and Philippon, M.: Monitoring a commercially operating submarine telecom cable network in the Guadeloupe archipelago (Lesser Antilles) using Brillouin Optical Time Domain Reflectometry (BOTDR), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8569, https://doi.org/10.5194/egusphere-egu23-8569, 2023.

X2.106
|
EGU23-11782
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ECS
|
Marie Baillet, Alister Trabattoni, Martijn Van Den Ende, Clara Vernet, and Diane Rivet

Fiber-optic Distributed Acoustic Sensing (DAS) is of critical value for the expansion of seismological networks, particularly in regions that are hard to instrument. The work presented here is part of the 5-year ERC ABYSS project, which aims at building a permanent seafloor observatory to increase our ability to capture low magnitude seismic signals from the subduction fault zone in the DAS data recorded by offshore telecommunication cables along the central coast of Chile.

In preparation for this project, a first experiment named POST was conducted from October to December 2021 on a submarine fiber-optic cable connecting the city of Concón to La Serena. DAS data were recorded continuously for 38 days over a distance of 150 km from Concón, constituting more than 36700 virtual sensors sampling at 125 Hz. This experiment provided an opportunity to anticipate what will be recorded over the next 5 years of the project, and to allow us to develop routines that will be applied later for real-time data processing.

As a first step, we developed an automated routine for generating a preliminary earthquake catalog, comprising various conventional signal processing steps, including data denoising, change-point detection, and separating seismic events from transient instrumental noise making use of the two-dimensional character of the DAS data. Over a span of 38 days (worth 72 TB of data), our pipeline detected more than 900 local, regional, and teleseismic events with local magnitudes down to ML < 2 (based on the Centro Sismológico Nacional (CSN) public catalog). The size of our catalog, enriched with numerous off-shore events, is a significant improvement over the current CSN catalog, which may aid future studies into the Chilean margin subduction zone seismicity.

How to cite: Baillet, M., Trabattoni, A., Van Den Ende, M., Vernet, C., and Rivet, D.: A workflow to generate DAS based earthquake catalog, applied to an offshore telecommunication cable in central Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11782, https://doi.org/10.5194/egusphere-egu23-11782, 2023.

X2.107
|
EGU23-3437
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ECS
Julián Pelaez Quiñones, Anthony Sladen, Aurelien Ponte, Itzhak Lior, Jean-Paul Ampuero, Diane Rivet, Samuel Meulé, Frédéric Bouchette, Ivane Pairaud, and Paschal Coyle

Ocean water temperature measurements are fundamental to atmospheric and ocean sciences. Obtaining them, however, often comes along with major experimental and logistic challenges. Except for the uppermost ocean surface temperature, which can be measured from satellites, temperature data of the ocean is often poorly sampled or nonexistent, especially in deep-water regions.

Although Distributed Acoustic Sensing (DAS) technology has become popular because its high sensitivity to strains and mechanical vibrations, our work focuses on its usage on tens-of-kilometer-long underwater fibre-optic (FO) telecommunication cables to measure temperature anomalies at the seafloor at millikelvin (mK) sensitivity. This is possible because of the lack of dominant strain signals at frequencies less than about 1 mHz, as well as the poor coupling of the fibre with these signals while remaining highly sensitive to slow ambient temperature variations that locally affect its optical path length. DAS allows us to observe significant temperature anomalies at the continental shelf and slope of the Mediterranean sea, South of Toulon, France over periods of several days, with variability remaining relatively low at the deep ocean. By means of this approach, oceanic processes such as near-inertial internal waves and upwelling can be monitored at unprecedented detail.

Our observations are validated with oceanographic in-situ sensors and alternative Distributed Fibre Optic Sensing (DFOS) technologies established for temperature sensing. We outline key advantages of DAS thermometry over the aforementioned sensors in terms of spatial coverage, sensitivity, versatility and highest attainable frequency. At the current state of the art, DAS can only measure temperature anomalies as opposed to absolute temperature, a drawback that could be compensated via single temperature calibration measurements.

How to cite: Pelaez Quiñones, J., Sladen, A., Ponte, A., Lior, I., Ampuero, J.-P., Rivet, D., Meulé, S., Bouchette, F., Pairaud, I., and Coyle, P.: Monitoring temperature at the ocean seafloor with fibre optic cables and DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3437, https://doi.org/10.5194/egusphere-egu23-3437, 2023.

X2.108
|
EGU23-8327
Philippe Jousset, Gilda Currenti, Rosalba Napoli, Mario Pulvirenti, Daniele Pelligrino, Christian Cunow, Graziano Larocca, Alessandro Bonaccorso, Giuseppe Leto, and Charlotte Krawczyk

Volcano monitoring has been experiencing significant improvements in recent years, yet eruption forecasting and scenarios have still lack of understanding, due to the poor observations in low amplitude events and hindered by surface external noise of similar amplitudes. Volcanic events have been shown to be accurately recorded with fiber optic techniques at the surface. In this study, we present preliminary results of fibre optic cable deployed in a new 200 m deep borehole on the southern flank of Etna at about 6 km away from the summit crater. This borehole has been designed primarily for the future deployment of a new strain sensor type. We benefited from the drilling of this new borehole to deploy a single-mode fibre optic cable. We connected an interrogator and recorded dynamic strain rate during several periods: first, in 2020 for several days during the completion of the borehole and the final stage of the drilling; second, in 2021 for several weeks during an active volcanic period; and in December 2022 during a quiet activity period of several months. We present a selection of records of noise while drilling, local volcano-tectonic earthquakes and volcanic events and tremor that occurred during those periods. These examples show the benefit of deploying a fibre in a borehole far from the active area and demonstrate the great variety of signals fibre optic can record is such configuration.

How to cite: Jousset, P., Currenti, G., Napoli, R., Pulvirenti, M., Pelligrino, D., Cunow, C., Larocca, G., Bonaccorso, A., Leto, G., and Krawczyk, C.: Fibre-optic dynamic strain borehole sensing at Etna volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8327, https://doi.org/10.5194/egusphere-egu23-8327, 2023.

X2.109
|
EGU23-6422
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ECS
|
Mirko Bracale, Romain Brossier, Helle Pedersen, and Michel Campillo

In recent years, the use of rotational sensors and DAS has become a topic of increasing interest within the seismological community because of their increasing sensitivity and affordability. We analyze the sensitivity of wavefield gradients, in the form of normal strain and rotation, to localized shallow velocity changes in a homogeneous medium.
We performed several numerical simulations, using a suitably modified 3D-SEM code, to observe, in addition to wavefield itself, the normal strain and rotation as a direct output.
We analyzed two case studies in which a velocity anomaly is placed in a homogeneous medium. In the first case the velocity change between the anomaly and the surrounding medium is 10%, in the second case 70%. We analyzed the sensitivity of these new observables in terms of phase shift and amplitude change.
We observe a very local effect of the wavefield gradients, which show larger amplitude near the boundary between the medium and the anomaly, while away from it they behave like the displacement wavefield itself.

How to cite: Bracale, M., Brossier, R., Pedersen, H., and Campillo, M.: Effect of shallow heterogeneities on wavefield gradients measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6422, https://doi.org/10.5194/egusphere-egu23-6422, 2023.

X2.110
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EGU23-15048
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ECS
|
Marthe Faber and Andrew Curtis

It is of interest for environmental and resource applications to better characterise dynamic processes and properties of the near-surface critical zone of the solid Earth. Seismic wavefield gradiometry refers to a class of imaging techniques that estimate properties of the subsurface by calculating temporal and spatial gradients of incoming wavefields using dense array measurements, usually recorded at the Earth’s surface. One such method called wave equation inversion (WEI) has been shown to require only a few minutes of ambient seismic noise recordings to produce phase velocity maps, and shows promise for rapid field deployment.

Previous applications of WEI are based on the assumption that the 2D scalar Helmholtz wave equation adequately describes the dynamics of recorded wavefields. This approximation is severe for seismic waves because the Helmholtz equation fails to describe elastic wave dynamics. Since ambient noise recordings contain all kinds of interfering elastic wave types, the accuracy of subsurface material property estimates is compromised.

To investigate the potential to enhance the information available from WEI, we test the method synthetically using more sophisticated wave equations that represent wave propagation in the subsurface more accurately. Starting from a 3D seismic array geometry which provides wavefield gradient information both at the surface and at depth, WEI can be formulated in terms of the full elastic wave equation. From there we track approximations in both wave physics and field acquisition geometries that deplete information about the medium, eventually arriving at the conventional 2D scalar wave equation. These experiments highlight approximations that most deteriorate the solution, allowing us to target future effort to remove them.

One approximation made in all previous WEI studies is to assume that density is constant across the local array. In reality, subsurface density varies both laterally and with depth, yet remains poorly constrained in seismic imaging problems. Accurate density estimates would provide important insight into subsurface properties. This prompts us to test wavefield sensitivities to subsurface density contrasts via WEI. Synthetic results for 3D acoustic media suggest that it is possible to estimate relative density structure with WEI by using a full acoustic formulation for wave propagation along the surface. We show that using a constant density assumption for the medium can be detrimental to subsurface images, whereas the full acoustic formulation of gradiometry improves our knowledge of material properties. It allows us to estimate density as an additional material parameter as well as to improve phase velocity estimates by incorporating approximations to the density structure. By expanding this methodology to the elastic case, we will discuss the feasibility of estimating density with gradiometric WEI in the solid Earth.

How to cite: Faber, M. and Curtis, A.: On Seismic Wave Equation Gradiometric Inversion for Density, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15048, https://doi.org/10.5194/egusphere-egu23-15048, 2023.

X2.111
|
EGU23-14804
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ECS
Uncertainty assessment of the array derived rotation measurements
(withdrawn)
Roxanne Rusch, Olivier Sèbe, Stéphane Gaffet, Jean-Baptiste Decitre, Charly Lallemand, Daniel Boyer, Alain Cavaillou, and François Schindele
X2.112
|
EGU23-15062
|
ECS
|
Andreas Brotzer, Heiner Igel, Felix Bernauer, Joachim Wassermann, Robert Mellors, and Frank Vernon

In September 2022, a three-component rotational rate sensor (blueSeis-3A) provided by IRIS has been deployed at the underground vault of the Piñon Flat Observatory (PFO) near San Diego in California. A three-component broadband seismometer (Trillium 240s) is co-located on the granite pier, creating a 6C station for permanent observations of local and regional seismicity and wavefield studies. The permanent record is streamed online via IRIS and freely available with all required metadata (station: BlueSeis at Pinon Flat = BSPF). Additionally, the site offers observations of strain by optical fiber and vacuum laser strainmeters at PFO, allowing to study 7 components of the seismic wavefield in a quiet area with regard to seismic noise, but high seismicity (e.g. San Andreas fault zone, San Jacinto fault zone). Such a setup enables advanced studies of the seismic wavefield. Dense, large-N nodal experiments, temporarily deployed around PFO could provide dense sampling of the seismic wavefield for comparison studies. The seismic array of borehole sensors at PFO is well designed to compute array derived rotations with enables a direct comparison with the rotational record and applied methods. Moreover, the array is employed to compare array analysis with 6C methods (e.g. backazimuth estimation, wavefield separation, source tracking, local subsurface velocity changes). We present characteristics on the 6C station and preliminary analysis results.

How to cite: Brotzer, A., Igel, H., Bernauer, F., Wassermann, J., Mellors, R., and Vernon, F.: Observing and analysing seismicity with a permanet 6C station, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15062, https://doi.org/10.5194/egusphere-egu23-15062, 2023.

X2.113
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EGU23-14093
Johana Brokesova and Jiri Malek

Long Valley Caldera in the eastern part of California is a depression 32 km long and 18 km width, which was formed during a supervolcano eruption 760 000 years ago.  Weak volcanic activity manifested by hot springs, CO2 emmanations and earthhquake swarms in the caldera and neighboring Mammoth Mountain volcanic complex has been continuing until present. The seismicity in the area is the subject of intensive study. In 2016 - 2017 the monitoring system was supplemented by small-aperture array consisting of three short-period Rotaphone-D seismographs. The instruments were deployed in vaults few hundred meters apart at depts from 3.2 to 2.2 m. They are new short-period seismographs measuring three translational and three rotational components. The array enabled new methods of microearthquakes investigation. The noise from surface sources (mainly traffic along nearby highway) can be suppressed significantly by non-linear summing of redundant translational data from each Rotaphone. This enabled detection of very weak microearthquakes in the vicinity of the array with good signal-to-noise ratio. The true azimuth and phase velocity along surface are determined by two methods:  the zero-crossing point beamforming and rotation-to-translation relations. Based on these quantities, location of microearthquakes was performed and it was compared to the locations from the USGS catalogue of local earthquakes.

The six-component records in the Long Valley Caldera are extremely complex. Strong phases between P- and S-wave onsets and namely within the S-wave group are visible in most seismograms. They probably originated as reflection and refraction waves at distinctive interfaces beneath the sediment filling of the caldera. Six-component records enabled analysis of individual wavetypes in the seismograms. The seismic array was reinstalled in the summer 2021 with new data-acquisition system with bigger dynamic range (32 bits A/D converter). We expect even more sensitive measurements from this new observation. 

How to cite: Brokesova, J. and Malek, J.: Six-component records of local seismicity in the Long Valley Caldera, Californica, US, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14093, https://doi.org/10.5194/egusphere-egu23-14093, 2023.

X2.114
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EGU23-7563
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ECS
David Sollberger, Sebastian Heimann, Felix Bernauer, Eva P. S. Eibl, Stefanie Donner, Céline Hadziioannou, Heiner Igel, Shihao Yuan, and Joachim Wassermann

In the past decade, significant progress has been made in the acquisition and processing of seismic wavefield gradient data (e.g., recordings of ground strain and rotation). When combined with conventional multicomponent seismic data, wavefield gradients enable the estimation of local wavefield properties (e.g., the local wave speed, the propagation direction, and the wave type) and the reconstruction of spatially under-sampled seismic wavefields. However, the seismological community has yet to embrace wavefield gradient data as a new observable.

We present TwistPy (Toolbox for Wavefield Inertial Sensing Techniques), an open-source software package for seismic data processing written in Python. It includes routines for single-station polarization analysis and filtering, as well as array processing tools. A special focus lies on innovative techniques to process spatial wavefield gradient data and, in particular, rotational seismic data obtained from dedicated rotational seismometers or small-aperture arrays of three-component sensors. Routines currently included in the package comprise polarization analysis and filtering in both the time domain and the time-frequency domain (for three-component and six-component data), dynamic tilt corrections, and beamforming (Bartlett, Capon, and MUSIC beamformers).  

With TwistPy, we attempt to lower the barrier of entry for the seismological community to use state-of-the art multicomponent and wavefield gradient analysis techniques by providing a user-friendly software interface.

Extensive documentation of the software and examples in the form of Jupyter notebooks can be found at https://twistpy.org.

How to cite: Sollberger, D., Heimann, S., Bernauer, F., Eibl, E. P. S., Donner, S., Hadziioannou, C., Igel, H., Yuan, S., and Wassermann, J.: TwistPy: An open-source Python toolbox for wavefield inertial sensing techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7563, https://doi.org/10.5194/egusphere-egu23-7563, 2023.

X2.115
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EGU23-5701
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ECS
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Gizem Izgi, Eva Eibl, Frank Krüger, and Felix Bernauer

Rotational motions can be recorded directly or derived from translational motion recordings. Fairly new rotational sensors allow seismologists to directly record and investigate rotational motions. In order to further investigate and compare recently developed rotational sensors an experiment was made in Fürstenfeldbruck. Within this scope, a vibroseis truck was operated starting from 20 November 2019, 11:00 UTC until 21 November 2019, 14:00 UTC. We recorded 480 Sweep signals at 160 different locations. The truck was operating at 30%, 50%, and 70% relative to a peak force output of 276 kN exciting the ground vertically and each sweep lasted 15 seconds starting with 7 Hz increased up to 120 Hz. We derived back azimuths of each sweep from 6 rotational sensors and calculated root mean squares of each component. We observed that within the first day, the North component of all sensors recorded the largest ground motion energy SV type of energy is dominant. The sweep sources were distributed over two North–South profiles and two East–West profiles.  While the truck moved to the east and its location moved from west to south of the rotational sensors, the signals dominate more and more on the East component.. From our preliminary results, we state that although having different signal to noise ratios all rotational sensor calculated the direction of each sweep. Thus, we can follow the movements of vibroseis truck using all rotational sensors.

How to cite: Izgi, G., Eibl, E., Krüger, F., and Bernauer, F.: Investigating Vibroseis Sweeps using 6 Rotational Sensors in Fürstenfeldbruck, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5701, https://doi.org/10.5194/egusphere-egu23-5701, 2023.

X2.116
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EGU23-6379
Stefanie Donner, Johanna Lehr, Mathias Hoffmann, Frank Krüger, Sebastian Heimann, Rafel Abreu, and Stephanie Durand

In synthetic tests, rotational ground motion recordings proved to be beneficial for the wavefrom inversion for seismic moment tensors. In a next step, we want to verify these findings using real measurements. To do so, we installed two broadband rotational collocated to translational ground motion sensors in the West Bohemia / Vogtland area in summer 2022.

The area is characterised by regular seismic swarm activity, the last one occurring in December 2021. The seismic swarms are known to be connected with crustal flow of mantle fluids. However, the detailed mechanism of this connection is not well understood yet. Full seismic moment tensors, especially their non-double-couple part, will contribute to investigate the connection between swarm activity and fluid flow. So far, a lacking number of moment tensors and difficulties in the reliability of the non-double-couple part hampered the analysis in the study area. Including rotational ground motion recordings to waveform inversion will help to overcome these difficulties.

In seven months, we have recorded 120 events with magnitudes larger than M ≥ 0 in a distance of up to 35 km, thereof 35 around Nový Kostel, the center of the swarm activity. Considering that rotational sensors are about 2-4 times less sensitive than translational sensors (depending on the local phase velocity of the location) this is already a great success. Here, we show details of the sensor installations, first data analysis, and an estimate on the magnitude of completeness from rotational measurements.

How to cite: Donner, S., Lehr, J., Hoffmann, M., Krüger, F., Heimann, S., Abreu, R., and Durand, S.: Rotational ground motion recordings in the West Bohemia / Vogtland region for waveform inversion for seismic moment tensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6379, https://doi.org/10.5194/egusphere-egu23-6379, 2023.

X2.117
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EGU23-15589
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Yara Rossi, Konstantinos Tatsis, Yves Reuland, John Clinton, Eleni Chatzi, and Markus Rothacher

We demonstrate that the dynamic response of an engineered structure, including modeshape identification, can be obtained from just a single measurement at one position - if rotation is recorded in combination with translation. Such a single-station approach can save significant time, effort and cost when compared with traditional structural characterization using horizontal arrays. In our contribution we will focus on the monitoring of a high-rise building by tracking its dynamic properties and their variations due to environmental (e.g. temperature) and operational (e.g. wind) conditions (EOCs) over a 1-year period. We present a real-case structural identification procedure on the Prime Tower in Zurich. This is a 36-story tower of 126 m height, with a poured-in-place-concrete core and floors and precast-concrete columns; this concrete core structure, surrounded by a triple-glazed facade, is the third highest building in Switzerland. 
The building has been continuously monitored, over a 1-year period, by an accelerometer (EpiSensor), a co-located rotational sensor (BlueSeis) and a weather station located near the building center on the roof. Roof and vertical seismic arrays were deployed for short periods. The motion on the tower roof includes significant rotation as well as translation, which can be precisely captured by the monitoring station. More than 20 structural modes, including the first 6 fundamental modes, where translations are coupled with rotations, are tracked between 0.3 – 14 Hz. We will also show the variation of natural frequencies due to seasonal but also more short-term effects, in an effort to understand the effect of environmental and operational variability on structural deformation and response. Additionally, an amplification of the modes, not only during strong winds, but also during a couple of Mw 4.0 - 4.4 earthquakes at regional distance has been observed and analysed. The frequency band between 0.3 and 10 Hz is of key interest for earthquake excitation, making an investigation thereof essential. The work closes with a summary of the main benefits and potential in adopting collocated rotation and acceleration sensing for geo-infrastructure monitoring purposes.

How to cite: Rossi, Y., Tatsis, K., Reuland, Y., Clinton, J., Chatzi, E., and Rothacher, M.: Variations of the system properties of a high-rise building over 1 year using a single station 6C approach., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15589, https://doi.org/10.5194/egusphere-egu23-15589, 2023.

X2.118
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EGU23-9629
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ECS
Felix Bernauer, Shihao Yuan, Joachim Wassermann, Heiner Igel, Celine Hadziioannou, Frederic Guattari, Chun-Man Liao, Ernst Niederleitinger, and Eva P. S. Eibl

Observing motion within a building in six degrees of freedom (three components of translational motion plus three components of rotational motion) opens completely new approaches to structural health monitoring. Inspired by inertial navigation, we can monitor the absolute motion of a building or parts of it without the need for an external reference. Rotational motion sensors can directly measure harmful torsional modes of a building, which has always been challenging and prone to errors when using translation sensors only. Currently, we are developing methodologies including rotational motion observations for monitoring of material parameters in order to locate and characterize structural damage. Within the framework of the GIOTTO project (funded by the German Federal Ministry for Education and Research, BMBF) we explore these approaches.

Here, we introduce a newly developed 6C sensor network for structural health monitoring. It consists of 14 inertial measurement units (IMU50 from exail, former iXblue, France) that were adapted to the needs of seismology and structural health monitoring. We performed experiments at the BLEIB test structure of the Bundesanstalt für Materialforschung und -prüfung (BAM), a 24 m long concrete beam serving as a large scale bridge model. We present results on detecting changes in material properties (seismic wave speed) of the beam with varying pre-stress and load, as derived from a novel approach by comparing amplitudes of translational to rotational motions at a single measurement point. We compare our findings to results obtained with coda wave interferometry using rotational as well as translational motions.

How to cite: Bernauer, F., Yuan, S., Wassermann, J., Igel, H., Hadziioannou, C., Guattari, F., Liao, C.-M., Niederleitinger, E., and Eibl, E. P. S.: Monitoring material properties of civil engineering structures with 6C point measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9629, https://doi.org/10.5194/egusphere-egu23-9629, 2023.