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Recent advances in deformation sensing have led to new applications in various geophysical disciplines such as earthquake physics, broadband seismology, volcanology, seismic exploration, strong ground motion, earthquake engineering and geodesy.
New developments in translation, rotation and strain sensing enable the complete observation of seismic ground motion and deformation. Applications are manifold, ranging from the reduction of nonuniqueness in seismic inverse problems to the characterization, separation and reconstruction of the seismic wavefield.
Among others, fibre optic technologies is bound to become a standard tool for crustal exploration and seismic monitoring thanks to: (i) easier installation (low cost, simpler installation and maintenance, robustness in harsh environment); (ii) high spatial and temporal resolution over long distance; (iii) broader frequency band. There have been significant breakthroughs, applying fibre optic technologies to interrogate cables at very high precision over very large distances both on land and at sea, in boreholes and at the surface.
These developments overlap with considerable improvements in optical and atom interferometry for inertial rotation and gravity sensing which has led to a variety of improved sensor concepts over the last two decades.
We welcome contributions on theoretical advances and applications of novel sensing methodologies in seismology, geodesy, geophysics, natural hazards, oceanography, urban environment, geothermal investigations, etc. including laboratory studies, large-scale field tests and modelling.

We are happy to announce Nathaniel J. Lindsey as invited speaker.

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Co-organized by ERE6/NH4
Convener: Gilda Currenti | Co-conveners: David SollbergerECSECS, Philippe Jousset, Felix Bernauer, Shane Murphy, André Gebauer, Zack SpicaECSECS, Sneha SinghECSECS
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| Attendance Wed, 06 May, 14:00–18:00 (CEST)

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Session summary Download all presentations (279MB)

Chat time: Wednesday, 6 May 2020, 14:00–15:45

Chairperson: Shane Murphy, Gilda Currenti, David Sollberger, Felix Bernauer
D1602 |
EGU2020-12594<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
| solicited
| Highlight
Nathaniel Lindsey, Jonathan Ajo-Franklin, Craig Dawe, Lise Retailleau, Biondo Biondi, and Lucia Gualtieri

Emerging distributed fiber-optic sensing technology coupled to existing subsea telecommunications cables enable access to meterscale, multi-kilometer aperture, broadband seismic array observations of ocean and solid earth phenomena. In this talk, we report on two multi-day Distributed Acoustic Sensing (DAS) campaigns conducted in 2018 and 2019 with the Monterey Accelerated Research System (MARS) observatory tether cable. In both experiments, a DAS instrument located on shore was connected to a fiber inside the buried MARS cable and recorded a ~10,000-component, 20-kilometer-long, strain-rate array. We use the 8 TB DAS dataset to address three questions:

1. How can seafloor DAS earthquake records inform offshore seismic hazard assessments? Offshore seismic hazards are poorly characterized despite dense coastal populations. The MARS DAS array captured multiple unaliased earthquake recordings, which document phase conversions and abrupt S-wave delays of 0.25 s at mapped (and unmapped) faults that transect the cable. Minor earthquakes in Northern California produce seismic waves in the range 0.5 - 50 Hz, which interact with submarine faults lying just offshore. Spectral ratios and wavefield synthetics are used to explore how seismic waves from well-characterized earthquakes interact with poorly-characterized subsea faults.

2. How are ocean microseisms and other coastal processes recorded by subsea DAS? Horizontal seabed ambient noise recorded with the MARS DAS array matches the expected dispersion of primary microseisms (f~0.05-0.15 Hz) induced by shoaling ocean surface waves, but at a higher band than onshore observations. Separation of incoming and outgoing waves recorded over the DAS array validates the Longuet-Higgins-Hasselmann theory that bi-directional ocean wind-waves undergo nonlinear wave interaction, producing secondary microseisms (f~0.4-1.5 Hz), even when the outgoing energy is observed to be <1% of the incoming energy. Continuous wavelet transforms of sea state observations from buoys, onshore broadband seismometers, and subsea DAS provide insight into the physics of microseism generation and ocean-solid earth coupling. Additionally, DAS provides observation of post-low-tide tidal bores (f~1-5 Hz), storm-induced sediment transport (f~0.8-10 Hz), infragravity waves (f~0.01-0.05 Hz), and breaking internal waves (f~0.001 Hz) consistent with previous point sensor observations in Monterey Bay. 

3. How is the coastal seafloor structure organized from shore to shelf break? The northern continental shelf of Monterey Bay is comprised of allochthonous Cretaceous granite overlain by marine sediments of varying thickness, and is crosscut by abandoned (and subsequently filled) paleochannels. Noise interferometry applied to the full MARS DAS dataset in the 0.25 - 5 Hz range retrieves Scholte waves, which are dispersive and coherent over 2 - 6 kilometers. We apply fundamental mode dispersion (1.5D) imaging to subarray noise correlations in order to understand the sediment thickness distribution across the shelf. Our model is compared with recent seismic reflection profiling conducted by the USGS California Seafloor Mapping Program.

How to cite: Lindsey, N., Ajo-Franklin, J., Dawe, C., Retailleau, L., Biondi, B., and Gualtieri, L.: Seafloor seismology with Distributed Acoustic Sensing in Monterey Bay, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12594, https://doi.org/10.5194/egusphere-egu2020-12594, 2020

D1603 |
EGU2020-5369<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Marc-Andre Gutscher, Jean-Yves Royer, David Graindorge, Shane Murphy, Frauke Klingelhoefer, Chastity Aiken, Antonio Cattaneo, Giovanni Barreca, Lionel Quetel, Giorgio Riccobene, Salvatore Aurnia, Florian Petersen, Dietrich Lange, Morelia Urlaub, Seabstian Krastel, Felix Gross, Heidrun Kopp, Milena Moretti, Laura Beranzoli, and Nadia Lo Bue and the FOCUS Team

Laser reflectometry (BOTDR), commonly used for structural health monitoring (bridges, dams, etc.), for the first time is being tested to study movements of an active fault on the seafloor, 25 km offshore Catania Sicily (an urban area of 1 million people). Under ideal conditions, this technique can measure small strains (10E-6), across very large distances (10 - 200 km) and locate these strains with a spatial resolution of 10 - 50 m. As the first experiment of the European funded FOCUS project (ERC Advanced Grant), in late April 2020 we aimed to connect and deploy a dedicated 6-km long strain cable to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute). The work plan for the marine expedition FocusX1 onboard the research vessel PourquoiPas? is described here. First, microbathymetric mapping and a video camera survey are performed by the ROV Victor6000. Then, several intermediate junction frames and short connector cables (umbilicals) are connected. A cable-end module and 6-km long fiber-optic strain cable (manufactured by Nexans Norway) is then connected to the new junction box. Next, we use a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The targeted track for the cable crosses the North Alfeo Fault at three locations. Laser reflectometry measurements began April 2020 and will be calibrated by a three-year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) also started April 2020, to quantify relative displacement across the fault. During a future marine expedition, tentatively scheduled for 2021 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of OBS (Ocean Bottom Seismometers) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of types of slipping events along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal is the development of dual-use telecom cables with industry partners.

How to cite: Gutscher, M.-A., Royer, J.-Y., Graindorge, D., Murphy, S., Klingelhoefer, F., Aiken, C., Cattaneo, A., Barreca, G., Quetel, L., Riccobene, G., Aurnia, S., Petersen, F., Lange, D., Urlaub, M., Krastel, S., Gross, F., Kopp, H., Moretti, M., Beranzoli, L., and Lo Bue, N. and the FOCUS Team: The FOCUS experiment 2020 (Fiber Optic Cable Use for Seafloor studies of earthquake hazard and deformation), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5369, https://doi.org/10.5194/egusphere-egu2020-5369, 2020

D1604 |
EGU2020-13988<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Luis Matias, Yasser Omar, Fernando Carrilho, Vasco Sá, Rachid Omira, Carlos Corela, Rui A. P. Perdigão, and Afonso Loureiro

CAM is the acronym of the submarine telecommunication fibre optic cables that interconnect in a ring Portugal mainland, Azores and Madeira archipelagos. The current cables will cease their operation by 2024 (due to the end of cable lifetime), and the process of their replacement by a new set of cables is now under consideration by the Portuguese authorities with the technical requirements to be defined until mid-2020.

The CAM cables span along the plate boundary between Eurasia and Nubia, an offshore domain prone to generate destructive earthquakes and tsunamis. The impacts caused by these natural hazards can be mitigated by effective tsunami (TWS) and earthquake (EEWS) early warning systems that would benefit (but not only) Portugal, Spain and Morocco. In TWS, a confirmation that a tsunami was generated, and an evaluation of its amplitude, are only obtained after the recordings from the closest coastal tide-gauge are analysed. Hence, this information will not benefit large stretches of coastline. EEWS that rely on land station observations of strong motion will not profit the regions closest to the epicentre. Furthermore, the quality of the offshore earthquake parameters computed by the operational centres is less than optimal when land stations only are used.

All these difficulties can be overcome by deploying sensors integrated in the commercial telecom submarine cables to be installed in the future, without reduction of the reliability, lifetime, operational and functional requirements demanded by operators. Being closer to the tectonic sources, such sensors (and the cable itself) will record the geophysical parameters and transmit them to land much faster than the speed of destructive waves, providing the processing centres with critical lead time. This is the approach that has been advocated by the Joint Task Force led by three U.N. agencies (ITU, WMO and UNESCO-IOC) (Howe et al., Front. Mar. Sci. 6:424, 2019). Such initiative was given the name of SMART, for Science Monitoring and Reliable Telecommunications.

In this work we evaluate the contribution of a SMART CAM fibre optic ring of cables, with repeaters equipped with geophysical sensors, to three critical aspects of TWS and EEWS: 1) quality of fast earthquake parameters; 2) earthquake early warning lead time; 3) tsunami confirmation warning time. The performance parameters selected where: i) azimuthal gap between the minimum set of stations required for an earthquake location to be accepted; ii) size of the estimated location error ellipse; iii) error on the focal depth estimation; iv) gain in P-wave advance time for the minimum set of stations required by the EEWS; v) gain in tsunami travel time to the closest tide-gauge or pressure sensor.

The methodology and results obtained are valuable to encourage national authorities to implement the SMART cable concept in the technical specifications for future telecommunication submarine cables. This has been recently suggested by the ANACOM President (the Portuguese regulator for telecommunications advising the national authorities) for the CAM cables that must be operational in early 2024. The first author would like to acknowledge the financial support from FCT through project UIDB/50019/2020-IDL.

How to cite: Matias, L., Omar, Y., Carrilho, F., Sá, V., Omira, R., Corela, C., Perdigão, R. A. P., and Loureiro, A.: The contribution of the CAM fibre optic submarine cable telecom ring to the early warning of tsunami and earthquakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13988, https://doi.org/10.5194/egusphere-egu2020-13988, 2020

D1605 |
EGU2020-12055<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Masanao Shinohara, Tomoaki Yamada, Takeshi Akuhara, KImihiro Mochizuki, and Shin'ichi Sakai

Distributed Acoustic Sensing (DAS) measurements which utilize an optical fiber itself as a sensor can be applied for various purposes. An observation of earthquakes using an optical fiber deployed on the seafloor with DAS technology is attractive because DAS measurements enable a dense seismic observation as a long linear array. Spatial resolution of the observation reaches a few meters. The length of the array is determined by the measurement range of the DAS interrogator deployed on the optical fiber, and a fine spatial sensor interval can be configured. DAS measurements have become increasingly accurate and the current state of technology exhibit high signal quality. Because DAS measurement is useful for earthquake observation, there were some trials for an observation of earthquakes using an optical fiber deployed on the land or the seafloor. However, There are few observations using DAS technology on seafloor until the present.

In 1996, a seafloor seismic tsunami observation system using an optical fiber cable was deployed off the coast of Sanriku by Earthquake Research Institute, the University of Tokyo. The system has three seismic stations and two tsunami-meters, and a length of the cable is approximately 115 km. The system has six spare (dark) optical fibers which are dispersion shifted single mode type, and have been incorporated for future extension of the observation system. We have started development of a seafloor seismic observation system utilizing DAS technology on the Sanriku cable observation system as a next generation of marine seismic observation system. In 2019, we performed DAS measurements using a dark fiber from Sanriku seafloor observation system three times. An interrogator was installed in the cable landing station temporarily. Data were recorded with various values of parameters, such as length of data collection (array aperture), gauge length, ping rate, acquisition offset, for evaluation of data quality and signal to noise ratios. The total recording period for three measurements was approximately three weeks. As a result, many earthquakes including micro-earthquakes were recorded. The obtained data will be used to develop data processing techniques for seismic observations utilizing DAS measurements.

 

How to cite: Shinohara, M., Yamada, T., Akuhara, T., Mochizuki, K., and Sakai, S.: Precise Distributed Acoustic Sensing measurements by using seafloor optical fiber cable system for seismic monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12055, https://doi.org/10.5194/egusphere-egu2020-12055, 2020

D1606 |
EGU2020-8484<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
| Highlight
Itzhak Lior, Daniel Mata, Gauthier Guerin, Diane Rivet, Anthony Sladen, and Jean-Paul Ampuero

The use of underwater optical fibers, such as those currently traversing most of the world's oceans, for distributed acoustic sensing (DAS) holds great potential for seismic monitoring by complementing on-land seismic observations, especially near underwater faults. The analysis of underwater DAS records presents special challenges due to the noisy environment and the uneven cable-seafloor coupling. To fully exploit the potential of these records, automatically detecting and extracting seismic signals is imperative. To this end, a new automatic earthquake detection scheme is presented, based on waveform-similarity. Cross correlations between nearby records along the fiber are continuously calculated in short overlapping intervals. Earthquakes are detected as abrupt increases in cross correlation values over large segments of the cable. This procedure is applied to records of four existing fibers: one on land (Near Teil, south of France) and three underwater (one in Toulon, south of France, and two in Pylos, south-west Greece). Detected earthquakes are compared to earthquake catalogs and detection thresholds are obtained. That several of the detected earthquakes do not appear in any earthquake catalog demonstrates the proposed method's robustness. The cross correlation time shifts are then used to perform moveout corrections to the time series and phase weighted stacking (PWS) is applied to groups of neighboring traces. Unlike simple stacking approaches, PWS significantly enhances signal to noise ratios, allowing for more precise earthquake analysis and characterization. Further developing and applying such automatic techniques to ocean bottom fibers will enhance the performance of earthquake early warning systems, improving alert times for earthquakes occurring on underwater faults.

How to cite: Lior, I., Mata, D., Guerin, G., Rivet, D., Sladen, A., and Ampuero, J.-P.: Automatic Earthquake Detection and De-noising for Distributed Acoustic Sensing: Examples from On-land and Underwater Fibers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8484, https://doi.org/10.5194/egusphere-egu2020-8484, 2020

D1607 |
EGU2020-11133<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Olivier Bour, Nataline Simon, Nicolas Lavenant, Gilles Porel, Benoit Nauleau, Behzad Pouladi, and Laurent Longuevergne

Active-Distributed Temperature Sensing is a new method that has been recently developed for quantifying groundwater fluxes in the sub-surface along fibre-optic cables with a great spatial resolution. It consists in measuring and modelling the increase of temperature due to a heat source, dissipated through heat conduction and heat advection, depending on groundwater fluxes. Here, we propose to estimate the applicability and limitations of the method using sandbox experiments where flow rate and temperature are well controlled. For doing so, active-DTS experiments have been achieved under different flow rates and experimental conditions. In addition, we compare three different and complementary methods to estimate in practice the spatial resolution of DTS measurements. 

Active-DTS experiments have been conducted by deploying a fiber optic cable in a large PVC tank (1.6m long; 1.2 m width and 0.3 m height) and filled with 0.4-1.3 mm diameter sand. The height of water in water reservoirs on either side of the sandbox can be adjusted to control the head gradient and the flow rate through the sand. Heating was done by injecting during at least 8 hours for each experiment, a well-controlled electrical current along the steel armouring of the fiber optic cable. The three methods for estimating spatial resolution were applied and compared using FO-DTS measurements obtained on the same fiber-optic cable but with two different DTS units having different spatial resolution. Results show that a large range of groundwater fluxes may be estimated with a very good accuracy. Finally, we compare the advantages and complementarities of the different methods proposed for estimating the spatial resolution of measurements. In particular, the spatial resolution estimated using a temperature step change is both dependent on the effective spatial resolution of the DTS unit but also on heat conduction induced because of the high thermal conductivity of the cable. By showing the applicability of the method for a large range of flow rates and with an excellent spatial resolution, these experiments demonstrate the potentialities of the method for quantifying fluid fluxes in porous media for a large range of applications.

How to cite: Bour, O., Simon, N., Lavenant, N., Porel, G., Nauleau, B., Pouladi, B., and Longuevergne, L.: Testing in sandbox experiments the potentialities of active-Distributed Temperature Sensing to quantify distributed groundwater fluxes in porous media, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11133, https://doi.org/10.5194/egusphere-egu2020-11133, 2020

D1608 |
EGU2020-22234<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Manos Pefkos, Pieter Doornenbal, Arjan Wijdeveld, Ebi Meshkati Shahmirzadi, and Pauline Kruiver

Distributed Temperature Sensing (DTS) measurements were conducted in the Port of Rotterdam as part of the INTERREG NWE SURICATES project. In the Port of Rotterdam a program is running to retain sediments in the harbor for river bank protection, and to lower the costs of transferring sediment from the port to the offshore dump locations. The aim of the DTS monitoring is to find spatial patterns in sediment deposition and erosion and thus determining the sediment balance before, during and after re-allocation. Fibre optic cables were installed in two layouts. Two fibre optic cables of lengths 1.2km and 750m were laid out flat parallel and perpendicular to the shore and they passively recorded temperature. Another cable was wrapped helically on a vertical pole condensing 150 m of length into 0.77m, increasing the spatial resolution. This cable was used for passive measurements and active heating experiments. The acquired data span the period from May to September 2019.

The active heating experiments showed that the water-sediment interface along the pole can be tracked from the difference in response between the time when the heating cable is switched on and off. The pole’s passive temperature analysis indicates that signals from the water phase exhibit high variability with time, whereas those from the sediment phase have low variability. Frequency domain analysis of the water phase shows clear peaks in the Fourier Amplitude Spectrum (FAS) at one day and half-day cycles, with the half-day cycle peak having the highest magnitude. The same peaks are present in the sediment phase’s FAS, but their magnitudes are about an order of magnitude lower.

The Fourier amplitude at frequencies corresponding to half-day periods was used for classification of the phases along the pole. The interface between water and sediment is defined as the maximum in the derivative of the Fourier amplitude with height. The interface’s height and thus the occurrence of erosion or deposition was tracked over time. The analysis shows that the sediment interface varied around 5cm over a period of 2.5 months between two dredging actions.

Representative signals from the Fourier amplitude at half-day cycles from the pole were used to derive sediment coverage over the flat passive cables. However, further research is required to establish the minimum horizontal distance over which coverage can be established.

We conclude that, by comparing the spectral properties of the temperature signal of water and sediment phases, sediment coverage over fibre optic cables can be monitored with DTS measurements. The finest time and spatial resolution over which this coverage can be found remains to be decided and can be the subject of future work.

How to cite: Pefkos, M., Doornenbal, P., Wijdeveld, A., Shahmirzadi, E. M., and Kruiver, P.: Monitoring sediment coverage from Distributed Temperature Sensing measurements in the Port of Rotterdam, the Netherlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22234, https://doi.org/10.5194/egusphere-egu2020-22234, 2020

D1609 |
EGU2020-9825<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Kentaro Emoto, Takeshi Nishimura, Hisashi Nakahara, Satoshi Miura, Mare Yamamoto, Shunsuke Sugimura, Takahiro Ueda, Ayumu Ishikawa, and Tsunehisa Kimura

First DAS observation at Mt. Azuma, Japan was conducted in July 2019 using buried fiber optic cable along the road access to the volcano. Mt. Azuma is an active volcano located in the Tohoku region. Different from non-volcanic regions, wavefields in the volcano is more complex due to its topography and the strong heterogeneities beneath the volcanic edifice. The strength of the scattering of seismic waves due to small-scale velocity heterogeneities in the volcano is reported to be more than one order higher than that in the non-volcanic region. To estimate small-scale heterogeneities, a dense observation network is necessary. The high spatial resolution is one of the advantages of the DAS observation. Therefore, DAS observation in the volcano might be a good chance for the estimation of the small-scale heterogeneity.

 

We used 14km length of the fiber optic cable buried along to the access road to the observatory near the summit installed by the Ministry of Land, Infrastructure, Transport and Tourism to monitor the volcanic activities. The spatial and temporal samplings were 10m and 1000Hz, respectively. The observation period was for 3 weeks. In addition to regional and teleseismic earthquakes, volcanic earthquakes were also observed. A teleseismic P-wave was analyzed to investigate the effect of small-scale heterogeneities. Because the incident angle of the teleseismic P-wave is almost vertical to the portion of the fiber optic cable used for the DAS observation, a simple model can be used. We calculate the cross-correlation coefficient (CCC) of waveforms between channels and analyze its dependence on the distances between channel pairs. The recorded wavefield was fluctuated by scattering due to the small-scale heterogeneities and different waveforms were recorded even though the propagation distances are the same. Therefore, the spatial variation of the waveforms of teleseismic P-wave recorded at surface stations would be related to the small-scale heterogeneities beneath of the array.

 

The CCC decreases with increasing separation distance and converges to a constant value. This shape can be modeled by the Gaussian function and we defined the spatial scale of CCC by fitting the Gaussian function. The scale decreases with increasing frequency. The finite difference simulation of the wave propagation was performed by changing the velocity structure and compare the synthetic and observed CCCs. We found that the effect of the topography is most significant on the CCC. Because analyzed waveforms mainly consist of the converted surface wave from the teleseismic P-wave, the effect of subsurface small-scale heterogeneities is not significant. Our result shows that it is necessary to consider the effect of the topography in analyses of DAS data recorded in volcanoes.

How to cite: Emoto, K., Nishimura, T., Nakahara, H., Miura, S., Yamamoto, M., Sugimura, S., Ueda, T., Ishikawa, A., and Kimura, T.: Effect of complex topography on the wavefield recorded by DAS and buried fiber optic cable at Azuma volcano, Northeast Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9825, https://doi.org/10.5194/egusphere-egu2020-9825, 2020

D1610 |
EGU2020-18084<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Umberto Giacomelli, Enrico Maccioni, Giorgio Carelli, Daniele Carbone, Salvatore Gambino, Massimo Orazi, Rosario Peluso, and Fiodor Sorrentino

Rock strains detection is one of the principal ways to monitor geohazards. Classic strainmeters are cumbersome, hard to install and very expensive. Opto-electronics devices based on fiber Bragg grating technology allow to realize strainmeters with high sensitivity, low-cost, small volume and high performance.
We present the long term result of continuous soil strain monitoring on the Etna mount by a three-axial fiber Bragg grating sensor. The sensor has been developed in the framework of European Project MED-SUV (MEDiterranean SUpersite Volcanos). The installation site is a 8.5 meters deep borehole at a distance of about 7 km South-West from the summit craters of the Etna mount, at an elevation of about 1740 meters. This kind of sensor has a resolution better than 100 nanostrains on a daily timescale. Despite it is only a prototype, the sensor has worked for four years with a duty-cycle higher than 90% detecting both fast event, as earthquakes, and slow event, as epochal rocks strain behavior.

How to cite: Giacomelli, U., Maccioni, E., Carelli, G., Carbone, D., Gambino, S., Orazi, M., Peluso, R., and Sorrentino, F.: Four years of soil strain monitoring on Etna Volcano Mount by means of a Three-axial Fiber Bragg Grating Sensor, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18084, https://doi.org/10.5194/egusphere-egu2020-18084, 2020

D1611 |
EGU2020-14022<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Takeshi Tsuji, Tatsunori Ikeda, and Koshun Yamaoka

We have developed a permanent seismic monitoring system using a continuous seismic source and distributed acoustic sensing (DAS). The active seismic source system continuously generates waveforms with wide frequency range. By stacking the continuous waveforms, our monitoring system improves signal-to-noise ratio of the seismic signal. Thus, less-energy vibration using small-size source could be utilized for the exploration of deeper geological targets. Presently, we have deployed the small-size monitoring source system in the Kuju geothermal field in the northeast Kyushu Island, Japan. Although our monitoring source system is small and generates high frequency vibrations (10-20Hz), the signal propagated >80 km distance using two-month continuous source data. Our field experiments demonstrate that variation of seismic velocity of the crust could be identified with high accuracy (~0.01 %). To record the monitoring signal from continuous source system, we need to deploy seismometers. Deployment of many seismometers increase spatial resolution of the monitoring results. Recently, we have deployed the DAS system close to the continuous seismic source system. Using DAS, dense and long seismometer network can be realized, and we succeeded to identify the temporal variation of seismic velocity. By using both continuous source and DAS, we are able to monitor wide area with lower cost. Our monitoring system could accurately monitor the larger-scale crust and smaller-scale reservoir in high temporal resolution.

How to cite: Tsuji, T., Ikeda, T., and Yamaoka, K.: Continuous source system and distributed acoustic sensing for reservoir to crust monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14022, https://doi.org/10.5194/egusphere-egu2020-14022, 2020

D1612 |
EGU2020-10096<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Baoshan Wang, Xiangfang Zeng, Jun Yang, Yuansheng Zhang, Zhenghong Song, Xiaobin Li, Rongbin Lin, Manzhong Qin, and Congxin Wei

Recently large-volume airgun arrays have been used to explore and monitor the subsurface structure. The airgun array can generate highly repeatable seismic signals, which can be traced to more than 200 km. And the airgun source can be ignited every 10 minutes. The airgun source makes it possible to precisely monitor subsurface changes at large scale. The spatial resolution of airgun monitoring is poor subjecting to the receiver distribution. The distributed acoustic sensing (DAS) technique provides a strategy for low-cost and high-density seismic observations. Two experiments combing DAS technique and airgun source were conducted at two sites with different settings. At the first site, a telecommunication fiber-optic cable in urban area was used. After moderate stacking, the airgun signal emerges on the 30-km DAS array at about 9 km epicentral distance. In the second experiment, a 5-km cable was deployed from the airgun source to about 2 km away. About 800-m cable was frozen into the ice above the air-gun, the rest cable was cemented on the road crossing through a fault. And the airgun has been fired continuously for more than 48 hours with one-hour interval. On the stacking multiple shots’ records, the wavefield in fault zone emerges too. These two experiments demonstrate the feasibility of using various fiber-optic cables as dense array to acquire air-gun signal in different environments and to monitor the subsurface changes.

How to cite: Wang, B., Zeng, X., Yang, J., Zhang, Y., Song, Z., Li, X., Lin, R., Qin, M., and Wei, C.: High precision and high resolution monitoring of subsurface changes with DAS and airgun, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10096, https://doi.org/10.5194/egusphere-egu2020-10096, 2020

D1613 |
EGU2020-7495<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Camille Jestin, Clément Hibert, Gaëtan Calbris, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) is an innovative technique which has been recently employed for near-surface geophysics purposes. It involves the use of fibre-optic cable as a sensor. The fibre is analysed by sending a laser pulse from an interrogator unit. The phase of the backscattered signal contains the information on the strain on the cable, enabling the detection of a passing acoustic wave with enough energy for the cable excitation. Allowing the interrogation of long profiles and the generation of a dense spatial sampling, uneasy to obtain with classic geophysical techniques, DAS instrumentation then proved its relevance for seismic applications but also for infrastructure monitoring.

During DAS acquisition, and more precisely when closely looking at infrastructures integrity, it is necessary to clearly identify the source of the acoustic vibrations at the structure neighbourhood. Indeed, in the context of pipeline monitoring for example, it appears important to be able to classify events which generate seismic signals recorded by DAS systems and which can be related to a potential threat for the structure. In order to launch an alarm if necessary, the source identification must be fast, accurate and robust. Moreover, because DAS acquisition can generate traces every few meters along fibres of tens of kilometres, the used machine-learning algorithm must demonstrate its ability to handle a big amount of data.

In this study, we analyse the efficiency of the Random Forests (RF) machine-learning algorithm applied to data acquired with DAS system for the discrimination of event sources. RF algorithm has been selected because of its ability to handle large numbers of attributes related to signal characteristics and to enable a good reliability for the discrimination of sources. This algorithm has already proved its efficiency for automated classification of seismic waveforms (e.g. earthquakes, volcanic tremors, rock falls, avalanches, etc.).

We focus our study on tests lead along a gas pipeline instrumented with fibre-optic cable. Different third-party works have been conducted: excavation, saw sections, drill, jackhammer, etc. We work on the discrimination of six classes of seismic source. After running a detection phase based on a threshold on signal energy, we obtain several hundred of exploitable seismic traces to inject to the RF algorithm. We demonstrate the efficiency of the application of machine learning on DAS data to discriminate seismic waveforms from the correct class, with an overall precision on our test set of 99%.

How to cite: Jestin, C., Hibert, C., Calbris, G., and Lanticq, V.: Integration of Machine Learning on Distributed Acoustic Sensing Surveys , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7495, https://doi.org/10.5194/egusphere-egu2020-7495, 2020

D1614 |
EGU2020-20516<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Frédéric Guattari, Philippe Gueguen, Coralie Aubert, and Théo Laudat

Civil engineering structures are often modeled as single-degree-of-freedom systems, taking into account only horizontal translation forces. However, their response to seismic loading produces rotational forces that can in some cases generate considerable stresses and resultant damage. These rotational forces are essentially related to (1) rotational deformation about both horizontal axes (rocking), resulting from ground-structure interactions, considering the structure as a rigid body; (2) rotation about the vertical axis (torsion), essentially activated when the centre of mass (i.e. where the seismic inertial forces apply) is offset from the centre of rigidity (i.e. where the elastic forces apply). The simplified model including the rotations of the ground-structure interaction is based on modal decomposition, i.e. each component of the motion is assumed to be independent of the others. Thus, in structures, only translational sensors are usually installed and the rotational components are evaluated via the spatial derivatives of the horizontal and vertical components. However, there are combinations of translations and rotations and rotations can only be evaluated by measuring all 6 components of motion (3 translations and 3 rotations). In this presentation, a simple analysis is made to explain the rotations observed in the City Hall building in Grenoble (France), a 12-storey reinforced concrete building. This building has been continuously monitored for 10 years, with 3-component accelerometers located at the bottom and top. Modal decomposition is performed using ambient vibrations. A set of earthquake records is then used to evaluate rotations using derived functions and compared with the records of a 6C rotation sensor temporarily installed at the top of the building. The comparison between the direct rotation measurement and the spatially derived rotation is performed. 

How to cite: Guattari, F., Gueguen, P., Aubert, C., and Laudat, T.: Rotation in civil engineering structures: analysis of the City-Hall (Grenoble) building using 3C and 6C sensors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20516, https://doi.org/10.5194/egusphere-egu2020-20516, 2020

D1615 |
EGU2020-10742<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Eileen Martin, Tieyuan Zhu, Junzhu Shen, Srikanth Jakkampudi, Weichen Li, and Ayush Dev

The FORESEE Distributed Acoustic Sensing (DAS) Array records roughly 1/3 terabyte of data per day along 5 kilometers of dark fiber optic telecommunications cable underneath the Pennsylvania State University campus. The campus sits in the Allegheny Mountain region of the US, and our aim is to understand urban hydrology and detection of geohazards (particularly karst features). We have verified a number of features of these data similar to prior urban seismic studies, both in ambient noise and in distant earthquake records, which builds further evidence that dark fiber can be a useful tool for seismology in cities.

These data also contain a number of new signals not observed on previous dark fiber arrays. We see a stronger response to air waves than prior experiments. For instance, musical bass lines are clearly observed in the 30-100 Hz range during a concert, and we can see the spatial decay of higher versus lower frequencies throughout the array. This is the first dark fiber array in the eastern US, where thunderstorms occur with some frequency, and we have observed clear recordings of ground motion due to thunder. Source inversion of the waveforms throughout the array leads to locations that show reasonable agreement compared to the National Lightning Detection Network. These thunderquake signals could be an important source of broadband energy for seismic imaging in an area with little earthquake seismicity.

We have performed ambient noise interferometry throughout the array with a variety of pre-processing workflows, but some subsets of the array are strongly affected by nearby sources. With the wide variety of natural and manmade signals in these data, we are working towards further efficient automation to detect repeatable signals that could be used for targeted interferometry, and methods to automate filtering of non-ideal noise sources. As one example of filtering a specific noise, we were surprised the array is able detect the paths of individuals walking along a sidewalk by the fiber. While this array records data on a public college campus, a likely future area of research may include urban areas with a mix of commercial and residential purposes, so we desire tools to remove individual signals as they are recorded. Thus, we have developed a neural network to detect and remove footsteps from data before those data are shared with researchers. To encourage others working on urban seismic acquisition to remove similar signals, we are generalizing these methods for footstep removal to different scales.

How to cite: Martin, E., Zhu, T., Shen, J., Jakkampudi, S., Li, W., and Dev, A.: Fiber Optics foR Environmental SEnsE-ing (FORESEE) at Pennsylvania State University, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10742, https://doi.org/10.5194/egusphere-egu2020-10742, 2020

D1616 |
EGU2020-7343<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Patrick Paitz, Pascal Edme, Cédric Schmelzbach, Joesph Doetsch, Dominik Gräff, Fabian Walter, Nathaniel Lindsey, Athena Chalari, and Andreas Fichtner

With the upside of high spatial and temporal sampling even in remote or urban areas using existing fiber-optic infrastructure, Distributed Acoustic Sensing (DAS) is in the process of revolutionising the way we look at seismological data acquisition. However, recent publications show variations of the quality of DAS measurements along a single cable. In addition to site- and orientation effects, data quality is strongly affected by the transfer function between the deforming medium and the fiber, which in turn depends on the fiber-ground coupling and the cable properties. Analyses of the DAS instrument response functions in a limited part of the seismological frequency band are typically based on comparisons with well-coupled conventional seismometers for which the instrument response is sufficiently well known to be removed from the signal.

In this study, we extend the common narrow-band analyses to DAS response analyses covering a frequency range of five orders of magnitude ranging from ~4000 s period to frequencies up to ~100 Hz. This is based on a series of experiments in Switzerland, including (1) active controlled-source experiments with co-located seismometers and geophones, (2) low-frequency strain induced by hydraulic injection in a borehole with co-located Fiber-Bragg-Grating (FBG) strain-meters, and (3) local to teleseismic ice- and earthquake recordings with  co-located broadband stations.

Initial results show a site-unspecific, approximately flat instrument response for all experiments.

The initial results suggest that the amplitude and phase information of DAS recordings are sufficient for conventional geophysical methods such as event localisation, full-waveform inversion, ambient noise tomography and even event magnitude estimation. Despite the promising initial results, further engagement by the DAS community is required to evaluate the DAS performance and repeatability among different interrogation units and study sites.

How to cite: Paitz, P., Edme, P., Schmelzbach, C., Doetsch, J., Gräff, D., Walter, F., Lindsey, N., Chalari, A., and Fichtner, A.: Distributed Acoustic Sensing from mHz to kHz: Empirical Investigations of DAS Instrument Response, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7343, https://doi.org/10.5194/egusphere-egu2020-7343, 2020

D1617 |
EGU2020-18525<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Björn Lund, Anna Stork, Michael Roth, Ari David, Andy Clarke, Carl Nygren, and Sam Johansson

As part of the preparations for a microseismic network on the planned nuclear waste repository in Forsmark, Sweden, we carried out a suite of measurements for site characterisation and instrument testing using geophones and DAS fiber-optic technology. Three high-sensitivity 240 V/m/s geophones were grouted into a 200 m deep borehole together with a linear, a helical and a helical engineered fiber-optical cable. Two different interrogators were used for DAS acquisition. We performed a walk-away vertical seismic profile (VSP) survey with 10 m source spacing out to 1.1 km offset and compare the responses of the four different measurement systems. The complete transfer functions of the fiber-optic systems have not yet been determined, and depend on factors such as incidence angle, signal frequency content and the fiber gauge length. Preliminary results show that all systems record signals with high signal-to-noise ratio and that which system has highest performance depends on source-receiver distance, signal frequency content and wave incidence angle. Due to incomplete knowledge of the fiber transfer functions we cannot match the DAS velocity signal with the geophone signal. Investigation of the detection capabilities of the fiber and geophone systems is underway and will be presented together with a discussion of the relative merits of the various systems for microseismic monitoring.

How to cite: Lund, B., Stork, A., Roth, M., David, A., Clarke, A., Nygren, C., and Johansson, S.: Comparing high-sensitivity geophones to fiber-optic DAS technologies in a hard-rock VSP survey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18525, https://doi.org/10.5194/egusphere-egu2020-18525, 2020

D1618 |
EGU2020-12695<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Raghukanth Stg and Varun K singla

 

In recent times, seismic rotational motions have received significant attention of seismologists as well earthquake engineers. The measurement of rotational motions is useful not only for the complete characterization of the ground motion, but also for estimating the additional risk to civil engineering structures posed by these motions. With the development of state-of-the-art instruments such as the ring-laser and fiber-optic gyroscopes, and mechanical and magneto-hydrodynamic devices, it is now possible to measure these motions over a large frequency bandwidth with accuracy. Nevertheless, nearly all earthquake-prone regions of the world lack the instrumentation to record these motions and the existing database of recorded rotational motions thus remains limited. In such situations analytical methods can provide estimates of rotational ground motions. It is thus common to simulate these motions and most analytical methods simulate rotations as curl of the displacement field. Because this relation (refer to as ‘curl-based’) is based on the ‘small deformations’ assumption, the ‘curl-based’ rotations are in a sense an approximation of the exact rotations, the latter being computed by using the rotational matrix directly extracted from the deformation gradient using the polar decomposition theorem. Despite this, no study has so far discussed the situations in which the ‘curl-based’ relation no longer holds. This paper therefore attempts to shed light on this issue by conducting two numerical studies. In the first study, a simple case of a point kinematic dislocation shear source buried in a homogeneous, elastic half-space is considered to get a qualitative idea about the combinations of the source and medium parameters that can lead to appreciable errors in the ‘curl-based’ rotations. The second study considers the finite-fault source model of Chi-Chi earthquake to illustrate these errors in a realistic scenario. Both these studies indicate that the ‘curl-based’ rotations can be in appreciable error when ‘exact’ rotations are in excess of  20 degrees and that this can happen in the near-field regions of surface-rupturing faults.

How to cite: Stg, R. and K singla, V.: Simulation of Rotational ground motion in the near field region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12695, https://doi.org/10.5194/egusphere-egu2020-12695, 2020

D1619 |
EGU2020-7381<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Heiner Igel, Felix Bernauer, Joachim Wassermann, Shihao Yuan, Andre Gebauer, and Ullrich Schreiber

The ROMY ring laser was constructed with 4 non-orthogonal triangular-shaped cavities of 12 m side length in the Geophysical Observatory outside Munich, Germany, in 2016. The large dimensions of the individual rings have the benefit of allowing high sensitivity surpassing in principle the sensitivity of the G-ring at the Fundamentalstation Wettzell. However, the concrete construction of ROMY is geometrically less stable than the G-ring that is built on a rigid Xerodur plate. Each of the four rings has its own Sagnac frequency. The horizontal triangular ring laser at the top of the inverted tetrahedral ROMY structure allows direct comparison of teleseismic signals and noise with the G-ring at a distance of 200km. It also serves as redundant component. In principle, three orthogonal components of rotational ground motion can be obtained by linear combination from any combination of three rings, that - due to the variable Sagnac frequency - have different noise characteristics. We report on the behavior and observations of ROMY from a seismological point of view. It is fair to say that ROMY provides the most accurate direct 3-component rotational ground motion seismic observations to date. In combination with a collocated broadband seismometer as well as a surrounding small-scale seismic array, we analyse regional, teleseismic events, and ocean-generated noise and compare with array-derived rotation.

How to cite: Igel, H., Bernauer, F., Wassermann, J., Yuan, S., Gebauer, A., and Schreiber, U.: The ROMY project: A 4-component ring laser for geophysics and geodesy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7381, https://doi.org/10.5194/egusphere-egu2020-7381, 2020

D1620 |
EGU2020-8434<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Remi Geiger, romain gautier, leonid sidorenkov, and arnaud landragin

Cold-atom inertial sensors target several applications in navigation, prospection, geoscience and tests of fundamental physics. The operation of these sensors is based on atomic interferometry taking advantage of superpositions between quantum states of different momentum of an atom. These superposition states are obtained by means of optical transitions with two (or more) photons communicating momentum to the atom and acting as beam splitters and mirrors for the matter waves. The SYRTE cold-atom gyroscope currently represent the state of the art of atomic gyroscopes with a short-term sensitivity of 40 nrad/s/sqrt(Hz) limited by vibration noise (using a 4 Hz sampling rate), a long term stability of 3e-10 rad/s and an accuracy of 10 nrad/s. The detection noise limit of the sensor (quantum projection noise) is currently 5 nrad/s/sqrt(Hz) in the band DC-1 Hz, which already represents an interest to sense ground rotations in a typical frequency range between 1 mHz and 1 Hz. A second horizontal axis of measurement is currently being implemented. Moreover, we are designing a new experiment which aims a reaching a (quantum projection noise limited) sensitivity of 1 nrad/s/sqrt(Hz) in this frequency band along two axes of measurement, which represents an interesting perspective for the field of rotational seismology. This contribution will present the results recently achieved with the SYRTE gyroscope experiment to reach state-of-the-art performances and present the route to applications of this sensor in geosciences.

 

How to cite: Geiger, R., gautier, R., sidorenkov, L., and landragin, A.: Towards a two-axis cold-atom gyroscope for rotational seismology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8434, https://doi.org/10.5194/egusphere-egu2020-8434, 2020

D1621 |
EGU2020-13360<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Roland Hohensinn, Nikolaj Dahmen, John Clinton, Alain Geiger, and Markus Rothacher

In this paper we highlight the potential of geodetic high-precision and high-rate GNSS (Global Navigation Satellite System) sampling (1 to 100 Hz) for resolving seismic ground motions, of both the near and the far field of an earthquake. The analysis of the budget and characteristics of the error of high-rate GNSS displacement time series yields results, discussion, and conclusions on the sensitivity and waveform resolvability as well as on the derivation of a minimum detectable displacement (in the statistical sense).

Based on these analyses, we show how GNSS can contribute to optimal broadband displacement and velocity waveform products by means of data fusion by combining measurements taken from co-located sensors – e.g. accelerometers or gyroscopes – in real-time, near real-time and postprocessing mode. Concerning the inclusion of GNSS for such an analysis, we also briefly explore the ability of GNSS to record signals from different earthquake magnitudes and epicentral distances. We show that high-rate GNSS is sensitive to displacements down to the level of a few millimeters, and even below – an example also comes from the detection of very small vibrations from 100 Hz GNSS data.

We analyze measurements of synthetized signals obtained from experiments with a shake table, as well as from real data from strong earthquakes, namely the 6.5 Mw event of 2016 near the city of Norcia (Italy) and the 7.0 Mw Kumamoto earthquake of 2016 (Japan). Based on these data and our main findings, we finally discuss the role of GNSS in Earthquake Early Warning in terms of a fast hypocenter localization and reliable magnitude estimation.

How to cite: Hohensinn, R., Dahmen, N., Clinton, J., Geiger, A., and Rothacher, M.: Resolving dynamic ground motions with high-rate GNSS and implications for data fusion in broadband seismology and Earthquake Early Warning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13360, https://doi.org/10.5194/egusphere-egu2020-13360, 2020

Chat time: Wednesday, 6 May 2020, 16:15–18:00

Chairperson: Zack Spica, Sneha Singh, David Sollberger, Philippe Jousset
D1622 |
EGU2020-21787<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Olivier Sèbe, Stéphane Gaffet, Roxanne Rusch, Jean-Baptiste Decitre, Charly Lallemand, Daniel Boyer, Alain Cavaillou, Jean-Marc Koenig, Serge Olivier, and François Schindele

In the last 20 years, seismologists have recognized that a better sensing of the seismic wavefield is obtained by considering the rotational ground motions in addition to the translation measurements usually provided by seismometers. Even though recent technological developments have resulted in new portable rotation sensors with a sensitivity and a bandwidth suited to seismological applications requirements, the ground rotations have for a long time been estimated indirectly by dense seismic arrays.

The Low Noise Underground Laboratory (LSBB) includes a dense 3D seismic antenna composed of 6 STS2 broad-band seismometers since March 2005. From 2016, this array has been upgraded by the installation of about 10 new seismometers at the surface and inside the galleries of the laboratory. Thanks to these dense and small aperture seismic networks, the vertical and horizontal rotations of the ground motion have been estimated by finite difference approximation of the spatial derivatives of the local ground motions. These measurements provide the opportunity to conduct six degree of freedom (6DOF) analysis (3C translations and 3C rotations) to find out the direction of the wave propagation and to estimate the seismic wave local phase velocity.

The performance of this seismic array in deriving the local spatial gradient of the seismic wavefield, as well as the rotation tensor, will be illustrated by several selected seismic records such as the 2016 central Italy crisis (Amatrice and Norcia events) as well as the recent local Teil earthquake. In addition, the Array Derived Rotations (ADR) from the LSBB antenna are compared with the rotations measured by different kinds of rotation sensors including 2 prototypes of the new BlueSeis3A and a Lily Borehole Tiltmeter.

How to cite: Sèbe, O., Gaffet, S., Rusch, R., Decitre, J.-B., Lallemand, C., Boyer, D., Cavaillou, A., Koenig, J.-M., Olivier, S., and Schindele, F.: The seismic broad-band antenna of the Low Noise Underground Laboratory (LSBB, Rustrel, France): a tool for measuring the rotation ground motion., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21787, https://doi.org/10.5194/egusphere-egu2020-21787, 2020

D1623 |
EGU2020-15258<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Andreino Simonelli, Matteo Desiderio, Umberto Giacomelli, Gaetano De Luca, Aladino Govoni, and Angela Di Virgilio

In the present work, we analyze rotational and translational ground motions, in order to retrieve the local wavefield properties. We apply the same method of analysis to both earthquake and ambient noise signals, in order to estimate the wave field direction and the phase velocity as a function of frequency.
For the first case, the vertical rotation rate is measured by a large ring laser gyroscope (named GINGERino). Translational motions, on the other hand, are recorded by a broad-band seismometer (a station of the INGV national seismic network IV, code-named GIGS). These instruments are colocated in a gallery inside the facilities of the Laboratorio Nazionale del Gran Sasso (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN), at 1km depth, and constitute a 4 Components (4C) station. We examine the data recorded in late November 2019 i.e. the earthquakes in Northern Albania, Balkan region and off the coast of Crete. An additional event that struck the Mugello Region (Italy) in early December 2019 is also analyzed. We focus on the rotational motions induced by S and Love waves. In the second case, we exploit a temporary array (named XG) of 3-component broad-band seismometers (code-named GIN*) installed in the facilities of the LNGS. Here, the rotation rate is derived trough a finite-difference scheme involving the stations of the array. First, we test the reliability of the ADR method XG with simulated earthquake data. In a second step we analyse the secondary microseism signal recorded during a sea storm that occurred in the Mediterranean basin in early January 2019. Such workflow is also compared to an f-k analysis, that is a common array data processing method. Finally, theoretical P body waves noise sources are computed and compared to the estimated BAZ.

How to cite: Simonelli, A., Desiderio, M., Giacomelli, U., De Luca, G., Govoni, A., and Di Virgilio, A.: Direct and array-derived rotations in the Gran Sasso underground laboratory: application to earthquakes and seismic noise. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15258, https://doi.org/10.5194/egusphere-egu2020-15258, 2020

D1624 |
EGU2020-15252<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Charlotte Krawczyk, Philippe Jousset, Gilda Currenti, Michael Weber, Rosalba Napoli, Thomas Reinsch, Giorgio Riccobene, Luciano Zuccarello, Athena Chalari, and Andy Clarke

Volcanic and seismic activities produce a variety of phenomena that put population at risk. Etna volcano provides an example where volcanic and tectonic processes are strongly coupled. Distributed Acoustic Sensing (DAS) technology has been for the first time tested both in 2018 and 2019 as a new tool for monitoring the complex tectonic and volcanic interactions at Etna volcano from summit to the sea floor. We connected up to 3 iDAS interrogators, sometimes simultaneously, to optical cables close to the summit, in urban areas and offshore. Each iDAS measured the dynamic strain rate along the whole length of the optical fibre, from the interferometric analysis of the back-scattered light.

In the summit area, we connect an iDAS interrogator inside the Volcanological Observatory of Pizzi Deneri (2800 m elevation close to Etna summit) to record dynamic strain signals along a 1.5 km-long fibre optic cable that we deployed in the scoria of Piano delle Concazze. We recorded signals associated with various volcanic events, local and distant earthquakes, thunderstorm, as well as many other anthropogenic signals (e.g., tourists). To validate the DAS signal we collocated along the fibre cable multi-parametric arrays (comprising geophones, broadband seismometers, infrasonic arrays). During the survey periods, Etna activity was mainly characterized by moderate but frequent explosive and/or effusive activity from summit craters. Our observations suggests that DAS technology can record volcano-related signals (in the order of tens nanostrain) with unprecedented spatial and temporal resolutions, opening new opportunities for the understanding of volcano processes.

In urban environments, taking advantage of the existence of fibre optic telecommunication infrastructures, we connected iDAS interrogator to fibre optic cables, known to cross active faults linked to the volcano eastern flank dynamics. We recorded dynamic strain rate along a 4 km cable for about 20 days in Zafferana village and along a 12 km-long cable running from Linera to Fleri. We also tested DAS recording along a 40 km-long fiber optic telecommunication cable on the western side of the volcano, at the border between the sedimentary layer and the volcano edifice.

On the sea floor, we connected an iDAS interrogator to a 30-km long fibre within a cable transmitting data from sub-marine instrumentation to INFN-LNS facility at the Catania harbour. We record dynamic strain signals from local and regional earthquakes and detect some previously unknown faults offsetting the sea floor below the eastern flank of the volcano.

Our results demonstrate that DAS technology is able to contribute to the monitoring system of earthquake and volcanic phenomena at Etna volcano, and thereby could improve the volcanic and seismic hazard assessment in the future.

How to cite: Krawczyk, C., Jousset, P., Currenti, G., Weber, M., Napoli, R., Reinsch, T., Riccobene, G., Zuccarello, L., Chalari, A., and Clarke, A.: Monitoring volcanic and seismic activity with multiple fibre-optic Distributed Acoustic Sensing units at Etna volcano, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15252, https://doi.org/10.5194/egusphere-egu2020-15252, 2020

D1625 |
EGU2020-11641<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Gilda Currenti, Philippe Jousset, Athena Chalari, Luciano Zuccarello, Rosalba Napoli, Thomas Reinsch, and Charlotte Krawczyk

We explore a unique dataset collected by Distributed Acoustic Sensing (DAS) technology at the summit of Etna volcano in September 2018. We set-up an iDAS interrogator (Silixa) inside the Observatory Pizzi Deneri to record strain rate signals along a 1.3 km-long fibre optic cable deployed in Piano delle Concazze. This area is affected by several North-South trending faults and fractures, that are originated to accommodate the extension of the nearby North-East Rift zone, where magmatic intrusions often occur. The field evidence of the segments of these faults and fractures is hidden by lava flows and volcano-clastic deposits (e.g. scoria and lapilli) produced by the effusive and explosive activity of Etna volcano.

We propose a new technological and methodological framework to validate, identify and characterize volcano-related dynamic strain changes at an unprecedented high spatial (2 m) and temporal (1 kHz) sampling over a broad frequency range. The DAS record analysis and the validation of the iDAS response is performed through comparisons with measurements from a dense network of conventional sensors (comprising 5 broadband seismometers, 15 short-period geophone and two arrays of 3 infrasound sensors) deployed along  the fibre optic cable.  Comparisons between iDAS signals and dynamic strain changes estimated from the broadband seismic array shows an excellent agreement, thus demonstrating for the first time the capability of DAS technology in sensing seismic waves generated by volcanic events.

The frequent and diverse Etna activity during the acquisition period (30 August - 16 September 2018) offers the great opportunity to record a wide variety of signals and, hence, to test the response of iDAS to several volcanic processes (e.g. volcanic tremor, explosions, strombolian activity, local seismic events). Here, we focus the analysis on the signals recorded during a small explosive event on 5 September 2018 from the New South-East Crater (NSEC). This explosive event generated both seismic waves (recorded by the seismometers) propagating in the ground, and acoustic pressure signals (recorded by the infra-sound arrays) propagating in the atmosphere. We show that the DAS records catch both, as confirmed by the conventional sensors records.

Spectrogram analyses of the DAS signals reveal that the frequency content is confined in two distinctive frequency bands in the ranges 0.5-10 Hz and 18-25 Hz, for the seismic and acoustic wave, respectively. The amplitude and frequency response of the ground to the arrival and propagation of the seismo-acoustic wave along the fibre reveal spatial characteristic patterns that reflect local geological structures. For example, the finer spatial sampling of the iDAS records allows catching details of the variability of dynamic strain amplitudes along the fibre. Amplified signals are found at localized narrow regions matching fracture zones and faults. There, a decrease in the propagation velocity of the seismo-acoustic waves is also clearly pinpointed. 

These preliminary findings demonstrate the DAS potentiality to revolutionize the study of volcanic process by discovering new signal features undetectable with traditional sensors and methodologies.

How to cite: Currenti, G., Jousset, P., Chalari, A., Zuccarello, L., Napoli, R., Reinsch, T., and Krawczyk, C.: Fibre optic Distributed Acoustic Sensing of volcanic events at Mt Etna , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11641, https://doi.org/10.5194/egusphere-egu2020-11641, 2020

D1626 |
EGU2020-2321<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Renato Somma, Claudia Troise, Luigi Zeni, Alessandro Minardo, Alessandro Fedele, Maurizio Mirabile, and Giuseppe De Natale

Monitoring volcanic phenomena is a key question, for both volcanological research and for civil protection purposes. This is particularly true in densely populated volcanic areas, like the Campi Flegrei caldera, including part of the large city of Naples (Italy). Borehole monitoring of volcanoes is the most promising way to improve classical methods of surface monitoring, although not commonly applied yet. Fiber Optics technology is the most practical and suitable way to operate in such high temperature and aggressive environmental conditions. In this paper, we describe a fiber optics DTS (Distributed Temperature Sensing) sensor, which has been designed to continuously measure temperature all along a 500 m. deep well drilled in the West side of Naples (Bagnoli area), lying in the Campi Flegrei volcanic area. It has been then installed as part of the international ‘Campi Flegrei Deep Drilling Project’, and is continuously operating, giving insight on the time variation of temperature along the whole borehole depth. Such continuous monitoring of temperature can in turn indicate volcanic processes linked to magma dynamics and/or to changes in the hydrothermal system. The developed monitoring system, working at bottom temperatures higher than 100 °C, demonstrates the feasibility and effectiveness of using DTS for borehole volcanic monitoring.

How to cite: Somma, R., Troise, C., Zeni, L., Minardo, A., Fedele, A., Mirabile, M., and De Natale, G.: Long-Term Monitoring with Fiber Optics Distributed Temperature Sensing at Campi Flegrei: The Campi Flegrei Deep Drilling Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2321, https://doi.org/10.5194/egusphere-egu2020-2321, 2020

D1627 |
EGU2020-8442<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Camilla Rasmussen, Peter H. Voss, and Trine Dahl-Jensen

On September 16th 2018 a Danish earthquake of local magnitude 3.7 was recorded by distributed acoustic sensing (DAS) in a ~23 km long fibre-optic cable. The data are used to study how well DAS can be used as a supplement to conventional seismological data in earthquake localisation. One of the goals in this study is extracting a small subset of traces with clear P and S phases to use in an earthquake localisation, from the 11144 traces the DAS system provide. The timing in the DAS data might not be reliable, and therefore differences in arrival times of S and P are used instead of the exact arrival times.
The DAS data set is generally noisy and with a low signal-to-noise ratio (SNR). It is examined whether stacking can be used to improve SNR. The SNR varies a lot along the fibre-optic cable, and at some distances, it is so small that the traces are useless. Stacking methods for improving SNR are presented.

A field test at two location sites of the fibre-optic cable was conducted with the purpose of comparing DAS data with seismometer data. At the field sites, hammer shots were recorded by a small array of three STS-2 sensors located in a line parallel to the fibre-optic cable. The recordings generally show good consistency between the two data sets. 
In addition, the field tests are used to get a better understanding of the noise sources in the DAS recording of the earthquake. There are many sources of noise in the data set. The most prominent are a line of windmills that cross the fibre-optic cable and people walking in the building where the detector is located. Also, the coupling between the fibre-optic cable and the ground varies along the cable length due to varying soil type and wrapping around the fibre-optic cable, which is also evident in field test data. Furthermore, the data from the field tests are used to calibrate the location of the fibre-optic cable, which is necessary for using the DAS data in an earthquake localisation.
Data processing is done in Matlab and SEISAN.

How to cite: Rasmussen, C., Voss, P. H., and Dahl-Jensen, T.: Danish earthquake recorded by distributed acoustic sensing (DAS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8442, https://doi.org/10.5194/egusphere-egu2020-8442, 2020

D1628 |
EGU2020-6767<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Roxanne Rusch, Olivier Sebe, Jean-Baptiste Décitre, and Stéphane Gaffet

Rotational seismology refers to the study of the 3 components of rotation that are part of the
seismic wave field equation (Aki and Richards, 2002). Using the Geodetic Method (GM)
[Spudich et al, 1995], that is, using spatial finite differences of the local ground motions, the
3C of rotations were calculated at the dense broadband seismic array of the LSBB (Low
background noise underground research Laboratory, France, http://lsbb.eu). A catalog of 3C
rotations was created by systematically applying this method to several seismic events. The
uncertainty of the rotation measurements has been estimated through a sensitivity analysis.
This catalog will be presented and illustrated using examples. The analysis of the rotational
motions relatively to the seismic events source’s properties will be discussed as well.

How to cite: Rusch, R., Sebe, O., Décitre, J.-B., and Gaffet, S.: Catalog of 3C rotations measured at the LSBB’s antenna., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6767, https://doi.org/10.5194/egusphere-egu2020-6767, 2020

D1629 |
EGU2020-16191<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
David Sollberger, Heiner Igel, Cedric Schmelzbach, Felix Bernauer, Shihao Yuan, Joachim Wassermann, André Gebauer, Ulrich Schreiber, and Johan Robertsson

The analysis of the relative amplitudes of a passing seismic wave recorded on a single seismometer measuring six degrees of freedom of ground motion (translation and rotation) theoretically allows one to extract information on the wave that can conventionally only be obtained from receiver arrays. In the past, it has been shown on numerical data that the extension of conventional three-component (3C) polarization analysis techniques to six-components, allows one to unambiguously identify the wave type of a passing wave and characterise it in terms of its propagation direction (without the 180° ambiguity inherent in 3C data) and local wave speed. Additionally, due to the increase in the dimensionality of the data, two waves arriving at a station at the same time can be simultaneously characterised under ideal conditions (low noise).

Attempts to apply such 6-C polarization analysis techniques to field data have so far been met with limited success. Varying noise levels on the individual components and complex wavefields (with more than two interfering waves arriving at the station at the same time) usually prevent the stable recovery of wave parameters using single-station 6-C polarization analysis.

Here we discuss first attempts to overcome these issues. We (1) test the robustness of different wave parameter estimators (maximum likelihood, MUSIC) towards high levels of noise and (2) we try to reduce the number of interfering events in the analysis window by performing 6-C polarization analysis on time-frequency decomposed seismograms (i.e. spectrograms) using the S-transform.

The new techniques are extensively tested on field data recorded on the high-performance ROMY ringlaser.

How to cite: Sollberger, D., Igel, H., Schmelzbach, C., Bernauer, F., Yuan, S., Wassermann, J., Gebauer, A., Schreiber, U., and Robertsson, J.: Towards field data applications of six-component polarization analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16191, https://doi.org/10.5194/egusphere-egu2020-16191, 2020

D1630 |
EGU2020-11000<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Rosalba Napoli, Gilda Currenti, Athena Chalari, Camille Jestin, Danilo Contrafatto, Philippe Jousset, Graziano Larocca, Daniele Pellegrino, Mario Pulvirenti, and Antonino Sicali

We present the use of distributed acoustic sensing of telecommunication fibre to perform seismic monitoring on the lower eastern flank of Etna volcano. Eastern flank of Etna is structurally characterized by the existence of many faults until under the sea. One of the clearest morphological feature is the Timpe Fault System (TFS) crossing highly populated urban areas. The TFS is formed by several main segments producing shallow seismicity with a dominant normal faulting style and a right-lateral component, related to WNW-ESE regional extension. This area is highly seismogenic, with occurrence of a very frequent seismic activity punctuated by destructive earthquakes with magnitude ranges 4.3≤ML≤5.1 and a mean recurrence time of about 20 years.

To monitor the seismic response of this area we deployed an “intelligent” Distributed Acoustic Sensing (iDAS) system (SILIXA) in order to interrogate a 12-km-long telecommunication fibre-optic cable, managed by TELECOM Italia internet provider. The telecom cable runs from Linera to Zafferana villages along two primary directions roughly N-S and E-W and crosses the Santa Venerina and the Fiandaca faults, both part of the TFS. The former was entirely hidden until the 2002 eruption when a ML 4.4 earthquake exposed the fault at the surface and heavily damaged Santa Venerina village. The latter has been reactivated during the 2018 Etna activity, when a ML4.8 earthquake strongly damaged the Fleri village.

The iDAS was in acquisition for three months (11 September - 9 December 2019) and recorded the strain rate from natural and anthropogenic sources at a sampling frequency of 1 kHz with 2-m spatial resolution and a gauge length of 10 m. A second fibre in the same cable, was interrogated simultaneously by a FEBUS A1 system (FEBUS OPTICS) from 2 to 9 December 2019 with a spatial resolution and a gauge length of 5 m at a sampling frequency of 200 Hz. To validate the DAS measurements, gathered by both systems, two broadband seismometers (Trillium Compact 120 s) were deployed in the vicinity of the cable. We located using hammer shots along the cable at key positions.

During the acquisition period more than 800 local seismic events occurred on Etna with ML ranging between 0.4 and 3.4. Several regional earthquakes from Greece and Albania also occurred up to ML6.1. These seismic sources allows for investigating the response of the fibre and the detectability thresholds of iDAS and FEBUS A1 in urban areas with heterogeneous installation conditions of the telecommunication cable (cased conduit, attached conduit, aerial track).  We perform data analysis to characterize DAS amplitude and frequency responses to better estimate the coupling of the fibre to the ground.

How to cite: Napoli, R., Currenti, G., Chalari, A., Jestin, C., Contrafatto, D., Jousset, P., Larocca, G., Pellegrino, D., Pulvirenti, M., and Sicali, A.: Challenges of DAS measurements in seismic urban areas: case study at Etna volcano eastern flank, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11000, https://doi.org/10.5194/egusphere-egu2020-11000, 2020

D1631 |
EGU2020-8225<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Krystyna Smolinski, Patrick Paitz, Daniel Bowden, Pascal Edme, Felix Kugler, and Andreas Fichtner

Anticipating the risks natural hazards pose to an urban environment requires an understanding of the shallow Earth structure of the region. While urban infrastructure often hinders the deployment of a traditional seismic array, Distributed Acoustic Sensing (DAS) technology facilitates the use of existing telecommunication fibre-optic cables for seismic observation, with spatial resolution down to the metre scale.

Through collaboration with the SWITCH foundation, we were able to use existing, in-situ fibres beneath Bern, Switzerland for seismic data acquisition over two weeks, covering a distance of 6 km with a spatial resolution of 2 m. This allowed for not only real-time visualisation of anthropogenic noise sources (e.g. road traffic), but also of the propagation of resulting seismic waves.

Data is analysed in the time and frequency domain to explore the range of signals captured and to assess the consistency of data quality along the cable. The local velocity structure can be constrained using both noise correlations and deterministic signals excited by traffic.

Initial results reveal the ability of DAS to capture signals over a wide range of frequencies and distances, and show promise for utilising urban DAS data to perform urban seismic tomography and hazard analysis.

How to cite: Smolinski, K., Paitz, P., Bowden, D., Edme, P., Kugler, F., and Fichtner, A.: Urban Distributed Acoustic Sensing Using In-Situ Fibre Beneath Bern, Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8225, https://doi.org/10.5194/egusphere-egu2020-8225, 2020

D1632 |
EGU2020-20200<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Jiri Vackar, Jiri Malek, and Johana Brokesova

Rotaphones are seismic sensor systems consisting of parallel pairs of geophones attached to a rigid frame anchored to ground. Such an arrangement allows to measure both translational and rotational ground motions. Translations are measured by individual geophones while rotations are determined using differential records from the paired geophones. The individual geophones are calibrated simultaneously with each measurement utilizing overdetermined rotational components. A new prototype, Rotaphone CY has been recently developed. The design has been improved taking into account experience with field measurements performed using older prototypes. The device is optimized for recording weak ground motions from local microearthquakes, both natural or induced, in a high-frequency range. The instruments were carefully tested in laboratory conditions. Tests were followed by pilot field deployments in various places in the Czech Republic. A local network of six Rotaphones CY has been deployed in the scope of Litomerice geothermal project to investigate induced seismicity related to the production of geothermal energy. The instrument has also been recently deployed at the nuclear power plant Dukovany to monitor local seismicity with the aim to improve seismic hazard estimate. A small-aperture array of four these instruments was installed at the Geophysical Observatory Fürstenfeldbruck, Germany, in the frame of a comparative rotation sensors experiment. Examples of 6-component records from these pilot measurements are shown.

How to cite: Vackar, J., Malek, J., and Brokesova, J.: New prototype of 6-component seismograph Rotaphone CY: laboratory testing and pilot measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20200, https://doi.org/10.5194/egusphere-egu2020-20200, 2020

D1633 |
EGU2020-19873<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Christian Schubert, Waldemar Herr, Sven Abend, Naceur Gaaloul, Dennis Schlippert, Wolfgang Ertmer, and Ernst M. Rasel

Quantum sensors utilising atom interferometry enable absolute measurements of gravity (1) and gravity gradients (2). This contribution will introduce the operation principle of atom interferometers, discuss their current state of the art and limitations, and outline the key techniques for improvements. It will report on our developments for transportable (3) and stationary high-perfomance devices (4) and give a perspective for space-borne quantum sensors in the frame of geodetic missions (5).
The presented work is supported by the CRC 1227 DQmat within the project B07, the German Space Agency (DLR) with funds provided by the Federal Ministry of Economic Affairs and Energy (BMWi) due to an enactment of the German Bundestag under Grant No. DLR 50WP1700, 50WM1952, by "Niedersächsisches Vorab" through "Förderung von Wissenschaft und Technik in Forschung und Lehre" for the initial funding of research in the new DLR-SI Institute, and through the "Quantum and Nano- Metrology (QUANOMET)" initiative within the project QT3.

(1) V. Ménoret et al., Scientific Reports 8, 12300, 2018; A. Trimeche et al., Phys. Rev. Appl. 7, 034016, 2017; C. Freier et al., J. of Phys.: Conf. Series 723, 012050, 2016; A. Louchet-Chauvet et al., New J. Phys. 13, 065026, 2011; A. Peters et al., Nature 400, 849, 1999.
(2) P. Asenbaum et al., Phys. Rev. Lett. 118, 183602, 2017; G. Rosi et al., Nature 510, 518, 2014; J. M. McGuirk et al., Phys. Rev. A 65, 033608, 2002.
(3) S. Abend et al., Proceedings of the International School of Physics "Enrico Fermi" 197, 393, 2019; S. Abend et al., Phys. Rev. Lett. 117, 203003, 2016.
(4) D. Schlippert et al., arXiv:1909.08524; J. Hartwig et al., New J. Phys. 17, 035011, 2015.
(5) A. Trimeche et al., Class. Quantum Grav. 36, 215004, 2019; K. Douch et al., Adv. Space. Res. 61, 1301, 2018.

How to cite: Schubert, C., Herr, W., Abend, S., Gaaloul, N., Schlippert, D., Ertmer, W., and Rasel, E. M.: Quantum sensors for gravimetry and gravity gradiometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19873, https://doi.org/10.5194/egusphere-egu2020-19873, 2020

D1634 |
EGU2020-19987<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Anna Kurzych, Leszek R. Jaroszewicz, Michał Dudek, Zbigniew Krajewski, Jerzy K. Kowalski, Sławomir Niespodziany, Felix Bernauer, Joachim Wassermann, and Heiner Igel

Nowadays rotational seismology has become rapidly developing field of study which can deliver completely new  perspectives for earthquakes analysis or torsional effects in engineering structures. Rotational seismology as a scientific field has been clarified in 2009 as a field for researching all aspects of rotational ground movements generated by earthquakes, explosions, and ambient vibrations. Nevertheless, technical requirements for sensors in this field are very strict and rigorous, especially taking into account measuring range from 10-7 rad/s event up to few rad/s. In order to fulfill all technical requirements for sensors which can be applied in rotational seismology measurements we designed and constructed device based on an optical fiber gyroscope (FOG). Fibre-Optic System for Rotational Events&phenomena Monitoring (FOSREM) is a an interferometric optical fiber sensor designed to continuously observe rotational effects. It uses closed-loop configuration which is based on the compensatory phase measurement method as well as specific electronic system. It should be noticed, that the coupling of the FOSREM’s optical part which detects critical low value of signal with specialized electronic system which requires precise analog to digital conversion as well as data transfer with different sampling rate is the source of differences between constructed devices even in the same technology. In this paper we present laboratory investigation of FOSREMs including Allan variance analysis indicating that Angle Random Walk is equal to 10-7 rad/s. Expect laboratory verification of proper FOSREMs’ operation we carried out field tests taking into account that validity and reliability of the research instruments are crucial during field application. The quality of data utilised in any research determines the outcome of the research and its importance for further research work and relevance to scientific community and knowledge. The data reliability can be determined by comparison between records from several sensors. We present first data from international field research which was focused on efforts to achieve uniformity in collecting and data processing. This experiment involved more than 40 rotational and strain sensors and took place in Geophysical Observatory Fürstenfeldbruck, LMU Munich, Germany. Authors applied four FOSREMs in this experiment and the presented analysis was focused on their data comparability as well as consistency.

How to cite: Kurzych, A., Jaroszewicz, L. R., Dudek, M., Krajewski, Z., Kowalski, J. K., Niespodziany, S., Bernauer, F., Wassermann, J., and Igel, H.: Assembly of optical fiber sensors for rotational seismology - data coherence and comparability issues in field application , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19987, https://doi.org/10.5194/egusphere-egu2020-19987, 2020

D1635 |
EGU2020-11887<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Bruce Townsend, Andrew Moores, and Sylvain Pigeon

The new Nanometrics Pegasus now available to the scientific community provides a compelling comprehensive solution for easily and quickly deploying portable seismic stations. Use cases include RAMP, local and regional hazard monitoring, passive seismic imaging and local or regional seismicity assessments. Because the technology platform on which Pegasus Portable is based is extensible and versatile, it has the potential to address additional use cases. The benefits of the Pegasus technology would apply to new use cases: optimal SWaP (Size, Weight and Power), Modularity (the versatility permits wide choice of sensors and power to serve various situations), Ease-of-Use (workflows designed for planning-to-publishing efficiency), Complete Ready-to-Use Datasets (including automatically generated station response), and Quick (such as ultra-fast boot, rapid data download). We explore the potential extensions to Pegasus that can enable additional use cases for autonomous geophysical monitoring.

An example is large-N mixed-mode nodal deployments in which hundreds of stations are quickly deployed that can include a mix of sensor types such as broadband seismometers, geophones, microbarometers, and weather stations. A key focus for large-N campaigns is to scale efficiently. One proposed element for consideration is a cloud-based campaign planning and post-deployment auditing service in which a master plan can be readily distributed to many field operators to facilitate automatic station configuration and later reconciliation of on-the-ground actions with the master plan. 

Another compelling use case for Pegasus is ocean bottom seismometry, where technology enablers would include OBS-specific actions and workflows (managing the datalogger and its power sources without having to open marine pressure vessels, synchronizing timing to GNSS, applying time corrections to retrieved data and the like). These and other use cases and related technology extensions are discussed.

How to cite: Townsend, B., Moores, A., and Pigeon, S.: Extending the Pegasus Portable Technology Platform to Apply to More Geophysical Monitoring Use, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11887, https://doi.org/10.5194/egusphere-egu2020-11887, 2020

D1636 |
EGU2020-6145<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"></span>
Gabi Laske and Adrian Doran

A standard ocean bottom seismometer (OBS) package of the U.S. OBS Instrument Pool (OBSIP) carries a seismometer and a pressure sensor. For broadband applications, the seismometer typically is a wide-band or broad-band three-components seismometer, and the pressure sensor is a differential pressure gauge (DPG). The purpose of the pressure sensor is manifold and includes the capture of pressure signals not picked up by a ground motion sensor (e.g. the passage of tsunami), but also for purposes of correcting the seismograms for unwanted signals generated in the water column (e.g. p-wave reverberations).
Unfortunately, the instrument response of the widely used Cox-Webb DPG remains somewhat poorly known, and can vary by individual sensor, and even by deployment of the same sensor.

Efforts have been under way to construct and test DPG responses in the laboratory. But the sensitivity and long‐period response are difficult to calibrate as they  vary with temperature and pressure, and perhaps by hardware of the same mechanical specifications.  Here, we present a way to test the response for each individual sensor and deployment in situ in the ocean. This test requires a relatively minimal and inexpensive modification to the OBS instrument frame and a release mechanism that allows a drop of the DPG by 3 inches after the OBS package settled and the DPG equilibrated on the seafloor. The seismic signal generated by this drop is then analyzed in the laboratory upon retrieval of the data. 

The results compare favorably with calibrations estimated independently through post‐deployment data analyses of other signals such as Earth tides and the signals from large teleseismic earthquakes. Our study demonstrates that observed response functions can deviate from the nominal response by a factor of two or greater with regards to both the sensitivity and the time constant. Given the fact that sensor calibrations of DPGs in the lab require very specific and stable environments and are time consuming, the use of in-situ DPG calibration frames pose a reliable and inexpensive alternative. 

How to cite: Laske, G. and Doran, A.: In-Situ Calibration of Differential Pressure Gauges on OBSIP Ocean Bottom Seismometers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6145, https://doi.org/10.5194/egusphere-egu2020-6145, 2020

D1637 |
EGU2020-4256<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Felix Bernauer, Joachim Wassermann, Katrin Behnen, Heiner Igel, Stefanie Donner, Pascal Edme, David Sollberger, Patrick Paitz, Jonas Igel, Gizem Izgi, Eva P.S. Eibl, Stefan Buske, Christian Veress, Frederic Guattari, Olivier Sebe, Basil Brunner, Anna T. Kurzych, Piotr Bonkovsky, Piotr Bobra, and Johana Brokesova and the Fürstenfeldbruck Experiment Team

Interest in measuring seismic rotation and strain is growing in many areas of geophysical research. This results in a great need for reliable and field deployable instruments measuring ground rotation and strain. To further establish a high quality standard for rotation and strain measurements in seismology, researchers from the Ludwig-Maximilians University of Munich (LMU), the German Federal Institute for Geosciences and Natural Resources, the University of Potsdam and the ETH Zürich organized a comparative sensor test experiment which took place in November 2019 at the Geophysical Observatory of the LMU in Fürstenfeldbruck, Germany. More than 40 different sensors such as ring-laser and fiber optic gyroscopes, a Distributed Acoustic Sensing (DAS) cable and interrogator, liquid-based as well as mechanical rotation sensors were involved in addition to 12 classical broadband
seismometers and a 80 channel, 4Hz geophone chain. The experiment consisted of two parts: during the first part, the sensors were co-located in a huddle test recording self noise and signals from small, nearby explosions. In a second part, the sensors were distributed into the field in various array configurations recording active seismic signals generated by small amounts of explosive and a vibro-seis truck. This contribution presents details on the setup of the experiment and first results on sensor performance characteristics and signal similarities.

How to cite: Bernauer, F., Wassermann, J., Behnen, K., Igel, H., Donner, S., Edme, P., Sollberger, D., Paitz, P., Igel, J., Izgi, G., Eibl, E. P. S., Buske, S., Veress, C., Guattari, F., Sebe, O., Brunner, B., Kurzych, A. T., Bonkovsky, P., Bobra, P., and Brokesova, J. and the Fürstenfeldbruck Experiment Team: Rotation and Strain Instrument Performance Tests with Active Seismic Sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4256, https://doi.org/10.5194/egusphere-egu2020-4256, 2020

D1638 |
EGU2020-15759<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Yara Rossi, Eleni Chatzi, Markus Rothacher, John Clinton, and Cédric Schmelzbach

Current best practice in monitoring earthquake strong motion are dense networks comprising strong motion accelerometers that measure acceleration over a broad frequency and amplitude range. These instruments are capable of measuring translational motions of large earthquakes, but lack sensitivity to very low frequencies or permanent displacements. However, it is widely accepted that during earthquakes the rotational component of the ground motion, both static and dynamic, is large enough to contaminate the derived displacements from these sensors. Modern rotational sensors, are also very broadband, have a large dynamic range, and are not sensitive to translational motions. We explore the value of complementing accelerometers with these rotational sensors at seismic strong motion monitoring stations.

The assessment of the errors introduced into accelerometer records from rotational ground motions is only possible with co-located rotational instruments sensitive enough to record the small rotation rates accompanying the translational motion. Operating accelerometers alongside gyros and additionally GNSS instrumentation should allow us to record the full 6 components (6C) of near-field earthquake motions, with increasing fidelity across a very broad frequency band for the strongest motions.

We aim to demonstrate how, using a combination of the three sensor types, we can recover the full 6C ground motion, and hence also more reliable displacement records, using a versatile industrial six-axis robot that can produce controlled and repeatable 6C motion across a broad frequency band. Through the precise feedback loop used by the robot to stabilize its precise trajectory, we get a 6C recording of the driven motion represented by Euler rotations and displacements, which we use as ground truth. By simulating a combination of translational and rotational motions on the robot, we show that the 6C Kalman filter can accurately reproduce the clean simulated translational motion. By using a Kalman filter, we attempt to combine the different data sets using prediction and weighting of the observation data for an optimal solution. Our methodology tries to take into account the strengths and weaknesses of the individual instruments that are providing partly redundant and partly complementary ground motion information.

How to cite: Rossi, Y., Chatzi, E., Rothacher, M., Clinton, J., and Schmelzbach, C.: Assessing a 6C Kalman filter using experimental datasets from an industrial robot, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15759, https://doi.org/10.5194/egusphere-egu2020-15759, 2020

D1639 |
EGU2020-7759<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Pascal Edme, Patrick Paitz, Ana Nap, Francois Martin, Valentin Metraux, Luca Guglielmetti, Cedric Schmelzbach, Vincent Perron, Daniel Bowden, David Dupuy, Andrea Moscariello, Andreas Fichtner, and Johan O. A. Robertsson

Distributed Acoustic Sensing (DAS) is an optical interferometry based ground motion sensing technology which has the potential to revolutionize the field of seismological data acquisition. It offers the possibility to replace very large numbers of cost-intensive conventional point sensors (seismometers or geophones) by interrogating a single low-cost optic-fibre cable. Being unaffected by spatial aliasing, DAS is emerging as a potential next-generation broad-band geo-hazard (e.g. earthquakes, landslides) and reservoir (e.g. geothermal, oil and gas) seismic monitoring tool.

For borehole applications, with the cable appropriately coupled with the casing, the reliability and benefit of DAS-based VSP acquisition is now widely recognized. At the surface however, for reflection seismic for example, the adequate deployment procedure is less well documented, and experiments are performed with cables sometimes directly deployed on the surface, or sometimes buried quite deep (e.g. one meter) in the ground. Especially for non-permanent monitoring, the trenching effort can be substantial or unaffordable due to logistic or permitting issues. One may wonder if such an effort with its associated cost is actually beneficial.

We present here the results of a surface-based active seismic experiment conducted in Switzerland in the context of a geothermal reservoir characterization project with “co-located” stretches of cable deployed at different depths. The repeatability of the DAS measurements is quantified and compared to a dense array of conventional multi-component geophones. The study shows that deeply (50 cm) deployed cables offers only marginal data quality improvements compared to very shallow (2 cm) cables. In contrast, the parts of the cable directly laid down at the surface exhibit much larger noise levels and very poor repeatability (approximately one order of magnitude larger NRMS). Our study suggests that only a minor amount of elastic material covering the cable is enough to provide a good coupling and that a modest machine to conveniently perform such a shallow deployment would greatly benefit the growing DAS user community.

How to cite: Edme, P., Paitz, P., Nap, A., Martin, F., Metraux, V., Guglielmetti, L., Schmelzbach, C., Perron, V., Bowden, D., Dupuy, D., Moscariello, A., Fichtner, A., and Robertsson, J. O. A.: Deployment recommendation for Distributed Acoustic Sensing at the surface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7759, https://doi.org/10.5194/egusphere-egu2020-7759, 2020

D1640 |
EGU2020-5602<span style="font-size: .8em!important; font-weight: bold; vertical-align: super; color: green!important;"><span title="Early career scientist: an ECS is an undergraduate or postgraduate (Masters/PhD) student or a scientist who has received their highest degree (BSc, MSc, or PhD) within the past seven years. Provided parental leave fell into that period, up to one year of parental leave time may be added per child, where appropriate.">ECS</span></span>
Gizem Izgi, Stefanie Donner, Felix Bernauer, Daniel Vollmer, Klaus Stammler, Mathias Hoffmann, and Eva P.S. Eibl

Rotational motions play a key role in measuring seismic wavefield properties. To fully understand and describe the behavior of seismic waves, both translational and rotational components should be properly investigated. Portable blueSeis-3A (iXblue) sensors allow to measure 3 components of rotational motions with high sensitivity in a frequency range from 0.001 Hz to 50 Hz.

A huddle test was performed in Fürstenfeldbruck, Germany by the University of Potsdam in collaboration with the Ludwig-Maximilians University of Munich (LMU) and Federal Institute for Geosciences and Natural Resources (BGR) between 26 of August and 02 of September 2019, in order to further investigate the performance of multiple rotational instruments in combination with seismometers. Within the scope of this test, 5 rotational and 3 translational sensors were deployed on the basement of the observatory on decoupled plinth. Our preliminary results show good correlation between all components and rotational sensors. To investigate the coherent noise between sensors, we applied a 50 Hz low-pass filter and 100 Hz sampling rate. To better illustrate, probabilistic power spectral densities and spectrograms have been created. In general, we will discuss the reliability of the data recorded by rotational sensors for further investigations.

 

How to cite: Izgi, G., Donner, S., Bernauer, F., Vollmer, D., Stammler, K., Hoffmann, M., and Eibl, E. P. S.: Multiple 6C-station Huddle Test in Fürstenfeldbruck, Germany , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5602, https://doi.org/10.5194/egusphere-egu2020-5602, 2020