Sensing ground translation, rotation, and strain - instrumentation, theory and applications


Sensing ground translation, rotation, and strain - instrumentation, theory and applications
Co-organized by GI5/PS7
Convener: Felix BernauerECSECS | Co-conveners: Stefanie Donner, Eva EiblECSECS, Sneha SinghECSECS, David SollbergerECSECS
vPICO presentations
| Wed, 28 Apr, 13:30–14:15 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Stefanie Donner, Sneha Singh, Felix Bernauer
On Ki Angel Ling, Simon Stähler, Domenico Giardini, and the AlpArray Working Group

The AlpArray Seismic Network (AASN) is a large-scale multidisciplinary seismic network in Europe that consists of over 600 3-component (3C) broadband stations with mean inter-station distance of 30-40km. This dense array allows the recording of the seismic wave propagation of distant earthquakes at a resolution of typical body and surface waves.

By animating the spatially-dense seismic recordings of the AASN, we can visualize seismic waves propagating across the European Alps as a function of space and time. Our 3C ground motion animations illustrate the full spatial-temporal evolution of global body and surface waves and demonstrates how a dense array allows the transformation from translation measurements at single stations to spatial gradients of the wavefield at the surface, capturing both small- and large-scale wave propagation phenomena. The addition of travel-time estimation, ray path illustration, and array-specific information such as slowness vector of incoming waves facilitate identification of seismic phases and their arrival-angle deviations. We will highlight some interesting observations of different seismic wave types in the animations of a few example teleseismic events during the course of the AASN between 2016-2019. Application for future research and education will also be discussed.

How to cite: Ling, O. K. A., Stähler, S., Giardini, D., and Group, T. A. W.: Visualizing the Seismic Wavefield with AlpArray, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-859,, 2021.

Dariusz Nawrocki, Maciej Mendecki, and Lesław Teper

The seismic observations of the rotational signals are a field of seismology that is constantly developed. The recent research concerns sensors technology and its potential application in seismic tests. This study presents the results of a comparative analysis of rotational and translational seismic records using the horizontal-to-vertical spectral ratio (HVSR) method. In terms of transitional signal ratio, we have used the name of HVSR, but in terms of rotational component spectra, we have introduced a torsion-to-rocking spectral ratio (TRSR) which corresponds to horizontal rotation spectrum to vertical rotation spectrum. It has to be noticed that rotation in the horizontal axes has a vertical character and rotation in the vertical axis has a horizontal character.

The comparison was carried out between velocity signals of translational and rotational records, as well as, between acceleration signals respectively. All seismic data were recorded by two independent sensors: the rotational seismometer and translational accelerometer at the Imielin station, located in the Upper Silesia Coal Basin (USCB), Poland. The seismic data composed of three-component seismic waveforms related to 56 recorded tremors which were located up to 1,5 km from the seismic station and they resulted from the coal extractions carried out in the neighboring coal mines. The rotational acceleration was obtained by numerical differentiation and the translational velocity was produced by numerical integration.

The conducted spectral analyses allowed to estimate the range of frequency in which the rotational HVSR and the corresponded translational HVSR are comparable. The analysis of HVSR/TRSR curves (in the selected frequency range of 1Hz to 10Hz) showed a strong correlation between the spectral ratios for the velocity signals (translational and rotational) in the frequency range of 1Hz to 2Hz. Respectively, the comparison of the accelerometer signals indicated the correlation between HVSR/TRSR curves in the frequency range of 1Hz to 3Hz. Moreover, both of the TRSR (for velocity and acceleration) showed additional maxima in the same frequency range of 3Hz to 5Hz. These relatively high-frequency maxima did not correspond to translational spectra.  

How to cite: Nawrocki, D., Mendecki, M., and Teper, L.: Spectral ratio comparison between translation and rotational records from induced seismic events., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8817,, 2021.

Ivan Lokmer, Varun Kumar Singla, and John McCloskey

The seismic waves responsible for vibrating civil engineering structures undergo interference, focusing, scattering, and diffraction by the inhomogeneous medium encountered along the source-to-site propagation path. The subsurface heterogeneities at a site can particularly alter the local seismic wave field and amplify the ground rotations, thereby increasing the seismic hazard. The conventional techniques to carry out full wave field simulations (such as finite-difference or spectral finite element methods) at high frequencies (e.g., 15 Hz) are computationally expensive, particularly when the size of the heterogeneities is small (e.g., <100 m). This study proposes an alternative technique that is based on the first-order perturbation theory for wave propagation. In this technique, the total wave field due to a particular source is obtained as a superposition of the ‘mean’ and ‘scattered’ wave fields. Whereas the ‘mean’ wave field is the response of the background (i.e., heterogeneity-free) medium due to the given source, the ‘scattered’ wave is the response of the background medium excited by fictitious body forces. For a two-dimensional laterally heterogeneous elastic medium, these body forces can be conveniently evaluated as a function of the material properties of the heterogeneities and the mean wave field. Since the problem of simulating high-frequency rotations in a laterally heterogeneous medium reduces to that of calculating rotations in the background medium subjected to the (1) given seismic source and (2) body forces that mathematically replace the small-scale heterogeneities, the original problem can be easily solved in a computationally accurate and efficient manner by using the classical (analytical) wavenumber-integration method. The workflow is illustrated for the case of a laterally heterogenous layer embedded in a homogeneous half-space excited by plane body-waves.

How to cite: Lokmer, I., Singla, V. K., and McCloskey, J.: Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-Space, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6446,, 2021.

Geoffrey Bainbridge, Valarie Hamilton, and Timothy Parker

The Streckeisen STS-1 set a very high performance and lasting broadband (VBB) sensor standard that has been hard to match by other instruments, but these sensors also required a very careful emplacement and shielding from environmental changes and conditions, along with the high costs of ensuring the conditions for this level of instrument performance.  Recent developments have demonstrated equivalent and broader bandwidth sensors that enable deploying these types of sensors in most any terrestrial environment.  These new instruments, in many types of form factors, all magnetically shielded, open up new opportunities for continuing and expanding these VBB observations, democratizing the observations of these long period signals and opening up the possibilities of better performance through deep boreholes and observations of less developed sites that have harsher environmental conditions, along with recapitalizations of sites where STS-1s are no longer supported.   We will describe recent testing results of Trillium 360 GSN vault, borehole, and posthole sensors as well as the Horizon 360 from many observatories and new potential use cases, some in polar environments that were impractical until now, and discuss development of the new Horizon 360 OBS.

How to cite: Bainbridge, G., Hamilton, V., and Parker, T.: Democratizing and Densifying Low Noise Long Period Broadband Stations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13490,, 2021.

Pascal Edme, Patrick Paitz, David Sollberger, Tjeerd Kiers, Vincent Perron, Cedric Schmelzbach, Andreas Fichtner, and Johan O.A. Robertsson

Distributed Acoustic Sensing (DAS) is becoming an established tool for seismological and geophysical applications. DAS is based on Rayleigh scattering of light pulses conveyed in fibre optic cables, enabling unprecedented strain rate measurements over kilometers with spatial resolution of less than a meter. The low cost, logistically easy deployment, and the broadband sensitivity make it a very attractive technology to investigate an increasing number of man-made or natural phenomena.

One key restriction however is that DAS collects axial strain rate instead of the vector of ground motion, resulting in a poor sensitivity to broadside events like (at the surface) vertically incident waves or surface waves impinging perpendicular to the cable. Helically wound cables partially mitigate the issue but still do not provide omni-directional response as the typical vertical component of seismometers or geophones.

The present study is about the potential of using unconventional DAS cable layouts to replace and/or complement traditional sensors. We investigate the possibility of estimating the divergence and the vertical rotational components of the wavefield from cables deployed in a square or circular shape. The impact of the size of the arrangement as well as that of the interrogation gauge length is discussed.  Real data are shown and the results suggest that DAS has the potential to offer additional seismic component(s) useful for wave type identification and separation for example.

How to cite: Edme, P., Paitz, P., Sollberger, D., Kiers, T., Perron, V., Schmelzbach, C., Fichtner, A., and Robertsson, J. O. A.: On the use of Distributed Acoustic Sensing for seismic divergence and curl estimations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12443,, 2021.

Felix Bernauer, Louisa Murray-Bergquist, Felix Strobel, Joachim Wassermann, Heiner Igel, Eva P.S. Eibl, Cun-Man Liao, Ernst Niederleithinger, Sneha Singh, and Celine Hadziioannou

Characterizing earthquake induced building damage in an efficient, automated and non-
invasive way is a crucial support for the decision on further usability of critical infras-
tructure. In the GIOTTO project (Gebäudeschwingungen: kombinierte Zustandsanalyse
mit innovativem Sensorkonzept) we propose to use 6 degrees of freedom sensors (6DoF)
to monitor the complete movement of a building structure in three rotational and three
translational degrees of freedom. On one side, we develop 6DoF sensor networks for
strong motion building monitoring on the basis of 20 inertial measurement units (IMU50
by iXblue, France) originally designed as north-finding gyroscopes, on the other side we
incorporate the new observable of rotational ground motions into the concept of coda wave
interferometry for continuous real-time structural health monitoring. In this contribution
we show first results (1) from laboratory experiments for sensor performance characteriza-
tion as well as (2) from a 6DoF active source experiment at a horizontal 24 m long concrete
beam (the BLEIB test structure hosted by the Bundesanstalt für Materialforschung und
-prüfung, south of Berlin, Germany).

How to cite: Bernauer, F., Murray-Bergquist, L., Strobel, F., Wassermann, J., Igel, H., Eibl, E. P. S., Liao, C.-M., Niederleithinger, E., Singh, S., and Hadziioannou, C.: The GIOTTO Project - Building Monitoring with 6DoF Sensors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8438,, 2021.

Xinding Fang

A new type of portable six-component seismometer is invented and used in the development of a seismic imaging method for shallow subsurface anomaly detection. This new six-component seismometer contains a mini-MEMS-array for acceleration and rotational velocity measurements. The self-noise for acceleration measurement is about 8 µg/√Hz, and the self-noise for rotational velocity measurement is about 5 µrad/s/√Hz. The frequency band is DC-1000 Hz. Different from the traditional seismic imaging methods that require the deployment of an array of either one-component or three-component seismometers, our imaging method is established based on the data recorded at individual six-component seismometer. Because the rotational field (i.e., the curl field) gives information about the spatial gradient of a seismic wavefield, so the translational field together with the rotational field can be used to derive the frequency-dependent velocity (i.e., dispersion) of the formation right beneath a seismic station. This single station velocity inversion approach delivers localized subsurface velocity information, making it suitable for imaging of small-scale underground anomalies. Especially, the Rayleigh wave dispersion is used in our method as Rayleigh wave is generally the dominant signal in surface seismic data. An underground velocity model can be immediately constructed by consolidating the dispersion curves derived from individual receivers. In our study, we first demonstrate the accuracy of our imaging method through numerical modeling of various scenarios of subsurface anomalies and then conduct an experiment to further verify the performance of our self-invented six-component seismometer and the field applicability of our imaging method.

How to cite: Fang, X.: Application of a new type of six-component seismometer for underground anomaly detection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8551,, 2021.

Martina Rosskopf, Eva P. S. Eibl, Gilda Currenti, Philippe Jousset, Joachim Wassermann, Daniel Vollmer, Graziano Larocca, Daniele Pellegrino, Mario Pulvirenti, and Danilo Contrafatto

The field of rotational seismology has only recently emerged. Portable 3 component rotational sensors are commercially available since a few years which opens the pathway for a first use in volcano-seismology. The combination of rotational and translational components of the wavefield allows identifying and filtering for specific seismic wave types, estimating the back azimuth of an earthquake, and calculating local seismic phase velocities.

Our work focuses on back-azimuth calculations of volcano-tectonic and long-period events detected at Etna volcano in Italy. Therefore, a continuous full seismic wavefield of 30 days was recorded by a BlueSeis-3A, the first portable rotational sensor, and a broadband Trillium Compact seismometer located next to each other at Mount Etna in August and September of 2019. In this study, we applied two methods for back-azimuth calculations. The first one is based on the similarity of the vertical rotation rate to the horizontal acceleration and the second one uses a polarization analysis from the two horizontal components of the rotation rate. The estimated back-azimuths for volcano-tectonic events were compared to theoretical back-azimuths based on the INGV event catalog and the long-period event back-azimuths were analyzed for their dominant directions. We discuss the quality of our back azimuths with respect to event locations and evaluate the sensitivity and benefits of the rotational sensor focusing on volcano-seismic events on Etna regarding the signal to noise ratios, locations, distances, and magnitudes.

How to cite: Rosskopf, M., Eibl, E. P. S., Currenti, G., Jousset, P., Wassermann, J., Vollmer, D., Larocca, G., Pellegrino, D., Pulvirenti, M., and Contrafatto, D.: Performance of a rotational sensor at Etna, Italy focusing on back-azimuth estimations of volcano-seismic events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10927,, 2021.

Frédéric Guattari, Pierrick Auregan, Elliot de Toldi, Theo Laudat, and Laurent Mattio

To install a seismometer with a properly defined orientation - inside a vault or into a borehole - as a single station including various instruments or as a part of an array - an ‘adequate’ tool and an ‘absolute’ reference are needed.

In the past, and sometimes it persists nowadays, magnetic North have been used as a reference for Z-orientation of seismic station. Several studies have extensively measured the orientation error that have been made with this method, using an optical gyrocompass providing True-North as a reference, and their work will be summarized here.

In these studies, optical Gyrocompass is said to be the good solution, even if it is too heavy, expensive, and difficult to export. This paper will explain how iXblue has overcome these limitations to design the new-born Seistans Optical Gyrocompass.

Moreover, to aim True-North with a reliable accuracy is not the only think you need to do on the field. The method to transfer the North-line from the gyrocompass to the instrument to aligned must not induce errors that ruined the accuracy obtained using state-of-the-art gyrocompass. So an exhaustive study of the different ways to transfer the orientation from the compass to the aligned sensor will be presented, and corresponding added uncertainty will be evaluated, which is a good way to promote good practice on the field.

Finally, some figures will be gathered and shared from literature to quantify the precision needed for the alignment of a seismic sensor. There are today so few papers about this important matter that it is worth to spread their information.

How to cite: Guattari, F., Auregan, P., de Toldi, E., Laudat, T., and Mattio, L.: Short Review of True-North Alignment Method on the Field Demonstrating the benefits of the use of an Optical Gyrocompass, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16524,, 2021.

From prototypes to first production units: blueSeis-1C Fiber Optical Gyroscope industrial solution for broadband ground motion rotation measurement at the best self-noise
Kevin Gautier, Pierrick Auregan, Theo Laudat, and Frédéric Guattari