Kathrin Behnen

Last Name

Behnen

First Name

Kathrin

ORCID

0009-0000-0393-6128

Organisational unit

03476 - Giardini, Domenico / Giardini, Domenico

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Publications 1 - 5 of 5

Understanding seismic anisotropy in the Rotondo granite: investigating stress as a potential source
Behnen, Kathrin; Hertrich, Marian; Maurer, Hansruedi; et al. (2025)
Solid Earth
The hypothesis of stress-induced seismic anisotropy was tested in the Bedretto Lab, a deep underground rock laboratory in the Swiss Alps. Several comprehensive cross-hole seismic surveys were acquired to analyze the directional dependency of seismic-wave velocities in the undisturbed host rock. This requires precise knowledge on the source and receiver positions as well as good data quality that allows the determination of travel times for different wave types. A tilted transverse isotropic (TTI) model that explains the measured data to a first-order approximation can be established. All relevant model parameters are well constrained using P- and S-wave arrival times. However, a systematic misfit distribution indicates that a more complex anisotropy model might be required to fully explain the measurements. This is consistent with our hypothesis that seismic anisotropy has a significant stress-induced component. More controlled laboratory experiments on the centimeter to decimeter scale were performed to validate our field measurements. These measurements show a comparable order of P- and S-wave anisotropy in the rock volume. The knowledge on the driving mechanism for anisotropy in igneous rocks can potentially help to enhance the monitoring of stress field variations during geothermal operations, thereby improving hazard assessment protocols.
Seismic anisotropy analysis based on synthetic and measured data for crystalline rock characterization
Behnen, Kathrin; Hertrich, Marian; Maurer, Hanruedi; et al. (2023)
EGUsphere
The prior characterization of a reservoir volume as well as the monitoring of potential changes during heat extraction is highly important to ensure an economic and safe engineering and operation of a geothermal reservoir. While the use of active seismic measurements from the surface and in boreholes is commonly used to describe the seismic velocity field in the subsurface, its potential to analyze the seismic anisotropy is often neglected. We used active seismic crosshole measurements to analyze seismic anisotropy at the field scale to provide important information about the elastic properties and take advantage of this information for the analysis of the in-situ rock-physical conditions. For the analysis of seismic anisotropy, a reliable data set is essential. We studied the sensitivity of the resulting anisotropy model to inaccuracies in the survey geometry by computing synthetic data and showed that inaccuracies of only a few degrees in dip and azimuth of the borehole orientation can significantly change the resulting anisotropy model of the volume. Especially the orientation of the symmetry axis used to describe a transverse isotropic model (TI) is highly sensible to source and receiver positions. Beyond the analysis of the synthetic data, the focus of our study was on the exploitation of real measurement data. These data were recorded in a campaign in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) in Ticino, Switzerland. The laboratory provides the opportunity to record crosshole data with high quality in a controlled environment. The geometry of the boreholes that we used allows a high coverage of ray path orientations which is crucial for the analysis of anisotropic wave propagation. The recorded data were used to create an anisotropy model of the subsurface based on a grid search and optimization algorithm, searching for both the optimized Thomsen parameters and the ideal orientation of the symmetry axis of the tilted TI model. The results give evidence of an ambient elastic anisotropy, while the host rock (Rotondo Granite) has proven negligible intrinsic anisotropy in previous laboratory measurements at sample scale. Further investigation will analyze the effect of the fracture inventory and ambient state of stress as potential controlling factors of the observed anisotropy. This relation can potentially help to monitor changes in the stress field during geothermal operations for a better hazard assessment.
Investigation of Seismic Anisotropy in the Undisturbed Rotondo Granite
Behnen, Kathrin; Hertrich, Marian; Maurer, Hansruedi; et al. (2024)
EGUsphere
The hypothesis of stress-induced seismic anisotropy was tested in the Bedretto Lab, a deep underground rock laboratory in the Swiss alps. Several comprehensive crosshole seismic surveys were acquired to analyze the directional dependency of seismic wave velocities in the undisturbed host rock. This required precise knowledge on the source and receiver positions as well as a good data quality that allow the determination of traveltimes for different wave types. A tilted transverse isotropic (TTI) model could be established that explains the measured data to a first order. All relevant model parameters could be well constrained using P- and S-wave arrival times. However, a systematic misfit distribution indicates that a more complex anisotropy model might be required to fully explain the measurements. This is consistent with our hypothesis that seismic anisotropy has a significant stress-induced component. More controlled laboratory experiments on the centimeter to decimeter scale were performed to validate our field measurements. These measurements show a comparable order of P- and S-wave anisotropy in the rock volume. The knowledge on the driving mechanism for anisotropy in igneous rocks can potentially help to enhance the monitoring of stress field variations during geothermal operations, thereby improving hazard assessment protocols.
Rotation, Strain, and Translation Sensors Performance Tests with Active Seismic Sources
Bernauer, Felix; Behnen, Kathrin; Wassermann, Joachim; et al. (2021)
Sensors
Interest in measuring displacement gradients, such as rotation and strain, is growing in many areas of geophysical research. This results in an urgent demand for reliable and field-deployable instruments measuring these quantities. In order to further establish a high-quality standard for rotation and strain measurements in seismology, we organized a comparative sensor test experiment that took place in November 2019 at the Geophysical Observatory of the Ludwig-Maximilians University Munich in Fürstenfeldbruck, Germany. More than 24 different sensors, including three-component and single-component broadband rotational seismometers, six-component strong-motion sensors and Rotaphone systems, as well as the large ring laser gyroscopes ROMY and a Distributed Acoustic Sensing system, were involved in addition to 14 classical broadband seismometers and a 160 channel, 4.5 Hz 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 seismic signals that were generated by small amounts of explosive and a Vibroseis truck. This paper presents details on the experimental setup and a first sensor performance comparison focusing on sensor self-noise, signal-to-noise ratios, and waveform similarities for the rotation rate sensors. Most of the sensors show a high level of coherency and waveform similarity within a narrow frequency range between 10 Hz and 20 Hz for recordings from a nearby explosion signal. Sensor as well as experiment design are critically accessed revealing the great need for reliable reference sensors.
Investigating Anisotropic Wave Propagation in Cros Hole Measurements
Hertrich, Marian; Behnen, Kathrin; Maurer, Hansruedi (2023)
EarthDoc ~ Seventh EAGE Borehole Geophysics Workshop

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Kathrin Behnen

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