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Fault zone signatures from ambient vibration measurements - a case study in the region of Visp

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Baumann Cyrill, Burjanek Jan, Michel Clotaire, Haeh Donat, Dalguer Luis,
Project Development of Earthquake Source Physics Models for the seismological assessment of future earthquakes and ground motion prediction in the Alpine regions
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Original article (peer-reviewed)

Journal Swiss Journal of Geosciences
Title of proceedings Swiss Journal of Geosciences

Abstract

Investigations of tectonic features, such as faults, are important challenges for geologists and engineers. Although direct investigational methods, such as boreholes and trenches, have the potential to provide accurate data, these direct methods are usually expensive, time consuming and give only punctual insights into the ground. Geophysical methods, for example electric surveys and ground penetrating radar, are less expensive and faster to implement. However, these geophysical methods may be difficult or sometimes even impossible to apply in regions with rough topography or those highly urbanized. In this study, we propose an easy-to-use and affordable method to detect fault zones based on ambient vibration observations. We apply this method in the region between Visp and Unterstalden on a small secondary fault branch, which has no explicit surface expression, and which is linked to the Simplon Line. The assumption is that the fault of interest is surrounded by damage zone consisting of fractured rock, resulting in lateral change of both seismic velocity and attenuation. The objective was first to identify such lateral changes in the observed seismic wavefield, and second, to map such an anomaly and combine it to the available geological information. In this way, we were able to follow the fault trace even without a clear surface expression of the fault. Our observations showed the existence of a signature in the power spectra of the seismic noise that may correspond to a damage zone. Such signature is observed along the trace of the expected fault.
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