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Zusammenfassung:
The two geothermal power plants of Insheim and Landau in the Upper Rhine Graben in Southwest Germany are located close to the village of Rohrbach. Around Rohrbach, two seismic stations monitor the induced seismicity as part of a research network. One of these stations is surface station TMO54, the other one, ROTT, a combined surface and borehole station at 300 m depth. We used passive seismic arrays to characterize the shallow underground around Rohrbach, and evaluated seismograms to assess amplification effects. Velocity profiles were obtained by inverting the obtained Love and Rayleigh wave dispersion curves and Rayleigh wave ellipticity. Around station ROTT, we found small-scale variations of the site effects. Close to a creek, we identify a 4 m thick layer of very soft sediments with shear-wave velocity below 100 m/s, which is not present at a different investigated location at a distance of only 100 m. The VS30 values of these two locations are about 210 m/s and 270 m/s, respectively. For other locations around Rohrbach, VS30 ranges between 290 m/s and 340 m/s, where the highest value corresponds to the location of station TMO54. The seismograms of a catalog of around 3000 induced earthquakes were analyzed to verify the amplification effects. Furthermore, the assessed site effects were incorporated to improve the deterministic estimation of ground motion for several strong events in the framework of seismic hazard assessment of induced seismicity.
