P- and S-wave velocity models for the INSIDE study area

The INSIDE project aims at enhancing our understanding of processes associated with induced seismicity in the southern Munich area, particularly around the active geothermal sites of Schäftlarnstraße and Pullach, as well as the planned Baierbrunn project. This report describes the construction of a 3D velocity model for the propagation of compressional (P-) and shear (S-) seismic waves in this zone. The velocity models should be as reliable as possible since they control the localization of seismic events and, consequently, their hypocenter and origin time inaccuracy.
First of all, this document presents the study area, which covers the geothermal sites under focus in INSIDE but also the Unterhaching and Oberhaching sites where a major part of the seismicity is observed. The datasets available to construct the models (borehole measurements, VSP surveys and previously developed seismic and structural models) are presented too. Then, the procedure to create layer-cake velocity models is explained. The seismic horizons resulting from the GRAME 3D project were used to define the geological interfaces where strong velocity changes occur. ... mehrFrom borehole data acquired in several geothermal wells in the study area, the assumption could be made that the shear and compressional velocities are constant over the horizons and that the velocity can vary linearly within a layer, with a particular case for the “Liegende-Tonmergel” layer in which linear increase and decrease were considered. A model with constant velocity per layer was also investigated. The last part of the document presents several tests carried out to check the reliability and consistency of the created models with the VSP data acquired in the Pullach TH3 well. In particular it shows the adequacy of the VSP data with the reference KIT model. Finally, the impact of varying the reference KIT model on the seismicity recorded during INSIDE project is quickly discussed.