High resolution P- and S-wave velocity and attenuation models for the SAFOD site from visco-elastic full seismic waveform inversion of the SAFOD-2003 data

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This study applies Visco-Elastic (VE) Full Waveform Inversion (FWI) to active-source seismic data acquired in 2003 across the San-Andreas-Fault (SAF) at the site of the SAFOD drill-hole. FWI is a tomographic technique to improve the resolution of seismic travel-time models by inverting full seismograms. In contrast to acoustic implementations, fully-elastic FWI is adapted to cope with high impedance contrasts, and it provides P- and S-wave velocity models at high resolution.Increasing the resolution of the seismic models generally aims at a more detailed site characterization. The goal is to improve the connection between the models and the localized borehole information in order to better determine the spatial extent of the downhole observations. Specifically, imaging the low-velocity-zones below the Salinian granite is one of the primary goals, including a thin damage zone that accommodates the combined motion of fault creep and microseismicity. The ability to image this zone is of utmost importance for a seismic study of the SAF. In addition, the high-resolution seismic models have the potential to detect over-pressured or other anomalous zones that are of tectonophysical importance. The models from this study can also be of future use, e.g., for reverse time migration of the active-source reflection data.