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

本研究将粘弹性（VE）全波形反演（FWI）应用于2003年在SAFOD钻孔现场跨圣安德烈亚斯断层（SAF）采集的有源地震数据。FWI是一种通过反演全地震记录来提高地震走时模型分辨率的层析成像技术。与声学实现相反，全弹性FWI适于科普高阻抗对比，并且它提供高分辨率的P波和S波速度模型。增加地震模型的分辨率通常旨在更详细的场地表征。目标是改善模型与局部钻孔信息之间的联系，以便更好地确定井下观测的空间范围。具体来说，成像的低速带下的Salinian花岗岩的主要目标之一，包括一个薄的损伤区，可容纳断层蠕动和微震活动的组合运动。对该区域成像的能力对于SAF的地震研究至关重要。此外，高分辨率地震模型有可能探测具有构造物理重要性的超压区或其他异常区。本研究中的模型也可以在未来使用，例如，用于主动源反射数据的逆时偏移。

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.