Fault delineation using earthquake energy as a source for pre-stack depth imaging

Abstract

The San Andreas Fault Observatory at Depth (SAFOD) is a deep borehole observatory constructed to investigate the source of recurring earthquakes at a specific location on the San Andreas Fault. Numerous geophysical datasets were acquired at the SAFOD site to characterize the subsurface environment. Among these, we collected three independent seismic datasets to characterize the local geologic structure. These datasets include VSP, drill-bit noise, and earthquake recordings. Initially, interferometric deconvolution was applied to the drill-bit noise using Schlumberger patented methods to determine the reference signal from rig-based receivers. Next, it was applied in a modified processing flow to determine the reference signal from downhole receivers. Finally, as a result of the application of the technique to earthquake data, we obtained high resolution imaging of the San Andreas Fault at depths exceeding 2.5 km. In conjunction with the other seismic datasets collected at the site, we interpret the complex system of faults and fractures to constitute a flower structure which is partially exposed at Middle Mountain northeast of the SAFOD site.