To advance our understanding of the crustal structure and geodynamics of southern California, a new crustal seismic imaging project is carried out to significantly improve the mapping of the regional 3D crustal velocity structure and major reflection events across the San Andres fault system. The data include the earthquake readings compiled by the Southern California Earthquake Center (SCEC) and seismic reflection records from the Los Angeles Regional Seismic Experiment (LARSE). An innovation of the project is the use of a new deformable-layer tomography to directly map the geometry of P-wave and S-wave velocity discontinuities in the crust and uppermost mantle, and constrained by known crustal thickness variations from receiver functions and other analyses. In addition, an advanced wave equation prestack depth migration is applied to provide new reflection images for the LARSE profiles. The preliminary results from this project indicate that the new tomography method produces sharper vertical resolution and more realistic representations of lens-shaped geologic features like the edges of basins and lithologic pinchouts, which is a significant improvement over traditional tomography that inverts for velocity values on fixed-in-space mesh grids. The LARSE reflection images obtained so far indicate that prestack depth migration can better handle near surface lateral velocity variations and improve the resolution and reflector continuity over previous images of the LARSE datasets. Interestingly, the results from this project suggest that the presence of high noise level, strong lateral velocity heterogeneity and crooked survey geometry argue for, rather than against, the use of prestack depth imaging over the simple CMP stack techniques. This two-year project is expected to provide significantly improved 3D P-wave and S-wave crustal velocity models for southern California and prestack depth migrated images beneath two onshore LARSE surveys across the San Andres fault system. The broader impacts of the project include field demonstration of innovative seismic imaging techniques for future crustal and mantle studies, such as those envisioned for EarthScope/USArray, as well as promotion of crossbreeding in ideas and training between solid Earth geophysics and exploration geophysics that will lead to a fundamental modification of undergraduate and graduate education in seismic imaging.
