ACTIVE DEFORMATION AND THE ROLE OF INHERITED STRUCTURES IN THE SACRAMENTO-SAN JOAQUIN DELTA, NORTHERN CALIFORNIA, CONSTRAINED USING A COMPILATION OF GEOMORPHIC, GEOLOGIC, AND GEODETIC DATASETS
We address these challenges by integrating surface observations with a compilation of subsurface, bedrock geology, and geodetic datasets from the Delta and from the Coast Ranges and Diablo Range to the northwest and southwest, respectively. Structural geologic data from the surrounding region highlights the significant influence that Tertiary-age forearc structures exert on the geometry and kinematics of major Quaternary-active structures within the Delta. These inherited structures include both extensional and reverse faults associated with deformation within the Farallon subduction system forearc prior to the initiation of the transform plate boundary. They have been reactivated as part of the modern plate boundary, and exhibit a range of geometries and kinematics in a region generally dominated by right-lateral strike-slip Quaternary faulting. The approximately plate-boundary-parallel Pittsburg-Kirby Hills and Midland faults which formed as extensional structures in the early Tertiary exhibit a component of reverse displacement in the Quaternary based upon geomorphology and subsurface datasets. A clearer understanding of subsurface geometries and structural relationships, built upon the regional tectonic history, provides insight into modern deformation accommodated on older structures and may help inform interpretations of seismic hazard within the Delta, where traditional paleoseismological investigations are of limited use.