iPlex Lunch spring-2015

New mapping of two active transpressional fault zones in the California Continental Borderland, the Santa Cruz-Catalina Ridge fault and the Ferrelo fault, was carried out to characterize their geometries, using over 4500 line-km of new multibeam bathymetry data collected in 2010 combined with existing data. Faults identified from seafloor morphology were verified in the subsurface using existing Borderland seismic reflection data including single-channel and multi-channel seismic profiles compiled over the past three decades. The two fault systems are parallel and are capable of large lateral offsets and reverse-slip during earthquake faulting. The geometry of the fault systems shows evidence of multiple segments that could experience through-going rupture over distances exceeding 100 km. Published earthquake hypocenters from regional seismicity studies further define the lateral and depth extent of the historic fault ruptures. Historical and recent focal mechanisms obtained from first-motion and moment tensor studies confirm regional strain partitioning dominated by right-slip on major through-going faults with reverse-oblique mechanisms on adjacent structures. The two systems resemble onshore active fault zones and provide additional information for understanding the full Pacific-North America plate boundary evolution, as well as transpressional fault systems along the plate boundary. Because of their potential for dip-slip rupture, they may also be capable of generating local tsunamis that would impact southern California coastlines, including populated regions in the Channel Islands.