San Diego Bay Pull-apart Basin

Inner California Borderland High-Resolution Fault Mapping: Rose Canyon Fault Releasing Stepover in San Diego Bay Pull-apart Basin

(in prep)

Abstract

The releasing stepover in San Diego Bay is characterized by a pull-apart basin geometry between the southern termination of the Rose Canyon fault around downtown San Diego and the Descanso fault offshore along the USA-Mexico coastline. Although the step between these two strike-slip faults is considered too large for through-going rupture, the complexity of fault segments within the San Diego Bay pull-apart basin is not well defined and might considerably increase the seismic hazard for the city of San Diego. We use a combination of geophysical techniques (multi-channel seismic, Chirp sub-bottom, multibeam bathymetry) and onshore geotechnical surveys to create a novel fault model of the northern San Diego Bay pull-apart basin. We estimate Holocene active deformation of the Spanish Bight fault, East Bay fault, and Harbor Island fault with fault-related bay floor deformation. Further, we calculate subsidence rates between 0.15 and 0.21 mm/yr around the San Diego International airport, accommodated by the East Bay fault, and observe overall transtensional kinematics with down-to-the-east displacement. The fault model proposed in this work contributes to determining the San Diego Bay pull-apart basin evolution, understanding the mechanisms driving slip transfer and earthquake propagation across the releasing stepover, and increasing the resolution of Southern California rupture forecast models.