Recent faulting in south San Diego Bay: Potential rupture pathways for future earthquakes on the southern Newport-Inglewood-Rose Canyon Fault system

The Rose Canyon Fault (RCF) is the southern segment of the larger Newport-Inglewood-Rose Canyon Fault system, which underlies or is within 10 km of the most populated areas of coastal southern California. While recent work on offshore segments north of San Diego has shown a complex but connected network of faults, less well understood is the southern terminus of the fault system. South of downtown San Diego, San Diego Bay occupies a pull-apart basin formed by a 10 km stepover between the northwest-oriented RCF and offshore Descanso Fault. Several more northerly oriented active faults link these two master strike-slip segments across San Diego Bay. However, in the southern portion of the Bay, and outside of the pull-apart basin boundaries, numerous northwest-oriented faults suggest that the classical pull-apart basin model may not sufficiently describe the current geometry. One hypothesis is that the San Miguel-Vallecitos fault, which trends northwesterly and is mapped south of the Bay in Mexico, may transfer slip to the RCF system in the southern Bay. We will present result from reprocessed multi-channel seismic (MCS) data collected in San Diego Bay, with improved resolution at depth that illuminates deeper structure. The deeper-penetrating MCS data image a northwest trending fault that appears to hinge deposition in the southern portion of the Bay with vertical separation down to the east. To image the upper ~50 meters of bay deposits in more detail, the MCS data were combined with high-resolution Chirp data that show faulting close to the Bay floor. In the southwest portion of the Bay, Chirp data have imaged a northwest trending fault that offsets a reflector with the geometry and character that suggests it is the transgressive surface. Borehole data from geohazard reports and where available USGS water wells will be used to ground truth both the MCS and Chirp data. If active, these faults in the southern portion of the Bay could represent a connection between the RCF and the San Miguel-Vallecitos Fault that has important implications for rupture dimensions of future earthquakes in the region.