Thesis Defense – Drake Singleton (PhD)

Neotectonics in San Diego, California: Paleoseismology, Slip Rate, and Offshore Structure of the Rose Canyon Fault

Abstract
The Newport-Inglewood-Rose Canyon (NIRC) fault system is a major structural boundary that extends along coastal southern California from Los Angeles to San Diego. The southern segment, the Rose Canyon fault (RCF), directly underlies the city of San Diego and represents the largest seismic hazard to the San Diego-Tijuana metropolitan region. The material presented in this dissertation provides new data that resolve uncertainties in fault behavior and characteristics for the RCF.

Stratigraphic evidence from newly opened paleoseismic trenches are used to interpret six surface-rupturing earthquakes on the RCF in the past 3,300 years. Paleoearthquake ages constrained by radiocarbon dating suggest a late-Holocene recurrence interval of ~700 years, with the most recent large-magnitude event occurring in the mid-1700s. When combined with previous paleoseismic studies, the new paleoearthquake ages show an apparent temporal correlation of earthquake occurrence between the southern and northern segments of the NIRC fault system, suggesting a possible northward-cascading sequence of earthquakes.

The RCF includes a significant onshore segment, which provides an opportunity to use traditional geodetic techniques to resolve slip rate. Surface velocities from a combined campaign and continuous GPS network that spans the RCF are used to constrain elastic half-space models. The best-fitting model suggests a rate that is toward the higher end of geologic estimates, as well as a potential rheological contrast across the fault trace. The GPS surface velocities further suggest a more easterly trace for the RCF, and a possible connection with the San Miguel-Vallecitos fault system.

South of downtown San Diego, the RCF splays out into a complex network of faults that accommodate the subsidence beneath San Diego Bay. Using legacy multi-channel seismic data and recently collected high-resolution chirp profiles, the fault structure and stratigraphic character beneath San Diego Bay are examined. Gridded surface horizons and fault maps show widespread down-to-the-east displacement. Fault orientations in the western portion of the San Diego Bay pull-apart basin are well described by a Rose Canyon–Descanso pull-apart basin, but faults in the eastern portion of the basin lie outside of this model. A separate but related Rose Canyon–San Miguel-Vallecitos pull-apart basin may explain the faulting seen in the eastern portion of the basin.