SCEC Award Number 16195 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Paleoseismic investigation of the Rose Canyon fault zone, San Diego, CA
Investigator(s)
Name Organization
Jillian Maloney San Diego State University
Other Participants Drake Singleton
SCEC Priorities 4b, 2a, 4c SCEC Groups Geology, USR, WGCEP
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
 The project objective was to resolve the paleoseismic history and along strike variations in fault characteristics, complexity, and slip history of the Rose Canyon fault zone (RCFZ) through the San Diego, California region. We compiled and analyzed existing cone penetrometer test (CPT) and borehole data from onshore geotechnical studies, and high resolution seismic data collected from within San Diego Bay. This project focused on the southern RCFZ and Spanish Bight fault (SBF), located at the edge of the San Diego pull-apart basin where the RCFZ steps offshore to the Descanso fault zone. We completed detailed mapping of fault zone, which shows that the SBF splays from the south into San Diego Bay. The SBF appears to terminate within the Bay and a fault that trends more parallel to the main RCFZ strands appears to accommodate slip to the north. We observe a high degree of fault complexity within this region with changes in the fault zone moving from south to north. We observe possible surface rupture on the SBF within the Bay that can be constrained based on dredge history to a rupture in the last 72 years. The most recent event dated on the main Rose Canyon fault zone is ~1650 AD suggesting that these faults do not always rupture synchronously. This research illustrates the value of compiling multiple small scale datasets to observe larger scale patterns in fault characteristics that could be used in future seismic hazard assessments.
Intellectual Merit Our data and analysis establish along strike variations in fault characteristics, complexity, and slip history on a major strike-slip fault in southern California (SCEC Priority 4b). We observe a high degree of fault complexity within this region with changes in the fault zone moving from south to north that include changes in displacement, geometry, and sense of slip. Furthermore, numerous laboratory and numerical models describe the theoretical formation and evolution of pull-apart basins, but few field studies have examined the character of faults as they approach releasing bends and step-overs. Variability of fault character approaching step-overs could have significant controls on tectonic geomorphology and earthquake rupture dynamics. The results of this research provide a detailed description of a major strike-slip fault zone as it enters into a pull-apart basin.

This research included investigation of earthquake ages and displacements along the Rose Canyon fault zone (SCEC Priority 2a). Although more work is needed to improve rupture timing constraints, particularly in the offshore region, we have observed evidence of a surface rupture along the Spanish Bight fault and confirmed that the faults within San Diego Bay are Holocene active. Our preliminary data suggest that the offshore Spanish Bight fault and onshore Rose Canyon fault do not always rupture synchronously.

This research also produced detailed mapping of fault segments within a complex area of the Rose Canyon fault zone where it approaches a step-over across San Diego Bay. This part of the fault zone crosses beneath the San Diego Airport and steps offshore in close proximity to downtown San Diego. The data synthesized here will contribute to and improve the community fault model (Priority 4c), by updating fault maps and improving our understanding of slip history and complexity along the fault.
Broader Impacts This research was primarily conducted by students at SDSU under supervision by the PI. Students gained experience working with multiple software packages including Kingdom Suite, ArcGIS, and Chesapeake Bay Technologies. They also re-processed Chirp data using Sioseis and Seismic Unix, both unix based software that required coding. The student leader on this project was Eui-jo Marquez, a female veteran of Hispanic background. In order to obtain the geotechnical data for the reports, Eui-jo reached out to several consulting firms and was able to work with professionals in the community, secure copies of the data, and establish a cooperative agreement for sharing software licenses between SDSU and Fugro Geoservices. She was soon offered an internship at AECOM, which will be an incredible asset for her as she enters the geotechnical workforce with her Masters degree at the end of the academic year. Eui-jo also gained experience mentoring younger undergraduate students that she enlisted to help work on the project.

The database created through this project contains the most diverse sources of data available on faults located around the northern San Diego Bay – San Diego International Airport area. Data include CPTs, borings, cross sections, radiocarbon dates, Chirp profiles, and deeper penetrating seismic data from both academic and geotechnical studies. This type of data compilation is extremely useful for detailed studies of fault zone architecture and paleoseismology. Each individual dataset provides a snapshot over some portion of the fault zone, but analyzing the datasets together can elucidate changes along strike and give a better understanding of the fault zone as a whole. We anticipate that this database will grow as we expand our research to other segments of the Rose Canyon fault zone. To disseminate our results to the earthquake science community, this research was presented at the 2016 SCEC meeting and we anticipate a student led publication to be generated in the coming months. The products generated through this project (fault maps, cross sections, Chirp profile interpretations, rupture history) will be made available to the SCEC community through appropriate SCEC resources. Furthermore, they will be made available to assist with the ongoing effort to update the Earthquake Planning Scenario for San Diego and Tijuana.
Exemplary Figure Figure 2: a) Geotechnical cross section of borehole and CPT data from San Diego International Airport, showing northern extent of the western Spanish Bight fault strand within the study area (modified from Kleinfelder, 2013). b) Chirp seismic line showing both segments of the Spanish Bight fault in the northern part of San Diego Bay. c) Chirp seismic line showing down-to-the-east slip of the three Bay faults, and evidence of offset increasing with depth. The western strand shows disturbance of the seafloor in this location. d) Geotechnical cross section of borehole and CPT data from Coronado Island, showing negative flower structure of the Spanish Bight fault, south of the convergence of the western and eastern strands (modified from Construction Testing & Engineering Inc., 2013). WSBF = western Spanish Bight fault; ESBF = eastern Spanish Bight fault; EBF = Eastern Bay fault. Fault strands are drawn as red lines, and dashed where inferred. TWTT = Two-way travel time; Qaf = Artifical fill; Qb = Bay deposits; Qbp1, Qbp2, and Qbp3 = Late to Middle-Pleistocene marine terrace units (5e, 9e and 11e respectively), distinguished by fossil content; Qudf = Quaternary undocumented fill; Qbd = Quaternary bay deposits; Qop-6 = Quaternary older paralic deposits; Qvop = Quaternary very old paralic deposits.
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