SCEC Award Number 25304 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title Field investigation of complex faulting across the San Diego Bay step-over
Investigator(s)
Name Organization
Jillian Maloney San Diego State University Karl Mueller University of Colorado, Boulder Kim Olsen San Diego State University Thomas Rockwell San Diego State University
SCEC Milestones A1-3, A3-1, A3-4 SCEC Groups Geology, PBS, CCB
Report Due Date 03/15/2026 Date Report Submitted 05/06/2026
Project Abstract
 We propose a field investigation of faults south of San Diego Bay that were recently mapped in Lidar and aerial imagery data and that may link to the Rose Canyon fault zone (RCFZ) to the north, impacting the regional seismic hazard. The Holocene active RCFZ is a known hazard to the city of San Diego and is well mapped and studied where it trends onshore in San Diego, from La Jolla to downtown. However, south of downtown, the fault zone splays into San Diego Bay and it remains unclear how slip is transferred between the RCFZ and faults to the south. New fault mapping, based on Lidar and aerial imagery from south of San Diego Bay, revealed several potential fault strands that could elucidate connections between the RCFZ and major fault systems to the south (La Nacion fault zone and San Miguel Vallecitos fault zone). We propose to groundtruth the Lidar mapped fault strands by compiling existing geotechnical studies and conducting new geophysical surveys (seismic refraction, gravity, magnetic, resistivigy, and GPR) and vibracore transects across mapped fault strands in the Tijuana River National Estuarine Research Reserve and on the Silver Strand. These data will be used to characterize the subsurface stratigraphy and identify evidence of faulting. The work will support an SDSU Masters thesis and will be incorporated into two SDSU undergraduate advanced field classes.
Intellectual Merit The identification of faulting south of San Diego Bay is a critical component of assessing the validity of possible rupture scenarios through different fault step-over models. We used geotechnical and geophysical data to map faults and identify sites conducive to earthquake geology studies (A1-3). Based on our results, future trenching in the Tijuana River Estuary or Chula Vista regions would clarify questions about faults that pass through populated areas (A3-4). Furthermore, this work improved mapping of the geometry of the La Nacion Fault zone and newly identified faults, previously missing from the CFM database (A3-1).
Broader Impacts Jillian Maloney and Kim Olsen taught undergraduate advanced field methods classes in Spring 2025, in Sedimentology and Stratigraphy and Geophysical Methods, respectively. The geophysical data collected in the Tijuana River Estuary were collected with both classes and were used as a primary field project in the Geophysical Methods class. The students processed and interpreted data, and submitted a written report. Students gained experience planning and conducting a preliminary fault investigation using geophysical methods. SDSU alumni make up a large fraction of the geotechnical workforce in San Diego and these activities prepared students for future careers as earthquake scientists.
Project Participants San Diego State University - Jillian Maloney, Thomas Rockwell, Kim Olsen
University of Colorado, Boulder - Karl Mueller
Exemplary Figure Fig. 6: ERT profile along partial length of northern Profile 1 with 2 m electrode spacing. Note a strong, vertical change in resistivity ~160 m along the profile, as indicated by the red arrow, which may be caused by a fault in the subsurface. Bottom – Gravity survey data across part of Profile 1 (see Fig. 3 for location). Note the large gravity anomaly slightly west of the resistivity change.
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