SCEC Award Number 18038 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Collection of very high-resolution topography along the southern San Andreas Fault to resolve slip distribution in recent surface ruptures
Investigator(s)
Name Organization
Thomas Rockwell San Diego State University Allen Gontz San Diego State University
Other Participants Chelsea Blanton
SCEC Priorities 1a, 5d, 5c SCEC Groups Geology, SAFS, WGCEP
Report Due Date 03/15/2019 Date Report Submitted 05/03/2019
Project Abstract
 Structure from Motion (SfM) Photogrammetry, based on unmanned aerial vehicle (UAV) flights, was implemented along the southern San Andreas fault (sSAF) to acquire a dense, high-resolution topographic dataset from which to interpret fault-related offsets of small geomorphic features and to develop a model of late Holocene slip-per-event. This study better constrains slip estimates from recent earthquakes along the sSAF and combines new slip data with ages of past earthquakes from paleoseismic studies (Philibosian et al., 2011, Rockwell et al., 2018). We evaluate slip per event for paleoearthquakes which ruptured this segment of the sSAF and investigate the relationship between co-seismic slip events and aseismic creep. The data show that the Coachella Valley segment of the SAF likely follows a quasi-periodic recurrence model for large earthquakes. Statistical analysis of our offsets suggests at least 4 large surface rupturing events with average displacements of 2.7 – 2.9 m per event. Analysis also reveals small-scale offset clusters that we attribute to climate-modulated channel incision across the fault, followed by subsequent creep. These offset clusters support a creep rate of ~3 mm/yr at both Mecca Hills and Box Canyon for the past ~160 years.
Intellectual Merit This project applied the latest technology to collect imagery along sections of the southernmost San Andreas fault, which has not ruptured in 300 years and is the most likely to produce a major earthquake in the near future, with the purpose of resolving the amount of displacement in the past several earthquakes. The resulting estimate of 2.7-2.9 m per event is about half of that which has accumulated since the most recent large earthquake. Possible explanations are that the next earthquake will be larger than any earthquake in the past 1000 years in the Salton Trough region (characteristic model), or that there may be multiple large earthquakes in a short period of time (non-characteristic model) to account for the accumulated elastic strain.
Broader Impacts This project was the focus of Chelsea Blanton, a MS student at SDSU. She had three undergraduate women as field assistants. Some of the data collection (aerial imagery and field observations) were conducted as part of Rockwell's neotectonics graduate class. Benefits to society include a better understanding of the past behavior of the southern San Andreas fault, which is the most likely to rupture in a major earthquake in the near future.
Exemplary Figure Figure 5