SCEC Award Number 18124 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Cajon Pass Earthquake Gate Area: Active fault mapping and evaluation of potential sites to measure the Holocene slip rate along the Glen Helen and San Jacinto faults in the Cajon Pass area.
Investigator(s)
Name Organization
Nate Onderdonk California State University, Long Beach Paula Figueiredo University of Cincinnati Ray Weldon University of Oregon
Other Participants
SCEC Priorities 1a, 3a, 2e SCEC Groups SAFS, Geology, WGCEP
Report Due Date 03/15/2019 Date Report Submitted 03/08/2019
Project Abstract
 The purpose of this study is to investigate the relationship between displacement along the northern San Jacinto fault zone and the San Andreas fault in the Cajon Pass area as part of the larger SCEC effort to understand the Cajon Pass Earthquake Gate. We are working to determine where slip transfer between the two faults occurs, and if the two faults occasionally rupture together. We will document the late Quaternary slip-rate and slip distribution along the three strands of the San Jacinto fault zone in the Cajon Pass area. In 2018 we began to construct a map of surface deformation along the three primary strands of the San Jacinto fault zone, and investigated potential slip rate and paleoseismic sites. We have begun to focus on a promising slip-rate site on the Glen Helen strand within a narrow step-over between the San Jacinto and San Andreas faults. Our mapping and slip-rate measurements will illustrate which strands have experienced recent surface deformation, and the rates at which these strands are accumulating strain. This will reveal how and where slip transfers between the SAF to the SJF, and aid in estimating future rupture patterns.
Intellectual Merit This project contributes to the primary SCEC goal of understanding how fault systems work. Specifically, we are addressing how separate fault strands interact in terms of strain transfer both between and during earthquake ruptures. The area being investigated has been targeted as a focus location for understanding “earthquake gates”, and what controls when ruptures entering the earthquake gate will continue through, stop, or jump to a separate fault.
Broader Impacts This project has supported the teaching and training of a Masters student, and has contributed to course materials in the form of lectures, labs and field trips at CSULB. A field trip and seminar for 20 visiting Chinese earthquake scientists in December of 2018 was largely based on work resulting from this project. Ultimately the outcome of this work will improve public safety and estimates of seismic risk for key infrastructure in the Cajon Pass area.
Exemplary Figure Figure 1. Faults in the Cajon Pass area mapped with key locations mentioned in the text: A= Sycamore Canyon, B= Scotland, C= Applewhite Campground, D= Glen Helen Regional Park, E= Texas Hill. Inset map shows location of Cajon Pass with slip-rate data (in mm/yr) from nearby sites on the San Jacinto and San Andreas faults. Credit= Nate Onderdonk