Late Quaternary deformation and recency of faulting of the northernmost San Jacinto fault zone, and implications for slip transfer to San Andreas fault

Drake D. Kerr, Nate W. Onderdonk, & Paula M. Figueiredo

Published August 14, 2019, SCEC Contribution #9630, 2019 SCEC Annual Meeting Poster #101

Paleoseismic and geologic data on the southern San Andreas fault (SAFZ) show that there is a significant difference in earthquake recurrence and slip rate on the fault north and south of Cajon Pass. The northern end of the San Jacinto fault zone (SJFZ) forms a 2km wide releasing-step with the SAFZ in the Cajon Pass area. Transfer of slip from the SAFZ to the SJFZ is the likely cause of the decrease in slip rate, and paleoseismic data suggest some ruptures on the SAFZ have diverted down the SJFZ. A better understanding of the fault structure and measurements of slip rate on the northern SJFZ are needed to test these hypotheses. We are working to understand where slip is transferred between the SAFZ and the SJFZ in the Cajon Pass area by mapping and dating offset geomorphic features along the three major strands of the SJFZ from where it exits the San Bernardino basin to its termination in the northwest in the San Gabriel Mountains. Remote mapping along the northernmost SJFZ using the B4 lidar imagery dataset, San Bernardino County lidar dataset, existing geologic maps, and satellite imagery is presently ongoing in Google Earth, QGIS, and ArcMap. We are identifying and mapping geomorphic features such as offset and deflected streams, fault scarps, shutter ridges, alluvial fans, landslides, and fluvial terraces, to investigate the fault structure and look for potential slip rate or paleoseismic sites. Remote mapping and field investigations have so far revealed several sites along the northern SJFZ that have the potential to bracket the timing of faulting.

Key Words
San Jacinto fault, San Andreas fault, Earthquake Gate, Cajon Pass, earthquake geology

Citation
Kerr, D. D., Onderdonk, N. W., & Figueiredo, P. M. (2019, 08). Late Quaternary deformation and recency of faulting of the northernmost San Jacinto fault zone, and implications for slip transfer to San Andreas fault. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology