SCEC Award Number 14122 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title SoSAFE- San Jacinto: Chronologic support to extend and refine the paleoseismic record for the northern San Jacinto fault zone at Mystic Lake
Investigator(s)
Name Organization
Nathan Onderdonk California State University, Long Beach Sally McGill California State University, San Bernardino Thomas Rockwell San Diego State University
Other Participants
SCEC Priorities 2a, 1a, 2d SCEC Groups SoSAFE, Geology, Geodesy
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Paleoseismic trenching at the Mystic Lake site has resulted in a record of 15 earthquakes over the past 3700 years on the Claremont fault segment of the northern San Jacinto fault zone. We believe we have a complete record for the past 2000 years during which there were 11 or 12 earthquakes. Our record for the preceding 1700 years (0 to 1700 BC) only includes 3 or 4 earthquakes and is most likely not complete due to missing stratigraphic section. The recurrence interval for the last 2000 years is between 160 and 190 years, and the last ground rupturing earthquake occurred around 1800 AD. The 215 years that have passed since the last rupture is equal or slightly larger than the longest hiatuses between earthquakes in the past 2000 years, suggesting the fault may be near the end of its earthquake cycle. However, the recurrence time between the last 4 events was shorter than the 2000-year average, and additional data from the Quincy site on the same fault shows that these last 3 events were larger than average, which suggests that accelerated strain release between 1420 and 1850 has resulted in a relatively quiet period for the last 200 years.
Intellectual Merit The project generated new data and interpretations regarding the seismic behavior of the San Jacinto fault zone during the past 2000 years. This was one of the primary goals of the SOSAFE project and will contribute to more accurate evaluations of earthquake hazards in southern California.
Broader Impacts Numerous SCEC interns as well as CSU graduate and undergraduate students were involved with the field work and data analysis components of this project. These students worked in the fault trenches, assembled digital photographs, helped with interpretations, and prepared posters for presentations at SCEC annual meetings.
Exemplary Figure Figure 9. Comparison of event ages from the Wrightwood, Mystic Lake, and Hog Lake paleoseismic sites. Event PDFs are shown in gray for each site and possible correlations are shown as green or orange lines.