SCEC Award Number 16260 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative Research: Completion of the paleoseismologic record of the central Garlock fault at the El Paso Peaks site: Documentation of the Early Holocene record
Investigator(s)
Name Organization
James Dolan University of Southern California Ed Rhodes University of California, Los Angeles Sally McGill California State University, San Bernardino
Other Participants Alexandra Hatem (USC Ph.D. student)
CSUSB MS student
SCEC Priorities 1a, 2a, 2d SCEC Groups Geology, WGCEP, SoSAFE
Report Due Date 03/15/2017 Date Report Submitted 07/25/2017
Project Abstract
 During the past year, we (Dolan, McGill, Rhodes, and a dozen USC, CSUSB, and UCLA graduate and undergraduate students) dug sample pits and collected 15 post-IR IRSL225 luminescence samples from offset fluvial terraces at two sites. Specifically, we re-sampled two incompletely dated older terraces at McGill et al.’s (2009) Clark Wash site near the eastern end of the western segment of the Garlock. We also remapped the offset fluvial-alluvial terraces at the Ganev et al. (2012) slip-rate site in the Summit Range on the west-central Garlock. Our 2016 re-mapping shows that what we had initially interpreted as a single terrace is actually two separate fluvial terraces that are offset ~58 and ~70 m, respectively. The luminescence samples (to be dated as part of our recently funded NSF project), will provide additional early Holocene-latest Pleistocene rate constraints on our increasingly detailed incremental slip rate record for the Garlock fault, in turn providing context for our planned trenches at the El Paso Peaks and Christmas Canyon West sites. We also expended considerable effort in terms of permitting. Specifically, we began preliminary permit discussions with the Bureau of Land Management for permission to excavate trenches at the El Paso Peaks site, which we anticipate will be completed during Spring 2018. We also made substantial progress during the year in pushing through our long-delayed trenching permit for the Christmas Canyon West site, and we hope to receive final permits in late Summer 2017 so we can finally begin this key paleoseismic study.
Intellectual Merit There is mounting evidence that the occurrence of large earthquakes on both single faults and fault systems is not a random process. Earthquakes often cluster in both space and time, leading to episodic increases in slip that can extend over multiple earthquake cycles. Comparisons between geodetic and longer-term geologic rates demonstrate that such clusters and lulls may in some instances coincide with transiently elevated or decreased periods of elastic strain accumulation. Moreover, observations from several plate boundaries suggest the coordinated waxing and waning of slip on mechanically complementary regional fault systems. Key to developing a better understanding of these phenomena is the documentation of detailed patterns of strain release along major plate boundary faults. Yet there are too few sites where paired paleo-earthquake age data and incremental fault slip rates are available to determine the spatial and temporal behavior of major plate-boundary fault systems over earthquake-by-earthquake time and displacement scales. The dearth of such data sets motivates our ongoing research on the Garlock fault. Our overarching goal is to generate a highly detailed incremental record of slip along this important fault.

Specifically, in this project we are generating or will generate incremental slip rates at multiple sites and paleo-earthquake ages at two trench sites. These anticipated results from our ongoing studies, coupled with earlier results by us as part of our long-term SCEC-funded research, and results from other groups, will provide an exceptionally detailed record of incremental latest Pleistocene-Holocene fault slip on the Garlock fault, both through time and along strike. These data will facilitate comparison with similar data from other major fault systems in southern California (e.g., San Andreas & ECSZ faults), which is a critically important step in improving our understanding of basic controls on the spatio-temporal occurrence of large-magnitude earthquakes on the major plate boundary faults.
Broader Impacts Our results will help the community to understand how major faults accommodate deformation in time and space – the keys to developing more accurate, next-generation seismic hazard assessment strategies, as well as the basis for future modeling efforts aimed at understanding the causes of such phenomena. The strong educational component of our research involves multiple graduate students from USC, CSU-San Bernardino, and UCLA (where collaborator Ed Rhodes was a Professor until recently moving to Sheffield University). This group includes both female (USC Ph.D. student Alexandra Hatem) and students from under-represented groups (CSUSB M.S. students Bryan Castillo and James Burns, both of whom are Hispanic). These students have been broadly trained in an interdisciplinary manner that includes paleoseismology, tectonic geomorphology, lidar digital topographic data analysis, and geochronologic techniques. We have also included more than 10 CSUSB undergraduate students (many from under-represented groups) in our 2016-2017 field work. Finally, we will present our results in high-profile peer-reviewed journals and at international meetings.
Exemplary Figure Figure 1. Map showing showing Summit Range East (SRE) Garlock fault slip-rate sampled for post-IR IRSL225 dating during 2016 field work, as well as planned trench sites at El Paso peaks (EPP) and Christmas Canyon West (CCW), for which permit requests are pending.
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