SCEC Award Number 10118 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title USING PRECARIOUSLY BALANCED ROCKS (PBRs) TO CONSTRAIN ACTIVITY OF UCERF "B" FAULTS AND EVALUATE RUPTURE DIRECTION
Investigator(s)
Name Organization
Lisa Grant Ludwig University of California, Irvine James Brune University of Nevada, Reno
Other Participants Tyanna Schlom, Dylan Rood, Rasool Anooshehpoor, Greg Balco, Katherine Kendrick
SCEC Priorities B4, A9, B2 SCEC Groups Geology, GMP, SHRA
Report Due Date 02/28/2011 Date Report Submitted N/A
Project Abstract
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Intellectual Merit With 2007-2010 SCEC3 funding, we developed a method to date corestone PBRs in the granitic terrains of southern California using cosmogenic 10Be with a numerical model that accounts for nuclide production before, during, and after exhumation of the PBR from the subsurface. We measured 10Be concentrations from 9 corestone PBRs that provide constraints on ground motions associated with the San Andreas, San Jacinto, Elsinore, Cleghorn, and Pinto Mountain faults in southern California. To constrain the exhumation history of each PBR, we use a forward model and compare our 10Be data to predicted profiles for a range of surface denudation rates and exposure times. Fitting model to data yields the rate and timing of PBR exhumation and thus the length of time the feature was vulnerable to toppling by earthquake ground motions.
Broader Impacts There are several broader impacts of this research. First, we recruited Dylan Rood to begin work on the project when he was in the final stages of his Ph.D. work. This project became the basis for his successful application to NSF for Postdoctoral Fellowship. Second, the results of this work (i.e. the ages of precariously balanced rocks) can be used to calibrate seismic hazard maps in densely populated southern California. The hazard maps are the primary policy tool for mitigating seismic risk through building codes and structural design. Third, the fragility and age of PBRs will be useful for calibration of Cybershake and other SCEC community modeling efforts. Finally, preliminary results suggest some surprising rupture patterns of the San Andreas and San Jacinto faults, key sources of seismic hazard in densely populated areas of California.
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