SCEC Award Number 12073 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Name Organization
Glenn Biasi University of Nevada, Reno Lisa Grant Ludwig University of California, Irvine
Other Participants Student: Andrew Homan, UNR; James Brune, UNR; John G. Anderson, UNR
SCEC Priorities 6e, 6b, 6c SCEC Groups GMSV, Geology, WGCEP
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
Precariously balanced rocks (PBRs) provide unique physical constraints on unexceeded ground motions at return times of centuries to 1000’s of years (Anderson et al., 2011). As such they play an important role in evaluating predictions of physics-based ground motion efforts including CyberShake (Graves et al., 2011). This project continues development of PBR constraints in support of CyberShake. The goal of this project is to develop vector-valued survival probabilities (e.g., in joint PGA, PGV space) where PBR’s constrain ground motions of interest to CyberShake and southern California hazard estimation. To achieve this and to extend the scientific utility of PBRs, we have made great advances in compiling rock locations, dimensions, and fragilities. Over 9,000 images have been added. Over 1,900 distinct PBR and geologic features are included, doubling the resource during this year. New maps show the spatial extent of quantitative ground motion constraints. Structures in the map patterns include a ~25x25 km region between the northern San Jacinto and Elsinore faults within which ground motions are apparently rarely or never above about 0.7 g. Elsewhere PBRs occur in linear arrays, or locally, in islands of apparently low ground motions. A simple viewing mechanism is now available to display rock images on the basis of rock ID, locale, or static overturning angles.
Intellectual Merit Research progress this year with the precariously balanced rock photo collection has enabled us to identify areas and approximate maximum ground motion limits not exceeded in the past few thousand to perhaps 10,000 years. No similar data are available within SCEC community.
Broader Impacts Seismic hazard estimation is a fundamental societal benefit of SCEC research. This project compliments that research by providing data with which to constrain physics-based ground motion simulations. New data may also lead to new understandings of seismic wave propagation in southern California.
Exemplary Figure Figure 2. Detail from Figure 1 showing the spatial relationship among PBR overturning angle. Fine gray lines are major roads added for reference. Most fragile PBRs occur within zones outlined by rocks with lesser potential for toppling. In most cases an offset distance is observed from the faults to the PBRs. The quasi-uniform distribution of rocks in a ~25x25 km field centered on 33.8, -117.25 between the northern Elsinore and San Jacinto faults compares markedly with the linear array farther south and suggests different rupture patterns or earthquake sizes. The presence of several very fragile rocks very near the Pinto Mountain fault suggests that fault activity there is extremely low.