SCEC Award Number 11141 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Estimation of the Fragilities of Precariously Balanced Rocks from the 2-D Photographic Images in the UNR PBR Archive
Investigator(s)
Name Organization
Glenn Biasi University of Nevada, Reno
Other Participants
SCEC Priorities B4, B2, A6 SCEC Groups Geology, SHRA
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 In SCEC-3 year five we proposed to complete the 2-D screening of collected photos in the PBR archive and to apply the 2-D vector value regression-based estimation method of Purvance to PBRs identified in screening. A Matlab-based interface was designed at UNR to sort photos and to analyze useful ones for static overturning accelerations and where possible, rocking arm lengths. Over 5800 photos from southern California were screened by this method. The 2-D analysis yielded static overturning accelerations for ~1500 of them. This was the first comprehensive effort to tame this collection and assess what is in it. Approximately 550 rocks also had length scales and thus could be considered for vector-valued probability assessment. Of these 103 have two alpha angles less than 0.4 radians, the approximate range of validity for the regressions of Purvance et al. (2008). These were analyzed and probabilistic fragilities were developed in PGA vs. SA(1) space. Results were presented at the SCEC 2011 annual meeting. Eighteen rocks or clusters of rocks in the archive were subsequently identified as being near CyberShake field points and potential controls at long return times for CyberShake ground motion predictions. Many had been the subject of field testing and/or detailed 3-D photographic analysis, but were among a group of photos that had not been integrated into the archive. A special effort was undertaken to fill in the 2-D alpha and R values, and the corresponding vector-valued assessments. These results will be integrated into CyberShake ground motion validation efforts.
Intellectual Merit This work contributes probabilistic ground motion constraints at long return times for validation testing of CyberShake.
Broader Impacts The broader impact of this research will be through its contribution to direct computation of the seismic hazards in southern California, and consequent opportunities for earthquake risk reduction.
Exemplary Figure Figure 4. Rocks near CyberShake field points GV03 and GV05, and their corresponding PGA vs. SA(1) vector probability of overturning plots based on 2-D photo estimation. Titles of plots give alpha angles (a1, a2) and the rock scale (p2). Rock center of gravity is circled in (b), (c), and (d). The rock in (a) is relatively stable because of its size. Panels (c) and (d) are two views of the same rock, included here to give an idea of the sensitivity of the results to the angle of the photo. In this case the difference is relatively small.