Project Abstract
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Precariously Balanced Rock Orientations and Fragilities Compared with Cybershake Waveforms: Implications for Seismic Hazard and Possible Super-Shear Ruptures.
Earthquake recurrence forecasting has steadily improved in recent years. Similarly the numerical power for calculating seismic ground motion, based on various types of modeling and assumed input parameters, have greatly improved (regression methodologies. tera and peta scale computing, Cybershake broad-band waveforms). The weak link in proceeding to final estimates of seismic hazard is the validation of the various inputs and modeling procedures. There are simply not enough instrumental data from large earthquakes near-source, to validate the various programs and assumed source parameterizations. The study of precariously balanced rocks (PBRs) may be the only way to remedy the situation. In 2011 we studied critical rocks in the UNR archive of thousands of PBRs, rocks strategically selected to be most useful in constraining the next generation of seismic hazard maps. The advent of Cybershake ground motion calculations offers the possibility of developing a better understanding of the distribution of PBRs and PBR orientations. Dozens of PBRs in a number of areas in Southern California have been photographed for the Photomodeler computer program to produce digital shapes for use in further analysis. Of the rocks involved, approximately 20 have already been modeled to produce digital 3-D shape models. Of these, about 10 are in the present Cybershake broad band coverage area, and are being investigated by Jessica Donavan andTom Jordan at USC, and James Brune at UNR. Preliminary result are very encouraging, and indicate that future studies will greatly improve our understanding of earthquake hazard, a major step forward for further research in SCEC4. |
