Precarious Rocks along the Mojave Section of the San Andreas Fault, California: Constraints on Ground Motion from Great Earthquakes

It has been suggested that groups of precariously balanced rocks are effectively earthquake strong ground-motion seismoscopes that have been operating on solid rock outcrops for thousands of years, thus providing a constraint on the maximum ground motion that could have occurred during that time (Brune, 1996; Brune et al. , I996; Shi et al. , 1996; Bell et al. , 1998). Modern instrumental strong ground-motion recorders have only provided data for a few decades, have been very costly, and have not recorded data from any great earthquakes along the San Andreas Fault (great earthquakes occurred in 1852 and 1906, before modern instrumentation was available). Nevertheless, there has been a concerted effort to produce probabilistic seismic hazard maps for the U.S. and California (Wesnousky, 1986; WGCEP95, 1995; Ward, 1994; Frankel et al. , 1997), stimulated in part by the potential losses in great earthquakes and the high cost of earthquake-resistant seismic design. Preliminary results from...