This research follows previous successful NSF-supported work that investigated the nature of thrust-type plate boundary tectonics. In the present research, the roughness of the plate boundary at subduction zones and its control of the maximum size of thrust earthquakes is to be studied. This may be more important than subduction rate and plate age as controlling factors proposed previously. Also, based on evidence that seismic moment release increased in the few decades before four large California earthquakes, seismic moment will be investigated prior to large subduction zone events. Both subjects bear on the estimate of earthquake risk and hazard. This research is a component of the National Earthquake Hazard Reduction Program.
