This research is to obtain an estimate of the Loma Prieta earthquake rupture process first by analyzing the teleseismic records and then by simulating strong-motion seismograms. Using records from the new NSF/IRIS PASSCAL seismic instruments that were installed in the aftershock area, the research will involve analysis of aftershock activity including determination of crustal structure near the source region. This research is a component of the National Earthquake Hazard Reduction Program.