An Integrated Study of the Northridge Mainshock and Large Aftershocks

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9416219 Dreger This research is a multifaceted study of the Northridge mainshock and large aftershocks to address the issues of fault zone complexity, identification of slip planes, slip heterogeneity, as well as the source contribution to the observed strong ground motions. Moment tensor methods will be used to study events to the Mw4.5 level. Forward modeling of aftershocks will be used to refine theoretical Green's functions used in the moment tensor analysis. The Northridge sequence occurred in a geologically complex region on a south-dipping reverse fault, adjacent to the north-dipping structures involved in the 1971 San Fernando earthquake. Aftershocks do not define a clear fault plane at depths shallower than 10 km and these methods will help to resolve the complex geometry of faults in the region. This project is a contribution to the National Earthquake Hazard Reduction Program and is supported by the Northridge Earthquake Emergency Appropriation. ***