Analysis of Northridge Earthquake Aftershock Recording (Near 94) to Explain Enhanced Damage Zones

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9416213 Davis This research is to complete the archival and begin analysis of data from a 98 seismic station array installed immediately after the 1994 Northridge earthquake to explain the extreme damage from the main shock in Sherman Oaks and Santa Monica. Stations were clustered in the high damage zones as well as along two linear arrays that extended through the station clusters into the aftershock zone. One objective was to investigate whether the weak ground motion from the aftershocks could be used to understand the damage from the strong ground motion of the main shock, the question of strong-motion linearity. Over 300 aftershocks were recorded. Preliminary analysis reveals that badly damaged areas do indeed see large aftershock amplitudes relative to those of undamaged areas with some exceptions. This work seeks to analyze systematically the propagation from the hypocentral zone to the stations of the array to explain how propagation and site effects contribute to the damaging ground motion. Strong aftershock shaking will be compared with detailed maps of red-tagged zones provided by the LA City Council. This project is a contribution to the National Earthquake Hazard Reduction Program and is supported by the Northridge Earthquake Emergency Appropriation. ***