Intern	Institution	Mentor	Project Title
Justin Rubinstein	UCLA	Paul Davis, UCLA	Analysis of Azimuthal Variation in Amplitude Factors in Sherman Oaks During the Northridge Earthquake Aftershock Sequence

Abstract:

The Northridge earthquake caused unexpectedly high amounts of damage in Santa Monica and Sherman Oaks, two regions far removed from the rupture. My project was to investigate the cause of the anomalous high damage in both locations. Working with data from the Northridge Earthquake Aftershock Recording (NEAR) Experiment, a dependence of high amplitude areas upon source location was investigated. Analysis of data from the twenty-nine seismic stations placed in Santa Monica indicates that there is lens structure at depth which creates the enhanced damaged in the mid Santa Monica region. Using contour plots of amplitudes of the 29 stations in Santa Monica for each event indicated a movement of a "hot zone" where the amplitudes were much higher than the surrounding regions. Tracing rays through a moveable lens from the hypocenter of an event to the surface allows one to pinpoint the location of lens.  The finite nature of the lens indicates that the high damage in Santa Monica was dependent upon the location of the main shock. As evidenced from aftershocks in this data set, an earthquake of similar size in a slightly different location would most likely not reproduce this damage pattern. Sherman Oaks produced two regions of concentrated amplification, but no systematic azimuthal pattern as seen in Santa Monica was detected.

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