9415736 Borchardt Current methods of predicting earthquake damage generally assume that seismic intensity is a simple function of distance from the earthquake source, as modified by geologic effects. Preliminary observations, derived from detailed damage surveys, show evidence for north-south directivity involving a near-field pulse which seems to have occurred during the first cycle of motion of the 1994 Northridge, CA, Earthquake. The Northridge Earthquake, having occurred on a thrust fault in a heavily populated area, now provides a prime opportunity to examine, and perhaps ultimately to predict, near-field effects. The objective of the project is to test the hypothesis that elastic rebound in the Northridge Earthquake produced an initial pulse that was north-south directed in the near-field. More specific objectives are: 1. To relate the damage data to recorded ground motions. 2. To relate the phenomenon to the geologic, geodetic, and seismologic aspects of the earthquake. If substantiated, this hypothesis will have basic implications for the future design of structures. ***
