What Caused the Focusing Related Damage in Santa Monica During the Northridge Earthquake?
Shirley Baher and Paul Davis, University of California, Los Angeles Gary Fuis, U.S. Geological Survey, Menlo Park Rob Clayton, California Institute of Technology The city of Santa Monica sustained concentrated damage from the anomalous amplification of seismic energy during the 1994 Northridge earthquake. Several hypotheses have been developed to explain the high amplitudes of ground motion. These include 1) focusing by a deep geological structure which acted like an acoustic lens, 2) a combination of focusing and shallow basin effects, 3) shallow (less than 1 km) basin edge effects involving constructive interference of surface and bodywaves. As part of LARSE (Los Angeles Region Seismic Survey) we conducted a high resolution seismic survey of Santa Monica to test the various hypotheses. The experiment took place in two parts: 1) a refraction survey in October 1999 which involved recording arrivals from shots and earthquakes (including Hector Mine) on ~200 sensor array, and 2) a 10 km
