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Science 8 September 2000:
Vol. 289. no. 5485, pp. 1746 - 1750
DOI: 10.1126/science.289.5485.1746
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Reports

Northridge Earthquake Damage Caused by Geologic Focusing of Seismic Waves

Paul M. Davis,1* Justin L. Rubinstein,1 Kelly H. Liu,2 Stephen S. Gao,2 Leon Knopoff3

Despite being located 21 kilometers from the epicenter of the 1994 Northridge earthquake (magnitude 6.7), the city of Santa Monica experienced anomalously concentrated damage with Mercalli intensity IX, an intensity as large as that experienced in the vicinity of the epicenter. Seismic records from aftershocks suggest that the damage resulted from the focusing of seismic waves by several underground acoustic lenses at depths of about 3 kilometers, formed by the faults that bound the northwestern edge of the Los Angeles basin. The amplification was greatest for high-frequency waves and was less powerful at lower frequencies, which is consistent with focusing theory and finite-difference simulations.

1 Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA.
2 Department of Geology, Kansas State University, Manhattan, KS 66506-3201, USA.
3 Institute of Geophysics and Planetary Physics and Department of Physics, University of California, Los Angeles, CA 90095-1567, USA.
*   To whom correspondence should be addressed. E-mail: pdavis{at}ess.ucla.edu

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