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A Simple Crustal Structure Satisfying Strong Ground Motion Between Whittier and North Palm Springs

by R.J. Archuleta and Ruth A. Harris

Archuleta, R.J. and Ruth A. Harris(1989). A Simple Crustal Structure Satisfying Strong Ground Motion Between Whittier and North Palm Springs. SMIP 89 Seminar on Seismological and Engineering Implications of Recent Strong-Motion Data, p. 3-1 - 3-10.

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Abstract

The October 1, 1987, Whittier Narrows ML 5.9 earthquake produced a pattern of peak acceleration and intensity that showed a marked geographical asymmetry: the west and northwest regions had larger values than those to the east. A possible cause of this asymmetry was the earth's subsurface geological structure that managed to attenuate or defocus more severely the seismic waves that travelled east of Whittier than those travelling west or northwest. To investigate the subsurface S-wave structure we chose to consider a refraction profile generated by two natural sources, the Whittier Narrows earthquake and the July 8, 1986, North Palm Springs ML 5.9 earthquake, 135 km due east of Whittier Narrows. After analyzing strong motion data from the mainshocks, high-gain vertical seismograms of aftershocks, and synthetic seismograms we conclude that the strong motion data are consistent with a simple layered medium with a Poisson ratio of approximately 0.25.