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OSMS 92-10

by M. Huang, A. Shakal, T. Cao, P. Fung, R. Sherburne, R. Sydnor, P. Malhotra, C. Cramer, F. Su, R. Darragh and J. Wampole

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Introduction

Strong-motion accelerograms were recorded at 132 stations of the California Strong Motion Instrumentation Program (CSMIP) after the magnitude 6.6 Ms earthquake that occurred near Big Bear Lake, California on June 28, 1992. The epicenter is located in the San Bernardino Mountains, about 11 km southeast of Big Bear Lake and 45 km northeast of San Bernardino. The epicentral distance of the CSMIP stations ranges from 11 km for the closest (Big Bear Lake) to about 180 km for the farthest (Santa Felicia Dam). The greatest ground acceleration recorded by CSMIP ground-response stations was 0.57 g at Big Bear Lake. The greatest accelerations recorded on structures were 0.75 g recorded at a concrete tilt-up building and 1.02 g at a freeway interchange.

The estimated location and magnitude of the Big Bear earthquake are:
           Epicenter: 34.201N, 116.826W. Depth: 7 km (Caltech/USGS)
           Origin Time: 15:05:30.5, 28 June 1992 UTC (8:05 AM, PDT)
           Magnitude: 6.6 Ms (NEIC), 6.5 ML (Caltech), 6.4 Mw (Caltech)

Approximately 3 hours before the Big Bear earthquake, the magnitude 7.5 Ms Landers earthquake occurred about 35 km east of the Big Bear epicenter. CSMIP strong-motion records from the Landers earthquake are included in the OSMS 92- 09 report (1992a). Most of the damage due to the Big Bear earthquake was confined to the mountain communities in the Big Bear area. According to analyses by the USGS and Caltech, the earthquake had a left-lateral strike-slip mechanism along a N58E fault. There was no surface faulting reported. This report includes all CSMIP data from the Big Bear earthquake and supersedes the first Quick Report distributed on June 30 (CSMIP, 1992b) and the second Quick Report distributed on July 10 (CSMIP, 1992c).