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OSMS 92-09

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

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Introduction

The magnitude 7.5 Ms earthquake that occurred near Landers, California on June 28, 1992 is the largest event to occur in California since 1952 and the largest event with an extensive set of strong motion recordings. Landers is a small town in the Mojave Desert about 43 km north of Palm Springs and 80 km east of San Bernardino. The Landers earthquake occurred north of the epicenter of the ML 6.1 April 22, 1992 event (for reference, CSMIP records from that event are included in report OSMS 92-03, CSMIP 1992a). Extensive faulting was observed after the Landers earthquake along the Camp Rock Fault system which trends northwestward across the Mojave Desert. Right-lateral faulting was observed for over 70 km. The approximate location of rupture observed by field geologists from CDMG, USGS and other agencies is indicated in the map of Figure 1.

Approximately 3 hours after the Landers event, the Big Bear earthquake occurred with magnitude of 6.6 Ms about 35 km west of the Landers epicenter. This earthquake also triggered many strong motion stations in Southern California. Preliminary data from this event is given in two Quick Reports (CSMIP; 1992a, b); the full set of strong-motion data from this event is included in another report in preparation (OSMS 92-10).

The estimated location and magnitude of the Landers earthquake are:
           Epicenter: 34.217N, 116.433W. Depth: 9 km (Caltech/USGS)
           Origin Time: 11:57:34.1, 28 June 1992 UTC (4:58 AM, PDT)
           Magnitude: 7.5 Ms (NEIC)

Analysis by the USGS and Caltech indicates that the earthquake had a right lateral strike-slip mechanism. The maximum horizontal offset was reported at as much as 21 feet. Most of the damage and injuries were confined to the desert and mountain towns in the epicentral area.

This report includes all CSMIP data from the Landers earthquake and supersedes the first Quick Report distributed on June 30 (CSMIP, 1992b) and the second Quick Report distributed on July 10 (CSMIP, 1992c).