CSMIP Strong-Motion Records from the Chalfant Valley, California Earthquakes of July and August 1986

OSMS 86-06

by R.W. Sherburne, D.L Parke, M.J. Huang and A.F. Shakal

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During the months of July, August, and September in 1986, a series of earthquakes occurred in the rural Chalfant Valley, located about 18 km (11 miles) northeast of Bishop. This series of shocks was reported to have caused about $2.7 million in damages (The Sacramento Bee, September 11, 1986). Approximately 50 mobile homes in the Chalfant area were knocked from their foundations during these earthquakes. In addition, several non-mobile homes were heavily damaged, and one frame house nearly collapsed (The Sacramento Union, July 22, 1986).

Field geologists identified approximately 11.5 km (7 miles) of surface faulting on several traces of the White Mountain fault zone (Kahle et al., 1986). A maximum of 5 cm of right lateral slip was observed. East-west extension across cracks which occurred in conjunction with known fault segments was also observed.

Many earthquakes of this series were recorded at strong-motion stations of the California Strong Motion Instrumentation Program (CSMIP), and the U.S. Geological Survey (USGS). Records recovered from USGS stations during the July 21 mainshock are given in Maley et al. (1986). This report presents copies of 36 accelerograms recorded at CSMIP stations during the four largest shocks: 21 July 1986, ML 6.4 (mainshock); 20 July 1986, ML 5.9 (foreshock); 21 July 1986, ML 5.6 (called Aftershock #1 in this report); 31 July 1986, ML 5.8 (Aftershock #2). The location and origin times of these four earthquakes are given in Table 1. Table 1 also lists the number of records recovered for each earthquake by station type.