Processed Strong-Motion Records from the CSMIP/NSF Treasure Island Geotechnical Array for the Gilroy Earthquake of 16 January 1993

OSMS 93-09

by R. Darragh, M. Huang and A. Shakal

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Important data for geotechnical engineering was recorded at the joint CSMIP/National Science Foundation (NSF) Treasure Island Geotechnical Array near San Francisco. Low-amplitude accelerograms were recorded at the array from a distant ML 5.3 earthquake. The earthquake occurred near Gilroy, approximately 120 km away. In this soft-soil site-response array accelerometers are installed at the surface and in 5 nearby boreholes. The borehole accelerometers are located below the sandstone and shale bedrock surface (104 m) and at 4 intermediate locations in the soil profile (7, 16, 31, 44 m).

The peak acceleration, velocity and displacement at the array are 0.0142 g, 0.86 cm/sec and 0.08 cm, respectively. These peaks were recorded on channel 1, located on the surface in the north-south direction. In the north-south direction, peak acceleration ranged from 0.0032 g in bedrock to 0.0142 g at the surface. In the east-west direction, peak accelerations of 0.0024 and 0.0133 g were recorded in bedrock and at the surface, respectively. In contrast, on the vertical component the peak acceleration ranged from 0.0021 g in bedrock to 0.0044 g at the surface. The processing of these records occurred in parallel with digitization and processing of many large amplitude records from the Landers earthquake.