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OSMS 84-08

"Principal Features of the Strong-Motion Data From the 1984 Morgan Hill Earthquake"

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

Shakal, A.F., R.W. Sherburne and D.L. Parke (1984). Principal Features of the Strong-Motion Data From the 1984 Morgan Hill Earthquake. The 1984 Morgan Hill, California Earthquake, Division of Mines and Geology Speical Report SP-68.

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A strong directional dependence that can be correlated with the geometry of the earthquake fault rupture is exhibited by the strong motion data from the Morgan Hill earthquake. Higher accelerations were recorded at stations to the southeast of the earthquake than to the northwest. One of the southeast stations, Coyote Lake Dam, recorded a peak horizontal acceleration of 1.3 g. This acceleration exceeds that of the Pacoima Dam record from the 1971 San Fernando earthquake, the previous largest horizontal acceleration recorded. However, the peak velocity and displacement, as well as the duration, of the Coyote Dam record are less than those of the Pacoima Dam record. The records from the Gilroy strong motion array, also to the southeast of the earthquake, exhibit unusual high vertical accelerations. They also show alluvial amplification effects similar to those observed in corresponding records from the 1979 Coyote Lake earthquake. In addition to the ground motion data, many recordings of structural response to the ground shaking were obtained during this earthquake. These records provide unprecedented data for analysis of the rocking and torsional motion of structures as well as structural amplification.