Development of An Improved Representation of Near Fault Ground Motions

by Paul Somerville

Somerville, Paul (1998). Development of An Improved Representation of Near Fault Ground Motions. SMIP98 Seminar on Utilization of Strong-Motion Data, p. 1 - 20.

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The principal objective of this study is to develop an improved parameterization for the engineering specification of near-fault ground motions. In addition to the response spectrum, we would like to include time domain parameters that describe the near-fault pulse, such as its period, amplitude, and number of half-cycles. We have developed a preliminary model that relates time domain parameters of the near-fault ground motion pulse to the earthquake magnitude and distance. The model is for forward rupture directivity conditions, which produce a strong pulse of motion in the fault-normal direction. The pulse parameters that we have modeled are the period and peak amplitude of the largest cycle of motion of the velocity pulse. The records analyzed include 15 time histories recorded in the distance range of 0 to 10 km from earthquakes in the magnitude range of 6.2 to 7.3, augmented by 12 simulated time histories that span the distance range of 3 to 10 km and the magnitude range of 6.5 to 7.5.