Near-field ground motion from the Landers earthquake

Abstract

In order to investigate near-field ground motions, an important Lucerne Valley record from the Landers earthquake was studied. The Lucerne Valley record was recorded on the Kinemetrics SMA-2/EMA instrument located 2 km from the fault. Since the characteristics of the SMA-2/EMA instrument were not completely understood and the conventional data processing procedures have difficulty in recovering long-period information from near-field earthquake accelerograms, an instrument test on the SMA-2/EMA was conducted and a new data processing procedure was developed to perform the instrument and baseline corrections. For an electro-magnetic transducer, an additional parameter of corner frequency, other than natural frequency, electronic damping ratio and sensitivity, should be considered during instrument correction of the SMA-2/EMA recorded accelerograms. For this purpose, a special instrument correction filter was derived in support of instrument correction and a laboratory test of the SMA-2/EMA accelerograph was conducted for obtaining the characteristic parameters of the instrument. The possible error sources in data recording and playback procedure were also examined and an appropriate baseline correction scheme was formulated for effectively removing the nonphysical trend involved in the earthquake data. The new data processing procedure was verified by a set of SMA-2/EMA simulated long-period accelerograms and then applied to the Lucerne Valley record. The results of new data processing revealed the important features of near-field ground motion, which were a displacement offset parallel to the fault and a large pulse-like motion perpendicular to the fault. The response spectra and Fourier spectra were also calculated and compared to those of the conventionally processed record. With these investigations, a number of important conclusions are obtained and several suggestions for future studies are given.

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