Comments on Baseline Correction of Digital Strong-Motion Data: Examples from the 1999 Hector Mine, California, Earthquake

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Abstract
Residual displacements for large earthquakes can sometimes be deter- mined from recordings on modern digital instruments, but baseline offsets of un- known origin make it difficult in many cases to do so. To recover the residual dis- placement, we suggest tailoring a correction scheme by studying the character of the velocity obtained by integration of zeroth-order-corrected acceleration and then see- ing if the residual displacements are stable when the various parameters in the par- ticular correction scheme are varied. For many seismological and engineering pur- poses, however, the residual displacements are of lesser importance than ground motions at periods less than about 20 sec. These ground motions are often recoverable with simple baseline correction and low-cut filtering. In this largely empirical study, we illustrate the consequences of various correction schemes, drawing primarily from digital recordings of the 1999 Hector Mine, California, earthquake. We show that with simple processing the displacement waveforms for this event are very similar for stations separated by as much as 20 km. We also show that a strong pulse on the transverse component was radiated from the Hector Mine earthquake and propagated with little distortion to distances exceeding 170 km; this pulse leads to large response spectral amplitudes around 10 sec.

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