Waveform Analysis of the 1999 Hector Mine Foreshock Sequence

Eva Zanzerkia, Gregory C. Beroza, & John E. Vidale

Published April 2003, SCEC Contribution #707

By inspecting continuous Trinet waveform data, we find 42 foreshocks in the 20-hour period preceding the 1999 Hector Mine earthquake, a substantial increase from the 18 foreshocks in the catalog. We apply waveform cross-correlation and the double-difference method to locate these events. Despite low signal-to-noise ratio data for many of the uncataloged foreshocks, correlation-based arrival time measurements are sufficient to locate all but three of these events, with location uncertainties from ~100 m to 2 km. We find that the foreshocks fall on a different plane than the initial subevent of the mainshock, and that the foreshocks spread out over the plane with time during the sequence as the time of the mainshock approaches.

Zanzerkia, E., Beroza, G. C., & Vidale, J. E. (2003). Waveform Analysis of the 1999 Hector Mine Foreshock Sequence. Geophysical Research Letters, 30(8), 1429. doi: 10.1029/2002GL016383.