Abstract

A pressure wave, initiated by water loading and propagating downward through subsurface water contained in fractures, has been hypothesized as a mechanism for triggering earthquakes along pre-existing faults at depths up to 15–20 km. Such a triggering wave might evidence itself by a coincident wave of descending seismicity. In the New Madrid region, seismicity has been reported to correlate with river stage, but usually with a lag of one to several months. River stage data from New Madrid and earthquake data from the St. Louis University’s microseismic network were examined for evidence of a time-lag in seismic activity with depth during the interval from Jan. 1, 1978, to May 31, 1987. The earthquake data include only events for which computed depths were available. The earthquakes were sorted by focal depth into two subsets of 3 km and 4 km thick layers, respectively. Earthquake data, represented by both number of events and strain factor [energy release], and river stage data were averaged over monthly intervals. Cross correlations were computed between stage and each layer. In addition, the earthquake sequences for each layer were cross correlated with those of the next layer. No evidence for a seismicity wave was found.

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