Temporal changes in shear wave splitting during an earthquake swarm in Arkansas

Shear wave splitting has been observed in seismograms of two aftershock and one foreshock sequence recorded over 12 days by a local network of nine three-component digital seismometers during the 1982 Enola, Arkansas, earthquake swarm. Polarizations of the faster split shear wave show alignments within the shear wave window which correlate with the regional stress field. The time delay between split shear waves appears to increase before, and to decrease at or after the time of each main shock. This behavior is similar to observations before and after a M = 6.0 event near the Anza seismic gap, southern California, and may correspond to variations in crack geometry caused by changes in the stress field before and after the earthquakes. There are indications that the decrease in delay may occur a few hours before the main shock and could be a possible precursor for earthquake prediction.

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