Unusual Microseisms Seen in the Reelfoot Fault Zone, Northern Tennessee, from a Reflection Experiment

Abstract

Abstract A swarm of microseisms with ground motions equivalent to earthquakes of M L -1 and smaller was fortuitously detected in 100 of 162, 14 sec-duration long-offset vibroseis shot gathers collected for a seismic reflection experiment near Mooring, Tennessee, directly over the Reelfoot fault zone on the afternoon of 16 November 2006. These natural events show up in the shot gathers as near-vertically incident P waves with a dominant frequency of 8–10 Hz and probably occurred at depths of greater than 10 km. The inferred seismicity rate of 250–1000 events per hour is 2–3 orders of magnitude higher than the background seismicity rate for the New Madrid seismic zone. This detection of microseismic swarms in the Reelfoot fault zone indicates active physical processes that may be similar to nonvolcanic tremor seen in the Cascadia and San Andreas fault zones and merits long-term monitoring to understand its source.