HR: 0800h
AN: T51D-0764    [Abstracts]
TI: Possible Non-volcanic Tremor Discovered in the Reelfoot Fault Zone, Northern Tennessee
AU: * Langston, C A
EM: clangstn@memphis.edu
AF: CERI, University of Memphis, 3876 Central Ave., Ste. 1, Memphis, TN 38152-3050, United States
AU: Williams, R A
EM: rawilliams@usgs.gov
AF: U.S. Geological Survey, P.O. Box 25046 Mail Stop 966, Denver, CO 80225-0046, United States
AU: Magnani, M
EM: mmagnani@memphis.edu
AF: CERI, University of Memphis, 3876 Central Ave., Ste. 1, Memphis, TN 38152-3050, United States
AU: Rieger, D M
EM: dmr6645@sru.edu
AF: CERI, University of Memphis, 3876 Central Ave., Ste. 1, Memphis, TN 38152-3050, United States
AB: A swarm of ~80 microearthquakes was fortuitously detected in 20, 14 second-duration long-offset vibroseis shotgathers collected for a seismic reflection experiment near Mooring, TN, directly over the Reelfoot fault zone on the afternoon of 16 November 2006. These natural events show up in the shotgathers as near-vertically incident P waves with a dominant frequency of 10-15 Hz. The reflection line was 715m in length consisting of 144 channels with a sensor spacing of 5m, 8Hz vertical geophones, and recording using a Geometrics 24bit Geode seismograph. Small variations in event moveout across the linear array indicate that the seismicity was not confined to the same hypocenter and probably occurred at depths of approximately 10 km. The largest events in the series are estimated to have local magnitudes of ~-1 if at 10 km distance from the array. This is about 2.5 magnitude units lower than the threshold for local events detected and located by the CERI cooperative network in the area. The seismicity rate was ~1000 events per hour based on the total time duration of the shotgathers. The expected number of earthquakes of ML greater than or equal to -1 for the entire central United States is only 1 per hour. This detection of microseismic swarms in the Reelfoot fault zone indicates active physical processes that may be similar to non-volcanic tremor seen in the Cascadia and San Andreas fault zones and merits long-term monitoring to understand its source.
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting