HR: 1340h
AN: T33B-1376    [Abstracts]
TI: Tidal Influences on Tremor Activity at East Pacific Rise 9-50 N Eruption Site
AU: * Monigle, P W
EM: pwmonigl@ncsu.edu
AF: Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, United States
AU: Bohnenstiehl, D R
AF: Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, United States
AU: Tolstoy, M
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, United States
AU: Waldhauser, F
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, United States
AB: Seismic activity along the East Pacific Rise (EPR) at 9-50 N was monitored by an Ocean Bottom Seismometer (OBS) array continuously from October 2003 to March 2006. These data are characterized by both discrete microearthquakes and short-period tremor signals with fundamental frequency in the 5-8 Hz band. The RMS amplitude of the velocity records within this 5-8 Hz band shows strong tidal periodicity with a spectral peak at 2 cycles per day. Early in the monitoring period, tremors commonly were initiated following discrete microearthquakes. However, closer to the January 2006 eruption, tremor activity becomes more sustained and intense, with less earthquake dependence. During this time, tremor signals also occurred preferentially during periods of positive extensional tidal strain rate (i.e., between times of maximum compression and maximum extension in the crust) and are highly concentrated along the ridge axis. Minor changes in the frequency of the tremor signals also are observed through the monitoring period. In February 2004, tremor was focused around 7 Hz with two harmonics. Precursory tremor activity in January 2006, however, showed tremor concentrated near 5.5 Hz with only one weak harmonic. Although the source of these tremor signals is not well understood, temporal changes in their properties may provide an indication of impending eruptive activity, enhancing our ability for short-term prediction.
DE: 7245 Mid-ocean ridges
DE: 7280 Volcano seismology (8419)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting