HR: 1340h
AN: T33B-1377    [Abstracts]
TI: Variability in Tidal Triggering of Microearthquakes at 9˚50'N East Pacific Rise
AU: * Stroup, D F
EM: danielle@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Bohnenstiehl, D R
EM: drbohnen@ncsu.edu
AF: Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Campus Box 8208, Raleigh, NC 27695, United States
AU: Tolstoy, M
EM: tolstoy@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Waldhauser, F
EM: felixw@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Weekly, R T
EM: rtweekly@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AB: In October 2003 through April 2004, an ocean bottom seismometer (OBS) array deployed between 9°49'N and 9°51'N East Pacific Rise (EPR) recorded over 7,500 double difference relocated microearthquakes (M_L < 2.0). The deployment represents the longest period of continuously recorded microearthquake data analyzed for tidal triggering at a fast-spreading (~110 mm/yr) mid-ocean ridge. At this location, high temperature hydrothermal vents and a shallow (~1.4 km depth) axial magma chamber create a critically stressed upper crust that is susceptible to tidal influence. Although the amplitude of semidiurnal tidal stress changes at this location are small (< 2.5 kPa), seismicity is found to be tidally triggered during times of peak extensional stress associated with the solid Earth tide (Stroup et al., 2007). Furthermore, the number of earthquakes that occur during times of encouraging (extensional) stress is linearly dependent on the amplitude of peak-to-peak tidal stress. When the frequency of seismicity is compared with the combined Earth and ocean tide stresses, microearthquake activity at times of maximum extension increases to ~5 times the background frequency for stress amplitudes > 2 kPa. However, preliminary analysis of microearthquakes with along-axis depth and magnitude suggests that tidal triggering is not uniform. The along- axis variations in tidal triggering may reflect differences in the background state of stress associated with the axial magma chamber and hydrothermal vent circulation.
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3025 Marine seismics (0935, 7294)
DE: 3035 Midocean ridge processes
DE: 4560 Surface waves and tides (1222)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting