HR: 0800h
AN: T31A-0485    [Abstracts]
TI: Microearthquakes beneath the Hydrothermal Vent Fields on the Endeavour Segment of the Juan de Fuca Ridge: Results from the Keck Seismic/Hydrothermal Observatory
AU: * Bowman, D
EM: wilcock@u.washington.edu
AF: Macalester College, 1600 Grand Avenue, St. Paul, MN 55105 United States
AU: Parker, J
EM: joparker@mines.edu
AF: Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401 United States
AU: Wilcock, W
EM: wilcock@u.washington.edu
AF: University of Washington, School of Oceanography, Seattle, WA 98195 United States
AU: Hooft, E
EM: emilie@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AU: Barclay, A
EM: andrew@ocean.washington.edu
AF: University of Washington, School of Oceanography, Seattle, WA 98195 United States
AU: Toomey, D
EM: drt@uoregon.edu
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AU: McGill, P
EM: mcgill@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Stakes, D
EM: debra@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Schmidt, C
EM: callaschmidt@hotmail.com
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AU: Patel, H
EM: patel_hemalinee@yahoo.com
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AB: The W.M. Keck Foundation is supporting the operation of a small seismic network in the vicinity of the hydrothermal vent fields on the central portion of the Endeavour Segment of the Juan de Fuca Ridge. This is part of a program to conduct prototype seafloor observatory experiments to monitor the relationships between episodic deformation, fluid venting and microbial productivity at oceanic plate boundaries. The Endeavour seismic network was installed in the summer of 2003 and comprises seven GEOSense three-component short-period corehole seismometers and one buried Guralp CMG-1T broadband seismometer. A preliminary analysis of the first year of data was undertaken as part of an undergraduate research apprenticeship class taught at the University of Washington's Friday Harbor Laboratories and additional analysis has since been completed by two of the apprentices and by two IRIS undergraduate interns. Over 12,000 earthquakes were located along the ridge-axis of the Endeavour, of which ~3,000 occur within or near the network and appear to be associated with the hydrothermal systems. The levels of seismicity are strongly correlated with the intensity of venting with particularly high rates of seismicity beneath the Main and High Rise Fields and substantially lower rates to the north beneath the relatively inactive Salty Dawg and Sasquatch fields. We have used both HYPOINVERSE and a grid search algorithm to investigate the distribution of focal depths assuming a variety of one-dimensional velocity models. The preliminary results show that the majority of earthquakes occur within a narrow depth range and may represent an intense zone of seismicity within a reaction overlying the axial magma chamber at ~2.5 km depth. However, the mean focal depth is strongly dependent on the relative weights assigned to the S arrivals. We infer from the inspection of residuals that no combination of the P- and S-wave velocity models we have so far investigated are fully consistent with the arrival times. We have also determined focal mechanisms from first motions for well-recorded events within the array as well as their dependence on the uncertainty in earthquake location and depth. The preliminary results for 134 better-constrained focal mechanisms show a wide range of mechanisms and strikes.
DE: 3025 Marine seismics (0935, 7294)
DE: 3035 Midocean ridge processes
DE: 3050 Ocean observatories and experiments
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7245 Mid-ocean ridges
SC: Tectonophysics [T]
MN: Fall Meeting 2005