HR: 1330h
AN: B12A-0748    [PDF]
TI: A Long-Term Seismic Array on the Endeavour Segment of the Juan de Fuca Ridge
AU: * McGill, P R
EM: mcgill@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Rd, Moss Landing, CA 95039 United States
AU: Wilcock, W S
EM: wilcock@ocean.washington.edu
AF: School of Oceanography, University of Washington Box 357940, Seattle, WA 98195 United States
AU: Stakes, D S
EM: debra@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Rd, Moss Landing, CA 95039 United States
AU: Barclay, A H
EM: andrew@ocean.washington.edu
AF: School of Oceanography, University of Washington Box 357940, Seattle, WA 98195 United States
AU: Ramirez, T M
EM: tony@mbari
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Rd, Moss Landing, CA 95039 United States
AU: Toomey, D R
EM: drt@newberry.uoregon.edu
AF: Department of Geological Sciences, 105A Cascade Hall University of Oregon, Eugene, OR 97403 United States
AB: The Keck Foundation with additional support from the Monterey Bay Aquarium Research Institute and the University of Washington has funded a five-year, five-million dollar program for archetypic experiments on the northern Juan de Fuca Plate. The goal of this program is to constrain the linkages between deformation (earthquakes), fluid flow and chemistry, and microbial response across the northern Juan de Fuca Plate in the northeastern Pacific Ocean. A key component of these studies is an array of ocean-bottom seismometers to record the temporal and spatial distribution of seismic activity in the region. The current network, deployed in August of 2003, is comprised of eight autonomous instruments: one broadband seismometer and seven short-period seismometers. The instruments are distributed within and around the axial valley at the center of the Endeavour segment and spaced about 4 km apart, composing an array about 7 km wide and 9 km long. The short-period instruments, sensitive over a frequency range of 1 to 32 Hz, utilize an MBARI/GEOSense BH1 three-axis corehole geophone connected to an MBARI/GEOSense LP1 data logger. For five of these instruments the corehole sensor is inserted into a 7 cm diameter hole drilled into the basaltic basement rock, thus providing excellent coupling. For the other two instruments where suitable drilling sites were not available, the sensors are inserted into 55 kg concrete blocks placed on the sediment. The broadband instrument is a Guralp CMG-1T three-axis seismometer, sensitive over a frequency range of 2.8 mHz (360 sec) to 50 Hz. The sensor is completely buried in sediment inside a 60 cm deep by 60 cm diameter caisson, thus reducing the effects of water currents on the recorded data. A 20 m cable connects the sensor to an LP1 data logger and a 30 kW-hr battery sitting on the sediment. A complete data set will be recovered from the array when the instruments are revisited during the summer of 2004. However, data from two events, an M=7.5 teleseism in the Scotia Sea and an M=3.0 earthquake at the northern Endeavour segment, were recovered from the broadband instrument during a site revisit two weeks after its deployment. These high-quality recordings of both teleseismic and local events show low background noise levels and excellent instrument response. The small, but focused network should facilitate the recording of both tectonic and volcanic events along the spreading axis with a high degree of resolution.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL
DE: 7200 SEISMOLOGY
DE: 7294 Instruments and techniques
SC: Biogeosciences [B]
MN: 2003 Fall Meeting