HR: 0830h
AN: U11B-0002    [PDF]
TI: Monitoring co-seismic plate deformation and fluid flow with ODP hydrogeologic observatories
AU: * Davis, E
EM: edavis@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada 9860 W. Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Becker, K
EM: kbecker@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, University of Miami 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AU: Wang, K
EM: kwang@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada 9860 W. Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Edwards, K
EM: kedwards@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Science, University of Miami 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AU: Cassidy, J
EM: jcassidy@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada 9860 W. Saanich Rd., Sidney, BC V8L 4B2 Canada
AU: Dziak, R
EM: robert.p.dziak@noaa.gov
AF: Oregon State University/NOAA, Hatfield Marine Science Center, Newport,, OR 97365 United States
AU: Thomson, R
EM: thomsonr@pac.dfo-mpo.gc.ca
AF: Institute of Ocean Sciences, 9860 W. Saanich Rd., Sidney, BC V8L 4B2 Canada
AB: ODP CORK (Circulation Obviation Retrofit Kit) instrumentation was originally developed to seal holes and determine fluid flow rates and driving forces in hydrologically active settings. Over the first decade of CORK monitoring, a number of observations have been made that range well beyond these objectives. In several instances, records of formation pressure and temperature have provide quantitative information about local and regional (up to 250 km range) crustal strain and fluid flow associated with inter- and intra-plate seismogenic slip. These include two seafloor spreading events and associated seismic swarms on the Juan de Fuca Ridge, slip on the Nootka transform fault, a mid-plate earthquake on the Juan de Fuca Ridge flank, and two deep Mariana subduction zone earthquakes. With the exception of the Mariana events, signals associated with seismic wave ground motion are not resolved, although improvements to instrumentation will allow these to be studied in the future. Pressure transients of all the events observed to date include a co-seismic component that is believed to be the response to elastic plate strain, and a post-seismic component that reflects hydrologic diffusion along pressure gradients between volumes of rock with contrasting elastic response or drainage through the seafloor. The co-seismic components vary in sign and relative amplitude in a manner consistent with seismic moment tensors, although the absolute amplitudes of the strain-induced pressure anomalies are often much larger than predicted from seismic moment. The post-seismic transients occur over time scales that range from hours to a few hundred days, generally consistent with the hydrologic structure at the various borehole sites, but often indicating formation-scale permeabilities that are considerably higher than estimated from borehole pumping and flow experiments. Data from CORKs have also shown that transient changes in mechanical and hydrologic properties, inferred from changes in the formation-pressure response to seafloor tidal loading, result from plate strain. CORK monitoring continues on the axis and flank of the Juan de Fuca Ridge and at the Nankai and Middle America subduction zones, and opportunities exist for refurbishing old sites in the Cascadia, Mariana, and Barbados subduction zones and the Costa Rica Rift flank. It is our hope that long-term hydrologic monitoring at these and new sites will provide new knowledge and understanding of earthquake rupture and plate strain processes, and the role of water in both.
DE: 1242 Seismic deformations (7205)
DE: 1894 Instruments and techniques
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
SC: U
MN: 2003 Fall Meeting