HR: 0800h
AN: G21A-0138    [Abstracts]
TI: Seafloor Geodetic Measurements Reveal Locking Within 5 km of the Peru-Chile Trench at 12S
AU: * Gagnon, K L
EM: kgagnon@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, 8635 Discovery Way, La Jolla, CA 92037 United States
AU: Chadwell, C D
EM: cdc@mpl.ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, 8635 Discovery Way, La Jolla, CA 92037 United States
AU: Norabuena, E
EM: enorab@rsmas.miami.edu
AF: Rosenstiel School for Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149 United States
AB: A combination of GPS and acoustic travel time measurements were taken from the R/V Roger Revelle in 2001 and 2003 from two seafloor precision transponder arrays at 12øS off the coast of Peru. The objective was to locate the updip limit of locking between the downgoing Nazca plate and the South America plate; a critical measurement in understanding the earthquake cycle and the potential hazard of onshore tsunamis. High pressure between the plates creates a coupled, or locked zone, where strain increases and deforms the overriding plate. Shipboard GPS, seafloor transponders and an underwater survey package were used to measure the horizontal and vertical deformation above the thrust fault. 3D modeling of horizontal deformation has shown that locking occurs within 5 km of the trench. The initiation of locking at 12øS is thought to be dominated by a lack of sediment and pore water, compared to more southern latitudes of the Peru-Chile trench where locking begins deeper due to increased sediment and fluid volume. This is the first study to measure seafloor deformation above a subduction thrust fault and create a GPS network covering the width of the convergence zone. Land GPS sensors are not sensitive to this limit and seismic observations may need to cover a complete earthquake cycle to illuminate the seismogenic zone.
DE: 8110 Continental tectonics--general (0905)
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting