HR: 08:30h
AN: S41A-03    [PDF]
TI: CASA GPS Results: Lithospheric Deformation and the Earthquake Cycle in the Ecuador-Colombia Subduction Zone
AU: * Kellogg, J
EM: kellogg@sc.edu
AF: Dept. Geological Sciences, Univ. South Carolina, Columbia, SC 29208 United States
AB: The Ecuador-Colombia subduction zone is a potentially important laboratory for observing the effects of variations in lithospheric buoyancy on seismic coupling. Subduction of the aseismic Carnegie Ridge is associated with pronounced margin-parallel variations in crustal thickness and buoyancy of the downgoing lithosphere. The subduction zone has been ruptured repeatedly in 1906 (Mw = 8.8), 1942 (Mw = 7.9), 1958 (Mw = 7.8), and 1979 (Mw = 8.2). The 1958 and 1979 ruptures have been linked to asperities on the interplate surface. Simple elastic boundary element and viscoelastic models were used to simulate CASA (Central And South America) GPS-observed surface deformation. The results suggest that interseismic elastic strain accumulation is occurring evenly (50% apparent elastic locking) throughout the Ecuador-southern Colombia forearc. However, on-going postseismic relaxation of a viscous upper mantle (10E19 Pa S) following the 1979 earthquake masks the true total strain rate in southern Colombia. In southern Ecuador south of the ridge-trench intersection, despite apparent uniform interseismic elastic locking, no large historic earthquakes (Mw$>$7) have been recorded. The relationship between subducting lithospheric buoyancy and seismic coupling cannot be resolved yet because of the paradox of apparently uniform elastic locking but non-uniform historic seismicity restricted to asperities north of the ridge. The CASA observations of lithospheric deformation associated with the earthquake cycle in the Ecuador-Colombia subduction zone are tantalizing but tentative at this point, because of limited spatial resolution ($>$100 km average spacing) and limited temporal resolution (only one continuous GPS station in the Ecuador-southern Colombia forearc).
UR: http://estrella.geol.sc.edu/~agl/Projects.htm
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
DE: 7230 Seismicity and seismotectonics
DE: 8102 Continental contractional orogenic belts
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting