HR: 1340h
AN: G13A-0803    [Abstracts]
TI: Along-strike variations in post-seismic deformation in northern Chile and southern Peru
AU: * Pritchard, M E
EM: matt@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AU: Simons, M
EM: simons@caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: We use InSAR and GPS data to constrain the spatio-temporal evolution of post-seismic after-slip following three large subduction zone earthquakes in South America. Post-seismic deformation following the 1995 ${M}_{w}$~8.1 Antofagasta, Chile earthquake is barely above the InSAR detection limit, but by combining GPS observations with 36 interferograms we model the post-seismic deformation between the years 1995-2000. If the deformation is after-slip on the fault interface, the equivalent moment magnitude is 10-20% of the co-seismic moment, with the maximum deformation occurring 100 km from the maximum co-seismic slip. There is a pulse of deformation between large aftershocks in 1996 and 1998 that appears distinct from the general decay of after-slip with time. The low magnitude of post-seismic deformation is anomalous compared to other recent subduction zone earthquakes, including the nearby 2001 ${M}_{w}$~8.4 Arequipa, Peru earthquake. After-slip following the 2001 earthquake between 2001-2004 equals about 20-40% of the co-seismic moment. There is no definitive post-seismic deformation following the 1996 ${M}_{w}$~7.7 Nazca, Peru earthquake between 1997-1999, although there is no data spanning the first 51 days after the earthquake. Variations in the depth of rupture during these three earthquakes cannot solely explain the variations in after-slip. We suggest that variations in sediment subducted in each location may control the magnitude of after-slip. The larger thickness of sediments in the region of the 2001 earthquake might also explain why observed after-slip is located in the same area as the co-seismic slip, instead of down-dip, as in other subduction zones.
DE: 1206 Crustal movements--interplate (8155)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting