HR: 15:25h
AN: S43D-08    [Abstracts]
TI: Testing Predictions of Along-strike Variations in the Shallow Seismogenic Behavior of Subduction Zones
AU: * Simons, M
EM: simons@caltech.edu
AF: California Institute of Technology, 252-21, Pasadena, CA 91125 United States
AU: Ji, C
EM: jichen@gps.caltech.edu
AF: California Institute of Technology, 252-21, Pasadena, CA 91125 United States
AU: Lohman, R B
EM: fisheggs@gps.caltech.edu
AF: California Institute of Technology, 252-21, Pasadena, CA 91125 United States
AU: Pritchard, M E
EM: matt@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Song, T A
EM: alex@gps.caltech.edu
AF: California Institute of Technology, 252-21, Pasadena, CA 91125 United States
AU: Webb, F H
EM: fhw@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, MS 238-600, Pasadena, CA 91109 United States
AB: Large scale inter-arc differences in the seismogenic behavior of subduction zones are usually attributed to variations in the age and convergence rate of the subducting plate, and therefore to variations in normal tractions on the plate interface. In contrast to this focus on differences between subduction zones, two recent studies have found a clear global correlation between along-strike variations of gravity and topography within a given subduction zone and the principal locations of seismic moment release in large plate interface earthquakes (Song and Simons, Science, 2003; Wells et al., JGR, 2003). In particular, these studies (henceforth referred to as SS03 and W03) found that most large earthquakes occurring on the shallow subduction interface occur in regions where trench-parallel gravity and topography anomalies (TPGA and TPTA) are negative, and regions of positive TPGA and TPTA appear to not experience significant seismic moment release. These observations suggest that along-strike variations in seismic behavior within a given subduction zone are as great as differences between subduction zones and that frictional properties of the plate interface can vary over short distances and may control long-term seismic moment release. These conclusions suggest that asperities of great earthquakes are persistent and not ephemeral, that there is a close relationship between seismogenic behavior and geologic evolution of the forearc, and that we may be able to predict where areas of high moment release will be in the future. We test predictions of SS03 and W03 against the distribution of co-seismic and post-seismic deformation from recent events including the 2003 Mw 8.3 Tokachi-Oki (Japan) and the Mw 7.8 Rat Island (Aleutians) earthquakes, as well as against a recent reanalysis of seismic, GPS, and InSAR data for the 1995 Mw 8.1 Antofagasta, Chile earthquake. The location of coseismic slip in all cases, and the along strike variations in inferred post-seismic after-slip for the Antofagasta and Tokachi-Oki earthquakes are consistent with the predictions of SS03 and W03. In addition to considering patterns of coseismic and postseismic fault slip to test the predictions of SS03 and W03, we can also consider measuring along-strike variation in interseismic deformation. We suggest that the Kuril Arc provides the ideal location for such a blind test. The northern and southern Kurils have a history of large shallow earthquakes, while the central Kurils are relatively quiescent. There are two obvious possibilities -- either the large earthquakes in this region have yet to occur, or they will never occur. SS03 finds a large region of positive TPGA over the plate interface in the central Kuril, and thus predicts this region to be relatively uncoupled relative to the regions north and south of it. The predicted along-strike variation in convergence velocity measured on the arc is approximately 2 cm/yr, well within detectability limit of GPS surveys.
DE: 8122 Dynamics, gravity and tectonics
DE: 8164 Stresses--crust and lithosphere
DE: 7209 Earthquake dynamics and mechanics
DE: 3010 Gravity
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting