HR: 1340h
AN: S53A-0183    [Abstracts]
TI: Temporal and Spatial Correlations Between Interplate and Intraplate Subduction Zone Seismicity
AU: * Polet, J
EM: polet@crustal.ucsb.edu
AF: Institute for Crustal Studies, UC Santa Barbara, Girvetz Hall, Santa Barbara, CA 93106
AB: Subduction zone earthquakes on the interface between subducting and overriding plate represent some of the world's most destructive natural disasters. Updip from this interface, the outer rise comprises an upwarping of the oceanic lithosphere just before it descends into the trench. Previous work established the characteristics of the stress regime within the subducting lithosphere and has suggested that a temporal and spatial correlation may exist between interplate and intraplate seismicity, with intraplate earthquakes possibly serving as stress gauges for the large-scale deformation involved in subduction zones. We have compiled a new catalog of outer rise seismicity, using an automated search algorithm applied to the Harvard CMT catalog, and confirmed the preferential occurrence of normal faulting outer rise events after large interplate thrust events, in particular after tsunami earthquakes. However, any possible temporal pattern in compressional outer rise events is not as straightforward, which hints that a more complex physical mechanism may be at work in the seismogenesis of outer rise seismicity than simple elastic plate bending. A more likely candidate is a combination of downward plate bending and in-plane compression, with the former being the main contributor for outer rise tensional earthquakes and an elevated level of the latter being responsible for thrust faulting outer rise events. An inelastic analysis of lithospheric stress distributions predicts similar seismic behavior. We also investigated the spatial occurrence of outer rise events and found a correlation of heightened activity with increasing plate curvature, plate age as well as the dip of the subducting plate. Further investigations will also focus on the orientation of the source mechanisms with respect to the strike and dip of the subducting plate, with preliminary results indicating an unexpected asymmetry in the dips of the two fault planes. We plan to construct a more complete and enhanced catalog of intraslab seismicity, extending our analysis to greater depths (150 km) and lowering the magnitude threshold from 6.0 to 5.5 for the relatively infrequent compressional outer rise events. This catalog will aid in refining our understanding of the stress evolution within the subducting slab and the relationship between seismic coupling and intraplate seismicity. We will apply a teleseismic P-wave modeling technique to refine the depths of the intraplate events to a higher precision and homogeneity. Subsequently a source spectral analysis of the earthquakes with magnitude greater than 6.5 will be carried out to determine dynamic rupture parameters. These investigations will provide us with insight into a myriad of issues, including: the failure mechanism of intraplate and outer rise earthquakes, the state of stress in the subducting lithosphere, the origin of the hydration of the subducting plate and the mode of deformation of the outer rise.
DE: 7230 Seismicity and seismotectonics
DE: 7205 Continental crust (1242)
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting