HR: 10:35h
AN: T42A-02    [Abstracts]
TI: Relationship between bend-faulting at trenches and intermediate-depth seismicity
AU: * Ranero, C R
EM: cranero@icm.csic.es
AF: ICREA, Instituto de Ciencias del Mar, CSIC, Pg. de la Barceloneta 37-49, Barcelona, 08003 Spain
AU: Villasenor, A
EM: antonio@ija.csic.es
AF: Institute of Earth Sciences, CSIC, Lluis Sol‚ i Sabar¡s s/n, Barcelona, 08028 Spain
AU: Phipps Morgan, J
EM: jp369@cornell.edu
AF: Cornell University, EAS 4164 Snee Hall, Ithaca, NY 14853 United States
AU: Weinrebe, W
EM: wweinrebe@ifm-geomar.de
AF: IFM-GEOMAR and SFB754, Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: We have studied faulting associated with bending of the oceanic plate prior to subduction along segments of Middle America and Chile trenches. The fault structure of the oceanic plate at the trench has been compared to patterns of intermediate-depth intra-slab earthquakes in the corresponding slabs. Multibeam bathymetry shows that bending-related faulting forms patterns made of sets of faults with orientations ranging from parallel to almost perpendicular to the trench axis. The development of a particular set of faults is controlled by two main factors: Variations in the orientation of the tectonic fabric formed at the spreading center with respect to the bending axis, and variations in oceanic crust thickness. Changes in those factors cause that fault patterns may change along a single subduction zone within along-strike distances of several hundred km or less. Therefore, faulting at the trench is not simply controlled by regional bending stresses. Where available, near-trench intra-plate earthquakes show normal-fault focal mechanisms consistent with mapped bending-related normal faults. The comparison of the orientation of bend-faulting patterns and orientation of the nodal planes of intermediate-depth earthquakes shows that the strike of bend-faults is remarkably similar to the strike of the nodal planes, for each segment of the study areas. This similarity in strike is observed even for faults oriented very oblique to the trench and slab strikes. Furthermore, the strike of the nodal planes of intermediate-depth earthquakes is not consistent with rupture along the planes of maximum shear within the slab. Thus, in the studied subduction zones, results strongly support that much intermediate-depth seismicity occurs by reactivation of faults formed by plate bending near the trench. Additionally, a qualitative relationship between trench faulting and intra-slab seismicity is indicated by segments of the incoming plate with pervasive bend-faulting that correspond to segments of the slabs with higher intermediate-depth seismicity.
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8010 Fractures and faults
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005