HR: 08:00h
AN: T41D-01    [Abstracts]
TI: 3-D Imaging of Marlborough, New Zealand, Subducted Plate and Strike-Slip Fault Systems
AU: * Eberhart-Phillips, D
EM: eberhart@geology.ucdavis.edu
AF: GNS Science, PO Box 30368, Lower Hutt, 5040, New Zealand
AU: * Eberhart-Phillips, D
EM: eberhart@geology.ucdavis.edu
AF: Geology Dept., Univ. California Davis, One Shields Ave., Davis, CA 95616-8605, United States
AU: Bannister, S
EM: s.bannister@gns.cri.nz
AF: GNS Science, PO Box 30368, Lower Hutt, 5040, New Zealand
AB: We present a 3-D seismic velocity model of the northern South Island, New Zealand, using several passive and active data sets. This area is the transition from Hikurangi subduction in the North Island to oblique continental collision along the Alpine fault and the Southern Alps, and geodetically observed deformation is consistent with plate motion primarily taken up on a series of rotating strike-slip faults. We carry out simultaneous inversion for Vp and Vp/Vs and hypocenters using earthquake data from three temporary seismic arrays and the permanent seismic network, and active data recorded along offshore profiles and at onshore stations. We image the slab as a continuous unbroken feature extending from the active subduction zone to the north. Across the Marlborough region, the 3-D hypocenters define the slab as a smooth curved feature to over 250-km depth. Slab seismicity below 100-km depth abruptly ends in the section where the Awatere fault transfers to the Alpine fault. The subducting Pacific plate has a thick crust, including greywacke upper crust, which slows subduction. The downwarping interaction with the translating overlying plate forms a 50-km long zone of apparent crustal thickening with Vp < 7.0km/s to 40-km depth. The Australian plate has a high-velocity block to 65-km depth, aligned with the Separation Point pluton and trending oblique to the subducted slab. This zone of thicker Australian lithosphere may also hinder subduction. The Marlborough faults trend about 25 degrees to the strike of the underlying slab, so that their relation to the slab varies along the fault, and the overlying plate ranges from 20 to 50-km thick along the faults. Thus the fault interaction with the slab varies from translating material directly above the subducting plate to bottoming into a thick ductile region. The lower crust has high Vp/Vs under the Marlborough faults apart from the region of Haast schist, which may indicate excess fluid released by the subducted plate.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting