HR: 14:25h
AN: S53C-04    [Abstracts]
TI: Imaging the Alpine Fault, South Island, New Zealand, using local earthquake coda
AU: * Bannister, S
EM: s.bannister@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6305 New Zealand
AU: Louie, J
AF: Seismological Laboratory, University of Nevada, Reno, NV 89557-0141 United States
AU: Henrys, S
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6305 New Zealand
AB: The major strike-slip Alpine fault marks the boundary between the obliquely converging Pacific and Australian plates in South Island, New Zealand. Previous studies have inferred a total strike-slip displacement of c. 450 km along this transpressional section of the plate boundary, and an estimated c. 100 km of shortening, which has resulted in the uplift of the Southern Alps mountain range. Active-source seismic reflection imaging suggests that the Alpine fault dips southeast at c. 40 degrees, to a depth of around 22 km (Davey et al., 1998). Here, we attempt to directly image the Alpine fault zone using back-projection migration of local-earthquake coda. We specifically use records from aftershocks of the Mw 6.7 Arthur's Pass earthquake, the largest earthquake in the region for 65 years, which occurred about 25 km southeast of the Alpine fault. The aftershocks of this earthquake were well recorded by a 6-station portable array (Abercrombie et al., 2000). Pre-processing involved relocation of these aftershocks with the double difference technique, utilising cross-correlation differences between the waveforms. This relocation substantially improved relative event locations, and highlighted the Bruce fault and other secondary faults in the region. Subsequent back-projection imaging, using station gathers of the seismograms of the relocated events, results in reflectivity images of the mid-crust near the Alpine fault and beneath the aftershock sequence.
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
DE: 7205 Continental crust (1242)
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting