HR: 13:55h
AN: S43D-02    [Abstracts]
TI: The plate interface revealed across the Hikurangi subduction zone, offshore New Zealand.
AU: * Henrys, S
EM: s.henrys@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6008 New Zealand
AU: Pecher, I
EM: i.pecher@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6008 New Zealand
AU: Bannister, S
EM: s.bannister@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6008 New Zealand
AU: Reyners, M
EM: m.reyners@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6008 New Zealand
AB: The North Island GeopHysical Transect (NIGHT) was conducted in 2001 to study the detailed shallow structure of the Hikurangi subduction zone. The study included a multichannel seismic (MCS) reflection and a wide-angle seismic survey using ocean bottom seismometers (OBS) and offshore-onshore stations. One of the most interesting features in the pre-stacked MCS data is a marked change in dip from 3 to 16 degrees of the subducting oceanic crust (Hikurangi Plateau), at 13 km depth and 120 km from the trench. Splay faults propagate from this point on the plate boundary interface up into the overlying crust, coinciding with the actively deforming Kidnapper and Lachlan Ridges' in Hawke Bay. Modelling of a pronounced inflection in the Free-Air gravity gradient also confirms the presence of higher density basement rocks thrust upward from the bend in the plate boundary interface. Passive seismic data also suggest that the margin ridges mark a change from a decoupled (seaward) to a coupled (landward) interplate boundary and lend support to the idea that the active splay faults accommodate most of the elastic strain seaward of the locked zone on the plate interface. Structures we have observed along the central part of the Hikurangi subduction zone appear similar to those described in the Nankai Trough margin, Japan.
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting