HR: 1330h
AN: T52B-0268    [PDF]
TI: Seismic Reflction and Wide-Angle studies across the Hikurangi Subduction Zone Offshore New Zealand
AU: * Henrys, S A
EM: s.henrys@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, P O Box 30-368, Lower Hutt, 1 New Zealand
AU: Pecher, I
EM: i.pecher@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, P O Box 30-368, Lower Hutt, 1 New Zealand
AU: Bannister, S
EM: s.bannister@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, P O Box 30-368, Lower Hutt, 1 New Zealand
AU: Davey, F
EM: f.davey@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, P O Box 30-368, Lower Hutt, 1 New Zealand
AU: Nishimura, Y
EM: nishi@eos.hokudai.ac.jp
AF: Hokkaido University, Sapporo, Sapporo, 1 Japan
AU: Yamada, A
EM: ami@eos.hokudai.ac.jp
AF: Hokkaido University, Sapporo, Sapporo, 1 Japan
AU: Shimamura, H
EM: shima@lobs.sci.hokudai.ac.jp
AF: Hokkaido University, Sapporo, Sapporo, 1 Japan
AU: Night Working Group, .
EM: s.henrys@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, P O Box 30-368, Lower Hutt, 1 New Zealand
AB: The North Island GeopHysical Transect (NIGHT) was conducted in 2001 to study the Hikurangi subduction zone. The study included a multichannel seismic (MCS) reflection and a wide-angle seismic survey with ocean bottom seismometers (OBS) and offshore-onshore stations. We will present stacked and time-migrated images of the MCS. We used velocity information form the wide-angle experiment to stretch theses images to depth. A subducted seamount is displayed about 40 km landward of the trench. A small accretionary prism is forming seaward of this seamount. An up to 10-km-thick sedimentary basin seems to be present landward of the seamount. The margin is underlain by oceanic crust of the Hikurangi Plateau, a large igneous province. We estimate its thickness at 10-12 km based on wide-angle arrivals in the OBS records. The Hikurangi Plateau is being subducted at a dip of 2-3 degrees close to the trench. A pronounced increase of subduction dip about 120 km away from the trench is displayed in MCS sections. The change of dip of the subducted plate appears to coincide with the eastern termination of the sedimentary basin as well as a stratigraphic high; the Lachlan Ridge. From the offshore-onshore data, we infer the presence of a low velocity zone above the subducted plate at this location. We speculate that the increase of subduction dip may be linked to a major tectonic process shaping the East Coast of New Zealand's North Island, perhaps normal faulting of the Hikurangi Plateau caused by loading from the overriding plate. The low velocity layer may mark sediments entering the subduction zone.
DE: 7218 Lithosphere and upper mantle
DE: 8123 Dynamics, seismotectonics
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting