HR: 1340h
AN: T13C-1378    [Abstracts]
TI: Paleoecological Insights Into Subduction Zone Earthquake Occurrence, North Island, New Zealand.
AU: * Cochran, U
EM: u.cochran@gns.cri.nz
AF: Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AU: Berryman, K
AF: Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AU: Mildenhall, D
AF: Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AU: Hayward, B
AF: Geomarine Research, 49 Swainston Road, St Johns, Auckland, 1006 New Zealand
AU: Hollis, C
AF: Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AU: Wallace, L
AF: Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6009 New Zealand
AB: The boundary between the Pacific and Australian tectonic plates at the Hikurangi Subduction Zone, offshore of New Zealand's east coast, has not ruptured in a large earthquake in historical times. Therefore paleoseismological studies are required to elucidate the nature and history of subduction interface rupture. Multi-proxy reconstructions of paleoenvironments at two coastal sites arcward of the Hikurangi Trough provide evidence for significant Holocene subsidence. Radiocarbon dating, tephrochronology, stratigraphy and analysis of foraminiferal, diatom, spore and pollen assemblages enable assessment of vertical movement of the coastal plain relative to sea-level. Sequences outline a 9500-year history of coastal aggradation and progressive isolation from the sea. However the position of paleo-sea-level indicators almost 6 m below present mean sea level implies that subsidence has taken place since 7200 cal. years BP. A proportion of this subsidence appears to have happened suddenly in association with high-energy marine influx events and rapid infilling of newly created accommodation space. Two inferred coseismic subsidence events at c. 7100 and 5500 cal. years BP can be correlated with previously identified coseismic subsidence and tsunami inundation at a site 10 km away along the coast. Forward elastic dislocation models indicate the observed vertical deformation could occur in Mw 7.9 earthquakes on the subduction interface. However subsidence has not been recovered interseismically at these localities, and flights of raised marine terraces further trenchward suggest a large amount of permanent deformation is occurring along the margin. Reconstruction of earthquake records at additional sites is required to investigate the interplay of rupture on upper plate faults versus the subduction interface.
DE: 7221 Paleoseismology
DE: 4564 Tsunamis and storm surges
DE: 3030 Micropaleontology
DE: 1206 Crustal movements--interplate (8155)
DE: 1242 Seismic deformations (7205)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting