HR: 1330h
AN: T22A-0491    [PDF]
TI: Active interplay between strike-slip and extensional structures in a Back-Arc environment, Bay of Plenty, New Zealand
AU: Barnes, P M
EM: p.barnes@niwa.co.nz
AF: National Institute of Water and Atmospheric Research (NIWA) Ltd, PO Box 14901, Wellington, 6003 New Zealand
AU: * Lamarche, G
EM: g.lamarche@niwa.co.nz
AF: National Institute of Water and Atmospheric Research (NIWA) Ltd, PO Box 14901, Wellington, 6003 New Zealand
AU: Bull, J M
EM: J.M.Bull@soton.ac.uk
AF: Department of Geology, Southampton Oceanography Centre, Southampton, SO14 3ZH United Kingdom
AB: Active continental back-arc tectonics associated with the oblique Hikurangi subduction zone, North Island, New Zealand, is characterized by (1) extensional deformation distributed across a 40-50 km-wide zone, but presently concentrated in the east within the 20 km-wide, NE-striking Taupo Fault Belt (TFB) and Whakatane Graben (WG); (2) c. 12mm/yr extension rate at the Bay of Plenty coast; (3) 1-3 mm/yr subsidence in the WG; and (4) a seismogenic zone estimated to be 6-9 km thick. A component of the oblique convergence within the plate boundary is partitioned to the east onto the adjacent North Island Dextral Fault Belt (NIDFB), a large NNE-trending strike-slip fault system traversing the entire North Island. At the Bay of Plenty coast, the NIDFB strikes north, with an estimated strike-slip rate of at least 1 mm/yr. Both normal and strike-slip fault systems extend beneath the continental shelf in the Bay of Plenty, and because of differences in their strike, they converge and interact. Detailed mapping of faults using marine seismic reflection profiles and multibeam bathymetric data reveals the structure of the WG. Tilted basement blocks are associated with large west-dipping faults, numerous antithetic secondary faults, and domino-style fault arrays. Eastward migration of the principal extension zone during the last c. 1 Myrs has resulted in the encroachment and oblique overprinting of the NIDFB by the WG. The structure and geometry of the White Island Fault (WIF), currently the principal fault along the eastern margin of the graben, results from interaction and linkage of the two fault systems. The displacement profile of this fault reveals relatively young NE-striking sections that obliquely link more northerly-striking, inherited components of the NIDFB. Understanding of the fault structure and evolution may have implications for the interpretation of earthquake potential close to urban centres.
DE: 7223 Seismic hazard assessment and prediction
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting