HR: 11:25h
AN: T21E-05 INVITED     [PDF]
TI: Constraining fault interactions and vertical displacement rates in a compressive proto-back-arc environment, South Wanganui Basin, New Zealand
AU: * Lamarche, G
EM: g.lamarche@niwa.co.nz
AF: NIWA, PO Box 14901, Wellington, 6003 New Zealand
AU: Nodder, S D
EM: s.nodder@niwa.co.nz
AF: NIWA, PO Box 14901, Wellington, 6003 New Zealand
AU: Proust, J
EM: Jean-Noel.Proust@univ-rennes1.fr
AF: G‚osciences Rennes, Universit‚ Rennes1, Rennes, 35042 France
AB: The Kapiti-Manawatu Fault System (KMFS) is a 25 km-wide network of steep, reverse and normal faults that runs parallel, and 200 km to the west of the Hikurangi subduction margin, New Zealand. The KMFS separates the 4 km-thick Plio-Pleistocene South Wanganui Basin from the recently uplifted North Island axial ranges, to the west and east, respectively. The KMFS represents the westernmost expression of upper plate deformation associated with Hikurangi subduction over the last 2 million years. A seismic reflection network of lines acquired 1.5 km apart across the KMFS provides a way of constraining the Plio-Pleistocene tectonic activity in the region. Strike-projected, vertical separation profiles (D/L) demonstrate the interplay between faults, and indicate a regional southeast migration of the compressive system with time. Basement fault geometry suggests reactivation of a normal fault system and a minor amount of strike-slip motion. Fault terminations suggest that these faults have remained fixed with no lateral propagation since at least 1350 kyr. Cumulative D/L profiles have clear bell shapes, which contrast with the asymmetric shapes of individual D/L profiles. This suggests that the KMFS is a mature fault system with fault lengths initiated early in the evolution of the fault zone due to the pre-existing crustal heterogeneities under a constant regional strain regime. Long-term slip rates were derived from vertical separations across horizons dated 120, 620, 1000, 1350, 2400 and 3000+ kyr, for 21 fault segments. The maximum vertical slip rate on any one fault is less than 1 mm/yr, but the maximum long-term (1350 kyr) cumulative slip rate across the whole KMFS reaches 2.1+/-0.6 mm/yr. Late Quaternary deformation suggests slip rate magnitudes ranging from 0.1-1.4 mm.yr-1 over the last 10,000 years. Slip rates for the 0-120 kyr period increased, and the cumulative maximum slip rate for the KMFS reaches 5.0 +/- 1.5 mm/yr.
DE: 3025 Marine seismics (0935)
DE: 8010 Fractures and faults
DE: 8105 Continental margins and sedimentary basins
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting