HR: 1330h
AN: T22A-0492    [PDF]
TI: Displacement Accumulation in a Linked Segmented Normal Fault over the last 18 ka Within the Whakatane Graben, New Zealand.
AU: * Taylor, S
EM: susanna@fag.ucd.ie
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Bull, J
EM: J.M.Bull@soton.ac.uk
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Lamarche, G
AF: National Institute of Water and Atmospheres, Greta Point, Wellington, 14901 New Zealand
AU: Barnes, P
AF: National Institute of Water and Atmospheres, Greta Point, Wellington, 14901 New Zealand
AU: Cowie, P
AF: Edinburgh University, West Mains Road, Edinburgh, EH93JW United Kingdom
AU: Sanderson, D
AF: Imperial College London, South Kensington, London, SW7 2AZ United Kingdom
AU: Dix, J
AF: Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AB: The Whakatane Graben is a young ($<$2 Ma) and highly active structure situated on the New Zealand continental shelf where the sediment supply has been sufficient to infill accommodation space created by the rapidly displacing faults, thus providing a complete record of past fault motions. The shallow water (up to 200 m depth) of the graben on the continental shelf means it is well placed for acquisition of high-resolution seismic data and core samples. One of the most active faults in the Whakatane Graben is the Rangitaiki Fault, a 20 km long linked, segmented, normal fault. The central 9 km of the Rangitaiki Fault is imaged by over 97 closely spaced chirp sonar, 3.5 kHz and Boomer profiles covering an area approximately 5 km by 9 km, the outer sections of the fault are imaged by 12 more widely spaced high-resolution profiles. These data provide excellent quality high-resolution images of the top 50 - 60 m of sediments which include the post-glacial ($<$ 18 ka) transgressive sequence. Within the post-glacial sequence there are several strong and laterally continuous reflectors displaced by active extensional growth faults. Displacements on four of these horizons, dated 17 $\pm$ 1, 13.3 $\pm$ 1, 11.1 $\pm$ 1 and 9 $\pm$ 1 ka, are used to create displacement profiles and to calculate displacement rates. The segments of the Rangitaiki Fault are hard-linked throughout the last 18 ka, but the post-glacial displacement accumulation is still dominated by the location of the relict segment boundaries. The maximum displacement rate observed on the Rangitaiki Fault is 4.6 $\pm$ 2.3 mm/yr measured over 2 ka, a maximum of 3.4 $\pm$ 0.2 mm/yr measured over 18 ka. Displacement profiles of the last 9 ka of fault movement are regular and similar to profiles showing the last 300 ka of fault movement. In contrast, profiles showing only 2 ka of fault movement are highly irregular and show points of zero displacement on the larger faults. The variability of fault displacement rates over short ($<$ 2 ka ) timescales suggests that fault activity rates measured from geodetic surveys may not be adequately sampling the fault activity, and longer timescale estimates of displacement rate, such as are presented here, are more reliable an indicator of seismic risk and earthquake recurrence intervals.
DE: 3025 Marine seismics (0935)
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting