HR: 1340h
AN: S53A-1090    [Abstracts]
TI: A Long Time Scale, High-Resolution Record of Displacement Accumulation on an Active Normal fault: Implications for Models of Slip Accumulation During Repeated Earthquakes.
AU: * Bull, J M
EM: bull@soton.ac.uk
AF: National Oceanography Centre Southampton, SOES National Oceanography Centre, Southampton, SO14 3ZH United Kingdom
AU: Barnes, P
EM: p.barnes@niwa.co.nz
AF: NIWA, Greta Point 301 Evans Bay Parade, Wellington, 14901 New Zealand
AU: Lamarche, G
EM: g,lamarche@niwa.co.nz
AF: NIWA, Greta Point 301 Evans Bay Parade, Wellington, 14901 New Zealand
AU: Sanderson, D J
EM: david.sanderson@imperial.ac.uk
AF: Imperial College, Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ
AU: Cowie, P A
EM: cowie@glg.ed.ac.uk
AF: Edinburgh University, School of Geosciences West Mains Road, Edinburgh, EH9 3JW United Kingdom
AU: Taylor, S
EM: susannataylor@gmail.com
AF: National Oceanography Centre Southampton, SOES National Oceanography Centre, Southampton, SO14 3ZH United Kingdom
AB: The spatial and temporal accumulation of slip from multiple earthquake cycles on active faults is poorly understood. Here we provide constraints on this process using a high-resolution long-time-scale (the last 17kyr) fault displacement dataset over the Rangitaiki Fault, the most active normal fault within the Whakatane Graben, New Zealand, for time intervals as short as c. 2 kyr. The fault linked at c. 200-300 ka BP, and analysis of temporal periods within the last 17 kyr gives insight into steady-state behaviour. The maximum displacement rate observed on the Rangitaiki Fault is 3.7 ñ 1.1 mm yr-1 measured over 17 kyr. 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 determined for shorter time intervals (c. 2000 - 3000 yr) are highly irregular and show points of zero displacement on the larger faults. This indicates temporal and spatial variability in incremental displacement associated with ground-rupturing earthquakes. Some earthquakes appear to have been confined to specific segments, whereas larger composite ruptures have involved the entire fault. The short-term variability in fault behaviour suggests that fault activity rates inferred from geodetic surveys or surface ruptures from a single earthquake, may not adequately represent the longer-term activity nor reflect its future behaviour. Different magnitude events may incorporate the same fault segment, with asperities preventing whole segment rupture for smaller magnitude events. Variations in rupture length imply different length/width aspect ratios or different rupture depths, in different earthquakes. There is spatial variability in slip rates along fault segments, with minima at locations of fault interaction or where fault linkage has occurred in the past. The variations in displacement rate along the strike of the Rangitaiki Fault suggest that fault interactions and the history of fault linkage control the distribution of earthquake slip.
DE: 7209 Earthquake dynamics (1242)
DE: 7221 Paleoseismology (8036)
DE: 8002 Continental neotectonics (8107)
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: Fall Meeting 2005