New Zealand Journal of Geology and Geophysics abstracts

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New active fault data and seismic hazard estimates for west Otago, New Zealand

B. Pace

Geodynamics & Seismogenesis Laboratory
Dipartimento di Scienze della Terra
Via dei Vestini 30, 66013
Chieti, Italy

M. W. Stirling
N. J. Litchfield

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

U. Rieser

School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand

Abstract  We present new maps and slip rate estimates for the Blue Mountain and Spylaw Faults of west Otago, and a re-evaluation of the probabilistic seismic hazard for the area. Our mapping has resulted in an extension of the active section of the Blue Mountain Fault by about a factor of two, and reduction of the slip rates for the two faults by about a factor of two to five from the previous estimates. The incorporation of these revised fault data into the national seismic hazard model has resulted in the elimination of a zone of anomalously high seismic hazard in the national hazard maps, leaving behind a smooth gradient of increasing hazard from east to west across Otago towards the plate boundary. The study serves to show the magnitude of changes to seismic hazard estimates that result from significant changes to the recurrence parameters of individual fault sources. Future changes to hazard estimates may also be observed elsewhere in the country (e.g., Taupo Volcanic Zone) when significant updates to fault source data are made in the seismic hazard model.

Keywords  Blue Mountain Fault; Spylaw Fault; Otago; seismic hazard; neotectonics; active fault

G04008; Received 11 February 2004; accepted 9 June 2004; Online publication date 23 March 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48: 75–83
0028–8306/05/4801–0075 © The Royal Society of New Zealand 2005

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