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