New Zealand Journal of Geology and Geophysics abstracts
Estimates of the time-varying hazard of rupture of the Alpine Fault,
New Zealand, allowing for uncertainties
D. A. Rhoades
R. J. Van Dissen
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract The time-varying hazard of rupture of the Alpine
Fault is estimated using a renewal process model and a statistical method
that takes account of uncertainties in data and parameter values. Four different
recurrence-time distributions are considered. The central and southern sections
of the fault are treated separately. Data inputs are based on estimates of
the long-term slip rate, the average single-event displacement, and the dates
of earthquakes that have occurred in the last 1000 yr from previous studies
of fault traces, landslide and terrace records, and forest ages and times
of disturbance. Using these data and associated uncertainties, the current
hazard of rupture on the central section of the fault is estimated to be
0.0051, 0.010, 0.012, and 0.0073 events per year under the exponential, lognormal,
Weibull, and inverse Gaussian recurrence-time distributions, respectively.
The corresponding probabilities of rupture in the next 20 yr are 10, 18,
21, and 14%, respectively. The current hazard on the southern section of
the fault is estimated to be 0.0033, 0.0075, 0.0070, and 0.0053 events per
year for the four models, and the 20 yr probabilities 6, 14, 13, and 10%,
respectively. Increased precision in the date of the second to last event
on the southern section of the fault would result in only small changes to
these rates and probabilities. The indicated hazard under the lognormal model
is about double the long-term average rate but less than half of that estimated
in previous studies that did not take account of all the uncertainties. Dating
additional prehistoric ruptures is likely to have a greater effect on the
hazard estimates than improved precision in the existing data.
Keywords geologic hazards; earthquakes; New Zealand;
South Island; Alpine Fault; renewal process model; time-varying hazard
G02058; Received 8 November 2002; accepted 27 August 2003; online publication
date 13 November 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 479–488
0028–8306/03/4604–0479 $7.00/0 © The Royal Society of New Zealand
2003
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