Conditional probability of rupture of the Wairarapa and Ōhariu faults, New Zealand

Abstract

New information on the timing of past ruptures, size of single-event displacements and Holocene dextral slip rate of the Wairarapa and Ōhariu faults has become available from recent geological studies. This information is used to evaluate the conditional probability of rupture over the next 100 yr using four different recurrence–time models, allowing for data and parameter uncertainties. The sensitivity of estimates to data and distributional assumptions is examined. The southern Wairarapa Fault has a probability of rupture in the next 100 yr of c. 7.7, 1.3, 2.3 and 4.3% under the exponential, lognormal, Weibull and inverse Gaussian models, respectively, based on preferred data inputs. Corresponding estimates for the Ōhariu Fault are c. 4.3, 5.1, 3.9 and 5.1%. A logic tree with subjectively assigned weights is suggested to combine such differing time-dependent estimates. This gives a 100-yr conditional probability of rupture of c. 3.0% for the southern Wairarapa Fault and c. 4.9% for the Ōhariu Fault.