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 Ō hariu 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 recurrenceÁtime 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 Ō hariu 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 Ō hariu Fault.

Repeated giant earthquakes on the Wairarapa fault, New Zealand, revealed by Lidar-based paleoseismology

“…Our dense offset database provides a robust basis to identify the geomorphic markers most appropriate to date the identified earthquakes. Along with the measures of the largest and mean WP earthquake slips we provide here, this dating should help estimating the probability of rupture of the WP fault over the next 100 yrs 7,28,55 .…”

“…However, only sparse measurements of the slips it produced at the ground surface have been published 2,4,26,29 while its rupture length is debated 25 . Uplifted beach ridges in southern WP 30,31 and trenching along the fault 5 reveal that 4 large prior earthquakes occurred in the last ~6 kyrs 5,28 with possibly up to 10 in the Holocene 24 . However, their slips and rupture lengths are poorly constrained.…”

“…The possibility of a forthcoming earthquake on the WP fault in the near future thus needs to be considered 11,21,28 ). If the timing of such an event cannot be forecasted, its size may be by studying the past.…”

Variability of recurrence interval and single-event slip for surface-rupturing earthquakes in New Zealand

“…<10%) longrecurrence events which will impact the hazard. In the absence of an ability to predict the timing of future large earthquakes, knowing the timing of the last event on a fault and having a PDF for RI provides a basis for estimating the probability of future fault rupture over a specified period of time (Rhoades & Van Dissen 2003;Rhoades et al 2011;Van Dissen et al 2013;Biasi et al 2015). Although the RI PDF can vary between faults, the Weibull and log-normal average distributions identified in this study may be applied to active faults in the NSHM and provide a basis for examining the impact of RI variability on seismic hazard estimates.…”