RE-EVALUATION OF CONDITIONAL PROBABILITY OF RUPTURE OF THE WELLINGTON-HUTT VALLEY SEGMENT OF THE WELLINGTON FAULT

SUMMARY New information on the activity of the Wellington-Hutt Valley segment of the Wellington Fault, New Zealand, has become available from geological and modelling studies undertaken in the last several years as part of the “It’s Our Fault” project. There are now revised estimates of: 1) the timing of the most recent rupture, and the previous four older ruptures; 2) the size of single-event displacements; 3) the Holocene dextral slip rate; and 4) rupture statistics of the Wellington-Wairarapa fault-pair, as deduced from synthetic seismicity modelling. The conditional probability of rupture of this segment over the next 100 years is re-evaluated in light of this new information, assuming a renewal process framework. Four recurrence-time distributions (exponential, lognormal, Weibull and Brownian passage-time) are explored. The probability estimates take account of both data and parameter uncertainties. A sensitivity analysis is conducted, entertaining different bounds and shapes of the probability distributions of important fault rupture data and parameters. Important findings and conclusions include: 1. The estimated probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault in the next 100 years is ~11% (with sensitivity results ranging from 4% to 15%), and the probability of rupture in the next 50 years is about half of that (~5%). 2. In all cases, the inclusion of the new data has reduced the estimated probability of rupture of the Wellington Fault by ~50%, or more, compared to previous estimates.

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