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Abstract:
A wealth of data about earthquake behaviour in New Zealand has been obtained through numerous paleoseismic, geologic and geodetic studies in the past fifty years. These data have been compiled in the 2022 New Zealand National Seismic Hazard Model (NSHM), respectively within the Paleoseismic Site Database, Community Fault Model (CFM), and Geodetic Deformation Model. Here, we use these data to probabilistically estimate the mean recurrence interval (MRI) of earthquakes on key upper-plate faults at 81 sites throughout New Zealand. First, we take the timings of past earthquakes from the Paleoseismic Site Database and fit the inter-event periods at each site to Brownian Passage Time, lognormal, and Poissonian recurrence models. We iteratively explore wide ranges of possible MRI and dispersion in these models, and thereby derive Bayesian PDFs of both parameters at each site, following the approach of Biasi et al (2015). Then, we take single-event displacement data from the Paleoseismic Site Database, along with geologic and geodetic slip rates from the New Zealand CFM and Geodetic Deformation Model, and estimate MRI an alternate way by dividing each site’s PDF of mean single-event displacement by its PDF of mean slip rate. Finally, at every site where we have both timings data and single-event displacement and slip rate estimates, we multiply the PDFs of MRI from these two methods together to derive a more tightly constrained estimate of MRI and its uncertainty. These estimate formed a key input into the on-fault portion of the NSHM.
