Nicol, A.; Robinson, R.; Van Dissen, R.J.; Harvison, A. 2012 Variability of single event slip and recurrence intervals for large magnitude paleoearthquakes on New Zealand's active faults. Lower Hutt, N.Z.: GNS Science. GNS Science report 2012/41 57 p.
Abstract: Recurrence intervals and single event slip for large magnitude earthquakes that ruptured the ground surface can vary by more than an order of magnitude on individual faults. To quantify this variability we combine existing (published and unpublished) geological observations and synthetic earthquakes generated by numerical models for over 100 of New Zealand's active faults. Synthetic earthquakes generated for fault systems help fill information gaps in the natural (geological) data which may arise due to measurement uncertainty and to the brevity of the geological record (i.e. /= surface-rupturing events) are often asymmetric with modes less than, or equal to, the mean and a long recurrence (3-4 times the mean) tail. The resulting PDFs for recurrence interval more closely resemble log-normal or Weibull than normal distributions, in contrast to the single event slip for geological data and synthetic models which in many cases are approximately normal. Recurrence interval histograms for synthetic earthquakes show less variability between faults than the geological data, which may be partly due to the significantly larger number of events in the synthetic dataset. Histograms and PDFs for recurrence intervals of synthetic earthquakes are similar to the geological data in that they exhibit a long recurrence interval tail which constitutes a small proportion (<20%) of the total population. COV for recurrence interval (0.58+/-0.2 geological and 0.56+/-0.27 synthetic) and single event slip (0.4+/-0.2 geological) suggest that recurrence is more variable than single event slip. COV for single event slip (0.4+/-0.2) and recurrence interval (0.6+/-0.25) are inferred to have a minimum magnitude of completeness (Mc) for geological data of 7.2+/-0.2 and 6.1+/-0.2 for strike slip faults and normal faults, respectively. More data and analysis are required however to quantify the Mc for geological data and to understand better how this may be impacting on the geological and synthetic results. In addition, more research is required to define better the PDFs for recurrence interval and single event slip before these can be input into the New Zealand National Seismic Hazard Model (NSHM). Despite these outstanding questions, COV for recurrence interval and single event slip provide constraints on the variability of these parameters and could be applied to active faults in the NSHM for which there are insufficient data to constrain their paleoearthquake history. (auth)
