2016 – Estimating the Maximum Credible Earthquake (MCE) and its Application in Australia and New Zealand

Paul Somerville

This paper reviews methods used to estimate the MCE in Australia and New Zealand. In the ICOLD (2016), NZSOLD (2015) and proposed ANCOLD (2016) guidelines, the deterministic approach is applicable only to fault sources, whereas the probabilistic approach is applicable to both fault sources and distributed earthquake sources. Although ICOLD (2016) states that the use of a deterministic approach to develop the SEE “may be more appropriate in locations with relatively frequent earthquakes that occur on well- identified sources, for example near plate boundaries,” the proposed ANCOLD (2016) guidelines retain the use of the deterministic approach for critical active faults which show evidence of movements in Holocene time (i.e. in the last 11,000 years), or large faults which show evidence of movements in Latest Pleistocene time (i.e. between 11,000 and 35,000 years ago). In Australia, active faults make a significant contribution to the probabilistic MCE only at near-fault sites, and even in those cases most of the hazard comes from distributed earthquake sources. However, some sites may be close enough to nearby or even more distant identified active faults that a Deterministic Seismic Hazard Analysis (DSHA) produces MCE ground motions that are far larger than those obtained probabilistically even for very long return periods. Conversely, the deterministically defined MCE may be lower than the probabilistically defined MCE for very long return periods at near fault sites in New Zealand, requiring the probabilistic approach.

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