2018 – Impacts of New Knowledge and the 2018 Draft ANCOLD Guidelines on Ground Motion Levels at Dam Sites in Australia

Paul Somerville, Andreas Skarlatoudis, Jeff Bayless and Don Macfarlane

The revised magnitudes of the Geoscience Australia’s NSHA18 earthquake catalogue approximately halve the rate of occurrence of earthquakes of a given Mw magnitude in Australia. This yields probabilistic ground motion levels that are significantly lower than the present design levels at dam sites in Australia that are not near faults, and is expected to result in a general reduction in ground motion levels at dams not near faults estimated for all Risk Assessments, and for Deterministic Assessments for all consequence levels except Extreme Consequence. For the latter, the ANCOLD (2018) guidelines will tend to increase existing SEE ground motion estimates for both of the methods used to estimate the safety evaluation earthquake (SEE). By requiring the use of the Deterministic SEE if it is larger than the probabilistic SEE, and by requiring use of the 85th fractile of the Probabilistic SEE if it is larger than the Deterministic SEE, the ANCOLD (2018) guidelines for Deterministic Assessments are much more conservative than the ICOLD and NZSOLD guidelines for Extreme Consequence dams, especially at those located near faults.

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