AUSTRALIAN PALEOSEISMOLOGY: TOWARDS A BETTER BASIS FOR SEISMIC HAZARD ESTIMATION

In this presentation we review the limited history of paleoseismological investigation in Australia and discuss the potential contribution of active fault source data towards improving our understanding of intraplate seismicity. The availability and suitability of Australian active fault source data for incorporation into future probabilistic hazard models is assessed, and appropriate methods for achieving this proposed.

Perhaps the most important realisation from the palaeoseismological data collected to date from half a dozen Quaternary faults is that the methods employed to include active fault source zones into hazard assessments in countries such as New Zealand and the United States may not be appropriate for the Australian context. The data suggest that surface rupturing events on Australian Quaternary faults are separated by tens of thousands of years or more. If future investigations confirm this indication, each fault, when considered in isolation, is unlikely to contribute significantly to the hazard for normal structures. However, if other active faults are present in a region, as is certainly the case in many parts of Australia, then the hazard is proportionately larger.

In the western and central parts of Australia there is also an indication that the concept of recurrence of a 'characteristic' or 'maximum probable' magnitude event on a single fault may not be applicable. In this vast region there is no paleoseismological evidence, nor evidence in the landscape, of more than 2-3 surface rupturing events on any given fault. In this context, estimates of hazard must be driven by an understanding of the patterns in migration of seismicity, and on a knowledge of the distribution of potentially seismogenic faults. Faults active in the Quaternary may not themselves contribute to the hazard, but can provide critical information on the long–term character of the seismicity in an active 'region'.

There are many known Quaternary faults in Australia which have not yet been investigated in detail. Because of the sparsely inhabited nature of the Australian continent it is very likely that more Quaternary fault scarps will be found (despite high scarp degradation rates over much of arid Australia). Some of these fault scarps may even be related to historic events.