Earthquake Hazards and Neotectonics Project

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EH&N Project description:

Geoscience Australia (GA) runs a comprehensive program of earthquake monitoring, hazard research and risk modeling. It provides information on earthquake hazards to clients such as government agencies, industry, the media and the general public, and operates a 24-hour earthquake alert system for emergency managers. The Earthquake Hazard and Neotectonics (EH&N) Project's earthquake hazard research encompasses source studies, ground motion studies, neotectonics and palaeoseismology. The objective of this research is to enable better estimates of the hazard posed by earthquakes to communities so that hazard mitigation and disaster management strategies can be put in place.

Current estimates of the hazard in Australia are based on the premise that the historical seismicity indicates where future seismicity is likely to occur, and that the magnitude distribution within the region is known, and will not change with time. Both of these assumptions depend on having a good statistical sampling of the seismicity and confidence that we understand its underlying.

Unfortunately, the historical record in Australia is very short: for large earthquakes it is only about 150 years, and for smaller earthquakes, which are detected and located by the seismograph network, it is only complete in some areas since the 1960's or later. For large, potentially damaging earthquakes, with long return periods, this time frame is far too short for a reliable estimate of hazard based only on historical seismicity.

There is also no definitive model for the seismicity. Unlike interplate areas such as New Zealand, Japan and the western USA where the mechanism is well known, Australia is situated in an intraplate region where the seismic activity cannot be associated with any major dynamic plate boundary. We know that the earthquakes are caused by the prevailing stress field, but how it interacts with the geological structure to produce the pattern we see today is poorly understood. The problem this causes when trying to estimate the hazard was highlighted by the Tennant Creek earthquakes in 1988, where three large (greater than magnitude 6) earthquakes occurred in a region thought to be practically aseismic because of its low seismic activity. The region now appears in the hazard map as high-hazard, as do other areas where there have been isolated large events. This example, in which the hazard map changes significantly after large events, illustrates how unreliable hazard maps can be when based on an inadequate sampling of historical seismicity.

The EH&N Project aims to address both these shortfalls. Firstly, by better estimating the recurrence rate and spatial location of large damaging earthquakes from the palaeoseismic record, through identifying and dating fault scarps which formed during large pre-historic earthquakes; and secondly, by undertaking research into the underlying cause of the seismicity through studying earthquake source properties, the recent stress and strain field, the crustal structure and other attributes. The Project also aims to derive better attenuation relations for Australia which are used to estimate how much ground shaking will occur due to an earthquake, given its magnitude and the distance from it. Many hazard studies currently use attenuation relations derived for eastern and western North America, which may be inappropriate for Australian earthquakes.

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Project outcome:

The objectives of the EH&N Project are to:

• Provide advice and seismic information on potentially damaging earthquakes and tsunamigenic events in the Australian region to government agencies and other clients,
• Develop a revised seismicity model for Australia based on neotectonics and palaeoseismological investigations to improve earthquake hazard assessment,
• Develop a regional ground motion model applicable to Australia for input to earthquake hazard studies.

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Projects:

2003/04

• Information and Earthquake Alert System
• Neotectonics
• Ground Motion and Source Studies

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