Earthquake research at Geoscience Australia
Geoscience Australia is responsible for a comprehensive program of earthquake monitoring, hazard research and risk modelling. It provides information on earthquake hazards to clients such as government agencies, industry, the media and the public and operates a 24-hour earthquake alert system for emergency managers. The earthquake hazard research encompasses source studies and ground motion studies as well as investigations of prehistoric earthquakes (palaeoseismology) and the recent tectonics of Australia (neotectonics). The research is aimed at developing better methods for estimating the hazard posed by earthquakes so that mitigation and disaster management strategies can be put in place.
Current estimates of earthquake hazard in Australia are based on the premise that historical seismic activity indicates where future activity is likely to occur and that the magnitude distribution within the region is known and will not change with time. Both these assumptions depend on having a good statistical sampling of seismic activity and confidence in the understanding of its fundamental causes.
Unfortunately, the historical record in Australia is very short, extending only about 150 years for large earthquakes. For smaller earthquakes detected and located by the seismograph network the historical record in some areas is complete only since the 1960s 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 seismic activity.
Adding to this, there is no definitive model for seismicity such as that available for the interplate areas of New Zealand, Japan and the western United States where the mechanism are well known. In contrast, Australia is situated within an intraplate region where the seismic activity is not associated with any major dynamic plate boundary. Although it is known that earthquakes are caused by the prevailing stress field, little is understood about how that stress interacts with the geological structure to produce the pattern seen today. The inherent problem when trying to estimate the hazard was highlighted by the Tennant Creek earthquakes in 1988 when three large events measuring more than magnitude 6.0 on the Richter scale occurred in a region thought to be practically aseismic because of its low seismic activity. Now the region is recognised on the hazard map as high-hazard along with other areas where there have been isolated large earthquakes. Significant changes to the hazard map after large events helps to illustrate how unreliable earthquake hazard information can be when it is based on inadequate available sampling of historical seismic activity.
The earthquake research at Geoscience Australia aims to address both these shortfalls by better estimating the recurrence rate and spatial location of large damaging earthquakes. This is being achieved through the capture of palaeoseismic data which is acquired by identifying and dating fault scarps formed during large pre-historic earthquakes and by undertaking research into the underlying cause of the seismic activity. The cause can be established by studying earthquake source properties and the recent stress and strain field along with the crustal structure and other attributes. The research also aims to derive better attenuation relations for Australia which are used to estimate how much ground shaking will occur as the result of an earthquake given the magnitude of the event and the distance from its epicentre. Many hazard studies currently use attenuation relations derived for eastern and western North America, which may be inappropriate for Australian earthquakes.
Topic contact: firstname.lastname@example.org Last updated: August 24, 2012