Above - earthquakes in Central Australia to 2004 on Digital terrain model
figure courtesy of Geoscience Australia
Gravity map for above area (Geoscience Australia data)
The 1991 map of earthquake risk in Australia, published by the Australian Earthquake Engineering Society, shows three main areas of high earthquake risk in Central Australia. Each of these areas relates to sustained levels of high earthquake activity at certain points in Central Australia. These points are 1) Tennant Creek Area 2) Simpson Desert and 3) Lake Tobin area of eastern Western Australia.
Figure - Geoscience Australia map of March 2004 Tennant Creek earthquake superimposed on 1991 earthquake risk map.
The Simpson Desert, in the southeast of the Northern Territory, near the SA border, saw a series of large earthquakes in the 1930's, beginning with a magnitude 6.5 event on 28 Oct 1937. Another series of large events commenced with another magnitude 6.5 event on 27 June 1941. After a long period of inactivity, a magnitude 6.2 event occurred in the area on 28 Aug, 1972.
The earthquakes of the 1930's and 1940's occurred before the development of the modern seismographic network, which began to take shape in the 1960's. Consequently, the accuracy of the locations given is not high. The error in locations is probably of the order of +/- 50 km. Although there is some scatter in the location of the events, the location accuracy does not discount the possibility that they are more closely grouped than the map suggests.
Lake Tobin, WA.
Activity in this region began on 24 March 1970, with a magnitude 6.4 earthquake. Numerous other quite large events occurred in approximately the same location overn the ensuing years. A magnitude 5.0 event on 13 June 1992, near the location of the magnitude 6 events, is probably an aftershock of these events.
While seismic station coverage was much better for these events than the Simpson Desert events, the lack of close stations again means that location accuracy is not as high as might be hoped, particulary for the smaller events in the region.
Reference Denham, D., Everingham, I., and Gregson, P. Journal of the Geological Society of Australia, 1974.
Activity in this region began on 7 Jan 1987 with a magnitude 5.2 event, followed by another of the same size two days later. Prior to these events, the region had been classified as aseismic. Activity died away after these two events, but resumed on a much greater scale a year later, on 7 Jan 1988, when three magnitude 6 events occurred there on the same day, and a major surface fault scarp, approximately 35 km long was created. The southern block was thrust over the northern block, and the maximum vertical displacement was approximately 1 m. The maximum horizontal displacement was approximately 2 m.
Magnitudes have been given as 6.3, 6.4 and 6.7, but the values may vary slightly, according to the agency which computed the magnitudes. Major damage was caused to the SA to Darwin gas pipeline. Unlike the earlier events, these events occurred close to a major array of seismic recorders ( the Warramunga array), and the subsequent locations have a relatively high degree of accuracy.
Seismic activity at this location has remained at above average levels since the magnitude 6 events. Small earthquakes are still occurring, the latest being a magnitude 2.9 event in January 2004. Larger earthquiakes from this location can still be expected.
Reference: Crone, A., Machete, M., & Bowman, J., US Geological Survey Bulletin 2032 (1992)
On 30 March 1986, a magnitude 5.9 earthquake occurred at Marryat Creek, at the eastern end of the Musgrave Ranges, and about 10 km south of the SA-NT border. A 13 km long, L shaped fault scarp was created by this event. The maximum displacement was approximately 0.6 m. vertically, and 0.8 m in an E-W direction.
A magnitude 5.6 aftershock occurred near the March event on 11 July 1986. The remoteness of these two events means that location accuracy is not high, and the two events could be closer than the earthquake coordinates suggest.
For more information, refer to the PIRSA website.
Other important earthquakes in Central Australia
On 28 May, 1989, a magnitude 5.8 event occurred in a remote area, west of Mt. Olga. It has been titled the "Uluru" earthquake. It was felt over a wide area, including Alice Springs, but did no damage. Unlike many other large earthquakes of central Australia, no aftershocks were recorded, even though portable seismographs were positioned near the epicentre shortly after the earthquake.
On 11 Feb 2004, a magnitude 5.4 earthquake occurred in the SW on the Northern Territory, near the WA border. A magnitude 5.0 foreshock occurred 15 minutes before the main shock.