A century of earthquake recording in Australia  

Authors / CoAuthors

Leonard, M.

Abstract

A new catalogue of Australian earthquakes has been complied which contains 28000 earthquakes of which 17000 are considered main-shocks. The catalogue is complete for all of Australia above M5.5 since 1910, M5 since 1960, M4 since 1970 and M3.5 since 1980. In southern Australia it is complete above M3.5 since 1965 and M2 since 1980. Due to the generally sparse network the location uncertainty of Australian earthquakes is high with only 60% of contemporary earthquakes being located with an uncertainty of 10 km or less. This percentage will be smaller for earthquakes prior to 1980 with very few earthquakes prior to 1960 being located to within 10km. Most of the well located earthquakes are in the southern areas of the continent. The depth of Australian earthquakes are mostly between 8 and 18 km, except for the southwest corner of the continent where they are shallower than 5 km. Local magnitude scales were developed for Australia around 1990, prior to which the Richter magnitude scale was generally used. However at 600 km, a typical hypo-central distance in Australia, the Richter formula gives an overestimate of the magnitude of around 0.5 units. This results in the catalogues pre and post the early 1990's possibly being discrepant. The seismicity in some areas of Australia including the southeast corner, Adelaide fold belt, and the northwest corner, has been ongoing at a steady level for at least 100 years. The seismicity in the southwest corner the seismicity jumped by at least six in the 1940s and has been ongoing since then. The seismicity of much of the rest of Australia appears to be dominated by episodic seismicity. These episodes are characterised by a period of high activity lasting 1-10 years normally associated with a large (M>6) earthquake. Following the large earthquake there is often a period of moderate activity lasting a few years to a few decades. Preceding and following each episode is a period of low activity lasting 0.1ka to 10ka. The seismicity during this quiet period is more than an order of magnitude lower than during the period of high activity. Using the earthquakes since 1970, in the new catalogue, Frequency-Magnitude relations were calculated. Gutenberg-Richter a and b values were calculated on an 85 km grid of Australia. Using the a and b values maps of the probability of a magnitude 5 or greater event per year were produced and are very similar to the GSHAP map for Australia. The resulting maps were used to define four large (> 20000km2) seismogenic zones. There are also several other small zones, some of which appear reflect recent episodes and others appear to be long lived. The expected number of magnitude 5 or greater, 6 or greater, strain rate and deformation rate is given for the four zones, the remainder of Australia and the whole Australian continent. Combining estimate of strain from seismic, GPS and SLR data suggests compressive deformation across Australia of 0.6?2.0mm per year.

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nonGeographicDataset

eCat Id

61617

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• earthquakes

( Theme )

• seismology

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2004-09-14T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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