Spatial and temporal variation of seismicity across Australia
Edelvays Spassov1, Cvetan Sinadinovski2 and Kevin McCue2
1Australian National University, Canberra, Australia.
Thessaloniki, School of Geology, Geophysical Laboratory, 54124 Thessaloniki, Greece.
2Australian Geological Survey Organisation, Canberra, Australia.
(Received 10 April 2002; accepted 16 July 2002)
Abstract:A first attempt has been made to quantify the variability in the seismic activity rate across the whole of Australia. Using the AGSO Earthquake Database (Lenz et al., 1992) updated to 1997, the most complete catalogue of Australian earthquakes to date, and the software tool ZMAP, spatial and temporal variations of the seismicity across the continent have been computed. Since the start of instrumental recording at the beginning of the century moment release rate in continental Australia has been fairly constant with a pseudo periodicity in seismic moment release with a period of about 20-25 years. The 'b' value relating the number of large to small earthquakes over the whole area is estimated to be 0.94 ± 0.15 for events with ML³ 4 in the period 1902-1997. The mapped 'b' value varies dramatically from decade to decade but taking the whole century, we seem to have a region of high 'b' traversing north-south through the centre of the continent which is indicative of an area of high stress. An Alarm Cube, which highlights areas where there has been a significant drop in the seismicity rate, highlights two zones in the SE of the country. This anomaly in the most densely populated region has persisted since approximately 1985.
Key Words: Seismic Rate, 'b' value, Stress, Earthquake Catalogue, Australia.