Stress and faulting in southeast Australia as derived from the strongest earthquakes in the region

In an attempt to clarify the state of stress in Southeast Australia, the sp atial and dynamic behaviour of the strongest events in the region (with mag nitude greater than 5.0) has been studied in the light of the most recent n umerical modelling of the crust. Although the local seismicity has little o bvious spatial correlation with the mapped structures, the strongest events line up in a very narrow strip with a NW-SE direction. Composite fault-pla ne solutions, based on data from all of these earthquakes, allows the gener al characteristics of the local stress field to be determined, and shows th at the orientation of the main compressive stress lies in an E-W direction. Taking into account the number of inconsistent data (40%) for this composi te solution and the fault-plane solutions for some individual events, an im proved result can be obtained by domain analysis, which shows that northern and southern zones have different orientation of the compressional axes. A lthough the composite solution for the events in the northern domain shows the same E-W orientation of the main compression as for the whole region, t he composite solution for the southern zone reveals a rotation of the compr ession axis to an azimuth of 120-130 degrees From the relation between the energy and seismic moment the maximum value of the stress-drop for the whol e of SE Australia is estimated as similar to 2.0 MPa. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.