Recent crustal movement determined from repeat surveying—results from southeastern and southwestern Australia

Abstract

First-order geodetic measurements have been repeated in seismically active areas in southeastern and southwestern Australia. In both areas significant crustal movement is detected. The crustal movements give principal axes of compression parallel to those of in-situ stress measurements, and roughly consistent with those of earthquake focal mechanisms. The seismic moment rates calculated from the measured strain rates are higher than those calculated from the historic earthquake record. In southeastern Australia the strain rate is about 50 × 10−9 yr−1 over the whole area investigated, but with a gradually changing principal axis of compression. The rate of change of direction is similar to that found in Japan. In southwestern Australia the strain is detected only along zones of weakness, and the principal axis of compression is fairly uniformly east-west. The difference in the pattern of detected strain, together with a difference in the size of the areas in regional isostatic compensation, and a difference in average heat flow, are all consistent with a relatively weak, hot crust in southeastern Australia, and a relatively strong, cold crust in southwestern Australia.