3‐D Sedimentary Structures Beneath Southeastern Australia Constrained by Passive Seismic Array Data

Abstract

AbstractA high‐resolution sedimentary map of southeastern Australia is of great importance to explore natural resources as well as to evaluate seismic hazards. In this study, we build a 3‐D Vs model of the upper crust beneath southeastern Australia by jointly inverting Rayleigh wave phase velocity, ellipticity, and teleseismic P‐coda waves. At depths less than 3 km, sedimentary basins are revealed as prominent low‐velocity anomalies. The average sediment depth in the Murray Basin is ∼713 m with the maximum depth reaching 1,500 m, while, in the Sydney‐Gunnedah‐Bowen Basin (SGBB), the average sediment depth is 600 m with a maximum depth of ∼3,000 m. Vs of the sedimentary layer in the Murray Basin is lower than that in the SGBB, suggesting that the sediments in the Murray Basin are less consolidated compared with those in the SGBB. The unconsolidated sediments make the Murray Basin more vulnerable to seismic hazards. In the upper and middle crystalline crust, we image two low‐velocity zones: one beneath the Adelaide Fold Belt and the other beneath the Begargo Hill volcanic zone. The low‐velocity zone beneath the Adelaide Fold Belt is likely caused by high temperature and/or a weak granitic composition, which lead to the concentration of intraplate seismic activities in this area. The low‐velocity zone beneath the Begargo Hill Volcanic zone indicates that there exists magma in the upper to middle crust or the temperature there is still very high after the latest eruption.