Abstract
A network of seismograph stations has been operational in South Australia since 1963. A magnitude 2 event is locatable practically anywhere in the state. Presently, about 250 earthquakes/yr are being located. The greatest concentration of earthquakes occurs in the Flinders Ranges of the Adelaide Geosyncline. The other major zones are Eyre Peninsula and the Southeast corner of the state.
In the last 100 yr, South Australia has experienced 10 earthquakes of magnitude larger than 5, the most recent being in 1986. The largest earthquake to have occurred in the state's history was the Beachport-Kingston earthquake of 1897 (ML ∼ 6 1/2).
The focal depths for most South Australian earthquakes are quite shallow, being confined to the upper crust. Focal mechanisms have been obtained for six earthquakes occuring in the central Flinders Ranges. The predominant principal stress is northeast-southwest compression. This is consistent with surface uplift of the ranges causing crustal thickening.
The population center of Adelaide has the highest earthquake risk of any capital city in Australia. The 1954 (ML ∼ 5¼) Adelaide earthquake involved 30,000 insurance claims totalling $11 million (U.S. currency). Epicenters for microearthquakes in the Adelaide region show a correlation with known faults. Seismicity here appears to be associated with normal block faulting of the St. Vincent Gulf Graben structure.
