Local and regional earthquakes recorded by the Tasmania Seismic Net

Seismic research has been conducted in Tasmania since 1957, when the Fort Nelson station began operation in Hobart. Three additional stations, Tarraleah, Moorlands and Savannah, were installed in 1960 for the investigation of local seismicity. Fifty-eight earthquakes occurred in Tasmania in the three year period from September, 1960 to December, 1963. The main activity- was in the north west of Tasmania, and south of Macquarie Harbour, where the surface rock is mainly Precambrian and Cambrian sediments and metamorphics. Seismic evidence suggests that the crust in central Tasmania is significantly thicker than the conventional ,3 5 kilometers continental crust. High heat flow adds support to this view, al though the Bouguer gravity anomaly is consistent with the 35 km value. There is a regional distribution of earthquakes which give rise to T:-phase recordings in Tasmania. This results from the effect of bathymetry on the oceanic Sofar channel. There is poor excitation of the T-phase where the continental margin slopes gently from 1000 to 4000 metres near the earthquake, and attenuation of the T- phase where the water depth is less than 3000 - 4 000 metr.es along the wave path. However, in some cases, considerable horizontal curvature around the South Tasmania Ridge occurred. The average crustal thicknesses of the Tasman Sea and the South Tasmania Ridge were found to be approximately 12 k~ and 10 km respectively from Love wave dispersion.