New earthquake risk maps of Tasmania have been prepared depicting risk by contours of peak ground velocity, acceleration and intensity with a 10 per cent probability of being exceeded in a 50 year period. The Cornell- McGuire method was used. The maps are based on seismicity up to the end of 1984, including the events of the 1883-1892 earthquake swarm east of Flinders Island and other historical data. The earthquake process was assumed to be Poissonian, so foreshocks and aftershocks were eliminated from the analysis. For this earthquake risk assessment, average eastern Australian background seismicity and attenuation for average site conditions were used. The earthquake source zones most affecting the risk in the Tasmanian region are the West Tasman Sea Zone and the Western Tasmanian Zone. The West Tasman Sea Zone, east of Flinders and Cape Barren Islands, appears to have been the site of the 1883 - 1892 swarm, with at least three intensity-deduced Richter magnitude 6.0- 7.0 events. Consequently, the highest risk land areas are Flinders and Cape Barren Islands, which lie predominantly between the 60 mm.s-1/0.6 m.s-2 and 120 mm.s-1/ 1.2 m.s-2 contours, with the risk increasing to the east. In the Western Tasmanian Zone, the largest event recorded was in 1880. It had an intensity-deduced Richter magnitude of 5.5. The northern part of western Tasmania (enclosed by the 59 mm.s-1/ 0.55 m-2 contour) is the second highest risk region. At Hobart and Launceston, outside the source zones, the values are 23 mm-1 / 0.21 m.s-2 and 30 mm.s-1/ 0.29 m.s-2 respectively, corresponding to a 10 per cent chance of an intensity MMIV - V being exceeded in a 50-year period. However, it appears that site amplification of strong ground motion takes place in some parts of Launceston, and this should be considered when zoning for the Building Code. The chief contributions to uncertainty in the estimates of earthquake risk are uncertainties in early earthquake locations and magnitudes, and in strong ground motion attenuation.
