Landslides in the Sydney Basin - Geoscience Australia

Seismic Hazard in SydneyProceedings of the one day workshopNotes on the Tectonic setting of, andAttenuation in, the Sydney BasinKEVIN MCCUE 1AUSTRALIAN SEISMOLOGICAL CENTRE, PO BOX 324, JAMISON CENTRE ACT 2614,AUSTRALIATECTONIC SETTING OF THE SYDNEY BASINThe Australian continent is an island of continental crust with a surrounding halo of oceanic crustwithin the Australian Plate everywhere except through the island of New Guinea (Doutch, 1982)where continental Australia collides with the Pacific Plate. The Sydney Basin is a Mesozoic Basinon the southeastern edge of the Australian continent about 2000 km from the nearest recognisedplate boundary to the east stretching from northern New Zealand to Fiji (see Plate tectonic map inFigure 1 from Wikipedia).Figure 1 Tectonic plates showing the Australian continent’s settingThe term intraplate is used here to identify areas not affected by interplate activity. The city ofAuckland on the North Island of New Zealand is near the edge of the Australian/Pacific Plateboundary. It may not strictly be classified as interplate or intraplate because the plate boundary iswide and dips under the city, giving rise to the Recent volcanoes there. Across the Tasman Sea, theseismicity and earthquake hazard in the Sydney Basin are typical of eastern Australia as a whole.Earthquake epicentres do not correlate clearly with mapped faults or broad geological features andtend to be broadly diffused with embedded clusters through a 300 km wide area paralleling thesoutheast coast of Australia. Discrete areal zones have been defined by some authors (Brown andGibson, 2000) for convenient hazard assessment but the history is very short, the first usefulseismographs not installed until 1909 at Riverview Observatory so the zone boundaries will changeas the seismicity patterns become better defined. There are many areas of continental Australia,particularly the western cratonic areas, that are more seismically active than the Sydney Basin.The larger well-located Sydney Basin earthquakes actually occur in Lachlan Foldbelt basementunderlying the Basin or near its interface with the Basin, the largest in the last 200 years, a modest58