Landslides in the Sydney Basin - Geoscience Australia

Seismic Hazard in SydneyProceedings of the one day workshoplandslide (Tumbledown) is around 1,000 – 2,500 years, which is consistent with the return period ofan earthquake of magnitude 6 - 6.5 (see Appendix 1 for details). The estimated return period of a 30M m 3 landslide (Carne) is around 20 – 50 kyr, which is consistent with the return period of anearthquake of magnitude 7.5 or greater. Therefore, it is possible that higher magnitude earthquakesmay explain the occurrence of the larger, older landslides and the absence of earthquake inducedlandslides since European settlement where maximum recorded earthquake magnitude was 5.5(Burragorang) and 5.6 (Robertson).Figure 4: Detail of the south-west cluster of seismic events (Latitude -34.1 to -34.25; Longitude150.25 to 150.45) showing the location of the Burragorang earthquake epicentre. (Source:Geoscience Australia Earthquake Database http://www.ga.gov.au/oracle/quake/quake_online.jsp)Table 1: Timing, depth and magnitude of earthquakes within the south-west cluster (Latitude -34.1to -34.25; Longitude 150.25 to 150.45) Source: Geoscience Australia Earthquake Databasehttp://www.ga.gov.au/oracle/quake/quake_online.jsp)DATE OF EARTHQUAKE DEPTH (KM) MAGNITUDE NOTES02/09/1960 10 1.723/06/1962 0 1.910/07/1962 8 3.209/03/1973 21 5.5 Burragorang / Picton earthquake09/03/1973 to 23/07/1973 Max 38 Max 3.9 Aftershocks16/11/1974 0 1.206/03/1975 0 1.518/08/1976 16 2.426/01/1978 17 2.315/01/1979 24 2.819/04/1979 20 216/03/1982 23 2.231/12/1982 19 215/02/1986 24 1.702/04/1987 22 2.706/06/1996 20 2.526/06/2001 10 1.9CONCLUSIONSLandsliding may be an important process in valley widening and hillslope denudation of the incisedvalleys in the Blue Mountains Plateau, though the conditions or triggers of failure have not beendetermined. Earthquakes have been found to trigger landslides in Europe and elsewhere, andtherefore warrant consideration. Analysis of seismic records for the Sydney Basin revealed a105