Landslides in the Sydney Basin - Geoscience Australia

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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
Seismic Hazard in SydneyProceedings of the one day workshopclustered distribution of earthquakes particularly in the south-west of the basin at UpperBurragorang. The south-west cluster coincides with the occurrence of several large pre-Europeanlandslides. The age of the landslides however, precludes establishing a clear association. The onlylandslides to occur within the period of record do not show a consistent overlap in the timing offailure and are thought to be a direct response to underground coal mining. The largest magnitudeearthquakes on record (5.5 and 5.6), however, may not have been significant enough to trigger slopefailure. It may be that the larger, older landslides were triggered by higher magnitude events but weare unable to confirm this.ACKNOWLEDGMENTSThis contribution forms part of a collaborative research program with the Sydney CatchmentAuthority (2003/28).REFERENCESBembrick, C.S., Herbert, C., Scheibner, E., and Stuntz, J. 1973. Structural subdivision of the NewSouth Wales portion of the Sydney - Bowen Basin. Quarterly Notes of the Geological Surveyof NSW 11: 1-13.Berryman, K., and Stirling, M. 2003. Earthquake ground motion and fault hazard studies at theLucas Heights Research Reactor Facility, Sydney, Australia: evolution of methods andchanges in results. International Symposium on Seismic Evaluation of Existing NuclearFacilities, Vienna. August 2003, 43-47.Branagan, D.F., and Pedram, H. 1990. The Lapstone Structural Complex, New South Wales.Australian Journal of Earth Sciences 37: 23-36.Brunker, R.L., and Rose, G. 1967. Sydney Basin 1:500,000 Geological Sheet (Special). New SouthWales Department of Mines, Sydney.Cunningham, D.M. 1988. A rockfall avalanche in a sandstone landscape, Nattai North NSW.Australian Geographer 19 (2): 221-229.Dadson, S.J., Hovius, N., Chen, H., Dade, W.B., Hsieh, M.-L., Willett, S.D., Hu, J.-C., Horng, M.-J.,Chen, M.-C., Stark, C.P., Lague, D., and Lin, J.-C. 2003. Links between erosion, runoffvariability and seismicity in the Taiwan orogen. Nature 426: 648-651.Denham, D. 1976. Effects of the 1973 Picton and other earthquakes in Eastern Australia. Bulletin -Australia, Bureau of Mineral Resources, Geology and Geophysics 164: 15-27.Drake, L. 1974. The Seismicity of New South Wales. Journal and Proceedings of the Royal Societyof New South Wales 107: 35-40.— 1976. Seismic risk in New South Wales. Bulletin - Australia, Bureau of Mineral Resources,Geology and Geophysics 164: 5-8.Etheridge, R. 1893. Geological and ethnological observations made in the valley of the WollondillyRiver, at its junction near the Nattai River, counties Camden and Westmoreland. Records ofthe Australian Museum 2 (4): 46-54.Keefer, D.K. 1984. Landslides caused by earthquakes. Geological Society of America Bulletin 95:406-421.— 1994. The importance of earthquake-induced landslides to long-term slope erosion and slopefailurehazards in seismically active regions. Geomorphology 10: 265-284.Lithografica Artistica Cartographica 1979. Sydney and Environs 1:200,000 raised relief map. Geo-Maps Company, Sydney.Macris, J. 2002. Processes of Valley Slope Evolution; Evidence from the Western Blue Mountains,NSW. [Unpublished Honours thesis] Macquarie University, Sydney.McCue, K. 1999. The cause of current Australian intraplate volcanism. ACES Inaugural Workshop,31 January - 5 February 1999. Brisbane / Noosa, Queensland, Australia, 509-512.106
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Landslides in the Sydney Basin - Geoscience Australia

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