Landslides in the Sydney Basin - Geoscience Australia

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Seismic Hazard in SydneyProceedings of the one day workshopFigure 7: Map of peak ground velocity from the broadband simulation of the Puente Hillsrupture scenario. The largest simulated motions occur along the top edge of the rupture plane,and are the result of rupture directivity effects. These strong pulses of motion are channeleddirectly into the sediments of the Los Angeles basin and become trapped as basin generatedsurface waves. These large amplitude surface waves travel southward across the basin, givingrise to an elongated pattern of elevated PGV that extends across the basin. This patternresembles the pattern of ground shaking intensity from the 1987 Whittier Narrows earthquakeshown in Figure 4.would represent the Sydney Basin. Figures 5 and 7 show that the strongest ground motions wouldbe located around the surface trace of the Lapstone structure, due to rupture directivity effects. Theyalso show that there would be large ground motion amplitudes in the Sydney Basin, due to thetrapping of these strong directivity pulses by the thickening edge of the Sydney Basin.Particularly strong ground motion amplification can occur at the edge of a basin, if the basin has anabrupt edge caused by dip-slip faulting. The severe damage caused by the 1995 Kobe earthquake91
Seismic Hazard in SydneyProceedings of the one day workshopoccurred on the basin side of the fault, about 1 km from the fault that caused the earthquake. Thisnarrow band of damage has been attributed to basin edge effects (Pitarka et al., 1998) caused by theabrupt change in depth to crystalline basement (about 1 km) that occurs across the fault. An abruptincrease in depth to bedrock across the Santa Monica fault caused a similar basin edge effect duringthe 1994 Northridge earthquake (Graves et al., 1998). If there is an abrupt increase in depth tobedrock across the Lapstone Structure, then it could cause basin edge amplification effects in a zonewithin a few km to the east of the Lapstone Structure.REFERENCESDolan, J.F., S.A. Christofferson, and J.M. Shaw (2003). Recognition of paleoearthquakes on thePuente Hills Blind Thrust Fault, California. Science 300, 115-118.Graves, R. and A. Pitarka (2004). Broadband time history simulation using a hybrid approach.Proceedings of the 13 th World Conference on Earthquake Engineering, Vancouver, Canada,August 1-6, 2004, Paper No. 1098.Graves, R. W., A. Pitarka, and P. G. Somerville (1998). Ground motion amplification in the SantaMonica area: effects of shallow basin edge structure, Bull. Seism. Soc. Am., 88, 1224- 1242.Graves, R.W. (1996). Simulating earthquake ground motions in 3D elastic media using staggeredgridfinite-differences, Bull. Seism. Soc. Am. 86, 1091-1106.Hartzell, S., Liu, P., Mendoza, C. (1996). The 1994 Northridge earthquake: investigation of rupturevelocity, risetime, and high frequency radiation. J. Geophys. Res. 101, 20,091-20,108.Pitarka, A., K. Irikura, T. Iwata and H. Sekiguchi (1998). Three-dimensional simulation of the nearfaultground motion for the 1995 Hyogo-ken Nanbu (Kobe), Japan, earthquake. Bull. Seism.Soc. Am., 88, 428-440.Shaw, J.H., A. Plesch, J.F. Dolan, T.L Pratt, and P. Fiore (2002). Puente Hills blind-thrust system,Los Angeles, California. Bull. Seism. Soc. Am. 92, 2946-2960.Somerville, P.G., N.F. Smith, R.W. Graves, and N.A. Abrahamson (1997). Modification ofempirical strong ground motion attenuation relations to include the amplitude and durationeffects of rupture directivity, Seismological Research Letters, 68, 180-203.92
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Landslides in the Sydney Basin - Geoscience Australia

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