Landslides in the Sydney Basin - Geoscience Australia

Seismic Hazard in SydneyProceedings of the one day workshopBASIN GENERATED WAVESMany urban regions are situated on deep sediment-filled basins. A basin consists of alluvialdeposits and sedimentary rocks that are geologically younger and have lower seismic wavevelocities than the underlying rocks upon which they have been deposited. Basins have thicknessesranging from a hundred meters to over ten kilometers. Conventional criteria for characterizing siteresponse are typically based on the distribution of shear wave velocity with depth in the upper 30meters as determined from field measurements. The response of this soil layer is usually modeledassuming horizontal layering, following the method illustrated on the left of Figure 2. The wave thatenters the layer may resonate in the layer but cannot become trapped within the layer.Figure 2. Schematic diagram showing that seismic waves entering a sedimentary layer frombelow will resonate within the layer but escape if the layer is flat (left) but become trapped inthe layer if it has varying thickness and the waves enter it through its edge (right).86