Landslides in the Sydney Basin - Geoscience Australia

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Seismic Hazard in SydneyProceedings of the one day workshopinstrumentation used had limited dynamic range so would go full-scale for even moderate magnitudeearthquakes, so shear wave arrivals could not be read, and these events could not be locatedprecisely. The instrumentation had very limited seismic wave frequency bandwidth, limiting timingprecision and making earthquake magnitude estimates very difficult.Figure 2: Sydney region earthquakes, 1993 to 2005.Since 1992, most events larger than magnitude ML 1.5 can be located to a precision of a fewkilometres or better, including depth. The distinctive seismic character of shallow events(earthquakes, blasts and coal mine collapses) within the Mesozoic sediments of the Sydney Basin51
Seismic Hazard in SydneyProceedings of the one day workshopare very characteristic, making discrimination of earthquakes and blasts much easier. It is stillpossible that some shallow earthquakes have been mis-identified as a blast or coal mining collapse.Sydney Region Earthquake DepthsBefore 1992, earthquake depths were very difficult to determine with accuracy. For example, theBurragorang earthquakes of 1971 were located at all depths from near-surface to over 30 km, andappear in the cross-section as a vertical band. In reality the depths were probably only spread over arange of a few kilometres, probably at a depth of about 12 to 15 km. Some poorly constrainedearthquakes before 1992 were assigned depths at the surface, while others were located at depths of30 km or more. Earthquakes outside a network often locate too deep.Figure 3: Sydney region earthquakes with study area for sections delineated.Since 1992, there has been a significant improvement in earthquake location accuracy, especially fordepths. Almost all of the events that were positively identified as earthquakes are near or west of thesurface outcrop of the Lapstone Fault indicating that this fault system is active. The Lapstone Faultis the largest identified contributor to seismic hazard in the Sydney Region. Most of the earthquakes52
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Landslides in the Sydney Basin - Geoscience Australia

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