earthquakes
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Based upon a structural model for the LSC involving a large west-dipping thrust fault beneath the Lapstone Monocline, a recent study of seismic hazard in the Sydney Basin identified the LSC as a potential source for large and damaging earthquakes, and estimated a recurrence for MW >7.0 events at 15-30 ka (IGNS, 1999). The preliminary results presented here from Mountain Lagoon, a small lake abutting the Kurrajong Fault, indicate that only 15m of fault displacement has occurred since the catchments upstream became too dissected to generate significant fluvial flow. A qualitative assessment of the time required to reconstruct the catchment to a size where a sandstone fault barrier could be eroded suggests that the observed displacement is all that has occurred in the last several million years or more. This indicates potential recurrence rates for large earthquakes are, on average, in the order of hundreds of thousands of years or more.
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A bullentin outlining the seismicity and earthquake risk in Eastern Australia. The topics covered include:The Structure of the Crust and Upper Mantle Beneath Southeastern Australia. Seismic Risk in New South Wales. Geological Appreciation of the Seismicity of the Southern Portion of the Sydney Basin . The Picton Earthquake of 9 March 1973: A Seismic View of the Source. Effects of the 1973 Picton and Other Earthquakes in Eastern Australia Appendix 1: Claim Details Provided by the Fire and Underwriters Association of New South Wales. Some Structural Damage Caused by the 1973 Picton Earthquake. Seismotectonics of South Australia and Earthquake Trends. The Eden Fault and Its Effect on the Development of Adelaide. Progress Report on Seismic Zoning in Australia. Dynamic Response of Black Mountain Tower to Estimated Ground Motions. Seismic Considerations Affecting the Safety of Nuclear Plant. The Role of Local Geology in Seismic Intensity Predictions. Seismic Effects on Nuclear Power Plants The Effect of Large Dams on Earthquake Risk.
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This Atlas of isoseismal maps of Australian earthquakes contains the results of the ground intensity effects from all known Australian earthquakes for which adequate documentation is available. A total of 83 isoseismal maps are presented for 70 Australian earthquakes. The Atlas is arranged with each isoseismal map presented in chronological order, facing a page containing a brief description of the earthquake and the methods used to obtain the intensity data. References to the source of the map and to other publications that contain information on the earthquake's intensity are also given. The earliest map is from the July 1883 Mount Barker (SA) earthquake and the most recent from the November 1981 Suggan Buggan (NSW) earthquake. The largest recorded earthquakes from the Australian continent have occurred in Western Australia. These were the 1941 Meeberrie and 1968 Meckering events, which have magnitudes of about ML 7, and were felt at distances of about 900 and 800 kilometres from their respective epicentres. In South Australia, the 1897 Beachport earthquake (magnitude 6.5) produced the greatest shaking and was felt about 600 kilometres from the epicentre; in eastern Australia, the 1935 Gayndah (Qld), 1961 Robertson-Bowral (NSW), and 1973 Picton (NSW) earthquakes were felt out to about 400 kilometres and the 1918 Bundaberg (Qld) earthquake was felt at distances of about 650 km. The 1968 Meckering and June 1979 Cadoux earthquakes produced the highest observed ground shaking. Intensities of MM IX were experienced, and fault scarps, with throws of about a metre, extended over several kilometres for each earthquake. Intensities of MM VIII were recorded for the 1897 Beachport, 1902 Warooka, 1941 Meeberrie, 1949 Dalton-Gunning, and 1954 Adelaide earthquakes. Total damage caused by the June 1979 Cadoux earthquake was 3.8 million dollars (1979 prices) and the 1968 Meckering earthquake, 2.2 million dollars (1968 prices). The 1954 Adelaide earthquake caused 4 million pounds damage at 1954 prices.
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GPR data have been collected across confirmed palaeofault scarps at Hyden and Dumbelyung, and also the scarp created by the 1968 Meckering earthquake. In each case there is a nearby trench to allow GPR responses to be related to known geology. At Meckering and Hyden, where the near-surface material contains moderate amounts of clay and the groundwater is fresh, it has proved possible to collect high quality data that images colluvium and also disrupted bedrock features which allow faults to be inferred. At Dumbelyung, where the near surface is more conductive due to clay-rich alluvial deposits and saline groundwater, results were poor and no sub-surface features were confidently identified. Our results demonstrate that, subject to the satisfaction of a predictable set of ground conditions, GPR surveys are a valuable tool for studying palaeofaults in deeply weathered terrains. The results provide sufficient information to confirm a topographic feature is of seismic origin, and to aid in siting trenches for palaeoseismic studies.
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Recent earthquake disasters in Indonesia, such as the 2006 Yogyakarta (Mw 6.3, 5749 deaths) and the 2009 Padang (Mw 7.5, over 1100 deaths) earthquakes, together with a long history of earthquake occurrence suggesting the potential for even more lethal disasters in the future, highlight an urgent need for measures to reduce earthquake fatalities. Better land use planning, emergency management training based on credible earthquake scenarios, and improved building codes are all effective means for reducing earthquake fatalities, but these all need to be underpinned by a reliable earthquake hazard assessment. Moreover, a robust and sustainable process for periodically updating such assessments is needed in order to keep pace with developments in Indonesian geology and seismology that are rapidly improving the level of knowledge of earthquake occurrence and the propagation of seismic waves.
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The paucity of ground-motion data in Stable Continental Regions (SCRs) remains a key limitation when developing relations that seek to predict effects of strong ground-shaking from large damaging earthquakes. It is desirable to combine data from more than one SCR in order to increase database size, but this raises questions as to whether the source and attenuation properties of the SCRs are equivalent. We merge recently - compiled spectralamplitude databases from small-to-moderate events (moment magnitudes 2.0< - 5.0<) in both southeastern Australia and eastern North America in order to compare the key characteristics of ground motion in these two regions. Both are SCRs, but are widely separated, spatially and in tectonic history.