Legacy product - no abstract available

On 30 September 2009 a magnitude 7.6 earthquake struck West Sumatra. The earthquake significantly impacted the large coastal city of Padang with shaking estimated to be MMI 8. Widespread damage to buildings resulted and an estimated 1,117 lives in the Padang and Padang Pariaman Districts were lost. The Australia-Indonesia Facility for Disaster Reduction responded by supporting a team of Indonesian and international engineers and scientists who collected and analysed damage information that could subsequently be used for future disaster risk reduction in West Sumatra and Indonesia more broadly. The survey work had two primary aims. The first was to examine buildings in detail to identify the structural characteristics that may have contributed to their damage state. The second, activity was directed at systematically surveying complete populations of structures at a lower level of detail. The work was directed at the capture of statistically useful information on building performance. In total 3,896 buildings of all types and ages were surveyed. Buildings of all age categories were damaged and nominally engineered structures also suffered significant damage. Observations revealed poor structural configurations, poor detailing of reinforcement and the use of low quality construction materials. Vulnerability and fragility curves for building types well-represented in West Sumatra have been developed. The two survey strategies used, coupled with the post-survey activities, have provided knowledge of the nature of the built environment in Padang, its vulnerability to severe earthquakes, the factors behind this and how these can be effectively addressed through new and legacy construction.

We investigate two intraplate earthquakes in a stable continental region of southwest Western Australia. Both small-magnitude events occur in the top »1 km of crust and their epicenters are located with an accuracy of »100 m (1¾) using satellite Interferometric Synthetic Aperture Radar (InSAR). For the Mw 4.7 Katanning earthquake (10 October 2007) the average slip magnitude is 42 cm, over a rupture area of »1 km2. This implies a high stress drop of 14-27 MPa and, even for this very shallow earthquake, has important implications for regional seismic hazard assessment. The earthquake rupture extends from a depth of around 640 m to the surface, making it a rarely observed intraplate, surface-rupturing event. Using InSAR observations we estimate the coseismic slip distribution of the shallow earthquake, such estimates being rarely available for small magnitude events. For the Mw 4.4 composite Kalannie earthquake sequence (21-22 September 2005) we use a long-term time series analysis technique to improve the measurement of the co-seismic signal, which is a maximum of 27 mm in the line-of-sight direction. Double difference seismic analysis shows some relocated cluster seismicity which corresponds in timing, location and source parameters to the InSAR-observed deformation. This earthquake is the smallest magnitude seismic event investigated using InSAR and demonstrates the capability of the technique to provide important constraints on small-magnitude coseismic events. The shallow depth of both these events adds weight to the suggestion that earthquakes associated with tectonic processes in this area of Western Australia often initiate in the upper 1 km of crust.

An earthquake of magnitude 6.0-6.5 in the Sydney region of Australia is viewed by the global insurance community as one of the top 40 risks it faces worldwide from natural disasters . The high ranking of this perceived risk is due to the high population density, standards of construction and the level of insurance exposure in Sydney. Consequently, earthquake hazard and risk in Sydney is an important issue, and one that requires a focused and detailed study in order for the implications of such an earthquake to be fully understood. The presence of regolith (soils, sediments and weathered rock) can dramatically affect the level of ground shaking experienced during an earthquake. The relatively soft materials that constitute regolith tend to have low seismic velocities that amplify ground shaking during an earthquake, increasing the potential for damage to buildings and other infrastructure in the affected area. Therefore, models of the response of regolith to an earthquake (referred to as site response) form an integral part of any earthquake risk assessment. This report documents a preliminary study of potential ground motion amplification due to the regolith in the Botany area of Sydney, Australia. Botany was chosen due to the presence of a significant thickness of regolith and a high value and concentration of critical infrastructure. This report is intended to highlight the potential for significant levels of amplification within the study area, and draw attention to the need for more work on assessing the actual earthquake risk faced by the Sydney region. In order to determine the amount of ground motion amplification that could be seen in the Botany area, the regolith was classified into a series of four site classes. These regolith site classes are differentiated in terms of geotechnical properties that control ground shaking potential. This classification was based upon published and unpublished geotechnical data as well as seismic velocities obtained by Geoscience Australia. Once geotechnical models were defined for each regolith site class, amplification factors were calculated using a vertically propagating shear wave model. This model accounts for the softening and critical damping of the regolith column during large earthquakes. The results demonstrate that there is significant potential for amplification of ground shaking within the study area. For example, the site class that covers the vast majority of the study area has a maximum amplification factor greater than 3.0 at a fundamental site period of approximately 0.5 s. This period of motion would be expected to strongly affect the structures in the study area. The modelled amplification factors suggest that, should an earthquake impact the area, the potential for high levels of ground shaking would be dramatically increased due to the properties of the local regolith. An earthquake similar to the event experienced in Newcastle in 1989 was simulated, in order to demonstrate the potential amplification effect of the regolith during an earthquake. Whilst this simulation is in no way a full probabilistic risk analysis of the area, it does demonstrate that the amplification of ground shaking could cause response spectral accelerations in excess of 1.0 g, at periods of vibration that would be expected to cause damage to structures in the area. It is important to emphasise that this work is intended to provide a point of focus to initiate discussion rather than be a definitive seismic hazard assessment product. The results have been derived with limited geotechnical data, and without a detailed analysis of the uncertainties present within either the data or the modelling process. Nevertheless, this work does provide a starting point for recognising and addressing the potential risk that earthquakes pose to the study area.

The Australian Seismological Report 2012 provides a summary of earthquake activity for Australia for 2012. It also provides a summary of earthquakes of Magnitude 5+ in the Australian region, as well as an summary of magnitude 6+ earthquakes worldwide. It has dedicated state and territory earthquake information including: largest earthquakes in the year; largest earthquakes in the state; and tables detailing all earthquakes detected by Geoscience Australia during the year. There are also contributions from Department for Manufacturing, Innovation, Trade, Resources and Energy (DMITRE) and Environmental Systems & Services (ES&S) describing seismic networks and providing earthquake locations.

Legacy product - no abstract available

Legacy product - no abstract available

The Australian continent is actively deforming at a range of scales in response to far-field stresses associated with plate margins, and buoyancy forces associated with mantle dynamics. On the smallest scale (101 km), fault-related deformation associated with far-field stress partitioning has modified surface topography at rates of up to ~100 m / Myr. This deformation is evidenced in the record of historical earthquakes, and in the pre-historic record in the landscape. Paleoseismological studies indicate that few places in Australia have experienced a maximum magnitude earthquake since European settlement, and that faults in most areas are capable of hosting potentially catastrophic earthquakes with magnitudes in excess of 7.0. New South Wales is well represented in terms of its pre-historic earthquake record. Seismogenic faulting in the last 5-10 million years is thought to be responsible for locally generating up to 200 m of the contemporary topographic relief of the Eastern Highlands. Faults west of Sydney belonging to the Lapstone Structural Complex, and faults beneath the greater Sydney region, have been demonstrated to be associated with infrequent damaging earthquakes. . Decisions relating to the siting and construction of the built environment should therefore be informed with knowledge of the local neotectonics.

Legacy product - no abstract available

Legacy product - no abstract available