Proceedings of a conference held by the Australian Earthquake Engineering Society and Specialist Group on Solid-Earth Geophysics at Eagle House, Institution of Engineers, 25 September 1992 Sydney, New South Wales.

Stress Tensor reconstructions are presented for seven domains withinthe Australian crust based on formal inversion of four or more earthquake focal mechanisms in close geographic proximity. The data for inversion was sourced from a set of sixty-nine quality-ranked focal mechanisms forming part of the recently compiled AGSO focal mechanism database. When analysed in conjunction with in situ stress data held by the Australian Stress Map project, the new data makes possible for the first time a rigorous comparison of the Australian continental stress field at near-surface and seismogenic depths. A more complete picture of the character of the Australian intraplate stress field is thereby made available. The tensor data agrees well with in situ determinations in western, northern and far southeastern Australia suggesting that the continental stress field is homogeneous between shallow and seismogenic depth in these areas. Plate boundary forces are considered to be the dominant source of stress. In contrast, the results for the Sydney Basin and Flinders Ranges imply significant heterogeneity and influence by more localised sources of stress.

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.

The occurrence of the Indian Ocean Tsunami on 26 December, 2004 has raised concern about the difficulty in determining appropriate tsunami mitigation measures in Australia, due to the lack of information on the tsunami threat. A first step in the development of such measures is a tsunami hazard assessment, which gives an indication of which areas of coastline are most likely to experience tsunami, and how likely such events are. Here we present the results of a probabilistic tsunami hazard assessment for Western Australia (WA). Compared to other parts of Australia, the WA coastline experiences a relatively high frequency of tsunami occurrence. This hazard is due to earthquakes along the Sunda Arc, south of Indonesia. Our work shows that large earthquakes offshore of Java and Sumba are likely to be a greater threat to WA than those offshore of Sumatra or elsewhere in Indonesia. A magnitude 9 earthquake offshore of the Indonesian islands of Java or Sumba has the potential to significantly impact a large part of the West Australian coastline. The level of hazard varies along the coast, but is highest along the coast from Carnarvon to Dampier. Tsunami generated by other sources (e.g. large intra-plate events, volcanoes, landslides and asteroids) were not considered in this study, which limits our hazard assessment to recurrence times of 2000 years or less.

We have run several thousand tsunami propagation models in order to determine the effect of uncertainty in an earthquake's rupture parameters (specifically strike, dip, rake, depth and magnitude) on the maximum wave height of the tsunami that it creates. We have shown that even for the simple case of a tsunami propagating over flat bathymetry, the Coefficient of Variation (CoV) of the maximum wave height was a complex function of the choice of rupture parameter, distance and azimuth. For example, if the strike of the fault was varied, the CoV was at maximum on either side of the tsunami beam, but if the dip was varied the CoV was at a maximum along the strike of the rupture. We then created maps of the skewness of the distribution of the maximum wave height. They also showed a complex dependence on the choice of the rupture parameter, azimuth and distance. Finally, we have examined the effect of a realistic bathymetry on CoV and skewness by mapping them for three hypothetical earthquakes on different types of subduction zones (Kermadec, Java and the Solomon Islands). These examples showed that the areas of shallow bathymetry in either the local or far field can also make a significant difference to both the CoV and skewness of the distribution of maximum tsunami wave heights at a point.

The Australian Seismological Report 2008 provides a summary of earthquake activity for Australia for 2008. 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 Gary Gibson and Environmental Systems and Services describing Seismic Networks and providing Earthquake locations.

Probabilistic seismic hazard analyses in Australia rely fundamentally on the assumption that earthquakes recorded in the past are indicative of where earthquakes will occur in the future. No attempt has yet been made to assess the potential contribution that data from active fault sources might make to the modelling process, despite successful incorporation of such data into United States and New Zealand hazard maps in recent years. In this paper we review the limited history of paleoseismological investigation in Australia and discuss the potential contribution of active fault source data towards improving our understanding of intraplate seismicity. The availability and suitability of Australian active fault source data for incorporation into future probabilistic hazard models is assessed, and appropriate methodologies for achieving this proposed.

Through Australian Department of Foreign Affairs and Trade, Geoscience Australia has been working closely with the Government of Papua New Guinea technical agencies (Rabaul Volcano Observatory, Port Moresby Geophysical Observatory, and Engineering Geology Branch) since September 2010 to enhance their capabilities to monitor and assess natural hazards. The objective of this program is to support the Government of Papua New Guinea in developing fundamental information and practices for the effective response and management of natural hazard events in PNG. Earthquakes as natural hazards are one of the key focus points of this project, as they continue to cause loss of life and widespread damage to buildings and infrastructure in Papua New Guinea. The country’s vulnerability to earthquakes is evident from the significant socio-economic consequences of recent major events in Papua New Guinea, e.g., a magnitude 7.5 earthquake that occurred in the Hela Province of Papua New Guinea in 2018. Earthquake risk is likely to increase significantly in the years to come due to the growth in population and urbanization in Papua New Guinea. However, earthquake risk, unlike hazard, can be managed and minimized. One obvious example would be minimizing earthquake risk by constructing earthquake-resistant structures following building standards. The high level of earthquake hazard of Papua New Guinea has been long recognised and the suite of building standards released in 1982 contained provisions to impart adequate resilience to buildings based on the best understanding of seismic hazard available at that time. However, the building standards and incorporated seismic hazard assessment for Papua New Guinea has not been updated since the 1980s. The integration of modern national seismic hazard models into national building codes and practices provides the most effective way that we can reduce human casualties and economic losses from future earthquakes. This report aims at partially fulfilling this task by performing a probabilistic seismic hazard assessment to underpin a revision of the earthquake loading component of the building standards of Papua New Guinea. The updated assessment offers many important advances over its predecessor. It is based on a modern probabilistic hazard framework and considers an earthquake catalogue augmented with an additional four decades-worth of data. The revised assessment considers advances in ground-motion modelling through the use of multiple ground-motion models. Also, for the first time, the individual fault sources representing active major and microplate boundaries are implemented in the input hazard model. Furthermore, the intraslab sources are represented realistically by using the continuous slab volume to constrain the finite ruptures of such events. This would better constrain the expected levels of ground motion at any given site in Papua New Guinea. The results suggest a high level of hazard in the coastal areas of the Huon Peninsula and the New Britain–Bougainville region, and a relatively low level of hazard in the southern part of the New Guinea Highlands Block. In comparison with the seismic zonation map in the current design standard, it can be noted that the spatial distribution used for building design does not match the bedrock hazard distribution of this study. In particular, the high seismic hazard of the Huon Peninsula in the revised assessment is not captured in the current seismic zoning map, leading to a significant under-estimation of hazard in PNG’s second-largest city, Lae. It can also be shown that in many other regions and community localities in PNG the hazard is higher than that regulated for the design of buildings having a range of natural periods. Thus, the need for an updated hazard map for building design has been confirmed from the results of this study, and a revised map is developed for consideration in a revised building standard of Papua New Guinea.

Since the 2004 Sumatra-Andaman Earthquake, understanding the potential for tsunami impact on coastlines has become a high priority for Australia and other countries in the Asia-Pacific region. Tsunami warning systems have a need to rapidly assess the potential impact of specific events, and hazard assessments require an understanding of all potential events that might be of concern. Both of these needs can be addressed through numerical modelling, but there are often significant uncertainties associated with the three physical properties that culminate in tsunami impact: excitation, propagation and runup. This talk will focus on the first of these, and attempt to establish that seismic models of the tsunami source are adequate for rapidly and accurately establishing initial conditions for forecasting tsunami impacts at regional and teletsunami distances. Specifically, we derive fault slip models via inversion of teleseismic waveform data, and use these slip models to compute seafloor deformation that is used as the initial condition for tsunami propagation. The resulting tsunami waveforms are compared with observed waveforms recorded by ocean bottom pressure recorders (BPRs). We show that, at least for the large megathrust earthquakes that are the most frequent source of damaging tsunami, the open-ocean tsunami recorded by the BPRs are well predicted by the seismic source models. For smaller earthquakes, or those which occur on steeply dipping faults, however, the excitation and propagation of the resulting tsunami can be significantly influenced by 3D hydrodynamics and by dispersion, respectively. This makes it mode difficult to predict the tsunami waveforms.

The Indian Ocean Tsunami of December 26, 2004 made starkly evident the need for better information on tsunami hazard in the Indian Ocean. The tsunami threat faced by Indian Ocean countries consists of a complex mix of tsunami from local, regional and distant sources, whose effects at any particular location in the Indian Ocean are highly dependent on variations in sea floor shape between the source and affected coastlines, complicating tsunami disaster management and the design of tsunami warning systems for the Indian Ocean. In order to provide national governments in the Indian Ocean with the information they need to make informed decisions about tsunami mitigation measures, including development of a warning system, a comprehensive hazard and risk ass In this presentation we discuss the results of this assessment. The study focused on tsunami caused by subduction zone earthquakes, because they are the most frequent source of large tsunami, and tsunami hazard is expressed as annual probability of a tsunami exceeding a given amplitude at a given offshore depth. Because so little is known about the recurrence rates of large megathrust earthquakes in the subduction zones bordering the Indian Ocean, it was decided to develop two hazard maps: a 'low-hazard' end member, based on only those earthquake sources of tsunami for which there is definite evidence, and a 'high-hazard' end member, based on all potential megathrust earthquake sources, including hypothetical ones for which there is no historical or geological evidence, that may affect Indian Ocean coastlines. The actual hazard lies somewhere between these two end members, and the difference between the low hazard and high hazard maps is a simple and effective way to express the uncertainty in the hazard assessment. This uncertainty reflects the lack of knowledge of tsunamigenic earthquake occurrence, and can only be reduced through a better understanding of earthquake and tsunami occurrence in the Indian Ocean.