Long-term temporal and spatial patterns in large earthquake occurrence can be deduced from the Australian landscape record and used to inform contemporary earthquake hazard science. Seismicity source parameters such as fault slip-rates, large earthquake recurrence times and maximum magnitude vary across the continent, and can be interpreted within a framework of large-scale neotectonic domains defined on the basis of geology and crustal setting. While the suite of neotectonic fault behaviours may vary across Australia, as implied by the neotectonic domains model, one individual fault characteristic appears to be common to most Australian intraplate faults studied active periods comprising a finite number of events are separated by much longer periods of quiescence. Studies elsewhere in the world identify similar episodic behaviour on faults with low slip rates and suggest that the time between successive clusters of events (deformation phases) is highly variable but significantly longer than the times between successive earthquakes within an active phase. Furthermore, there is some indication that the temporal clustering behaviour emerging from single fault studies may be symptomatic of a larger picture of the more or less continuous tectonic activity from the late Miocene to Recent being punctuated by pulses of activity in specific, actively deforming regions. At present the underlying tectonic processes driving the observed variability in Australian seismicity are poorly understood. Questions remain as to whether stress accumulation and/or strain release is predictable, and at what scale. In this talk, we will outline some of the key challenges facing earthquake hazard scientists in Australia, and how these are being addressed.

Abstract for the Asia Oceania Geosciences Society (AOGS) conference on 24-28 June 2013.

In probabilistic seismic hazard modelling the choice of whether faults behave with Characteristic or Gutenberg-Richter recurrence statistics has a high impact on the hazard level. Compared to a model that does not include fault sources, the addition of a high slip rate (by intraplate standards) Characteristic fault results in a modest increase in hazard for a 500 years return period event, and a modest increase at longer return periods (i.e. ~2500 years). A Gutenberg-Richter fault with the same slip rate will result in a comparatively higher hazard at 500 years, similar hazard at 2500 years and a lower hazard a very long return periods (i.e. ~5000 years). Results from interplate and active intraplate paleoseismological investigations since the mid-1980s have been used to suggest that earthquakes recurrent on a given fault often have the same characteristic rupture length and amount of slip (i.e. a Characteristic Rupture Model). Stable asperities and barriers, which survive many earthquakes, are proposed to explain these results. The scarcity of data precludes definitive validation of the model in Australian Stable Continental Region crust. However, preliminary indications are that the Characteristic Rupture Model has some merit in cratonic regions of the country while faults in non-cratonic regions may behave in a more complex fashion.

Abstract: Compressional deformation is a common phase in the post-rift evolution of passive margins and rift systems. The central-west Western Australian margin, between Geraldton and Karratha, provides an excellent example of a strain gradient between inverting passive margin crust and adjacent continental crust. The distribution of contemporary seismicity in the region indicates a concentration of strain release within the Phanerozoic basins which diminishes eastward into the cratons. While few data exist to quantify uplift or slip rates, this gradient can be qualitatively demonstrated by tectonic landforms which indicate that the last century or so of seismicity is representative of patterns of Neogene and younger deformation. Pleistocene marine terraces on the western side of Cape Range indicate uplift rates of several tens of metres per million years, with similar deformation resulting in sub-aerial emergence of Miocene strata on Barrow Island and elsewhere. Northeast of Kalbarri near the eastern margin of the southern Carnarvon Basin, marine strandlines are displaced by a few tens of metres. A possible Pliocene age would indicate that uplift rates are an order of magnitude lower than further west. Relief production rates in the western Yilgarn Craton are lower still - numerous scarps (e.g. Mount Narryer) appear to relate individually to <10 m of displacement across Neogene strata. Quantitative analysis of time-averaged deformation preserved in the aforementioned landforms, including study of scarp length as a proxy for earthquake magnitude, has the potential to provide useful constraints on seismic hazard assessments in a region containing major population centres and nationally significant infrastructure.

On 23 March 2012 a MW 5.4 intraplate earthquake occurred in the eastern Musgrave Ranges of north-central South Australia, near the community of Ernabella (Pukatja). This was the largest earthquake recorded on mainland Australia in the past 15 years and resulted in the formation of a 1.6 km-long surface deformation zone that included reverse fault scarps with a maximum vertical displacement of ~0.5 m (average ~0.1 m), extensive ground cracking, and numerous rock falls. Fifteen months later, on 09 June 2013 a MW 5.6 earthquake (the Mulga Park earthquake) occurred ~15-20 km northwest of the 2012 rupture. The P-axes of the focal mechanisms constructed for both events indicate northeast-oriented horizontal compressive stress. However, the focal mechanism for the Mulga Park earthquake suggests strike-slip failure, with a sub-vertical northerly-trending nodal plane favoured as the failure plane, in contrast to the thrust mechanism for the 2012 event. Despite being felt more widely than the 2012 event, ground cracking and minor dune settlement were the only surface expressions relating to the Mulga Park earthquake. No vertical displacements were evident, nor were patterns indicative of a significant lateral displacement. An 18 km long north to north east trending arcuate band of moderate to high cracking density was mapped parallel to the surface trace of the Woodroffe Thrust, a major crust-penetrating fault system. A lobe of high-density cracking ~5km long, coincident with the calculated epicentral location, extended to the north from the centre of the main arc. We speculate that the rupture progressed to the south beneath the northern high-density lobe (consistent with the dimensions expected from new scaling relations), and that the larger arcuate band of cracking might relate to positive interference resulting from reflection of energy from the Woodroffe Thrust interface. Both events provide new insight into the rupture behaviour of faults in non-extended cratonic crust.

This release comprises the 3D geological model of the Yilgarn-Officer-Musgrave (YOM) region, Western Australia, as Gocad voxets and surfaces. The YOM 3D geological model was built to highlight the broad-scale crustal architecture of the region and extends down to 60 km depth.

Tectono-metallogenic systems are geological systems that link geodynamic and tectonic processes with ore-forming processes. Although fundamental geodynamic processes, which include buoyancy-related processes, crustal/lithospheric thinning and crustal/lithospheric thickening, have occurred throughout Earth's history, tectonic systems, which are driven by these processes, have evolved as Earth's interior has cooled. Although details remain controversial, tectonic systems are thought to have evolved from magma oceans in the Hadean through an unstable "stagnant-lid" regime in the earlier Archean into a proto-plate tectonic regime from the late Archean onwards. Modern-style plate tectonics is thought to have become dominant by the start of the Paleozoic. Although mineral systems with general similarities to modern or geologically recent systems have been present episodically through much of Earth's history, most of Earth's present endowment of mineral wealth was formed during and after the NeoArchean, when proto- or modern-style plate tectonic systems became increasinly dominant and following major changes in the chemistry of the atmosphere and hydrosphere. The characteristics of some mineral systems, such as the volcanic-hosted massive sulphide (VHMS) system, reflect these changes in tectonic style. Not only have tectono-metallogenic systems evolved in general over Earth's history, but specific tectono-metallogenic systems evolve over much shorter time frames. Most mineral deposits form in three general tectono-metallogenic systems: divergent systems, convergent systems, and intraplate systems. Although fundamental geodynamic processes have driven the evolution of these systems, their importance has changed as the systems evolved. For example, buoyancy-driven (mantle convection/plumes) and crustal thinning are the most important rocesses driving the early rift stage of divergent tectono-metallogenic systems, whereas buoyancy-driven processes (slab sinking) and crustal thickening are the most important processes during the subduction stage of convergent systems. Crustal thinning can also be an important process in the hinterland of subduction zones, producing back-arc basins than can host a number of mineral systems. As fundamental geodynamic processes act as drivers at some stage in virtually all tectonic systems, these cannot be used to identify tectonic systems. Moreover, as mineral systems are ultimately the products of these same geodynamic drivers, individual mineral deposits types cannot be used to determine tectonic systems, although mineral deposit assemblages can, in some cases, be indicative of the tectono-metallogenic system. Ore deposits are the products of geological (mineral) systems that operate over a long time frame (hundreds of millions of years) and at scales up to the craton-scale. In essence, mineral systems increase the concentrations of commodities through geochemical and geophysical processes from bulk Earth levels to levels amenable to economic mining. Mineral system components include the geological (tectonic and architectural) setting, the driver(s) of mineralising processes, metal and fluid sources, fluid pathways, depositional trap, and post-depositional modifications. All of these components link back to geodynamic processes and the tectonic system. For example, crustal architecture, which controls the spatial distribution of, and fluid flow, within mineral systems, is largely determined by geodynamic processes and tectonic systems, and the timing of mineralisation, which generally is relatively short (commonly < 1 Myr), correlates with local and/or far-field tectonic events.

This short video by the Geoscience Australia Education Team is targeted at upper primary students but is suitable for a wider audience. It introduces the concept of tectonic plates making use of a tectonic plates puzzle. Students are asked to predict the direction and speed of plate movement and consider where and why earthquakes happen on the Australian Plate. It is an introduction to major concepts of Earth science delivered in a light-hearted manner with an interactive presentation style.

The Cadell Fault, found in stable continental region (SCR) crust in southeastern Australia, provides a record of temporally clustered morphogenic earthquakes spanning much of the Cenozoic. The slip rate, averaged over perhaps as many as five complete seismic cycles in the period 70–20 ka, is c. 0.4–0.5 mm/a, compared with an average rate of c. 0.005–0.01 mm/a over the period spanning the late Miocene to Recent. If full length rupture of the 80 km long feature is assumed, the average recurrence for Mw 7.3–7.5 earthquake events on the Cadell Fault in the period 70–20 ka is c. 8 kyr. About 20 kyr, representing more than two average seismic cycles, have lapsed since the most recent morphogenic seismic event on the fault. It might therefore be speculated that this fault has relapsed into a quiescent period. Episodic rupture behaviour on the Cadell Fault, and nearby faults in Phanerozoic SCR crust in eastern Australia, might be controlled by their linkage into major crustal fault systems at depth, in apparent contrast with the style of deformation in non-extended Precambrian SCR crust. Periods of strain localization on these major crustal fault systems, effectively turning deforming regions ‘on’ and ‘off’, might be influenced by changes in distant plate boundary forces. If proved, this would have profound consequences for how the occurrence of large earthquakes is assessed in Australia, as the fundamental assumption of morphogenic earthquakes occurring as a result of the progressive build-up of strain, and thus being in some way predictable in their periodicity, is not satisfied. Documenting such fault behaviour in SCR crust assists in conceptualizing the points critical to understanding the hazards posed by SCR faults worldwide.

The Geoscience Australia Structural Measurements Database contains field measurements of geological structure features such as bedding, foliation, lineation, faults and folds from field sites, measured sections, and boreholes. The database is delivered as a layer in Geoscience Australia's "Geological Field Sites, Samples and Observations" web service.