We present a seismic reflection section acquired across the western margin of the Lake George Basin near Geary's Gap which images the stratigraphy of the basin sediments and the interaction between faults and these sediments. When coupled with high resolution topographic data, key aspects of the evolution of the Lake George Basin may be deduced. The Lake George Basin formed as the result of west-dipping reverse faulting and associated fault propagation folding at the eastern margin of the Lake George Range in the interval between ca. 3.93 Ma and the present. Assuming that elevated gravels in Geary's Gap and to the west along Brooks Creek are correlative with similar lithology at the base of the basin (as suggested by previous workers), vertical displacement in the order of 250 m has occurred in this time interval. This is one of the larger rates of displacement recorded for an Australian intraplate fault, averaged over a timescale of several million years. Three prominent angular unconformities, separating packages of approximately parallel strata, indicate that deformation was episodic, with up to 1 million years separating active periods on the fault. The ~75 km active length of the Lake George Fault is consistent with a MW7.4 characteristic earthquake. An event of this magnitude has the potential to cause significant damage to the Australian Capital Territory, given that the surface trace of the fault approaches to within 25 km of Parliament House. Assuming periodic recurrence, a characteristic event might be expected every ~3040 kyr. However, the evidence for temporal clustering suggests that such events might be much more tightly spaced in time (perhaps by an order of magnitude) in an active period on the fault. This neotectonic activity is allied to the Late Pliocene to Pleistocene `Kosciuszko Uplift, which may be responsible for adding several hundred metres of relief to the Eastern Highlands of Australia. Few crustal fault systems which might have accommodated such large-scale uplift have yet been characterised. Consequently, the seismic hazard of the Eastern Highlands, which is based largely upon the short historic record of seismicity, is likely to be underestimated. Nearby candidate faults for similar activity include the Queanbeyan, Murrumbidgee, Shoalhaven, Crookwell, Mulwaree, Binda, Tawonga, Khancoban-Yellow Bog and Jindabyne faults.

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.

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.

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) aims to collect long period magnetotelluric (MT) sites on a 0.5 degree (~55 km) grid across the Australian continent. Data and models produced from this program will help to inform our understanding of Australia’s lithospheric architecture and tectonic processes. The New South Wales component of AusLAMP is a collaborative project between Geoscience Australia and the Geological Survey of New South Wales. This new dataset will add to the coverage of the Victorian and South Australian AusLAMP programs, which are both complete. This presentation is prepared for the Mines and Wines Conference, 2019, and details the progress of the AusLAMP NSW program. These include data, models and preliminary interpretations that are coming out of the program. Presentation for Discovery in the Tasmanides (Mines and Wines), Wagga Wagga, NSW, 25-28 September 2019 (https://smedg.org.au/events/)

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.

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.

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.

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.

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.

Paleoproterozoic arc and backarc assemblages accreted to the south Laurentian margin between 1800 Ma and 1600 Ma, and previously thought to be indigenous to North America, more likely represent fragments of a dismembered marginal sea developed outboard of the formerly opposing Australian-Antarctic plate. Fugitive elements of this arc-backarc system in North America share a common geological record with their left-behind Australia-Antarctic counterparts, including discrete peaks in tectonic and/or magmatic activity at 1780 Ma, 1760 Ma, 1740 Ma, 1710-1705 Ma, 1690-1670 Ma, 1650 Ma and 1620 Ma. Subduction rollback, ocean basin closure and the arrival of Laurentia at the Australian-Antarctic convergent margin first led to arc-continent collision at 1650-1640 Ma and then continent-continent collision by 1620 Ma as the last vestiges of the backarc basin collapsed. Collision induced obduction and transfer of the arc and more outboard parts of the Australian-Antarctic backarc basin onto the Laurentian margin where they remained following later breakup of the Neoproterozoic Rodinia supercontinent. North American felsic rocks generally yield Nd depleted mantle model ages consistent with arc and backarc assemblages built on early Paleoproterozoic Australian crust as opposed to older Archean basement making up the now underlying Wyoming and Superior cratons. Appeared in Lithosphere (2019) 11 (4): 551–559, June 10, 2019.