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 contemporary crustal stress regime in south-eastern Australia can be traced back to the terminal Miocene. Increased coupling of the Australian and Pacific Plate boundary at this time resulted in regional-scale tilting, local uplift and erosion, and in the formation of unconformities in southern Australian basins. In the onshore Gippsland Basin the unconformity surface is overlain by an extensive sheet of fluvial sediment known as the Haunted Hill Formation (HHF). Open folds and flexures developed within the HHF over blind reverse and reverse oblique faults provide a record of deformation spanning much of the neotectonic period. The predominance of flexures and folds rather than discrete faulting at the surface complicates the assessment of slip rates over the last few seismic cycles. However, ages from an undeformed fill terrace bordering the Morwell River and crossing the Morwell Monocline suggest that it has been a minimum of 70 ka since the last deformation event on at least this structure. Stream profiles crossing the Snake Ridge, Yallourn and Rosedale Monoclines similarly reveal no evidence for recent tectonic displacement. Cosmogenic radionuclide (10Be and 26Al) burial ages of siliceous sediments sampled from tectonically uplifted HHF on the Yallourn, Morwell and Snake Ridge Monoclines provide constraint on the long-term evolution of these structures. Combined with stratigraphic and tectonic records from the offshore Gippsland Basin, these data provide a basis for informed seismic hazard assessment.

A deep seismic reflection profile and coincident refraction and magnetotelluric data were acquired across the northern Eyre Peninsula, Gawler Craton in 2008 to enhance the prospectivity of the Gawler Craton for uranium and geothermal energy, by establishing the regional geodynamic framework and improving our understanding of the crustal architecture. The seismic line crossed the western boundary of a region of elevated surface heat flow, termed the South Australian Heat Flow Anomaly (SAHFA). This broad zone correlates with elevated surface heat production values, predominantly associated with high heat producing granites, and thus the boundary is an isotopic and geochemical boundary. The seismic line crosses several tectonic domain boundaries in the Gawler Craton, including between the Archaean core of the craton and younger domains to the east and west. It also crossed the Kalinjala Shear Zone, which is a key structure in the southern and central Gawler Craton, defining a boundary between Hutchison Group sedimentary rocks and Donington Suite granites in the south. In the vicinity of the seismic section, this shear zone dips moderately to the east and appears to be a major crustal-scale fault which cuts through to the Moho; it separates mid to lower crust of differing seismic reflectivity, with strong reflectivity west of the fault, and a lower reflectivity to the east. The upper crust appears to be dominated by a series of thin-skinned thrust faults, most of which dip to the east. The seismic line also crossed the boundary between the Olympic Fe-oxide Cu-Au-U Province (host of Olympic Dam and Prominent Hill deposits) in the east, and the Central Gawler Au Province in the west, and tested the difference in crustal architecture between the two mineral provinces.

Faults of the Lapstone Structural Complex (LSC) underlie 100 km, and perhaps as much as 160 km, of the eastern range front of the Blue Mountains, west of Sydney. More than a dozen major faults and monoclinal flexures have been mapped along its extent. The Lapstone Monocline is the most prominent of the flexures, and accounts for more than three quarters of the deformation across the complex at its northern end. Opinion varies as to whether recent tectonism, or erosional exhumation of a pre-existing structure, better accounts for the deeply dissected Blue Mountains plateau that we see today. Geomorphic features such as the abandoned meanders at Thirlmere Lakes illustrate the antiquity of the landscape and favour an erosional exhumation model. According to this model, over-steepened reaches developed in easterly flowing streams at the Lapstone Monocline when down-cutting through shale reached more resistant sandstone on the western side of the LSC. These over-steepened reaches drove headward (westerly) knick point retreat, ultimately dissecting the plateau. However, a series of swamps and lakes occurring where small easterly flowing streams cross the westernmost faults of the LSC, coupled with over-steepened reaches 'pinned' to the fault zones in nearby larger streams, imply that tectonism plays a continuing role in the development of this landscape. We present preliminary results from an ongoing investigation of Mountain Lagoon, a small fault-bound basin bordering the Kurrajong Fault in the northern part of the LSC.

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 strain partitioning between inverting passive margin crust and adjacent oceanic and continental crust. The distribution of contemporary seismicity in the region indicates a concentration of strain release within the basins diminishing eastward into the cratons. Very few data exist to quantify uplift or slip rates, however this pattern 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. In the southern Carnarvon Basin, marine strandlines of unknown age are displaced by a few tens of metres, indicating uplift rates an order of magnitude lower than further west. Relief production rates in the western Yilgarn Craton are lower still - numerous scarps (e.g. Mt Narryer) appear to relate individually to <10 m of displacement across Neogene strata. The en echelon arrangement of such features distinguish them from those representing strain concentration in the craton proper, where scarps are isolated and typically <5 m high. 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 constraint on seismic hazard assessments in a region which contains major population centres and nationally significant infrastructure.

Seismic line 07GA-IG1, described here, forms part of the Isa-Georgetown-Charters Towers seismic survey that was acquired in 2007. The seismic line is oriented approximately northeast-southwest and extends from northwest of Cloncurry in the southwest to east of Croydon in the northeast (Figure 1). The acquisition costs for this line were provided jointly by Geoscience Australia and the Geological Survey of Queensland, and field logistics and processing were carried out by the Seismic Acquisition and Processing team from Geoscience Australia. Six discrete geological provinces have been interpreted on this seismic section (Figure 2). Two of these, the Numil and Abingdon Provinces, only occur in the subsurface. The Mt Isa Province occurs in the southwest, with the Kowanyama Province occurring on the middle of the section and the Etheridge province in the northeast. The Millungera Basin, first observed on two seismic lines in the 2006 Mt Isa seismic survey, occurs beneath shallow cover of the Jurassic-Cretaceous Carpentaria Basin and sits above the Kowanyama Province.

This is a combined metamorphic and strain map of the Eastern Yilgarn Craton. Inset maps of different phases of metamorphism are also shown. <p>Related material<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=68806">Metamorphic Evolution and Integrated Terrane Analysis of the Eastern Yilgarn Craton: Rationale, Methods, Outcomes and Interpretation</a> - Geoscience Australia Record 2009/023.</p>

Neotectonic faulting and uplift has previously been described from field evidence in higher relief erosional areas in far northwest NSW. In this study, airborne electromagnetics (AEM) and high resolution LiDAR datasets were used to identify buried neotectonic features in the Lower Darling Floodplain and adjacent lowlands. The AEM data (acquired over an area of 7,500 sq km and validated by 100 new boreholes) reveal that the top surface of the ?Late Pliocene to Pleistocene Blanchetown Clay, a widespread lacustrine fine grained unit deposited in palaeo Lake Bungunnia, has an undulating to sharply offset surface. Gridding of closely spaced points on AEM flight line sections suggests that it has been affected by local warping and faulting, as well as regional tilting due to basin subsidence or margin uplift. Local relief reaches 20m, with small highs and lows apparently controlled by networks of closely spaced intersecting faults that are mostly expressed as warps in the near surface. Across the entire area, the top of the Blanchetown Clay varies in elevation from 20 to 80 m AHD. Some of the up-warped areas are associated with local landscape highs, but most structures have no apparent surface expression. However, the Darling River and its anabranches (Talyawalka, Charlie Stones and Tandou Creeks, and the Great Darling Anabranch) follow zones of local structural lows, and some of the interpreted faults are echoed by linear river reaches and terrace edges interpreted from LiDAR DEM and satellite imagery. Geomorphic mapping and dating of scroll-bar sediments suggest that the main course of flow of the Darling River system has previously flipped between two preferred courses (the modern Darling, and a course following Talyawalka Creek/Tandou Creek/Redbank Creek/Great Darling Anabranch). This newly discovered structural control explains why the Lower Darling channel has apparently not migrated across the entire floodplain.

Understanding the nature of intraplate earthquakes in the South West Seismic Zone (SWSZ) in Western Australia, one of the most seismically active areas in Australia, has long been the focus of many scientists and has important implications for seismic hazard assessment. In order to measure the present-day surface deformation and the strain distribution in the SWSZ, a dense GPS network of 48 sites with an average inter-station separation of 50 km was established. To date, three campaigns have been conducted and analysed. The measurements made in 2002 and 2006 included observations of all 48 sites within the SWSZ, while only the core stations were observed in the 2004 campaign. Each site was observed for a minimum of four days. The daily solutions have repeatabilities of about 1-2 mm and 3-4 mm, in the horizontal and vertical components respectively, in each campaign. The campaigns, spanning four years, show no statistically significant interior horizontal motions at the sites, at the 95% confidence level with respect to the stable Australian plate, which sets an upper bound of 0.46 mm/yr at the 95% confidence level on the horizontal motion in the SWSZ region. Analysis of the geodetic strain between sites indicates the maximum likely average regional linear strain rates to be between 1.0×10-9/yr and 1.0×10-8/yr across the around 200km width of the SWSZ, with the azimuth of the axis of relative contraction being 133±21 degrees (95% confidence level), which is nearly orthogonal to the NNE direction of the Australian plate velocity. These findings are in general agreement with the geological, geodetic and seismic evidences, which themselves are discrepant. Future repeat occupations are expected to reduce the uncertainties and shed light on the apparent inconsistency between seismic and geological evidence.

Ongoing developments in geodetic positioning towards greater accuracies with lower latency are now allowing the measurement of the dynamics of the Earth's crust in near real time. However, in the Australian circumstance a sparsity of geodetic infrastructure has limited the application of modern, geodetic science to broader geoscience research programs. Recent enhancements to the Australian geodetic infrastructure, through the AuScope initiative, offer opportunities for research into refinement of geodetic accuracies, as well as their application to measuring crustal deformation.