School of Geography, Earth and Atmospheric Sciences - Research Publications
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ItemBayesian analysis of ground motion models using chimney fragility curves: 2021, 5.9-Mw Woods Point intraplate earthquake, Victoria, Australia(SAGE Publications, 2024-02-01)The 22 September 2021 (AEST) MW 5.9 Woods Point earthquake occurred in an intraplate setting (southeast Australia) approximately 130 km East Northeast of the central business district of Melbourne (pop. ∼5.15 million). A lack of seismic instrumentation and a low population density in the epicentral region resulted in a dearth of near-source instrumental and “felt” report intensity data, limiting evaluation of the near-source performance of ground motion models (GMMs). To address this challenge, we first surveyed unreinforced masonry chimneys following the earthquake to establish damage states and develop fragility curves. Using Bayesian inference, and including pre-earthquake GMM weightings as Bayesian priors, we evaluate the relative performance of GMMs in predicting chimney observations for different fragility functions and seismic velocity profiles. At the most likely VS30 (760 m/s), the best performing models are AB06, A12, and CY08SWISS. GMMs that were preferentially selected for utility in the Australian National Seismic Hazard Model (NSHA18) prior to the Woods Point earthquake outperform other GMMs. The recently developed NGA-East GMM performs relatively well in the more distal region (e.g. >50 km) but is among the poorest performing GMMs in the near-source region across the range of VS30. Our new method of combining analysis of engineered features (chimneys) with Bayesian inference to evaluate the near-source performance of GMMs may have applicability in diverse settings worldwide, particularly in areas of sparse seismic instrumentation.
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ItemNo Preview AvailableGround Penetrating Radar of Neotectonic Folds and Faults in South-Central Australia: Evolution of the Shallow Geophysical Structure of Fault-Propagation Folds with Increasing Strain(MDPI, 2022-11)Using ground penetrating radar (GPR) we investigate the near surface (~0–10 m depth) geophysical structure of neotectonic fault-propagation folds and thrust faults in south-central Australia in varying stages of fold and fault growth. Variations in neotectonic fold scarp heights are interpreted to reflect variations in accumulated slip on the underlying reverse faults. Fold scarps on the Nullarbor and Roe Plains are characterized by broad, asymmetric morphologies with vertical displacements of ~5 to ~40 m distributed over 1 to 2 km widths (~0.5 to ~4 m per 100 m). Within increasing scarp height there is an increase in the frequency and spatial density of strong reflector packages in the hanging wall that are attributed to material contrasts imposed by co-seismic fracturing and associated lithological and weathering variations. No evidence for discrete faulting is found at scarp heights up to 40 m (maximum relief of 4 m per 100 m). Where the principal slip zone of a fault ruptures to the surface, scarp morphologies are characterized by steep gradients (ca. 10 m per 100 m). Discrete faulting is imaged in GPR as structural lineaments, abrupt changes in the thickness of reflector packages with variations of amplitude, and/or hyperbolic diffraction packages indicative of the disturbance of reflector packages. Geophysical imaging of subtle changes in the shallow geological structure during growth of fault-propagation folds can be conducted using GPR informing the identification of locations for invasive investigations (e.g., trenching).
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ItemNo Preview AvailableCrustal transpressional fault geometry influenced by viscous lower crustal flow(GEOLOGICAL SOC AMER, INC, 2022-09)Abstract The San Andreas fault (California, USA) is near vertical at shallow (<10 km) depth. Geophysical surveys along the San Andreas fault reveal that, at depths of 10–20 km, it dips ~50–70° to the southwest near the Western Transverse Ranges and dips northeast in the San Gorgonio region. We investigate the possible origin of along-strike geometric variations of the fault using a three-dimensional thermomechanical model. For two blocks separated by transpressional faults, our model shows that viscous lower crustal material moves from the high-viscosity block into the low-viscosity block. Fault plane-normal flow in the viscous lower crust rotates the fault plane due to the simple shear flow at the brittle-ductile transition depth. This occurs irrespective of initial fault dip direction. Rheological variations used to model the lower crust of Southern California are verified by independent observations. Block extrusion due to lower crustal viscosity variation facilitates the formation of the Garlock Fault and sustains the geometric complexity of the fault.
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ItemNo Preview AvailableFluid-Enhanced Neotectonic Faulting in the Cratonic Lithosphere of the Nullarbor Plain in South-Central Australia(AMER GEOPHYSICAL UNION, 2022-07-28)Abstract The Nullarbor Plain is underlain by thick cratonic lithospheric mantle that is almost devoid of contemporary seismicity. Analysis of high‐resolution digital elevation models indicates neotectonic fault‐propagation fold traces on the nearly flat karst landscape that locally extend to lengths of >100 km, suggesting potential for hosting large (>7.3–7.5) moment magnitude earthquakes. Along‐strike maximum displacements are not proportional to neotectonic fold surface trace length but are spatially associated with crust‐scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the uppermost mantle (at depths < 60 km) along crustal scale shear zones. Conductivity in the uppermost mantle shear zones is higher than conductivity at increased depth, suggesting fluid‐enhanced enrichment with hydrogen and/or carbon. Lithospheric fluid localization associated with ancient slab subduction and/or hydrothermal alteration may have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain.
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ItemNo Preview AvailableTectono-Thermal Evolution of the Hope-Kelly Fault System, Southern Alps, New Zealand: Insights From Topographic Analysis and (U-Th)/He Thermochronology(AMER GEOPHYSICAL UNION, 2023-04)Abstract The fast‐slipping Alpine (∼30 mm/yr), Hope (∼10–20 mm/yr) and Kelly (∼6 mm/yr) faults in the South Island of New Zealand form a complex intersection zone that accommodates tectonic strain along the Australian‐Pacific plate boundary. Analysis of digital topography reveals evidence for stream capture, drainage divide migration, landscape responses to incipient fault development, and preserved enclaves of relic topography that collectively reflect complex interplays between active faulting and landscape evolution. (U‐Th)/He thermochronology of zircon (ZHe) and apatite (AHe) is used to investigate the low‐temperature thermal evolution of rocks in the intersection zone. Weighted mean sample ages for ZHe single grain ages (n = 13 samples) range from ∼9 to 2 Ma, and AHe multi‐grain and single grain aliquot ages (n = 9 samples) range from ∼1.5 to 0.5 Ma. Inverse and forward thermal history modeling reveals distinct spatiotemporal variations in thermal histories. Late Miocene exhumation rates (∼0.6–3.5 km/Myr, assuming geothermal gradients of 33–40 °C/km) through crustal depths of approximately 5–6 km, are interpreted to be controlled by proximity to the Alpine fault, with rocks proximal to the fault recording faster exhumation rates relative to distal samples. Establishment of the Hope‐Kelly fault system in the Quaternary structurally juxtaposed rocks with discordant cooling histories. Rocks throughout the study region record increased cooling rates from ∼2 Ma. Possible causal mechanisms include, spatial changes in rock uplift associated with transport toward the Alpine Fault, increased erosion rates associated with Quaternary climate change, or increased rock mass erodibility associated with development of the Hope‐Kelly fault system.
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ItemNo Preview AvailableFault geometry and slip rates from the Nullarbor and Roe Plains of south-central Australia: Insights into the spatial and temporal characteristics of intraplate seismicity(WILEY, 2023-02-01)Abstract Analysis of TanDEM‐X and Shuttle Radar Topography Mission (SRTM) data reveals geomorphic evidence for 292 fault‐propagation fold scarps across the Miocene Nullarbor and Pliocene Roe Plains in south‐central Australia. Vertical displacements (VD) are determined using topographic profiling of a subset (n = 48) of the fold traces. Fault dips (mean = 44 +16/−14° at 1σ) are estimated from seismic reflection data; the mean dip is assigned to faults with unknown dip and combined with VD to estimate net displacements (ND) and average net displacements (AD) for each fault. AD exceeds single‐event displacements estimated from fault‐length scaling regressions, indicating the identified faults have hosted multiple earthquakes. Combining AD with (i) faulted surface ages (Nullarbor ~10–5 Ma, Roe ~2.5 Ma), (ii) ages of faulted erosional–depositional features (e.g. relic Late Miocene dune fields and Pliocene paleochannels), and (iii) onset of the neotectonic regime in Australia at ~10 Ma yields average slip rates from <0.1 m Myr−1to >17 m Myr−1(mean = 1.1 m Myr−1). Summation of displacements across faults yields crustal horizontal shortening rates lower than geodetically detectable resolution (≤0.01 mm yr−1) since the Late Miocene. The ca. 10 Myr‐long record of neotectonic faulting on the Nullarbor Plain provides important insights into earthquake spatial–temporal behaviours in a slowly deforming intraplate continental region.
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ItemCorrection: Surface-Rupturing Historical Earthquakes in Australia and Their Environmental Effects: New Insights from Re-Analyses of Observational Data (Geosciences, (2019) 9, 408, 10.3390/geosciences9100408)(MDPI AG, 2022-02-01)The authors would like to correct the published article [...]
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ItemScience advocacy in political rhetoric and actions.(Springer Science and Business Media LLC, 2022)UNLABELLED: 'Science' is a proportionately small but recurring constituent in the rhetorical lexicon of political leaders. To evaluate the use of science-related content relative to other themes in political communications, we undertake a statistical analysis of keywords in U.S. Presidential State of the Union (SOTU) addresses and Presidential Budget Messages (PBM) from Truman (1947) to Trump (2020). Hierarchical clustering and correlation analyses reveal proximate affinities between 'science' and 'research', 'space', 'technology', 'education', and 'climate'. The keywords that are least correlated with 'science' relate to fiscal ('inflation', 'tax') and conflict-related themes ('security', 'war', 'terror'). The most ubiquitous and frequently used keywords are 'economy' and 'tax'. Science-related keywords are used in a positive (promotional) rhetorical context and thus their proportionality in SOTU and PBM corpora is used to define fields of science advocacy (public perception advocacy, funding advocacy, advocacy) for each president. Monte Carlo simulations and randomized sampling of three elements: language (relative frequency of usage of science-related keywords), funding (proposed funding and allocated discretionary funding of science agencies), and actions (e.g. expediency of science advisor appointments, (dis-) establishment of science agencies) are used to generate a science advocacy score (SAS) for each president. The SAS is compared with independent survey-based measures of political popularity. A myriad of political, contextual, and other factors may contribute to lexical choices, policy, and funding actions. Within this complex environment 'science' may have political currency under certain circumstances, particularly where public and political perceptions of the value of science to contribute to matters of priority align. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10669-022-09875-x.
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ItemNo Preview AvailableAustralia’s Unfolding Geoscience Malady(American Geophysical Union (AGU), 2021-11-01)Brutal university cuts are putting at risk an industry crucial to addressing climate change Down Under and around the world. Saving geoscience will require a community reckoning.