<div>Forecasting large earthquakes along active faults is of critical importance for seismic hazard assessment. Statistical models of recurrence intervals based on compilations of paleoseismic data provide a forecasting tool. Here we compare five models and use Bayesian model-averaging to produce time-dependent, probabilistic forecasts of large earthquakes along 93 fault segments worldwide. This approach allows better use of the measurement errors associated with paleoseismic records and accounts for the uncertainty around model choice. Our results indicate that although the majority of fault segments (65/93) in the catalogue favour a single best model, 28 benefit from a model-averaging approach. We provide earthquake rupture probabilities for the next 50 years and forecast the occurrence times of the next rupture for all the fault segments. Our findings suggest that there is no universal model for large earthquake recurrence, and an ensemble forecasting approach is desirable when dealing with paleoseismic records with few data points and large measurement errors. <b>Citation:</b> Wang, T., Griffin, J.D., Brenna, M. et al. Earthquake forecasting from paleoseismic records. <i>Nat Commun</i><b> 15</b>, 1944 (2024). https://doi.org/10.1038/s41467-024-46258-z

This ecat record refers to the data described in ecat record 123048. The data, supplied in shapefile format, is an input to the 2018 National Seismic Hazard Assessment for Australia (NSHA18) product (ecat 123020) and the 2018 Probabilistic Tsunami Hazard Assessment for Australia (PTHA18) product (ecat 122789).

The 2018 National Seismic Hazard Assessment (NSHA18) aims to provide the most up-to-date and comprehensive understanding of seismic hazard in Australia. As such, NSHA18 includes a range of alternative models for characterising seismic sources and ground motions proposed by members of the Australia earthquake hazard community. The final hazard assessment is a weighted combination of alternative models. This report describes the use of a structured expert elicitation methodology (the ‘Classical Model’) to weight the alternative models and presents the complete results of this process. Seismic hazard assessments are inherently uncertain due to the long return periods of damaging earthquakes relative to the time period of human observation. This is especially the case for low-seismicity regions such as Australia. Despite this uncertainty, there is a demand for estimates of seismic hazard to underpin a range of decision making aimed at reducing the impacts of earthquakes to society. In the face of uncertainty, experts will propose alternative models for the distribution of earthquake occurrence in space, time and magnitude (i.e. seismic source characterisation), and how ground shaking is propagated through the crust (i.e. ground motion characterisation). In most cases, there is insufficient data to independently and quantitatively determine a ‘best’ model. Therefore it is unreasonable to expect, or force, experts to agree on a single consensus model. Instead, seismic hazard assessments should capture the variability in expert opinion, while allowing that not all experts are equally adept. Logic trees, with branches representing mutually exclusive models weighted by expert opinion, can be used to model this uncertainty in seismic hazard assessment. The resulting hazard assessment thereby captures the range of plausible uncertainty given current knowledge of earthquake occurrence in Australia. For the NSHA18, experts were invited to contribute peer-reviewed seismic source models for consideration, resulting in 16 seismic source models being proposed. Each of these models requires values to be assigned to uncertain parameters such as the maximum magnitude earthquake expected. Similarly, up to 20 published ground motion models were identified as being appropriate for characterising ground motions for different tectonic regions in Australia. To weight these models, 17 experts in seismic hazard assessment, representative of the collective expertise of the Australian earthquake hazard community, were invited to two workshops held at Geoscience Australia in March 2017. At these workshops, the experts each assigned weights to alternative models representing their degree of belief that a particular model is the ‘true’ model. The experts were calibrated through a series of questions that tested their knowledge of the subject and ability to assess the limits to their knowledge. These workshops resulted in calibrated weights used to parameterise the final seismic source model and ground motion model logic trees for NSHA18. Through use of a structured expert elicitation methodology these weights have been determined in a transparent and reproducible manner drawing on the full depth of expertise and experience within the Australia earthquake hazard community. Such methodologies have application to a range of uncertain problems beyond the case of seismic hazard assessment presented here.

Geoscience Australia, together with contributors from the wider Australian seismology community, has produced a National Seismic Hazard Assessment (NSHA18) that is intended as an update to the 2012 National Seismic Hazard Maps (NSHM12; Burbidge, 2012; Leonard et al., 2013). This Geoscience Australia Record provides an overview of the development of the NSHA18. Time-independent, mean seismic design values are calculated on Standards Australia’s AS1170.4 Soil Class Be (at VS30=760 m/s) for the horizontal peak ground acceleration (PGA) and for the geometric mean of the spectral accelerations, Sa(T), for T = 0.1, 0.2, 0.3, 0.5, 1.0, 2.0 and 4.0 s over a 15-km national grid spacing. Hazard curves and uniform hazard spectra are also calculated for key localities. Maps of PGA, in addition to Sa(0.2 s) and Sa(1.0 s) and for a 10% probability of exceedance in 50 years (Figure A). Additional maps and seismic hazard products are provided in a separate Geoscience Australia Record (Allen, 2018). The NSHA18 update yields many important advances over its predecessors, including: - the calculation in a full probabilistic framework (Cornell, 1968) using the Global Earthquake Model Foundation’s OpenQuake-engine (Pagani et al., 2014); - the consistent expression of earthquake magnitudes in terms of moment magnitude, MW; - inclusion of a national fault-source model based on the Australian Neotectonic Features database (Clark et al., 2016); - the inclusion of epistemic (i.e. modelling) uncertainty: - through the use of multiple alternative source models; - on magnitude-recurrence distributions; - fault recurrence and clustering models; - on maximum earthquake magnitudes for both fault and area sources through an expert elicitation workshop; and - the use of modern ground-motion models, capturing the epistemic uncertainty on ground motion through an expert elicitation workshop.

Sites recording the extinction or extirpation of tropical–subtropical and cool–cold temperate rainforest genera during the Plio–Pleistocene aridification of Australia are scattered across the continent, with most preserving only partial records from either the Pliocene or Pleistocene. The highland Lake George basin is unique in accumulating sediment over c. 4 Ma although interpretation of the plant microfossil record is complicated by its size (950 km2), neotectonic activity and fluctuating water levels. A comparison of this and other sites confirms (1) the extinction of rainforest at Lake George was part of the retreat of Nothofagus-gymnosperm communities across Australia during the Plio–Pleistocene; (2) communities of warm- and cool-adapted rainforest genera growing under moderately warm-wet conditions in the Late Pliocene to Early Pleistocene have no modern analogues; (3) the final extirpation of rainforest taxa at Lake George occurred during the Middle Pleistocene; and (4) the role of local wildfires is unresolved although topography, and, elsewhere, possibly edaphic factors allowed temperate rainforest genera to persist long after these taxa became extinct or extirpated at low elevations across much of eastern Australia. Araucaria, which is now restricted to the subtropics–tropics in Australia, appears to have survived into Middle Pleistocene time at Lake George, although the reason remains unclear. <b>Citation:</b> Macphail Mike, Pillans Brad, Hope Geoff, Clark Dan (2020) Extirpations and extinctions: a plant microfossil-based history of the demise of rainforest and wet sclerophyll communities in the Lake George basin, Southern Tablelands of NSW, south-east Australia. <i>Australian Journal of Botany </i>68, 208-228.

Seismic hazard assessments in stable continental regions such as Australia face considerable challenges compared with active tectonic regions. Long earthquake recurrence intervals relative to historical records make forecasting the magnitude, rates and locations of future earthquakes difficult. Similarly, there are few recordings of strong ground motions from moderate-to-large earthquakes to inform development and selection of appropriate ground motion models (GMMs). Through thorough treatment of these epistemic uncertainties, combined with major improvements to the earthquake catalog, a National Seismic Hazard Assessment (NSHA18) of Australia has been undertaken. The resulting hazard levels at the 10% in 50-year probability of exceedance level are in general significantly lower than previous assessments, including hazard factors used in the Australian earthquake loading standard (AS1170.4–2007 [R2018]), demonstrating our evolving understanding of seismic hazard in Australia. The key reasons for the decrease in seismic hazard factors are adjustments to catalog magnitudes for earthquakes in the early instrumental period, and the use of modern ground-motion attenuation models. This article summarizes the development of the NSHA18, explores uncertainties associated with the hazard model, and identifies the dominant factors driving the resulting changes in hazard compared with previous assessments.

The 6th Generation seismic hazard model of Canada is being developed to generate seismic design values for the 2020 National Building Code of Canada (NBCC2020). Ground-motion models (GMMs) from the Next Generation Attenuation (NGA)-West 2 and NGA-East programs are used and epistemic uncertainty in ground-motion models is captured through the use of a classical weighted logic tree framework. For the first time, seismic hazard is computed directly on primary (e.g. A-E) seismic site classes from their time-averaged shear wave velocities in the upper 30 m of the crust (VS30). This approach simplifies the way end users will determine seismic design values for a given location and site class, while having other technical advantages such as capturing epistemic uncertainty in site amplification models. It will remove the need for separate site amplification look-up tables in the building code, enabling users to simply supply their location and site class to determine seismic design values. In general, the new ground- motion models predict higher hazard in most Canadian localities due to a variable combination of changes in median ground motions, site amplification and aleatory uncertainty.

Instrumentally observed earthquakes sequences typically show clusters of earthquakes interspersed with periods of quiescence. These ‘bursty’ sequences also have correlated inter-event times (‘long-term memory’). In contrast, elastic rebound theory forms the basis of the standard earthquake cycle model, and predicts large earthquakes to occur regularly through cycles of strain accumulation and release (periodicity). In this model the conditional probability of future large earthquakes is reduced immediately following fault rupture, and inter-event times are independent. Here we use the burstiness and memory coefficient metrics to characterize more than 100 long-term earthquake records. We find that large earthquake occurrence on the majority of Earth’s faults is weakly periodic and does not exhibit long-term memory; earthquakes occur more regularly than a random Poisson process although inter-event times are variable. In contrast, clustering occurs in slowly deforming regions (annual rates < 2 x 10-4), and is not explained by elastic rebound theory. <b>Citation:</b> Griffin, J. D., Stirling, M. W., & Wang, T. (2020). Periodicity and clustering in the long‐term earthquake record. <i>Geophysical Research Letters</i>, 47, e2020GL089272. https://doi.org/10.1029/2020GL089272

The 20 May 2016 MW 6.1 Petermann earthquake in central Australia generated a 21 km surface rupture with 0.1 to 1 m vertical displacements across a low-relief landscape. No paleo-scarps or potentially analogous topographic features are evident in pre-earthquake Worldview-1 and Worldview-2 satellite data. Two excavations across the surface rupture expose near-surface fault geometry and mixed aeolian-sheetwash sediment faulted only in the 2016 earthquake. A 10.6 ± 0.4 ka optically stimulated luminescence (OSL) age of sheetwash sediment provides a minimum estimate for the period of quiescence prior to 2016 rupture. Seven cosmogenic beryllium-10 (10Be) bedrock erosion rates are derived for samples < 5 km distance from the surface rupture on the hanging-wall and foot-wall, and three from samples 19 to 50 km from the surface rupture. No distinction is found between fault proximal rates (1.3 ± 0.1 to 2.6 ± 0.2 m Myr−1) and distal samples (1.4 ± 0.1 to 2.3 ± 0.2 m Myr−1). The thickness of rock fragments (2–5 cm) coseismically displaced in the Petermann earthquake perturbs the steady-state bedrock erosion rate by only 1 to 3%, less than the erosion rate uncertainty estimated for each sample (7–12%). Using 10Be erosion rates and scarp height measurements we estimate approximately 0.5 to 1 Myr of differential erosion is required to return to pre-earthquake topography. By inference any pre-2016 fault-related topography likely required a similar time for removal. We conclude that the Petermann earthquake was the first on this fault in the last ca. 0.5–1 Myr. Extrapolating single nuclide erosion rates across this timescale introduces large uncertainties, and we cannot resolve whether 2016 represents the first ever surface rupture on this fault, or a > 1 Myr interseismic period. Either option reinforces the importance of including distributed earthquake sources in fault displacement and seismic hazard analyses. <b>Citation: </b>King, T. R., Quigley, M., Clark, D., Zondervan, A., May, J.-H., & Alimanovic, A. (2021). Paleoseismology of the 2016 M-W 6.1 Petermann earthquake source: Implications for intraplate earthquake behaviour and the geomorphic longevity of bedrock fault scarps in a low strain-rate cratonic region. <i>Earth Surface Processes and Landforms</i>, 46(7), 1238–1256.

<p>The mechanisms that lead to the localisation of stable continental region (SCR) seismicity, and strain more generally, remain poorly understood. Recent work has emphasised correlations between the historical record of earthquake epicentres and lateral changes in the thickness, composition and/or viscosity (thermal state) of the lithospheric mantle, as inferred from seismic velocity/attenuation constraints. Fluid flow and the distribution of heat production within the crust have also been cited as controls on the location of contemporary seismicity. The plate margin-centric hypothesis that the loading rate of crustal faults can been understood in terms of the strain rate of the underlying lithospheric mantle has been challenged in that a space-geodetic strain signal is yet to be measured in many SCRs. Alternatives involving the release of elastic energy from a pre-stressed lithosphere have been proposed. <p>The Australian SCR crust preserves a rich but largely unexplored record of seismogenic crustal deformation spanning a time period much greater than that provided by the historical record of seismicity. Variations in the distribution, cumulative displacement, and recurrence characteristics of neotectonic faults provide important constraint for models of strain localisation mechanisms within SCR crust, with global application. This paper presents two endmember case studies that illustrate the variation in deformation characteristics encountered within Australian SCR crust, and which demonstrate the range and nature of the constraint that might be imposed on models describing crustal deformation and seismic hazard.