Modern probabilistic seismic hazard assessments rely on earthquake catalogs consistently expressed in terms of moment magnitude, MW. However, MW is still not commonly calculated for small local events by many national networks. The preferred magnitude type calculated for local earthquakes by Australia’s National Earthquake Alerts Centre is local magnitude, ML. For use in seismic hazard forecasts, magnitude conversion equations are often applied to convert ML to MW. Unless these conversions are time-dependent, they commonly assume that ML estimation has been consistent for the observation period. While Australian-specific local magnitude algorithms were developed from the late 1980s and early 1990s, regional, state and university networks did not universally adopt these algorithms, with some authorities continuing to use Californian magnitude algorithms. Californian algorithms are now well-known to overestimate earthquake magnitudes for Australia. Consequently, the national catalogue contains a melange of contributing authorities with their own methods of magnitude estimation. The challenge for the 2018 National Seismic Hazard Assessment of Australia was to develop a catalog of earthquakes with consistent local magnitudes, which could then be converted to MW. A method was developed that corrects magnitudes using the difference between the original (inappropriate) magnitude formula and the Australian-specific corrections at a distance determined by the nearest recording station likely to have recorded the earthquake. These corrections have roughly halved the rates of ML 4.5 earthquakes in the Australian catalogue. To address ongoing challenges for catalog improvement, Geoscience Australia is digitising printed and hand-written observations preserved on earthquake data sheets. Once complete, this information will provide a valuable resource that will allow for further interrogation of pre-digital data and enable refinement of historical catalogs. Presented at the 2019 Seismological Society of America Conference, Seattle in the special session on “Seismology BC(d)E: Seismology Before the Current (digital) Era”

We present the first paleoseismic investigation of the Hyde Fault, one of a series of north-east striking reverse faults within the Otago range and basin province in southern New Zealand. Surface traces of the fault and associated geomorphology were mapped using a lidar digital elevation model and field investigations. Trenches were excavated at two sites across fault scarps on alluvial fan surfaces. The trenches revealed stratigraphic evidence for four surface-rupturing earthquakes. Optically stimulated luminescence dating constrains the timing of these events to around 47.2 ka (37.5–56.7 ka at 95% confidence), 34.6 ka (24.7–46.4 ka),23.5 ka (19.7–27.3 ka) and 10.5 ka (7.9–13.1 ka). We obtain a mean inter-event time of12.4 kyr (2.3–23.9 kyr at 95% confidence) and the slip rate is estimated to be 0.22 mm/yr (0.15–0.3 mm/yr). We do not find evidence to suggest that earthquake recurrence on the Hyde Fault is episodic, in contrast to other well-studied faults within Otago, suggesting diverse recurrence styles may co-exist in the same fault system. This poses challenges for characterising the seismic hazard potential of faults in the region, particularly when paleoearthquake records are limited to the most recent few events. <b>Citation:</b> Jonathan D. Griffin, Mark W. Stirling, David J.A. Barrell, Ella J. van den Berg, Erin K. Todd, Ross Nicolls & Ningsheng Wang (2022) Paleoseismology of the Hyde Fault, Otago, New Zealand, <i>New Zealand Journal of Geology and Geophysics</i>, 65:4, 613-637, DOI: 10.1080/00288306.2021.1995007

The Devil’s Mountain fault is an active fault included in the 2014 USGS hazard model for Washington State. Recent neotectonic investigations have suggested that a west-northwestwards extension of the fault (the Leech River fault) has sea-bottom and onshore evidence pointing to recurrent young offsets. Accordingly, a logic tree model for the Leech River – Devil’s Mountain fault system (LRF-DMF) incorporating various fault lengths, slip rates of 0.25 mm/yr with upper and lower alternatives of 0.15 and 0.35 mm/yr, and interactions between the faults was developed and added to Canada’s 6th Generation seismic hazard model. The LRF was given a 50% chance of being active. Although the slip rate is low for an active tectonic region, the fault system passes through greater Victoria, British Columbia, and contributes to the overall seismic hazard for southernmost Vancouver Island. We calculate the hazard in greater Victoria with and without the LRF-DMF in order to estimate its effect. The hazard in downtown Victoria is already high (coming mainly from in-slab sources at short periods and the Cascadia subduction zone at long periods) and decreases slowly northwards. The hazard increment due to the LRF-DMF is quite small, even very close to the fault, and as expected its contribution to the hazard decreases away from the fault so that in Sidney at ~25 km distance it is insignificant. The importance would have been very different in a lower hazard region, or if the slip rate on the LRF-DMF had been considerably higher.

The Philippine archipalego is tectonically complex and seismically hazardous, yet few seismic hazard assessments have provided national coverage. This paper presents an updated probabilistic seismic hazard analysis for the nation. Active shallow crustal seismicity is modeled by faults and gridded point sources accounting for spatially variable occurrence rates. Subduction interfaces are modelled with faults of complex geometry. Intraslab seismicity is modeled by ruptures filling the slab volume. Source geometries and earthquake rates are derived from seismicity catalogs, geophysical datasets, and historic-to-paleoseismic constraints on fault slip rates. The ground motion characterization includes models designed for global use, with partial constraint by residual analysis. Shallow crustal faulting near metropolitan Manila, Davao, and Cebu dominates shaking hazard. In a few places, peak ground acceleration with 10% probability of exceedance in 50 years on rock reaches 1.0 g. The results of this study may assist in calculating the design base shear in the National Structural Code of the Philippines.

<div>Geoscience Australia, together with contributors from the wider Australian seismology community, have produced a new National Seismic Hazard Assessment (NSHA23), recommended for inclusion in proposed updates to Standards Australia’s&nbsp;AS1170.4. NSHA23 builds on the model framework developed for NSHA18, and incorporates scientific advances and stakeholder feedback received since development of that model. Key changes include: further refinement and homogenisation of the earthquake catalogue; revisions to the fault source model through inclusion of newly identified faults and revised activity rates on some faults; assessment of ground motion models through quantitative comparison against observations; and inclusion of a specific ground motion model for shaking from plate-boundary earthquakes in northern Australia. Expert elicitation was used to capture epistemic uncertainty surrounding model choices. The elicitation focused on decision points that sensitivity analysis had shown were more important for hazard, where new models had been developed, and where model choices had been controversial in NSHA18. Key questions included which catalogue to use as the basis for calculating hazard, the weighting of different source model classes (background, regional, seismotectonic, smoothed seismicity and smoothed seismicity with faults), and the selection and weighting of ground motion models for different tectonic regions. NSHA23 hazard results for capital cities show minor changes compared with NSHA18, with the exception of Darwin. Here the ground motion with a 10% probability of exceedance in 50 years increases significantly, a result that is attributed to inclusion of a new, more realistic ground motion model for plate-boundary earthquakes in this unique tectonic setting.</div><div><br>This paper was presented to the 2023 Australian Earthquake Engineering Conference 23-25 November 2023 (https://aees.org.au/aees-conference-2023/)</div>

An updated National Seismic Hazard Assessment of Australia was released in 2018 (the NSHA18). This assessment leveraged off advances in earthquake-hazard science in Australia and analogue tectonic regions to offer many improvements over its predecessors. The outcomes of the assessment represent a significant shift in the way national-scale seismic hazard is modelled in Australia, and so challenged long-held notions of seismic hazard amongst the Australian seismological and earthquake engineering community. The NSHA18 is one of the most complex national-scale seismic hazard assessments conducted to date, comprising 19 independent seismic source models (contributed by Geoscience Australia and third-party contributors) with three tectonic region types, each represented by at least six ground motion models each. The NSHA18 applied a classical probabilistic seismic hazard analysis (PSHA) using a weighted logic tree approach, where the model weights were determined through two structured expert elicitation workshops. The response from the participants of these workshops was overwhelmingly positive and the participants appreciated the opportunity to contribute towards the model’s development. Since the model’s publication, Geoscience Australia has been able to reflect on the choices made both through the expert elicitation process and through decisions made by the NSHA18 team. The consequences of those choices on the production of the final seismic hazard model may not have been fully appreciated prior to embarking on the development of the NSHA18, nor during the expert elicitation workshops. The development of the NSHA18 revealed several philosophical challenges in terms of characterising seismic hazard in regions of low seismicity such as Australia. Chief among these are: 1) the inclusion of neotectonic faults, whose rupture characteristics are underexplored and poorly understood; 2) processes for the adjustment and conversion of historical earthquake magnitudes to be consistently expressed in terms of moment magnitude; 3) the relative weighting of different seismic-source classes (i.e., background, regional, smoothed seismicity, etc) for different regions of interest and exceedance probabilities; 4) the assignment of Gutenberg-Richter b-values for most seismic source models based on b-values determined from broad neotectonic domains, and; 5) the characterisation and assignment of ground-motion models used for different tectonic regimes. This paper discusses lessons learned through the development of the NSHA18, identifies successes in the expert elicitation and modelling processes, and explores some of the abovementioned challenges that could be reviewed for future editions of the model. Abstract presented at the 17th World Conference on Earthquake Engineering (17WCEE )

Geoscience Australia has produced a draft National Seismic Hazard Assessment (NSHA18), together with contributions from the wider Australian seismology community. This paper provides an overview of the provisional peak ground acceleration (PGA) hazard values and discusses rationale for changes in the proposed design values at the 1/500-year annual exceedance probability (AEP) level relative to Standards Australia’s AS1170.4–2007 design maps. The NSHA18 update yields many important advances on its predecessors, including: consistent expression of earthquake magnitudes in moment magnitude; inclusion of epistemic uncertainty through the use of third-party source models; inclusion of a national fault-source model; inclusion of epistemic uncertainty on fault-slip-model magnitude-frequency distributions and earthquake clustering; and the use of modern ground-motion models through a weighted logic tree framework. In general, the 1/500-year AEP seismic hazard values across Australia have decreased relative to the earthquake hazard factors the AS1170.4–2007, in most localities significantly. The key reasons for the decrease in seismic hazard factors are due to: the reduction in the rates of moderate-to-large earthquakes through revision of earthquake magnitudes; the increase in b-values through the conversion of local magnitudes to moment magnitudes, particularly in eastern Australia, and; the use of modern ground-motion attenuation models. Whilst the seismic hazard is generally lower than in the present standard, we observe that the relative proportion of the Australian landmass exceeding given PGA thresholds is consistent with other national hazard models for stable continental regions. Abstract presented at the 2017 Australian Earthquake Engineering Society (AEES) Conference

<div>The presence of Pliocene marine sediments in the Myponga and Meadows basins within the Mt Lofty Ranges south of Adelaide is testament to over 200&nbsp;m of tectonic uplift within the last 5 Myr (e.g., Sandiford 2003, Clark 2014). The spatiotemporal distribution of uplift amongst the various faults within the range and along the range fronts is poorly understood. Consequently, large uncertainties are associated with estimates of the hazard that the faults pose to proximal communities and infrastructure.</div><div>&nbsp;</div><div>We present the preliminary results of a paleoseismic investigation of the southern Willunga Fault, ~40 km south of Adelaide. Trenches were excavated across the fault to examine the relationships between fault planes and sedimentary strata. Evidence is preserved for 3-5 ground-rupturing earthquakes since the Middle to Late Pleistocene, with single event displacements of 0.5 – 1.7 m. Dating of samples will provide age constraints on the timing of these earthquakes. This most recent part of the uplift history may then be related to the longer-term landscape evolution evidenced by the uplifted basins, providing an enhanced understanding of the present-day seismic hazard.</div> This abstract was presented at the Australian & NZ Geomorphology Group (ANZGG) Conference in Alice Springs 26-30 September 2022. https://www.anzgg.org/images/ANZGG_2022_First_circular_Final_V3.pdf

We present earthquake ground motions based upon a paleoseismically-validated characteristic earthquake scenario for the ~ 48 km-long Avonmore scarp, which overlies the Meadow Valley Fault, east of Bendigo, Victoria. The results from the moment magnitude MW 7.1 scenario earthquake indicate that ground motions are sufficient to be of concern to nearby mining and water infrastructure. Specifically, the estimated median peak ground acceleration (PGA) exceeds 0.5 g to more than ~ 10 km from the source fault, and a 0.09 g PGA liquefaction threshold is exceeded out to approximately 50-70 kilometres. Liquefaction of susceptible materials, such as mine tailings, may occur to much greater distances. Our study underscores the importance of identifying and characterising potentially active faults in proximity to high failure-consequence dams, including mine tailings dams, particularly in light of the requirement to manage tailing dams for a prolonged period after mine closure. Paper presented at Australian National Committee on Large Dams (ANCOLD) conference 2020, online. (https://leishman.eventsair.com/ancold-2020-online/)

Canada's 6th Generation seismic hazard model has been developed to generate seismic design values for the 2020 National Building Code of Canada (NBCC2020). The model retains most of the seismic source model from the 5th Generation, but updates the earthquake sources for the deep inslab earthquakes under the Straits of Georgia and adds the Leech River - Devil’s Mountain fault near Victoria. The rates of magnitude ~9 Cascadia earthquakes are also increased to match new paleoseismic information. Two major changes in the ground motion model (GMM) are A) replacement of most of the three-branch representative suite used in 2015 by suites of weighted GMMs, and B) use and adaptation of various GMMs to directly calculate hazard on various site classes with representative Vs30 values, rather than providing hazard values on a reference Class C site and applying F(T) factors as in 2015. Computations are now also being performed with the OpenQuake engine, which has been validated through the replication of the 5th Generation results. Seismic design values (on various Soil Classes) for PGA, and for Sa(T) for T = 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 s are proposed for NBCC2020 mean ground shaking at the 2% in 50-year probability level. The paper discusses chiefly the change in Site Class C values relative to 2015 in terms of the changes in the seismic source model and the GMMs, but the changes in hazard at other site classes that arise from application of the direct-calculation approach are also illustrated.