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>COMET (The Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics) uses satellite measurements alongside ground-based observations and geophysical models to study active faults and earthquakes. This talk provides an overview of COMET research products in Türkiye and Central Asia, where interseismic deformation and active faults are directly observable. It also touches on how these products highlight the complexity and difficulty of seismic hazard modelling in Australia.&nbsp;</div><div>Three COMET datasets will be discussed, which each contribute to seismic hazard models. Researchers at COMET have and continue to pioneer INSAR methods including co-seismic interferograms and time-series modelling. For example, the Türkiye (Türkiye) INSAR strain-rate map directly estimates strain-accumulation across faults, while the LICSAR portal and satellite cross-correlation methods are used to quantify co-seismic and post-seismic deformation (including after the devastating 2023 Türkiye-Syria earthquake).&nbsp;</div><div>Similar methods are applied in the Tien Shan, where active faults are identifiable in satellite imagery and elevation data, but rates of activity are uncertain and expensive to obtain through field work. Here COMET and GEM (the Global Earthquake Model) are collaborating to produce block-model informed PSHA inputs using active fault databases, GNSS, and INSAR.&nbsp;</div><div>While these methods are useful in tectonically active regions, they serve to highlight the difficulties facing Australian seismic hazard modelling where similar methods cannot be used due to low (to unobservable) tectonic strain and very long fault recurrence.&nbsp;</div> This paper was presented to the 2023 Australian Earthquake Engineering Conference 23-25 November 2023 (https://aees.org.au/aees-conference-2023/)

<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 city of Lae is Papua New Guinea (PNG)’s second largest, and is the home of PNG’s largest port. Here, a convergence rate of ~50 mm/yr between the South Bismarck Plate and the Australian Plate is accommodated across the Ramu-Markham Fault Zone (RMFZ). The active structures of the RMFZ are relatively closely spaced to the west of Lae. However, the fault zone bifurcates immediately west of the Lae urban area, with one strand continuing to the east, and a second strand trending southeast through Lae City and connecting to the Markham Trench within the Huon Gulf. </div><div>The geomorphology of the Lae region relates to the interaction between riverine (and limited marine) deposition and erosion, and range-building over low-angle thrust faults of the RMFZ. Flights of river terraces imply repeated tectonic uplift events; dating of these terraces will constrain the timing of past earthquakes and associated recurrence intervals. Terrace riser heights are typically on the order of 3 m, indicating causative earthquake events of greater than magnitude 7. </div><div>Future work will expose the most recently active fault traces in trenches to assess single event displacements, and extend the study to the RMFZ north of Nadzab Airport. These results will inform a seismic hazard and risk assessment for Lae city and surrounding region.</div> Presented at the 2023 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