Geoscience Australia, together with contributors from the wider Australian seismology community, have produced a draft National Seismic Hazard Assessment (NSHA18), recommended for inclusion in the 2018 update of Standards Australia’s Structural design actions, part 4: Earthquake actions in Australia, AS1170.4–2007 (Standards Australia, 2007). This Standard is prepared by Subcommittee BD-006-11, General Design Requirements and Loading on Structures of Standards Australia. The provisional seismic hazard values presented in this report have been submitted to comply with Standards Australia’s public comment and publication timelines. This report provides a brief overview of provisional mean peak ground acceleration values (equivalent to the seismic hazard factor Z in AS1170.4) and the approaches used. The hazard values are calculated on rock sites (AS1170.4 Site Class Be) for a probability of exceedance of 10% in 50 years (0.0021 per annum). Continued refinement of these values will occur throughout, and in response to, the first public comment period. While only minor changes are expected, the final NSHA18 will be completed prior to Standard Australia’s planned second public comment period (likely in late 2017). The NSHA18 update yields many important advances on its predecessors, including: • calculation in a full probabilistic framework (e.g., Cornell, 1968) using the Global Earthquake Model Foundation’s OpenQuake-engine (Pagani et al., 2014); • consistent expression of earthquake magnitudes in terms of moment magnitude, MW; • inclusion of epistemic uncertainty through the use of third-party source models contributed by the Australian seismology community; • inclusion of epistemic uncertainty on magnitude-frequency distributions; • inclusion of a national fault-source model based on the Australian Neotectonic Features database (Clark et al., 2012; Clark et al., 2016); • inclusion of epistemic uncertainty on fault-slip-model magnitude-frequency distributions and earthquake clustering; and • use of modern ground-motion models.

Papua New Guinea (PNG) lies in a belt of intense tectonic activity that experiences high levels of seismicity. Although this seismicity poses significant risks to society, the Building Code of PNG and its underpinning seismic loading requirements have not been revised since 1982. This study aims to partially address this gap by updating the seismic zoning map on which the earthquake loading component of the building code is based. We performed a new probabilistic seismic hazard assessment for PNG using the OpenQuake software developed by the Global Earthquake Model Foundation (Pagani et al. 2014). Among other enhancements, for the first time together with background sources, individual fault sources are implemented to represent active major and microplate boundaries in the region to better constrain the earthquake-rate and seismic-source models. The seismic-source model also models intraslab, Wadati–Benioff zone seismicity in a more realistic way using a continuous slab volume to constrain the finite ruptures of such events. The results suggest a high level of hazard in the coastal areas of the Huon Peninsula and the New Britain – Bougainville region, and a relatively low level of hazard in the southwestern part of mainland PNG. In comparison with the seismic zonation map in the current design standard, it can be noted that the spatial distribution of seismic hazard used for building design does not match the bedrock hazard distribution of this study. In particular, the high seismic hazard of the Huon Peninsula in the revised assessment is not captured in the current building code of PNG. <b>Citation:</b> Ghasemi, H., Cummins, P., Weatherill, G. <i>et al.</i> Seismotectonic model and probabilistic seismic hazard assessment for Papua New Guinea. <i>Bull Earthquake Eng, </i><b>18</b>, 6571–6605 (2020). https://doi.org/10.1007/s10518-020-00966-1

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 )

We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1–6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1–4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2–9.1 m Myr−1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows/liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.

Seismic hazard models, commonly produced through probabilistic seismic hazard analysis, are used to establish earthquake loading requirements for the built environment. However, there is considerable uncertainty in developing seismic hazard models, which require assumptions on seismicity rates and ground-motion models (GMMs) based on the best evidence available to hazard analysts. This paper explores several area-based tests of long-term seismic hazard forecasts for the Australian continent. ShakeMaps are calculated for all earthquakes of MW 4.25 and greater within approximately 200 km of the Australian coastline using the observed seismicity in the past 50 years (1970-2019). A “composite ShakeMap” is generated that extracts the maximum peak ground acceleration “observed” in this 50-year period for any site within the continent. The fractional exceedance area of this composite map is compared with four generations of Australian seismic hazard maps for a 10% probability of exceedance in 50 years (~1/500 annual exceedance probability) developed since 1990. In general, all these seismic hazard models appear to be conservative relative to the observed ground motions that are estimated to have occurred in the last 50 years. To explore aspects of possible prejudice in this study, the variability in ground-motion exceedance was explored using the Next Generation Attenuation-East GMMs developed for the central and eastern United States. The sensitivity of these results is also tested with the interjection of a rare scenario earthquake with an expected regional recurrence of approximately 5,000 - 10,000 years. While these analyses do not provide a robust assessment of the performance of the candidate seismic hazard for any given location, they do provide—to the first order—a guide to the performance of the respective maps at a continental scale. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

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/)

<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

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.

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.

<div>One of the key challenges in assessing earthquake hazard in Australia is understanding the attenuation of ground-motion through the stable continental crust. There are now a small number of ground-motion models (GMMs) that have been developed specifically to estimate ground-motions from Australian earthquakes. These GMMs, in addition to models developed outside Australia, are considered here for use in the updated national seismic hazard assessment of Australia. An updated and extended suite of ground-motion data from small-to-moderate Australian earthquakes are used to assess the suitability of the candidate models for use in the Australian context. Recorded spectral intensities are compared with those predicted by the GMMs. Both qualitative and quantitative approaches are considered for such comparisons. The goodness-of-fit results vary significantly among different GMMs, spectral periods and distance ranges; however, overall, the Australian-specific GMMs seem to perform reasonably well in estimating the level of ground shaking for earthquakes in Australia. This paper was presented to the 2022 Australian Earthquake Engineering Society (AEES) Conference 24-25 November (https://aees.org.au/aees-conference-2022/)