Probabilistic Seismic Hazard Model Research Articles

Probabilistic seismic hazard model and vulnerability analysis for typical regional structures

Probabilistic seismic hazard model and vulnerability analysis for typical regional structures

Using open-science workflow tools to produce SCEC CyberShake physics-based probabilistic seismic hazard models

Using open-science workflow tools to produce SCEC CyberShake physics-based probabilistic seismic hazard models

Scoring and ranking probabilistic seismic hazard models: an application based on macroseismic intensity data

Abstract. A probabilistic seismic hazard model consists of a set of weighted models/branches that describes the center, the body and the range of seismic hazard. Owing to the intrinsic nature of this kind of analysis, the weight of each model/branch represents its scientific credibility. However, practical uses of this model may sometimes require the selection of one or a few hazard curves that are sampled from the whole model, which often consists of thousands of branches. Here we put forward an innovative procedure that facilitates the scoring, ranking and selection of the hazard curves to account for the requirements of a specific application. The approach consists of a careful quality check of the data used for scoring and the adoption of a proper scoring rule. To show the applicability of this approach, we present an example that consists of scoring and ranking a set of multiple models/branches constituting a recent seismic hazard model of Italy. To score these branches, hazard estimates produced by each of them are compared with time series of macroseismic observations available in the Italian macroseismic database for a carefully selected set of localities deemed sufficiently representative, homogeneously distributed in space and complete with respect to time and intensity levels. The proper scoring parameter used for such a comparison is the logarithmic score, which can always be applied independently of the distribution of the data.

Probabilistic seismic collapse risk assessment of non-engineered masonry buildings in Malawi

This study presents the most recent development of a nationwide earthquake risk model for non-engineered masonry buildings in Malawi. Due to its location within the East African Rift, Malawi experienced several moderate earthquakes that caused seismic damage and loss. Recently, a new probabilistic seismic hazard model has been developed by considering fault-based seismic sources, in addition to conventional areal sources. The most recent 2018 national census data provide accurate exposure information for Malawian people and their assets at detailed spatial resolutions. To develop seismic fragility functions that are applicable to Malawian housing stocks, building surveys and experimental tests of local construction materials have been conducted. By integrating these new developments of seismic hazard, exposure, and vulnerability modules, a quantitative seismic building collapse risk model for Malawi is developed on a national scale. For the rapid computation of seismic risk curves at individual locations, an efficient statistical approach for approximating the upper tail distribution of a seismic hazard curve is implemented. Using this technique, a seismic risk curve for a single location can be obtained in a few seconds, thereby, this can be easily expanded to the whole country with reasonable computational times. The results from this new quantitative assessment tool for seismic impact will provide a sound basis for risk-based disaster mitigation policies in Malawi.

Probabilistic seismic hazard assessment framework for Uganda: a stochastic event-based modelling approach

Uganda lies between the eastern and western arms of the East African Rift System, the largest seismically active rift above sea level. With increasing population, urbanisation and rapid construction, seismic risk in the country is escalating fast and is compounded by the high vulnerability of the building stock and inadequate disaster prevention and mitigation strategies. Hence, there is an urgent need to assess Uganda’s resilience against seismic risks. This paper presents a Monte-Carlo based probabilistic seismic hazard model for Uganda, as the first step towards the development of a seismic risk and resilience assessment framework for the country. In addition to fault segment data, earthquake catalogues are compiled for the period between 1900 and 2022 to estimate recurrence parameters for source zones in the area of interest. Area source zones incorporating focal mechanisms are used to stochastically model a national hazard framework for Uganda. A logic tree approach is applied to implement four ground motion prediction equations for both stable continental and active shallow crust geologies. Mean hazard curves, uniform hazard spectra, earthquake disaggregation and spectral pseudo-accelerations for major Ugandan cities are derived in addition to hazard maps for the country. The findings are largely consistent with previous regional studies and confirm that western Uganda is exposed to the highest level of seismicity. The model presented herein can be used to kick-start the update and continuous improvement of Uganda Seismic Design Code and the National Policy for Disaster Preparedness and Management.

Impact of the Uncertainty in the Parameters of the Earthquake Occurrence Model on Loss Estimates of Urban Building Portfolios

AbstractUnderstanding the potential socioeconomic losses due to natural hazards, such as earthquakes, is of foremost importance in the field of catastrophe risk management. The construction of a probabilistic seismic risk model is complex and requires the tuning of several parameters essential to represent the seismic hazard of the region, the definition of the exposed inventory characteristics, and its vulnerability to ground motion. Because significant uncertainties could be associated with each model component, the loss estimates are often highly volatile. Nevertheless, to reduce the conceptual complexity and the computational burden, in many real-life applications these uncertainties are either not adequately treated or neglected altogether. The false high fidelity of the ensuing loss estimates can mislead decision-making strategies. Hence, it is useful to assess the influence that the variability in the estimated values of the model input parameters may exert on the final risk results and their relevant contributions. To this purpose, we have performed a sensitivity analysis of the results of an urban seismic risk assessment for Isfahan (Iran). Systematic variations have been applied to the values of the parameters that control the earthquake occurrence in the probabilistic seismic hazard model. Curves of input–output relative variations were built for different risk metrics with the goal of identifying the parameters most sensitive to input uncertainty. Our findings can be useful to support risk managers and practitioners in the process of building seismic hazard and risk models. We found that the Gutenberg–Richter a and b values, the maximum magnitude, and the threshold magnitude are large contributors to the variability of important risk measures, such as the 475 yr and the average annual loss, with the more frequent losses being, in general, most sensitive.

Objective Evaluation of the Source Models for Seismic Hazard Investigations Using the Logic Tree Approach: Case Study Semnan, Iran

Probabilistic seismic hazard analysis (PSHA) has become a fundamental tool in assessing seismic hazards and for estimating seismic design and seismic safety evaluation of ground motions. This report describes a study to test and verify the numerical approaches and software used in PSHA on Semnan, one of the important cities of Iran country. The geological and seismological data are integrated into a probabilistic seismic hazard model for the region. Historical and instrumental earthquake data, geology, tectonics, fault activity, and seismic source models associated with seismic events are taken into account. A probabilistic approach within a logic-tree framework is used to calculate seismic hazard for Semnan. The results were also displayed in terms of uniform hazard spectra for rock sites for return periods of 100, 475 and 2475 years, which is deemed appropriate for structural design standards in the Iran building code. As the results of this study have been displayed on the map for different return periods and different natural periods, it can provide the basis for the preparation of new seismic risk maps.

New Probabilistic Seismic Hazard Model for Nepal Himalayas by Integrating Distributed Seismicity and Major Thrust Faults

Nepal is one of the most seismically active regions in the world, as highlighted by the recent devastating 2015, Mw~7.8 Gorkha earthquake, and a robust assessment of seismic hazard is paramount for the design of earthquake-resistant structures. In this study, we present a new probabilistic seismic hazard assessment (PSHA) for Nepal. We considered data and findings from recent scientific publications, which allowed us to develop a unified magnitude homogenized seismicity catalog and propose alternative seismic source characterization (SSC) models including up-to-date parameters of major thrust faults like main frontal thrust (MFT) and main boundary thrust (MBT), while also considering existing SSC models and various seismic hazard modeling strategies within a logic tree framework. The sensitivity analyses show the seismic hazard levels are generally higher for SSC models integrating the major thrust faults, followed by homogenous volume sources and smoothed seismicity approach. The seismic hazard maps covering the entirety of Nepal are presented as well as the uniform hazard spectra (UHS) for five selected locations (Kathmandu, Pokhara, Biratnagar, Nepalganj, and Dipayal) at return periods of 475- and 2475-years considering Vs,30 = 760 m/s. The results obtained are generally consistent with most recent studies. However, a notable variability in seismic hazard levels and several discrepancies with respect to the Nepal Building Building Code NBC105: 2020 and global hazard model, GEM are noted, and possible causes are discussed.

Estimation of Damage Scenarios in Mexico City Caused by Nearby Crustal Earthquakes

ABSTRACT Mexico City has sustained severe damage from earthquakes located in the subduction zone and within the subducted Cocos plate. The city lies in the trans-Mexican volcanic belt (TMVB). Earthquakes in the TMVB are relatively infrequent but have reached Mw>6. A recent Mw 6.9 crustal earthquake occurred in 1912, 80 km from Mexico City. Damage scenarios are estimated for two hypothetical crustal earthquakes located 40 and 80 km from the city. The seismic sources represent hazard-critical earthquakes and are based on historical seismicity and on the geological record. The probability distribution of ground acceleration is determined by ground-motion models (GMMs) from similar tectonic regions. Site effects are included to account for the geotechnical zonation of the city, and vulnerability curves are calculated for residential buildings in the cadastral record of Mexico City. The results show that an earthquake near the 1912 earthquake would produce accelerations of 37 and 148 cm/s2 on firm ground and in the lake region, respectively. In this scenario, damage is concentrated in buildings 1-2 stories high located near the transition zone. The earthquake located ∼40 km from Mexico City shows accelerations of 79 and 318 cm/s2 on firm ground and in the lake region, respectively. This scenario concentrated potential damage in buildings 1-2 stories high and broadly distributed in the region underlain by soft clays. Under both scenarios, no damage is expected in buildings higher than ∼11 stories. A deterministic approach using two potential seismic sources instead of a probabilistic seismic hazard model is used because of the lack of background seismicity and the unknown recurrence times of events in the TMVB. The results show very different damage patterns for crustal earthquakes. The two scenarios presented here may be useful for decision makers and insurance companies to estimate physical damage and to implement mitigation programs.

Modelling site response at regional scale for the 2020 European Seismic Risk Model (ESRM20)

Quantitative estimation of seismic risk over a region requires both an underlying probabilistic seismic hazard model and a means to characterise shallow site response over a large scale. The 2020 European Seismic Risk Model (ESRM20) builds on the 2020 European Seismic Hazard Model (ESHM20), requiring additional information to firstly parameterise the local site condition across all of Europe, and subsequently determine its influence on the prediction of seismic ground motion. Initially, a harmonised digital geological database for Europe is compiled, alongside a model of topographic/bathymetric elevation and a database of 30 m averaged shearwave velocity measurements (V_{S30}), in order to produce separate 30 arc-second maps of inferred V_{S30} based on topography and on geology. We then capitalise on a large database of seismic recording stations in Europe for which site-to-site ground motion residuals (delta S2S_{S}) have been determined with respect to the shallow crustal ground motion model used in the ESHM20. These residuals allow us to incorporate site amplification functions into the European GMM calibrated upon either observed or inferred V_{S30}, or on the European geology and topography models. We present the resulting pan-European seismic site amplification model and assess its impact on seismic hazard and risk compared against other approaches. The new site amplification model fulfils the requirements of the ESRM20 and, providing uncertainty is fully propagated, yields estimates of seismic hazard and risk at a large space scale that may be comparable to other methods often applied at local/urban scale where better-constrained site information is available.

A Caribbean and Central America Seismic Hazard Model for Sovereign Parametric Insurance Coverage

ABSTRACTA fully probabilistic seismic hazard model with a single domain and sufficiently accurate resolution level for national analyses has been developed, for the Caribbean and Central America, to support the design of parametric earthquake policies offered by the Caribbean Catastrophe Risk Financing Facility to sovereign countries. This model provides updated earthquake hazard and risk information for 34 countries in the region, allowing to obtain detailed seismic hazard results at any location within the area of analysis. Besides a detailed zonation of subduction and crustal sources, updated seismicity and tectonic data have been utilized. Different seismicity, geometric, and rupture models have been adopted using state-of-the-art methodologies and tools. The main output of this model is a stochastic event-set, which is the hazard representation utilized not only to compute a long-term overview of the seismic hazard in the region but also to probabilistically estimate earthquake modeled losses at a national level that are used as triggers for underpinning parametric earthquake insurance. Although not of direct interest for parametric insurance purposes, this model also yields hazard maps and uniform hazard spectra for different return periods. For the operational purposes of the parametric insurance coverage, a postevent tool was developed to calculate, in near-real time, the ground-motion intensities associated with any earthquake within the region under study. This is done automatically by choosing a rupture plane from the moment tensor solution based on predefined rules while maintaining full consistency with all the assumptions made in the probabilistic seismic hazard analysis. The predicted ground motions in the region and the vulnerability functions developed for the exposed assets are then used to estimate whether the economic losses for each affected country exceed the trigger value stated in the country-specific insurance policy conditions and whether a payout should be issued, which is typically disbursed within 14 days.

A probabilistic seismic hazard model for Greenland

Greenland belongs to a stable continental region where seismic activity is low. Due to this factor and low population, only one probabilistic seismic hazard model of Greenland has been published, showing only a peak ground acceleration map. We constructed a probabilistic seismic hazard model for Greenland in order to complete our global earthquake risk map. We used a smoothed seismicity method due to the lack of recognized active faults. An earthquake magnitude-frequency distribution was derived based on the recorded earthquakes from 1933 to 2013. We assumed a maximum earthquake magnitude of 7.0 for the distribution, given that the magnitude of the largest recorded tectonic earthquake in the region is about 6.0. The NGA-East ground motion models were employed for ground shaking calculations. Finally, we presented seismic hazard maps in terms of peak ground acceleration, spectral acceleration at 0.2 ​s and 1.0 ​s, and hazard curves for several of the major cities.

An updated area-source seismogenic model (MA4) for seismic hazard of Italy

Abstract. A new probabilistic seismic hazard model, called Modello di Pericolosità Sismica 2019 (MPS19), has been recently proposed for the Italian territory, as a result of the efforts of a large national scientific community. This model is based on 11 groups of earthquake rupture forecast inputs and, particularly, on 5 area-source seismogenic models, including the so-called MA4 model. Data-driven procedures were followed in MA4 to evaluate seismogenic parameters of each area source, such as upper and lower seismogenic depths, hypocentral-depth distributions, and nodal planes. In a few cases, expert judgement or ad hoc assumptions were necessary due to the scarcity of data. MA4 consists of 20 seismicity models that consider epistemic uncertainty in the estimations of the completeness periods of the earthquake catalogue, of maximum magnitude values and of seismicity rates. In particular, five approaches were adopted to calculate the rates, in the form of the truncated Gutenberg–Richter frequency–magnitude distribution. The first approach estimated seismicity rates using earthquakes located in each area source, while the other approaches firstly calculated the seismicity rates for groups of areas considered tectonically homogeneous and successively partitioned in different ways the values to the area forming each group. The results obtained in terms of seismic hazard estimates highlight that the uncertainty explored by the 20 seismicity models of MA4 is at least of the same order of magnitude as the uncertainty due to alternative ground motion models.

A probabilistic deformation-based seismic hazard model for Iran

Probabilistic seismic hazard analysis, as the most prevalent approach to evaluate earthquake hazard, is commonly based on earthquake catalogs. Although previous studies show that the recurrence time of large-magnitude (Mw> 7.0) events in Iran is more than ~ 1000–2000 years, the available instrumentally recorded earthquakes are limited to less than 100 years. With the idea of having another proxy for seismicity rates, we propose a methodology to evaluate activity rates from strain rates in a combination of regional estimates of \(\beta\) and \(m_{\max }\). Considering the comprehensive deformation model of the Iranian Plateau, we found that the deformation-based occurrence rates are more than the catalog-based occurrence rates in all seismotectonic provinces in the Iranian Plateau. The ratios of the deformation-based to the catalog-based occurrence rate are between 1.34 and 2.35. For the first time, a probabilistic deformation-based seismic hazard model for the Iranian plateau is also developed and Peak Ground Acceleration (PGA) values for 10% and 2% POEs in 50 years are estimated. The highest levels of PGA are found in the Azerbaijan and Alborz seismotectonic provinces, where the highest value of strain rates is located. For all provinces, except the Zagros region, the spatial averages of PGA with 10% POE in 50 years from the deformation-based model are up to ~ 23% higher than those from a traditional probabilistic seismic hazard.

Development of probabilistic seismic hazard microzonation maps at the surface level for central-east Iran (Kerman region), using a hybrid site condition model

This study presents the spatial distribution of a grid-based probabilistic seismic hazard model at the surface level for the Kerman region in central-east Iran, using a hybrid site condition model. The hazard model has provided the variation of the peak ground acceleration (PGA), and 5% damped spectral accelerations (SA) at the fundamental periods of 0.2 and 1.0 seconds (s) on 0.05° grids. The study has used a seismotectonic dataset including ∼400 linear seismic sources to characterize the seismic source models. In order to capture the uncertainties of the seismic hazard sources, the model used a logic tree approach, including eight ground motion prediction equations (GMPEs), three characteristic source models, two different declustering methods, three choices for earthquake recurrence parameters, and three alternatives for the maximum credible earthquake. Besides, various GMPEs have been evaluated against local datasets. For this, a series of GMPEs developed based on local, regional, and global data have been selected to find their compatibility with the studied area through statistical analyses, so-called likelihood (LH), and log-likelihood (LLH) tests. Generally, the results display that a wide range of seismic hazards can be expected in the region. For instance, the horizontal PGA with a 10% probability of exceedance in 50 years, ranges between ∼(0.1–0.5)g in the north-eastern and south-western parts of the region, respectively. Moreover, the results indicate that the ad-hoc 1.5 factor to scale a 475-year return period (RP) spectrum for making the ground shaking similar to a 2475-year RP not only is unrealistic, but also creates substantially an underestimated ground shaking; thus, it seems too crude for the seismic design purposes. We have also developed some relationships, dependent on site conditions, for describing general relations between the obtained results in the return periods of 475- and 2475-years for PGA, SA (0.2s), and SA (1.0s). The computed hazard spectra have also been compared to the minimum acceptable level of seismic hazard in the region, according to the latest version of the Iranian national seismic hazard map. In addition, in order to make the results more transparent to the scientific and engineering community, the range of uncertainty contributed to the hazard modeling has also been explored in terms of a relative uncertainty metric. In total, the outcome of this study can make transparency into the picture of the seismic hazard level in central-east Iran and shed insight into possible developing plans.

Learning From Success, Not Catastrophe: Using Counterfactual Analysis to Highlight Successful Disaster Risk Reduction Interventions

In the aftermath of a disaster, news and research attention is focused almost entirely on catastrophic narratives and the various drivers that may have led to the disaster. Learning from failure is essential to preventing future disasters. However, hyperfixation on the catastrophe obscures potential successes at the local scale, which could serve as important examples and learning resources in effective risk mitigation. To highlight effective risk mitigation actions that would otherwise remain unnoticed, we propose the use of probabilistic downward counterfactual analysis. This approach uses counterfactual modelling of a past hazard event with consequences made worse (i.e. downward counterfactual) by the absence of the mitigation intervention. The approach follows probabilistic risk analysis procedures where uncertainties in the simulated events and outcomes are accounted for and propagated. We demonstrate the method using a case study of Nepal’s School Earthquake Safety Program, implemented before the 2015 Mw 7.8 Gorkha earthquake. Using a school building database for Kathmandu Valley, Nepal, we present two applications: 1) the quantification of lives saved during the Gorkha earthquake as a result of the retrofitting of schools in Kathmandu Valley since 1997, 2) the quantification of the annual expected lives saved if the pilot retrofitting program was extended to all school buildings in Kathmandu Valley based on a probabilistic seismic hazard model. The shift in focus from realised outcome to counterfactual alternative enables the quantification of the benefits of risk reduction programs amidst disaster, or for a hazard that has yet to unfold. Such quantified counterfactual analysis can be used to celebrate successful risk reduction interventions, providing important positive reinforcement to decision-makers with political bravery to commit to the implementation of effective measures.

A Probabilistic Physics-Based Seismic Hazard Model for the Alborz Region, Iran

ABSTRACTThe seismic activity rate is one of the most significant factors in seismic hazard modeling. Although it is usually estimated from observed seismicity, a complete picture of the possible earthquakes is not always available since catalogs of the observed earthquakes are short and incomplete. Long-term physics-based numerical simulations, providing a comprehensive range of earthquakes, are a decent way to overcome such deficiency. With this contribution, we built a seismic hazard model for the Alborz region, Iran, using a long-term physics-based synthetic earthquake catalog, enriched with the additional consideration of background seismicity derived from a deformation model. 200,000 yr synthetic catalogs for the Alborz region, Iran, are used and validated by considering the recurrence time of large-magnitude events estimated from the paleoseismological investigation on individual faults. The magnitude–frequency distribution (MFD) from the synthetic earthquake catalog is then compared with the MFD based on observation, which overall indicates good compatibility, although there are discrepancies for some faults. The estimated peak ground acceleration (PGA) for the Alborz region varies in the ranges of 0.16–0.52g and 0.27–1.0g for 10% and 2% probability of exceedance in 50 yr, respectively. The absolute natural logarithm differences averaged across the region are ∼0.21, corresponding to an average of 23% difference in PGA values in comparison with the most up-to-date observed-based hazard model. Hazard curves for several populated cities are also presented and compared with the other independent estimates. The proposed procedure could be an alternative approach to evaluate seismic hazard for a seismically active region, in particular for those without a complete catalog of observed earthquakes.

Seismic zonation and default suites of ground-motion records for time-history analysis in the South Island of New Zealand

The rise of performance-based earthquake engineering, in combination with the complexity associated with selecting records for time-history analysis, demonstrates an expressed need for localized default suites of ground motion records for structural designers to use in the absence of site-specific studies. In the current research investigation, deaggregations of probabilistic seismic hazard models (National Seismic Hazard Model, Canterbury Seismic Hazard Model, and Kaikōura Seismic Hazard Model) and the location-specific seismological characteristics of expected ground motions were used to define eight seismic hazard zonations and accompanying suite profiles for the South Island of New Zealand to satisfy the requirements of the New Zealand structural design standard NZS1170.5 for response-history analyses. Specific records, including 21 from the recent Kaikōura, Darfield, and Christchurch earthquakes, were then selected from publicly-available databases and presented as default suites for use in time-history analyses in the absence of site-specific studies. This investigation encompasses seismic hazards corresponding to 500-year return periods, site classes C (shallow soils) and D (deep soils), and buildings with fundamental periods between 0.4 and 2.0 seconds.

History of probabilistic seismic hazard assessment studies and seismic zonations in mainland France

This article aims to provide an overview of successive seismic zonations in mainland France and probabilistic seismic hazard studies performed over the previous ≈30 years. A short presentation is given on the engineering and regulatory framework that shapes the background of seismic zonation and hazard studies, followed by a scientific overview of published probabilistic seismic hazard estimations. The components of these past PSHA studies are summarized (seismic source models, ground-motion models, management of uncertainties). The evolution of hazard estimates with time is displayed for a set of representative cities. Finally, three generations of official seismic zonation maps in France are presented (1967, 1986, 2004), and the evolution of methods and results is highlighted. This review shows that the academic community has previously had little involvement in this topic. As current zonation relies on outdated models, there is an opportunity for scientific and engineering communities to efficiently work together to build the next generation of probabilistic seismic hazard models for France.

The power of the little ones: Computed and observed aftershock hazard in Central Italy

Seismic hazard in Central Italy due to the 2016–2017 seismic sequence is modeled using a standard probabilistic aftershock seismic hazard model. Two key features of the model are the consideration of time-dependent aftershock occurrence, modeled by stacking Omori decay curves associated with the three largest ( Mw > 5.5) events, and the incorporation of geologic information by modeling the locations of expected seismicity along realistic fault surfaces. The computed seismic hazard at Amatrice indicates higher hazard values compared to those computed using a conventional time-independent hazard analysis. We then compare the computed hazard curves against empirical hazard curves constructed for 12 individual recording stations in terms of peak ground acceleration, each with at least 35 (and up to 231) recordings. At eight sites, the observed exceedances fall within one standard deviation of the expected mean, while at the remaining sites, the observed exceedances fall outside this range indicating a poorer match. The soil sites are among the stations with the poorest match, suggesting that site effects may not be accurately modeled with the current approach.