Probabilistic Seismic Hazard Assessment Research Articles

Why do seismic hazard models worldwide appear to overpredict historical intensity observations?

Probabilistic seismic hazard assessments (PSHAs) provide the scientific basis for building codes to reduce damage from earthquakes. Despite their substantial impact, little is known about how well PSHA predicts actual shaking. Recent PSHA for California, Japan, Italy, Nepal, and France appear to consistently overpredict historically observed earthquake shaking intensities. Numerical simulations show that observed shaking is equally likely to be above or below predictions. This result from independently developed models and datasets in different countries and tectonic settings indicates possible systematic bias in the hazard models, the observations, or both. Analysis of possible causes shows that much of the discrepancy is due to a subtle and rarely considered issue: the conversion equations used in comparing the models-which forecast shaking as peak ground acceleration or velocity-and observations-parameterizations of qualitative shaking reports. Historical shaking reports fill a crucial data gap, but more research is warranted on how qualitative observations relate to instrumental shaking measures for earthquakes.

Site characterisation and probabilistic seismic hazard assessment in Tura City, Meghalaya

Site characterisation and probabilistic seismic hazard assessment in Tura City, Meghalaya

Probabilistic Seismic Hazard Assessment Studies on the Central-East of Iran—Kerman Region

Probabilistic Seismic Hazard Assessment Studies on the Central-East of Iran—Kerman Region

The Main Factors Controlling Probabilistic Seismic Hazard Variability Due to Epistemic Uncertainty in Greece: Results from a One-Factor-at-a-Time Analysis

Abstract We present a one-factor-at-a-time (OFAT) sensitivity study for the Probabilistic Seismic Hazard Assessment (PSHA) in Greece. The analysis examines several PSHA controlling factors, such as seismic source model (geometry, etc.), active tectonics (faulting type, etc.), as well as the employed ground-motion prediction equations (GMPEs). We have considered only peak ground acceleration (PGA) and peak ground velocity (PGV) for a typical PSHA scenario (10% probability of exceedance in 50 yr). OFAT results are presented using Tornado diagrams for 42 major urban centers of Greece that cover the study area revealing regions of different PSHA uncertainty. In general, the most critical factors controlling PSHA uncertainties are the Gutenberg–Richter (G-R) parameters (a and b), as well as the employed GMPE. However, significant spatial variability of these factors is observed with large differences between high- and low-seismicity regions, as well as between PGA and PGV. The results not only provide an objective assessment of the variability of PSHA uncertainties but also verify the need for additional work to minimize epistemic PSHA uncertainties, focusing on the most critical factors that control PSHA.

Unveiling earthquake hazard in Noida, India: a combined probabilistic and deterministic seismic hazard assessment

Unveiling earthquake hazard in Noida, India: a combined probabilistic and deterministic seismic hazard assessment

Uncertainty and sensitivity assessments on the inputs of probabilistic seismic hazard assessment: A case study of the North Tehran fault

Probabilistic seismic hazard analysis (PSHA) often incorporates significant uncertainty in its inputs, which have the potential to substantially affect the estimated hazards. To improve the reliability of seismic hazards, the present work examines how these uncertainties impact the variability of PSHA and disaggregation results. For this purpose, uncertainty and sensitivity analyses have been performed for different sites in the Tehran region, with the seismic source of the North Tehran Fault as a case study. The results show that uncertainties in the input parameters have a moderate to significant effect on the PSHA and disaggregation results. The uncertainty and sensitivity analyses of this study provide a better understanding of the various PSHA parameters and their associated uncertainties. Therefore, such analyses establish confidence in the PSHA results and expose the main sources of uncertainty, which enable the prioritization of endeavors to reduce hazard variability.

Comparison of geodetic slip-deficit and geologic fault slip rates reveals that variability of elastic strain accumulation and release rates on strike-slip faults is controlled by the relative structural complexity of plate-boundary fault systems

Comparison of geodetic slip-deficit rates with geologic fault slip rates on major strike-slip faults reveals marked differences in patterns of elastic strain accumulation on tectonically isolated faults relative to faults that are embedded within more complex plate-boundary fault systems. Specifically, we show that faults that extend through tectonically complex systems characterized by multiple, mechanically complementary faults (that is, different faults that are all accommodating the same deformation field), which we refer to as high-Coefficient of Complexity (or high-CoCo) faults, exhibit ratios between geodetic and geologic rates that vary and that depend on the displacement scales over which the geologic slip rates are averaged. This indicates that elastic strain accumulation rates on these faults change significantly through time, which in turn suggests that the rates of ductile shear beneath the seismogenic portion of faults also vary through time. This is consistent with models in which mechanically complementary faults trade off slip in time and space in response to varying mechanical and stress conditions on the different component faults. In marked contrast, structurally isolated (or low-CoCo) faults exhibit geologic slip rates that are similar to geodetic slip-deficit rates, regardless of the displacement and time scales over which the slip rates are averaged. Such faults experience relatively constant geologic fault slip rates as well as constant strain accumulation rate (aside from brief, rapid post-seismic intervals). This suggests that low-CoCo faultsd "keep up" with the rate imposed by the relative plate-boundary condition, since they are the only structures in their respective plate-boundary zone that can effectively accommodate the imposed steady plate motion. We hypothesize that the discrepancies between the small-displacement average geologic slip rates and geodetic slip-deficit rates may provide a means of assessing a switch of modes for some high-CoCo faults, transitioning from a slow mode to a faster mode, or vice versa. If so, the differences between geologic slip rates and geodetic slip-deficit rates on high-CoCo faults may indicate changes in a fault's behavior that could be used to refine next-generation probabilistic seismic hazard assessments.

Probabilistic seismic hazard assessment for the United Arab Emirates using integrated seismic source model

This study emphasizes the role of active faults as seismogenic sources in probabilistic seismic hazard assessments (PSHA) in the United Arab Emirates (UAE). An extensive PSHA analysis has been carried out in this study, which incorporates faults alongside area seismic sources within a logic tree-oriented framework. Seismicity is evaluated in terms of spectral acceleration (SA) and Peak ground acceleration (PGA) for return periods of 2,475, 975, and 475 years at 5 % damping. The results are compared with seismic hazard projections derived from previous PSHA studies that utilized only area sources. A key observation is the pronounced impact of the Dibba and Oman range frontal faults on the UAE's northeastern region due to the proximity of the faults. This contributes to higher seismic hazard in this region, with some return periods showing greater hazard levels than those documented in earlier studies. In order to aid seismic hazard design in the UAE, contour maps depicting the SAs at 0.2 and 1.0 s, along with PGA, are developed. The analysis reveals that the highest seismic hazard is predicted along the northeastern borders of the UAE, particularly the coastal area of Ras-Al Khaimah, with a PGA of 0.22 g for a return period of 2,475 years.

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.

Earthquake forecasting model for Albania: the area source model and the smoothing model

Abstract. We proposed earthquake forecasting models for Albania, one of the most seismogenic regions in Europe, to give an overview of seismic activity by implementing area source and smoothing approaches. The earthquake catalogue was first declustered to remove foreshocks and aftershocks when they are within the derived distance windows and time windows of mainshocks. Considering catalogue completeness, the events with M≥4.1 during the period of 1960–2006 were implemented for the learning forecast model. The forecasting is implemented into an area source model that includes 20 sub-regions and a smoothing model with a cell size of 0.2∘ × 0.2∘ to forecast the seismicity in Albania. Both models show high seismic rates along the western coastline and in the southern part of the study area, consistent with previous studies that discussed seismicity in the area and currently active regions. To further validate the forecast performance of the two models, we introduced the Molchan diagram to quantify the correlation between models and observations. The Molchan diagram suggests that the models are significantly better than a random distribution, confirming their forecasting abilities. Our results provide crucial information for subsequent research on seismic activity, such as probabilistic seismic hazard assessment.

Compilation of a Comprehensive Earthquake Catalog and Relocations in the Caucasus Region

Abstract Instrumental seismic monitoring has a long history in the Caucasus and started in 1899 when the first seismograph was installed in Tbilisi, Georgia. Much of the analog paper records from this time period are preserved in the Tbilisi archives because Georgia served as the regional data center. In the 1990s, due to the collapse of the Soviet Union and the political turmoil in the region, the analog networks and the communication between the newly formed national networks deteriorated. In Georgia, for the next 13 yr, the seismic network coverage was poor until the 2002 Tbilisi earthquake. Following this earthquake, the first permanent digital seismic station in Georgia was established in Tbilisi in 2003. The digital era progressively improved the ability to collect and archive data and today more than a hundred broadband seismic stations (including temporary arrays) are operating in the southern Caucasus. Until recently, the region lacked a coordinated effort to catalog all analog and digital era data collected by different countries into a single repository. As a result of collaboration between Lawrence Livermore National Laboratory, the Ilia State University, and the Republican Seismic Survey Center of Azerbaijan, a comprehensive earthquake catalog was compiled for the Caucasus and neighboring areas as part of a broader probabilistic seismic hazard assessment project. This project digitized Soviet-era paper bulletins, compiled a unified earthquake catalog from regional bulletins, developed 1D reference velocity model, and used it to relocate the events. The final catalog contains 16,963 events with magnitudes 3.7 and above, bringing together all the available data sets in the Caucasus region from 1900 to 2015, significantly improving locations, and generating the most complete earthquake catalog in the region, temporally and geographically.

Detailed seismic zoning of the East Kazakhstan region in the Republic of Kazakhstan

Kazakhstan is currently drafting new construction regulations that comply with the major provisions of the Eurocodes. Such regulations are created on the basis of seismic zoning maps of various degrees of detail, developed by our Institute of Seismology using a new methodological approach for Kazakhstan. The article is about creating the first normative map of the Detailed Seismic Zoning on a probabilistic foundation for the Republic of Kazakhstan's East Kazakhstan region. We carried out the probabilistic assessment of seismic hazard using a methodology consistent with the main provisions of Eurocode 8 and updated compared with that used in developing maps of Kazakhstan's General Seismic Zoning and seismic microzoning of Almaty. The most thorough and current data accessible for the area under consideration were combined with contemporary analytical techniques. Updates have been done to not only the databases being used but also the way seismic sources were shown, including active faults now. On a scale of 1:1000000, precise seismic zoning maps of the East Kazakhstan region were created for two probabilities of exceedance: 10 % and 2 % in 50 years in terms of peak ground accelerations and macroseismic intensities. The obtained seismic hazard distribution is generally consistent with the General Seismic Zoning of Kazakhstan's previous findings. However, because active faults were included and a thoroughly revised catalog was used, there are more pronounced zones of increased danger along the fault in the western part of the region. In the west of the territory, acceleration values also increased due to a more accurate consideration of seismotectonic conditions. Zoning maps are the basis for developing new state building regulations of the Republic of Kazakhstan.

Fault Source Models Show Slip Rates Measured across the Width of the Entire Fault Zone Best Represent the Observed Seismicity of the Pallatanga–Puna Fault, Ecuador

AbstractWe explore how variation of slip rates in fault source models affect computed earthquake rates of the Pallatanga–Puna fault system in Ecuador. Determining which slip rates best represent fault-zone seismicity is vital for use in probabilistic seismic hazard assessment (PSHA). However, given the variable spatial and temporal scales slip rates are measured over, significantly different rates can be observed along the same fault. The Pallatanga–Puna fault in southern Ecuador exemplifies a fault where different slip rates have been measured using methods spanning different spatial and temporal scales, and in which historical data and paleoseismic studies provide a record of large earthquakes over a relatively long time span. We use fault source models to calculate earthquake rates using different slip rates and geometries for the Pallatanga–Puna fault, and compare the computed magnitude–frequency distributions (MFDs) to earthquake catalog MFDs from the fault zone. We show that slip rates measured across the entire width of the fault zone, either based on geodesy or long-term geomorphic offsets, produce computed MFDs that compare more favorably with the catalog data. Moreover, we show that the computed MFDs fit the earthquake catalog data best when they follow a hybrid-characteristic MFD shape. These results support hypotheses that slip rates derived from a single fault strand of a fault system do not represent seismicity produced by the entire fault zone.

Determination of ground motion parameters of urban centers of Balochistan province

Ground motion prediction equations (GMPEs) are cornerstone of Probabilistic Seismic Hazard Assessment. A big pool of GMPEs is available nowadays for active crustal and subduction zone categories which are derived from dataset of different regions including the database of Middle East, Europe (non-NGA) and NGA WEST 2 database. For countries like Pakistan which do not have local GMPEs, selection of GMPE is difficult and is merely based on hit and trial. A Comparative analysis of latest set of GMPEs for these respective categories on seismic hazard of Pakistan is unknown. In this study, Probabilistic Seismic Hazard analysis is conducted on urban centers (Gwadar and Quetta) of Balochistan province, a sample from Pakistan is given their potential to become economic hubs as rapid infrastructure development is expected in the region. The analysis is based on area source approach along with the modelling of major active crustal faults of the region. Three sets of GMPEs are selected where first set consists of GMPEs developed by NGA WEST 2, the second set consists of non-NGA based GMPEs while the third set is a hybrid set in which NGA WEST 2 and non-NGA based GMPEs are used together. Logic tree method is employed in this work to take into consideration of the epistemic uncertainty in different GMPEs for each tectonic zone and the seismic source models as well. For 10% probability of exceedance in 50 years (return period 475 years), updated hazard maps for PGA and spectral acceleration for structural period of 0.1 s, 0.2 s, and 1 s are created. These results can be effectively used to reduce seismic risk, to develop effective disaster mitigation, and management strategies.

Assessment of Liquefaction Hazard for Sites in Romania Using Empirical Models

This paper is focused on the evaluation of the liquefaction hazard for different sites in Romania. To this aim, a database of 139 ground motions recorded during Vrancea intermediate-depth earthquakes having moment magnitudes MW ≥ 6.0 is employed for the evaluation of the equivalent number of cycles for this seismic source. Several functional forms for the empirical evaluation of the equivalent number of cycles considering various seismological or engineering parameters are tested and evaluated. The regression analysis shows smaller uncertainties for the empirical models based on ground motion engineering parameters. Considering the lack of information in terms of engineering parameters, a simpler empirical model which accounts for the earthquake magnitude, source–site distance and soil conditions is selected for the liquefaction hazard analysis. Based on the proposed empirical model, specific magnitude scaling factors for Vrancea intermediate-depth earthquakes are proposed for the first time as well. The liquefaction hazard analysis is performed for sites whose seismic hazard is generated by either the Vrancea intermediate-depth seismic source or by local shallow crustal seismic sources. In the case of some of the selected sites, liquefaction phenomena were observed during past large-magnitude earthquakes. Unlike previous studies dealing with liquefaction analyses for sites in Romania, in this research, the hazard assessment is performed for various ground motion levels evaluated based on probabilistic seismic hazard assessment. Liquefaction hazard curves are constructed for each analyzed site. The results of the liquefaction hazard analysis show that this phenomenon is more likely to occur in the areas exposed to Vrancea intermediate-depth earthquakes, compared to the areas affected by local shallow earthquakes. In the case of the analyzed soil profiles from Bucharest, Craiova and Ianca, the minimum liquefaction safety factors less than one even for seismic hazard levels having mean return periods of 100 years and less.

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.

The New Zealand Community Fault Model – version 1.0: an improved geological foundation for seismic hazard modelling

ABSTRACT The New Zealand Community Fault Model (NZ CFM) is a publicly available representation of New Zealand fault zones that have the potential to produce damaging earthquakes. Compiled through collaborative engagement between New Zealand earthquake-science experts, this first edition (version 1.0) of the NZ CFM builds upon previous compilations of earthquake-source active fault models with the addition of new and modified information. Developed primarily to support an update of the New Zealand National Seismic Hazard Model, the NZ CFM comprises two principal components. The first dataset is a two-dimensional map representation of the surface traces of 880 generalised fault zones. Each fault zone is assigned specific geometric and kinematic attributes, including uncertainties, supplemented with a subjective quality ranking focused primarily on the confidence in assigned slip rates. The second component is a three-dimensional representation of the fault zones as triangulated mesh surfaces that are projected down-dip from the two-dimensional mapped traces to a geophysically-defined maximum fault rupture depth. This article summarises the compilation and parameterisation of the NZ CFM, along with background on its relation to predecessor datasets, and forward applications to probabilistic seismic hazard assessment and physics-based earthquake models currently being developed for Aotearoa New Zealand.

Seismic Hazard in Greece: A Comparative Study for the Region of East Macedonia and Thrace

Greece is located in one of the most seismically active regions in Europe. Many seismic hazard studies have been performed for various sites around Greece, at a regional or local scale. However, the latest national seismic hazard map, currently used for the seismic design of buildings and infrastructure, was published in 2000 and has not been updated since then. In light of recent advances in seismic source and ground motion modeling, the present study focuses on a comparative Probabilistic Seismic Hazard Assessment (PSHA) for the region of East Macedonia and Thrace (EMTH), located in Northern Greece. Various seismic source models are implemented and compared against an updated earthquake catalog to form the necessary source model logic tree. The ground motion logic tree is composed of Ground Motion Prediction Equations (GMPEs), which have been proven suitable for implementation in Greece. PSHA results are presented for the most important cities of East Macedonia and Thrace in a comparative way, which highlights the variability of the seismic hazard among the various seismic source models. An updated seismic hazard map of the study area is proposed, and a comparative disaggregation analysis is performed to estimate the earthquake scenarios with the largest contribution to the seismic hazard.

Probabilistic seismic hazard and risk assessment of Mizoram, North East India

This paper presents seismic hazard and risk assessment for the state of Mizoram based on a classical probabilistic seismic hazard analysis and event-based probabilistic seismic risk analysis. For the seismic hazard estimation, analysis has been performed considering the areal source model, fault zone polygon, and smoothed gridded seismicity model. The earthquake activity rates for these source zones and smoothed gridded seismicity sources are estimated from the homogenized and declustered earthquake catalogue. The logic tree framework is applied in the seismic source models and Ground Motion Prediction equations (GMPEs) to account for the epistemic uncertainties. Five Next-generation attenuation (NGA) GMPEs for the active shallow region and three GMPEs for the Indo-Burma subduction zone have been used to evaluate the hazard at the reference rock condition (Vs30 ​= ​760 ​m/s). Peak Ground Acceleration (PGA) and Spectral Acceleration (SA) at 0.2 s and 1s are estimated for each eight districts headquarters of Mizoram for a 2% and 10% probability of exceedance in 50 years. The hazard curves and Uniform Hazard Spectra (UHS) are also presented. For seismic risk analysis, building exposure data are based on digitized building footprint and 2011 Housing Census data of India. All the buildings are classified into three classes, and seismic vulnerability functions are assigned to each building class. The area per building class is assigned from the digitized footprint. Building replacement costs per square meter have been chosen based on expert input and values identified from past study. Lastly, the study conducted a seismic risk analysis using the Open Quake-engine's probabilistic event-based methodology to estimate risk metrics at the district level, such as average annual losses and probability curves for loss exceedance. The study's findings provide valuable insights into the most high-risk areas, the building construction types that are most vulnerable to seismic activity, and the anticipated economic losses in the state of Mizoram. These results can serve as a guide for local government authorities in developing future city plans and implementing earthquake risk mitigation strategies.

A Logic-Tree Approach for Probabilistic Seismic Hazard Assessment in the Administrative Region of Attica (Greece)

Probabilistic Seismic Hazard Assessment (PSHA) was carried out for the administrative region of Attica (Greece). Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) values were calculated for return periods of 475 and 950 years for five sub-areas covering the entire region. PGA hazard curves and Uniform Hazard Spectra (UHS) in terms of spectral acceleration (Sa) values were generated for Athens, Methana, and the capitals of each island of Attica (Salamina, Aegina, Poros, Hydra, Spetses, Kythira, and Antikythira). Area sources were adopted from the Euro-Mediterranean Seismic Hazard Model 2013 (ESHM13) and its update, ESHM20, taking into account both crustal and slab tectonic environments. Ground Motion Prediction Equations (GMPEs) proposed for the Greek territory were ranked for PGA and PGV. Each GMPE was reconstructed as a weighted model, accounting for normal and non-normal focal mechanisms for each area source. PGA, PGV, and Sa values were computed using a logic tree, integrating the seismotectonic models as major branches and sub-logic trees, comprised of multiple ranked GMPEs for each area source, as minor branches. The results showed higher seismic hazard values in sub-areas near the Gulf of Corinth and the slab interface, which could indicate a need to revise the active building code in Attica.