Seismic Hazard Assessment Research Articles

Shear-wave velocity structure from the near-surface to mid-crust beneath the southern Korean Peninsula using P-wave polarization analysis

Abstract The near-surface velocity structure provides critical information for seismic hazard assessment, ground motion simulation, and site amplification studies. However, accurate estimation typically requires costly core sampling from boreholes and/or seismic exploration. As an alternative, we estimated near-surface to mid-crustal shear-wave velocities in the southern Korean Peninsula using P-wave polarization analysis, which utilizes only the incident angles of direct P waves from earthquakes. We extended the polarization analysis by employing several different frequency bands to estimate shear-wave velocities from the surface down to the mid-crust. P waveforms were bandpass-filtered with three different frequency bands (0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz) to determine shear-wave velocities at different depths. The P-wave polarization results show a strong correlation between geological features and velocity distributions across the frequency bands. The P-wave polarization results for the frequency bands of 0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz indicate velocity distributions of 3.50 ± 0.35 km/s, 3.00 ± 0.69 km/s, and 2.26 ± 0.69 km/s, respectively. Comparison with velocity structures estimated from Rayleigh-wave ellipticity and site surveys reveals that these values from frequency bands of 0.05–0.3 Hz, 0.5–2 Hz, and 3–10 Hz correspond to average velocities from the surface to depths of 3–16 km, 0.1–3 km, and 5–100 m, respectively. The polarization analysis demonstrates superior performance in estimating near-surface shear-wave velocity compared to the Rayleigh-wave ellipticity method.

Identification of anthropogenic activities interference in the seismic catalog for Banat and Danubian region, Romania

Abstract Banat and Danubian regions are among the most active zones in terms of crustal seismicity in Romania. Even though active seismic monitoring started in the early 20th century, the data sets got more performant with the development and expansion of seismic network monitoring in the late 1970’s. One particularity regarding seismic data acquisition is that in many cases anthropogenic activity, such as mining and quarry exploitation, interferes with natural seismicity. We aim to bring forward a series of data extracted from the ROMPLUS catalog to identify anthropogenic interference. To this aim, we propose a procedure based on multiple discrimination criteria, such as local time of event occurrence, magnitude, location concerning the nearest exploitation site, depth, and P wave input analysis (polarity and waveform). Identifying and filtering the anthropogenic events from the catalog will result in better imaging and characterizing of the natural seismic phenomenon in Banat and Danubian zones, improving the regional seismic hazard assessment this way.

High-resolution geological studies of seismogenic structures

Strong earthquakes rank among the most devastating natural disasters, with the potential to inflict catastrophic damage on communities and critical infrastructure worldwide. The structural geological and geophysical study of seismogenic features remains a cornerstone of earthquake research, providing essential insights into the dynamic processes driving these powerful events. High-resolution investigations in geomorphology, stratigraphy, and structural geology allow for a detailed understanding of the spatial and temporal characteristics of seismic deformations, encompassing co-seismic, post-seismic, and inter-seismic stages, potentially spanning multiple earthquake cycles. The integration of cutting-edge techniques—such as high-resolution data from Light Detection and Ranging (LiDAR), Structure from Motion (SfM), geophysical surveys, drilling, and frictional laboratory experiments—coupled with precise dating methods, enables quantitative analysis at high spatial resolutions across diverse temporal ranges, from years to millions of years. Recent advancements in frictional experimental techniques and numerical modeling have also significantly refined our understanding of deformation processes within seismogenic structures. This special issue compiles research on tectonic activities related to seismogenic structures from varied global tectonic setting, with a focus on leveraging high-resolution spatial data and sophisticated dating techniques. The contributions aim to deepen our understanding of the dynamics underlying strong earthquakes and improve our capacity for seismic hazard assessment.

Geodetic Strain Rates and Seismicity Rates Along the Apennines (Italy)

AbstractThe Apennines are a tectonically active belt that has experienced significant earthquakes (Mw6). The largest events primarily occurred along the chain axis, where a complex system of normal faults accommodates 2–3 mm/yr of SW‐NE oriented extension, as precisely measured by a dense Global Navigation Satellite System network. Geodetic strain rates are now frequently used in earthquake hazard models; however, the impact of using such estimates, computed through different methods, for seismic hazard assessments may be difficult to evaluate. This study explores the relationship between geodetic strain rates and seismicity rates in the Apennines using three distinct horizontal strain rate maps and an instrumental seismicity catalog. We find that the principal directions of geodetic strain rate are kinematically consistent with those of strain release. We estimate a spatially heterogeneous seismogenic thickness using the distribution of earthquake depths, and we isolate likely independent seismicity using three different declustering methods. We observe a correlation between independent seismicity rates and the magnitude of strain rate, which can be represented by either a linear or, more accurately, by a power‐law relationship. The variability in the strain‐seismicity relationship depends on the combination of independent seismic catalogs and strain rate maps. This relationship is primarily influenced by the declustering technique more than the choice of the strain rate map and, in particular, by the number of aftershocks excluded during declustering. Seismicity models derived from these combinations were used to estimate and compare the seismic moment release rate with the tectonic moment rate estimated from strain rate maps and seismogenic thickness. Findings indicate that the tectonic moment rate exceeds the seismic moment release rate. We highlight uncertainties and potential causes, one of which could be a possible aseismic release of part of the moment rate.

Global Research Trends in Performance-Based Structural Design: A Comprehensive Bibliometric Analysis

In the context of seismic hazard assessment and engineering design, a comprehensive understanding of local geological and geophysical factors is essential. However, previous studies have lacked crucial components such as local soil condition, ground response analysis, topographic influences, active fault characteristics, slip rates, groundwater behaviour, and slope considerations. To ensure the accuracy of the seismic hazard map of a country for the safe and cost-effective design of engineering structures in urban areas, a detailed analysis of these factors is imperative. Moreover, multidisciplinary investigations, such as logic-tree considerations, are needed to enhance seismic hazard maps. As a result, adopting a performance-based approach in structural design has become an essential priority. A performance-based approach allows engineers to design buildings to specified performance levels (IO, LS, CP) even without a reliable seismic hazard map. This approach is akin to a miracle for countries that do not have a reliable seismic hazard map. This study presents a systematic and comprehensive bibliometric analysis of the academic literature pertaining to performance-based design (PBD). By fostering collaborative efforts and expanding research networks, we aim to facilitate the development of coordinated initiatives within the field. Preferred journals, leading countries, leading organisations, and international institutions were identified utilizing the Scopus database. This study examined 3456 PBD-related publications spanning from 1969 to 2023 using VOSviewer version 1.6.19, a bibliometric mapping and visualization software tool. The analysis of co-citations revealed that performance-based design serves as the primary theoretical foundation for structural design and analysis. Furthermore, through a co-word analysis, we tracked the evolution of research topics within the PBD domain over time. This investigation uncovered noteworthy trends, including the steady growth of research output, the increasing prominence of the term “PBD”, and a focus on various types of performance-based analyses.

An Updated and Unified Complete Earthquake Catalog of the Shillong Plateau and Adjoining Region

Abstract The Shillong Plateau (SP) and adjoining regions are one of the world’s most seismically active regions and to conduct a thorough seismological investigation and improved seismic hazard assessment, an updated and unified earthquake catalog is a prerequisite. In the present study, we compiled a homogeneous declustered earthquake catalog for the SP and adjoining regions by utilizing updated earthquake data from various international and national databases and pertinent literature for the period 825–2024, which consists of 6877 earthquakes. Employing the generalized orthogonal regression, orthogonal distance regression, standard least square regression, and inverted standard least square regression methods, 30 empirical relations have been derived to achieve magnitude homogeneity. All the reported magnitudes are converted into moment magnitude (Mw) using the derived regression relations. Subsequently, the declustering of the compiled homogenous earthquake catalog has been carried out using three techniques to distinguish dependent and independent earthquakes. Three approaches are used to assess the completeness of the nondeclustered and declustered earthquakes in terms of time and magnitude. The compiled updated and unified catalog in the present study contains 6877 earthquakes of Mw≥3.5 for the period 825–2024 obtained out of a total of 19,499 earthquakes reported from all sources. The completeness periods of the GK74 declustered earthquake catalog obtained by the cumulative visual inspection method for different magnitudes range from 14 to 218 yr and by Stepp’s method, it ranges from 15 to 215 yr. The spatial distribution of the magnitude of completeness (Mc), cumulative a-value, and b-value of the GK74 declustered earthquake catalog varies from 4.71 to 4.99, 5.64 to 10.17, and 0.68 to 1.63, respectively. The compiled updated and unified earthquake catalog is expected to be an essential input for regional seismicity, earthquake hazard, seismotectonic, and seismic hazard analysis of the SP and adjoining region.

A Seismic Landslide Hazard Assessment in Small Areas Based on Multilevel Physical and Mechanical Parameters: A Case Study of the Upper Yangzi River

Many landslides triggered by earthquakes have caused a countless loss of life and property, therefore, it is very important to predict landslide hazards accurately. In this work, regional seismic landslide data were obtained via a field survey, remote sensing interpretation, and data collection, and a multilevel physical and mechanical parameter system for seismic landslide hazard assessment was established; this system included a landslide inventory, loose accumulation layers, and geological units, enabling higher accuracy in the data. The Newmark displacement model with a modified correlation coefficient was used to assess the regional seismic landslide hazard in four scenarios (a = 0.1, 0.2, 0.3, 0.4) to study the influence of the landslide hazard at different peak ground accelerations. Moreover, the information value model was used to modify the calculated results to improve their accuracy in the assessment. By assessing the potential seismic landslide hazard in Shimian County in the upper reaches of the Yangtze River, the regional landslide distribution and pattern at different peak ground accelerations were obtained. The results show that with decreasing parameter accuracy in the system, the importance of the landslide inventory increases. When the peak ground acceleration is a = 0.3, which can be defined as a high hazard grade, in which the landslide area demonstrates a large-scale sharp increase, a devastating hazard threshold is reached. As the peak ground acceleration increases, the factor controlling landslides transforms from the landslide inventory to the slope, which reflects the reasonableness of the parameters in the system. The input parameters were regarded as important factors for efficiently increasing the accuracy of the results of the Newmark displacement model in the discussion.

Seismic and GNSS strain-based probabilistic seismic hazard evaluation for northern Chile using DAS Magnitude Scale

BackgroundProbabilistic Seismic Hazard Assessment (PSHA) is a leading methodology for determining key ground motion parameters such as Peak Ground Acceleration (PGA) and spectral acceleration (SA), essential for structural design. This approach uses extensive earthquake data, typically spanning over a century, leveraging frequency and magnitude statistics. However, long-term ground shaking probabilities may not always be accurately captured by traditional data-driven methods. To address these limitations, this study develops a PSHA map for Northern Chile using both seismic and GNSS (Global Navigation Satellite System) data. A curated homogeneous earthquake catalog, based on the advanced seismic moment magnitude scale Mwg(Das Magnitude Scale), replaces the traditional Mw scale to ensure superior accuracy, particularly for intermediate and smaller earthquakes.ResultsUsing the earthquake catalog, seismicity parameters ‘a’ and ‘b’ from the Gutenberg-Richter relationship were derived. Seismogenic modeling and Ground Motion Models (GMMs) were applied to estimate ground motion probabilities for a 475-year return period. Additionally, a PSHA map was constructed using GNSS strain rates, translating velocity-derived strain rates into seismic moment rates and ground shaking probabilities for seismic source zones. Comparative analyses revealed higher PGA values from GNSS strain data compared to seismic catalog data. GNSS strain data proved invaluable for refining seismic segmentation in Northern Chile, enhancing the precision of PSHA calculations.ConclusionsA PSHA map for Northern Chile, synthesizing seismic catalog data and GNSS strain rates using a Logic Tree-based algorithm, has been developed for a 475-year return period. This map provides a critical tool for generating seismic hazard assessments aligned with building codes and emergency planning protocols. By integrating GNSS strain rates and seismic data, this study advances the reliability and accuracy of long-term ground shaking predictions.

Understanding earthquake potential for future hazard mitigation

This study re-examines a broad region of the Sumatran subduction zone and off-coast southern West Java, building on findings of relative quiescence and utilizing the modified probability gain (mG) concept. By comparing pre- and post-quiescence seismicity, we identify potential earthquake sources and assess associated tsunami hazards. We propose a novel combined model integrating normalized seismicity smoothing, geodetic moment rate, and mG to characterize earthquake likelihood better. This model, coupled with a robust seismicity rate model, enables a spatiotemporal earthquake potential hierarchy for refined seismic hazard assessment. Our results confirm prior quiescence findings in specific zones and identify novel potential source regions for significant future earthquakes. We estimate tsunami height, emphasizing the importance of multiple source areas and static stress loading. By examining pre- and post-event expectations, we aim to improve understanding of major earthquakes in the Sumatran Subduction Zone and inform disaster mitigation strategies. This study provides crucial insights for enhanced regional earthquake and tsunami preparedness.

Modelling noise H/V spectral ratio in a laterally inhomogeneous layered medium

SUMMARY Central to the task of seismic hazard assessment is the evaluation of potential amplifications due to site effects. The horizontal-to-vertical spectral ratio (HVSR) of ambient seismic noise (ASN) is a widespread measurement to assess the predominant soil frequency of a given site and estimate the wave velocities of the subsoil stratigraphy using inversion schemes. In practice, the inversions are currently made, assuming flat layers. In fact, HVSR measurements may show significant lateral and azimuthal changes due to the spatial variations of local geology, which can introduce uncertainties into the characterization of a site. This suggests the importance of considering detailed measurements of lateral and angular variations in layered settings. Inversion of soil properties at depth for horizontally layered media has become feasible assuming that ASN constitutes a diffuse field, that is, produced by equi-partitioned uniform illumination and/or by random sources and the ensuing multiple scattering by heterogeneities. Under the diffuse field assumption (DFA), the HVSR have been modelled by calculating the imaginary parts of the Green's function (IMGs) when source and observer coincide at the same point. In this work we use the 3-D indirect boundary element method (IBEM) to model the HVSR for each independent horizontal direction referred to here as directional-HVSR for layered media with lateral inhomogeneity. The IMGs at the source required to get HVSR have locality properties that depend on frequency and may imply significant economies in the calculation. For simple models we modelled the IMGs approximately using an adaptive meshing scheme that accounts both for the locality of the problem and the diffraction properties of waves at low and high frequencies. The obtained directional-HVSR displays variations in both frequency and azimuth. The results also show that layer interface variations can lead to ‘spots’ of higher wave excitation associated to local resonant modes. This shows the importance of HVSR in forecasting earthquake response and suggests the need for denser field measurements to study lateral and azimuthal variability. In order to show the reality of directional-HVSR, field data from Chalco, a soft soil site at the southern part of the Valley of Mexico, have been preliminarily analysed.

Preliminary study site characterization using HVSR microtremor in West Bandung Basin

Site characteristic become crucial factor in seismic hazard assessment correspond to the site response of earthquake motions. This study investigates site characterization in the western part of the Bandung Basin using the Horizontal-to-Vertical Spectral Ratio (HVSR) method. HVSR analysis was applied to the Rayleigh wave microtremor data that was conducted at observation sites i.e: Baros, Cibeber, Batujajar, and Giriasih. The analysis results revealed some soil parameters i.e: dominant period (Td) values ranging from 0.23 to 0.43 seconds, S-wave velocity structure down to a depth of 30 (Vs30) in a range of 173.25 m/s in Cibeber to the highest was 281.76 m/s in Baros. The result of Vs30 analysis were used to classify local site which is Baros site can be classified into the stiff soil (SD) category, Cibeber and Batujajar belong to the soft soil (SC) category, and Giriasih is classified as very soft soil (SE). The findings of this study provide valuable information for seismic hazard assessment, seismic site classification, and earthquake-resistant structural design in the western part of the Bandung Basin.

Probabilistic seismic hazard assessment associated with induced seismicity at geothermal sites in the Upper Rhine Graben (Southern Germany)

The extraction of geothermal energy is associated with induced seismicity. Depending on the extraction parameters, such as injection pressure and volume, the induced seismicity is time-dependent. We investigate the case of the two geothermal power plants of Insheim and Landau, which are located in the Upper Rhine Graben in Southwest Germany. The induced seismicity was observed by a local seismic network consisting of a total of 19 stations, resulting in an earthquake catalog comprising 930 events for the Landau reservoir and 1985 events for the Insheim reservoir, both between 2012 and 2022. Based on this earthquake catalog, seismic source areas are defined for both reservoirs, and a probabilistic seismic hazard assessment (PSHA) is performed. Using temporal subsets of the earthquake catalog, PSHA can also be performed for shorter time ranges, resulting in larger expected PGV values in times of higher induced seismicity. The seismic velocity profiles obtained by site effect studies based on ambient seismic noise measurements highlight relatively large variations of the site effects on short scales in the area. The consequences of these lateral variations on the seismic hazard assessment are also discussed.

Mapping near-surface S-wave attenuation in the onshore southeastern flank of the Red Sea Rifting system in Saudi Arabia

This study aims to quantify the site attenuation parameter, kappa (κ), in the southeastern flank of the Red Sea rifting system. To determine κ, a least-squares best-fit method was applied to three-component seismograms, allowing for the modelling of the Fourier amplitude spectra of S-waves. The dataset consisted of 53 earthquakes, ranging in local magnitudes from 3.0 to 4.8 ML. The estimates of κ for 17 sites in the southeastern flank of the Red Sea region revealed average values ranging from 0.026 ± 0.01s to 0.053 ± 0.01s. A statistical analysis of κ dependence on epicentral distance, near-surface geology, and earthquake magnitude demonstrated the dependence of κ on distance and surface geology rather than earthquake magnitudes. The spatial distribution of the parameter κ, which includes both path and site effects, shows higher values at soft rock sites in the eastern region than hard rock sites in the western area. Owing to surface geological conditions, the site-dependent parameter κo exhibited average values of 0.002 ± 0.003s and 0.024 ± 0.002s for the hard and soft rocks, respectively. The results may be used to improve seismic hazard assessments and earthquake ground motion simulations.

Sensitivity Analysis on the Impact of Input Parameters on Seismic Hazard Results: A Case Study of Central America

We present a sensitivity analysis on the impact of input parameters and methods used on the results of a probabilistic seismic hazard assessment (PSHA). The accurate estimation of the parameters in recurrence models (declustering and fitting methods), along with the selection of scaling relationships for determining maximum magnitude and the selection of ground motion models (GMMs), enhance control over epistemic uncertainties when constructing the logic tree, minimizing final calculation errors and producing credible results for the study region. This study focuses on Central America, utilizing recent data from seismic, geological, and geophysical studies to improve uncertainty analyses through classic statistical methods. The results demonstrate that proper fitting of the recurrence model can stabilize acceleration variations regardless of the declustering method or b-value fitting method used. Regarding scaling relationships, their low impact on the final results is noted, provided the models are tailored to the tectonic regime under study. Finally, it is shown that the GMM contributes the most variability to seismic hazard results; therefore, their selection should be conditioned on calibration with observed data through residual analysis where region-specific models are not available.

Seismic hazard assessment of Agartala agglomeration based on 1D nonlinear ground response analysis and empirically derived liquefaction susceptibility

Seismic hazard assessment of Agartala agglomeration based on 1D nonlinear ground response analysis and empirically derived liquefaction susceptibility

Combining Two Distinct Methods to Resolve Spatial Variation in Attenuation and Earthquake Source Parameters

ABSTRACT Stress drop is a fundamental parameter in ground-motion modeling and seismic hazard assessment, but spectral estimates are subject to considerable uncertainties. A variety of factors cause different methods to yield different results, including the complexity of the seismic source, the assumptions inherent in the models used, the limited range of frequencies available, and the inherent difficulty in removing the propagation effects along the wave path. A primary challenge is determining whether the observed variations in spectral stress-drop estimates represent characteristics of the seismic source or the propagation path. We compare the performance of two methods applied to the 2019 Ridgecrest, California, earthquake sequence, each of which addresses the trade-offs between propagation and source in different ways. The first method, referred to as the spectral-fitting approach, operates on the hypothesis that the path effects remain constant across the spatial and temporal range of the sources under investigation. This approach assumes a level of uniformity in the propagation effects that simplifies the analysis. The second method, referred to as the spectral ratio approach, is based on the hypothesis that a small, collocated event will experience identical propagation effects to the earthquake of interest, potentially accounting for smaller scale variation in propagation effects. Our comparison reveals that the choice of method is not only influenced by the specifics of the data and the seismic events but also significantly constrained by the geological heterogeneity and consequent spatial variability of site and propagation effects in the study area. If an approach involves assuming a homogeneous attenuation structure, any spatial variation in attenuation structure will lead to this variation being incorrectly mapped into apparent source stress-drop variations. Understanding the local geology and structural heterogeneity, combined with using methods with contrasting underlying assumptions are good approaches to improving the reliability of estimated spectral stress drops.

Automatic classification of near‐fault pulse‐like ground motions

AbstractThis study presents an automated, quantitative classification method for near‐fault pulse‐like ground motions, distinguishing between forward‐directivity and fling‐step (FS) motions. The method introduces two novel parameters—the pulse velocity ratio and pulse area ratio—which transform the classification standard from a qualitative to a quantitative framework. Combined with an enhanced pulse extraction technique that captures permanent displacement characteristics, these parameters significantly improve classification efficiency and repeatability. This automated approach overcomes the limitations of manual classification, providing reproducible results. The identified FS ground motions can be applied to the dynamic analysis of cross‐fault structures, enhancing the reliability of seismic hazard assessments.

A PGA amplification study for Varanasi city (India): Implications for seismic hazard assessment

A PGA amplification study for Varanasi city (India): Implications for seismic hazard assessment

Correlations between spectrum-based and other ground-motion intensity measures considering various damping ratios

Spectral acceleration at a given period, SA( T), is usually combined with other intensity measures (IMs) for vector-valued ground-motion selection and seismic hazard assessment. The correlations between SA( T) and other IMs have been extensively studied, based on the SA-related IM pairs with a damping ratio ( ξ) of 5%. Yet, ξ varies notably with various types of structures. This article thus investigates the correlations of SA( T, ξ) with 10 commonly used non-SA IMs (e.g. Arias intensity), and the correlations of damping-specific acceleration spectrum, spectrum, and displacement spectrum intensities, namely ASI( ξ), SI( ξ), and DSI( ξ), with the other IMs. Comprehensive correlation analyses are conducted to derive the correlations for the IM pairs considered based on the NGA-West2 database and compatible ground-motion models. The results indicate that increasing ξ generally yields stronger correlations, and the difference between the ξ-specific and 5%-damped correlation coefficients could be larger than 0.2. The neural network and polynomial regressions are subsequently used to develop parametric models for estimating the correlations of SA( T, ξ)-containing pairs and the other IM pairs, respectively. All the models developed exhibit good performance in terms of predictive accuracy. The application of the proposed models is demonstrated within the generalized conditional IM approach. The models proposed could be useful for ground-motion selection and seismic demand or risk assessment for structures with various ξ values.

Database of seismological observations in the Severomuysky region of the Baikal rift during the operation of the local network of stations

The Severomuysky region should be considered as one of the key areas of the northeastern flank of the Baikal rift zone. The most important infrastructure facilities of the Baikal-Amur Mainline, in particular the Severomuysky tunnel, require an objective assessment of the seismic hazard of this territory. The work on converting a unique set of seismological data obtained during the period of operation of the analog local network of seismic stations (1978-1993) into digital format was carried out at the BB GS RAS in order to ensure the safety of all primary seismological observation materials and comprehensive analysis. This information was presented in printed form only. A database has been developed. It provides a relational approach to storing and managing large volumes of data. The database contains complete information on 15,832 earthquakes with KP=4–13 (station information, catalogues, bulletins, etc.). A client application has been created for convenient work with the database. The article illustrates examples of working with a database when solving typical seismological problems. It is obvious that extensive seismological information presented in digital form is of great importance for assessment of seismic hazard of the study under region.