Seismic Hazard Maps Research Articles

Changing your perspective: the impact of different visualisation methods on seismic hazard maps

Changing your perspective: the impact of different visualisation methods on seismic hazard maps

SITE-SPECIFIC DISAGGREGATION ANALYSIS OF RECENT EARTHQUAKE ON THE AMBON COAST

Seismic activity in the eastern region of Indonesia, particularly in Ambon, has been a matter of great concern because of its high tectonic activity. The devastating magnitude 6.5 earthquake in September 2019, which resulted in fatalities and significant damage, highlighted the region’s vulnerability and emphasized the importance of understanding the area’s seismic hazards. Although previous studies have been conducted, this study aims to fill critical gaps in the literature by using the latest seismic data until 2022 and updated attenuation equations. Disaggregation analysis is employed to identify ground motion characteristics, that are crucial for calculating synthetic ground motion acceleration. Under risk-targeted maximum considered earthquake (MCER) conditions, the study results show a peak ground acceleration of 0.444 g, with spectral acceleration at 0.2 s reaching 1.093 g, which decreases to 0.350 g at 1.0 s. Notably, background earthquake sources play a dominant role in contributing to the region’s high seismic hazard potential. The results of this study highlight the urgency of updating Indonesia’s national seismic hazard map. The study also recommends future studies to explore additional parameters of newly discovered faults to enhance understanding of fault movements and their impacts in the study area.

Design response spectrum based on shock-waveform decomposition method

This study applies the shock-waveform (SW) decomposition method, originally developed for mechanical shock analysis, to earthquake ground motions. It reveals a general shape similarity between the envelope of the Pseudo-Spectral Accelerations (PSAs) of SW decomposed components and the PSA of the corresponding ground motion. Based on this similarity, a novel method to determine the characteristic period Tg, the long-period transition period TD, the shape correction period Tβ, and the Design Response Spectrum (DRS) is proposed and evaluated. New methods to determine Tg, TD and Tβ from the signal decomposition perspective are integrated into the normalized DRS in Eurocode 8–2022, enabling the construction of the normalized DRS based on SW method (SWDRS). Furthermore, simple ground motion attenuation regression equations are derived to relate the parameters (Tg, TD, Tβ) and the corresponding spectral ordinates of the normalized SWDRS model with seismic magnitude and site conditions. The SWDRS model is validated by randomly selecting two sites in United States. For each site, the SWDRS is determined by using the attenuation regression equations and the DRS spectral plateau value from the official seismic hazard map. Comparisons between the SWDRS, the latest local DRS, and the severest historical PSA recorded at the specific site demonstrate that the SWDRS provides more accurate spectral values over intermediate- and long-period ranges for structural seismic design.

Geotechnical Assessment of Seismic Vulnerability in the Built Environment of Fako Division, South West Region of Cameroon

Introduction: Volcanic earthquakes may trigger severe hazards with considerable impact on the natural and built environment and the surrounding population. Aim: Evaluate the geotechnical characteristics of soils in Fako division to estimate their seismic vulnerability and recommend suitable stabilization techniques to enhance the safety and resilience of built environments. Place and Duration of Study: This study was conducted over a period of 12 months beginning from June 2022 to May 2023. Methodology: It employed a multi-criteria geotechnical approach, involving soil sampling, laboratory analysis, and seismic risk analysis. Soil samples collected from various locations within the study area, were subjected to laboratory tests to determine their plasticity (Atterberg limits) and load-bearing capacity (California Bearing Ratio - CBR). Historical data analysis and seismic hazard mapping were used to assess seismic vulnerability which helped to identify highly susceptible and unstable areas that may require engineered interventions. Results: The findings revealed significant variations in soil plasticity and load-bearing capacity, correlating with observed settlement and instability issues in the region. Historical seismic events, highlighted significant structural damage in areas with high plasticity and low CBR values, underscoring the necessity for robust soil stabilization measures (geotechnical interventions) to mitigate seismic risks and enhance the resilience and safety of structures, reducing the risk of settlement and instability within the Mount Cameroon area, particularly Fako Division.

Co-seismic and rainfall-triggered landslide hazard susceptibility assessment for Uganda derived using fuzzy logic and geospatial modelling techniques

AbstractUganda has suffered from many damaging landslides like the 1966 Rwenzori, 1994 Kisomoro and 2010 Bududa events. Despite escalating landslide risks exacerbated by rapid deforestation, urbanization and population growth coupled with a substandard building stock, comprehensive national co-seismic and rainfall-induced landslide hazard and risk maps for Uganda do not exist. This study therefore aims to conduct landslide hazard assessment and zonation for Uganda using a geospatial-based fuzzy logic methodology. In this methodology, landslide frequency ratios obtained for the 1966 Toro and 1994 Kisomoro earthquakes are assigned to the stochastic event-based probabilistic seismic hazard map derived using OpenQuake-engine. The available co-seismic and rainfall-induced landslide inventory datasets are used to derive the distribution of landslide frequency ratios based on geology, topographic slope position index, slope aspect, slope angle, distance from streams, and proximity to major active faults. The spatial distribution of fuzzy membership functions obtained from frequency ratios are overlaid and aggregated to produce landslide susceptibility maps showing relative probabilities of landslide occurrences across Uganda. Results indicate that the highest overall landslide hazard susceptibility is expected in areas comprising highly weathered outcropping rocks of precambrian granites, dominantly metasedimentary, and granulites and gneisses geologies within 40 km from major active faults; where the bedrock peak ground acceleration ≥ 0.1 g, topographic position index ≥ 3.8, slope gradient ≥ 10°, and the distance from streams ≤ 1.25 km. These findings can inform Uganda’s directorate of disaster preparedness and management towards pioneering the development of co-seismic landslide risk mitigation measures for the country.

Site database for national strong motion stations in mainland China

Ground motion amplification and spectral content are significantly influenced by local soil and geological conditions. This article summarizes the development of the China Site Database (CNSDB) in the China Ground Motion Flatfile project. CNSDB contains site information for 1450 strong-motion recording stations within the National Strong Motion Observation Network System (NSMONS) in China. The primary site information in CNSDB includes the time-averaged shear-wave velocity in the upper 30 m (VS30), and site class according to the seismic design code in China. These site data are derived using different methods from various data sources. Priority is given to approaches that minimize bias and dispersion relative to measurement-based results. Recommended VS30 values and site class are derived from reliable velocity profiles or field survey results whenever available. A China-specific VS30 extrapolation model is developed using 6179 engineering boreholes and is then utilized to estimate VS30 for profiles <30 m. VS30 values and site class are estimated from horizontal-to-vertical spectral ratio (HVSR) curves of earthquake recordings using machine-learning techniques. For the remaining sites without velocity profiles or sufficient ground-motion recordings for HVSR computation, VS30 values are determined as the weighted average of proxy-based estimates using geological attributes, topographic slope, and terrain categories. We also discuss the potential application of CNSDB in the development of China seismic hazard map considering site amplification factors.

Risk-Targeted Seismic Design Maps with Aleatory and Epistemic Uncertainty in Tehran and Surrounding Areas

ABSTRACT This study aims to introduce a risk-targeted probabilistic model that facilitates seismic design hazard mapping. Here, we investigate how to incorporate hazard regional variations and different structural fragility typologies so as to achieve a uniform target risk across the map. This paper takes Tehran, the capital city, and its surrounding area as a case study and explores the highly digitized hazard curves conditioned on the time-dependent occurrence of an earthquake at a 50-year exposure time. We introduce a new set of parameterized quantile functions for Risk-targeted design Intensity Measure (IMR) as the seismic design hazard. A group of IMR maps is subsequently prepared based on a 1% collapse probability during the next 50-year lifetime. Furthermore, the quantile function corresponding to each fragility type is able to show the aleatory uncertainty at each site on the region map. The uncertainty maps illustrate relatively less inherent variability than what exists in the hazard curves themselves. Then, we tackle the source of uncertainty arising from percentile hazard curves into IMR, known as epistemic uncertainty, by deriving a new closed-form expression, which allows for a sampling-free estimation of the epistemic uncertainty. The risk-targeted seismic design hazard with its accompanying uncertainties can lead to a promising seismic design hazard with potential applications for the insurance industry, urban planners, and risk-aware building owners.

Optimizing Interpolation Methods and Point Distances for Accurate Earthquake Hazard Mapping

Earthquake hazard mapping assesses and visualizes seismic hazards in a region using data from specific points. Conducting a seismic hazard analysis for each point is essential, while continuous assessment for all points is impractical. The practical approach involves identifying hazards at specific points and utilizing interpolation for the rest. This method considers grid point spacing and chooses the right interpolation technique for estimating hazards at other points. This article examines different point distances and interpolation methods through a case study. To gauge accuracy, it tests 15 point distances and employs two interpolation methods, inverse distance weighted and ordinary kriging. Point distances are chosen as a percentage of longitude and latitude, ranging from 0.02 to 0.3. A baseline distance of 0.02 is set, and other distances and interpolation methods are compared with it. Five statistical indicators assess the methods. Ordinary kriging interpolation shows greater accuracy. With error rates and hazard map similarities in mind, a distance of 0.14 points seems optimal, balancing computational time and accuracy needs. Based on the research findings, this approach offers a cost-effective method for creating seismic hazard maps. It enables informed risk assessments for structures spanning various geographic areas, like linear infrastructures.

Seismic hazard zonation map and definition of seismic actions for Greece in the context of the ongoing revision of EC8

The Greek National Annex for current Eurocode 8 has adopted the seismic hazard zonation map published in 2003 as part of the modifications to the Greek Seismic Code EAK 2000 (EAK 2003). This map, which followed the catastrophic earthquakes that hit the country between 1978 and 2001, includes three seismic hazard zones with peak ground acceleration (PGA) ranging between 0.16 and 0.36 g. In this paper, following the significant progress that has been made worldwide in the last two decades towards the improvement of the definition of seismic actions and the seismic hazard maps using fully probabilistic models, we make a complete proposal for the Greek National Annex of the ongoing revision of Eurocode 8, which includes a new seismic hazard zonation map for Greece, as well as a novel site categorization scheme and related site amplification factors. To this end, we use the results of the European Seismic Hazard Model, ESHM20, as reported by Danciu et al. (The 2020 update of the European Seismic Hazard Model: Model Overview, 2021) which will be adopted as informative reference for the seismic hazard at European level in the forthcoming revision of Eurocode 8 (CEN/EC8). The herein proposed ground shaking zonation for rock conditions includes five zones with PGA values ranging between 0.13 and 0.37 g. For each zone, two newly proposed ground motion parameters, i.e., Sα,475 and Sβ,475, are provided, which are the two parameters used for anchoring the elastic response spectrum as defined in CEN/EC8, along with all the other necessary parameters for the definition of the elastic response spectrum, including site amplification. The proposal for the new seismic zonation is supported by a preliminary investigation of the impact of its adoption on the seismic design of new structures and on the seismic risk of the current building stock in Greece, to help gain a better insight on how important the differences imposed by the new zonation might be for the end-users and the administration.

Assessment of Site Effects and Numerical Modeling of Seismic Ground Motion to Support Seismic Microzonation of Dushanbe City, Tajikistan

In the territory of Dushanbe city, the capital of Tajikistan, detailed geological and geophysical data were collected during geophysical surveys in 2019–2020. The data comprise 5 microtremor array measurements, 9 seismic refraction tomography profiles, seismological data from 5 temporary seismic stations for standard spectral ratio calculations, 60 borehole datasets, and 175 ambient noise measurements. The complete dataset for Dushanbe was used to build a consistent 3D geologic model of the city with a size of 12 × 12 km2. The results of the seismological and geophysical surveys were compared and calibrated with borehole data to define the boundaries of each layer in the study area. The Leapfrog Works software was utilized to create a 3D geomodel. From the 3D geomodel, we extracted six 12 km long 2D geological cross-sections. These 2D geological cross-sections were used for 2D dynamic numerical modeling with the Universal Distinct Element Code software to calculate the local seismic response. Finally, the dynamic numerical modeling results were compared with the amplification functions obtained from the seismological and ambient noise data analysis. The 2D dynamic numerical modeling results allowed a better assessment of the site effects in the study area to support seismic microzonation and the determination of local peak ground acceleration changes in combination with regional seismic hazard maps. In addition, our results confirm the strong seismic amplification effects noted in some previous studies, which are attributed to the influence of local topographic and subsurface characteristics on seismic ground motions.

Developing design response spectra for Benghazi city including soil magnification effects

Earthquakes in some countries worldwide cause loss of lives and properties. In Libya, design of structures to resist earthquake forces was based on a paper work published by Mallick in 1976. In 1977, and after small changes in the earthquake zoning map of Libya, the ministry of housing, at that time, adopted it as a draft code of practice for the design of structures to resist earthquake forces. With Benghazi city undergoing significant rehabilitation and development programs, including major national projects, there is a pressing need to estimate updated probabilistic seismic hazard maps and design response spectra specific to the city. This study presented updated probabilistic seismic hazard ground motion for Benghazi city, considering different return periods and accounting for peak ground acceleration (PGA) values with various soil conditions. Proposed design response spectra for Benghazi City unveils substantial PGA amplifications in soft soil areas.

Development of new seismic hazard maps of the Philippines using the neo-deterministic seismic hazard assessment approach

Development of new seismic hazard maps of the Philippines using the neo-deterministic seismic hazard assessment approach

Reliability-based seismic liquefaction hazard mapping of Kolkata Metropolitan City, India, using ordinary kriging technique

Reliability-based seismic liquefaction hazard mapping of Kolkata Metropolitan City, India, using ordinary kriging technique

Probabilistic seismic hazard maps and uniform hazard spectra with site effect integration for northern of Algiers

Probabilistic seismic hazard maps and uniform hazard spectra with site effect integration for northern of Algiers

Empirical Fragility Analysis of Haitian Reinforced Concrete and Masonry Buildings

This study develops empirical fragility curves for concrete and masonry buildings in Haiti, utilizing data from the 2021 earthquake. A dataset of 3527 buildings from the StEER database, encompassing a diverse range of building types, is used. These buildings types include reinforced concrete structures with masonry infills, confined masonry buildings, reinforced masonry bearing walls, and unreinforced masonry bearing walls. Shakemaps from the USGS are utilized to assess the earthquake’s intensity at each building, with the peak ground acceleration (PGA) as the intensity measure. Damage is classified into five distinct states: no damage, minor, moderate, severe, and partial or total collapse. For each of these states, the corresponding probabilities of exceedance are calculated, and log-normal cumulative distribution functions were fitted to those data to produce empirical fragility curves. The results show a notable similarity in performance among the four types, each having high probability of failure even under low-intensity earthquakes. Total fragility curves (including all four building types) are developed subsequently and they are convolved to the probabilistic seismic hazard map of Haiti to assess the seismic risk. This includes estimating the annual probability of partial/total collapse and the probability of partial/total collapse in the event of 475-year and 2475-year earthquakes. The results indicate a significant risk, with up to 64% probability of collapse in certain areas for the 2475-year earthquake and a probability of collapse of 15% for a 475-year earthquake. These findings underscore the critical vulnerability of Haiti’s buildings to seismic events and the urgent need for their retrofit.

Seismic Hazard Map of ASEAN Countries towards Risk Assessment and Sustainability of Structures and Infrastructures

This study contains the most recent seismic hazard map of Southeast Asia. This area is located to the south of the Eurasian plate. The Ring of Fire that surrounds the region makes it one of the most active in terms of earthquakes and volcanoes. Malaysia, Indonesia, Thailand, Singapore, the Philippines, Myanmar, Vietnam, Laos, Cambodia, and Brunei are among the countries being studied. The goals of this project are to provide Peak Ground Acceleration (PGA) values for all regions in ASEAN countries, and then to create seismic zoning maps for these countries so that zones with non-seismic regions can be identified and zones with no special steel reinforcement-detailing requirements can be specified. The final step is to create design response spectra. Based on each nation's most recent body of literature, the PGA hazard map is created. There are two maps that need to be created, one for 10% and one for 2% probability of exceeding. The PGA contours of all the compiled maps were then reconstructed, and the baseline colours were compared to an Indonesia seismic hazard map. The maximum PGA value for Southeast Asia is as high as 0.8g at 10% and 2.0g at 2% probability of exceedance, respectively, whereas the minimum PGA value is typically equal to 0.0g at both 10% and 2% probability of exceedance. The design response spectrum distribution of the stable with moderate earthquake region from 0 to 4 s (including West Malaysia, Sabah and Sarawak of East Malaysia) and the distribution of spectra for active earthquake regions including Indonesian cities (including Acheh, Padang and Palu) are plotted. Then, the design response spectra for the selected cities in regions of moderate seismicity and active earthquakes are integrated.

Seismic Hazard Maps of the Eastern Himalaya Syntaxis by Integrating the Surface Topography and Site Effects

Seismic Hazard Maps of the Eastern Himalaya Syntaxis by Integrating the Surface Topography and Site Effects

Regional seismic risk assessment based on the Unified Scaling Law for Earthquakes: The Lake Baikal railway system

Seismic hazard assessment (SHA) and evaluation of seismic risk (SR) require an adequate understanding of the actual distribution of earthquakes over magnitude, space, and time ranges. Neo-deterministic seismic hazard assessment (NDSHA) methodologies have been developed to improve the reliability and accuracy of reproducible seismic hazard maps. In the last decade, the application of NDSHA in many regions of the world has confirmed the availability of reliable and effective input for mitigating object-oriented earthquake risks NDSHA results have passed intensive testing by historical evidence and realistic modelling of scenario earthquakes. We used two NDSHA tools – (i) Unified Scaling Law for Earthquakes (USLE) and (ii) anisotropic propagation of the seismic effect – to evaluate SR for the Lake Baikal regional railroad system represented by Open Street Map (OSM) data of tracks, bridges and tunnels on the basis of seismic hazard maps of maximum macroseismic intensity expected in 50 years with 10%, 5%, and 1% probability of exceedance. We compare the achieved USLE−based results with the SR evaluations based on the General Seismic Zonation 2016 maps at identical levels of probability of exceedance.

Assessing seismic risk in the built environment of Istanbul: High-resolution hazard mapping and ground motion analysis in the sea of Marmara region

This research scrutinizes the seismic threat looming over Istanbul, potentially subject to a substantial earthquake. We analyze six plausible earthquake scenarios, utilizing six ground motion prediction equations (GMPEs), to forge high-resolution seismic hazard maps. These maps reveal not only peak horizontal ground accelerations but also spectral acceleration values across varying temporal frames, integrating the amplification effects of softer sediments. Our approach delineates that Istanbul’s western shoreline faces heightened risk, with median spectral accelerations at 0.3 s approaching 1 g, signifying intense shaking potential. In contrast, the area encompassing the financial district exhibits lower values, around 0.3 g. The granularity of these findings lays bare the seismic vulnerabilities of the region, offering a window into the risks and potential damages facing this bustling metropolis. This enhanced understanding paves the way for strategic urban planning and risk mitigation efforts aimed at safeguarding Istanbul’s populace and infrastructure. This article succinctly condenses our study’s pivotal conclusions, presenting a clarion call for proactive measures to diminish earthquake impacts on this dynamic urban landscape.

Mapping Seismic Hazard for Canadian Sites Using Spatially Smoothed Seismicity Model

The estimated seismic hazard based on the delineated seismic source model is used as the basis to assign the seismic design loads in Canadian structural design codes. An alternative for the estimation is based on a spatially smoothed source model. However, a quantification of differences in the Canadian seismic hazard maps (CanSHMs) obtained based on the delineated seismic source model and spatially smoothed model is unavailable. The quantification is valuable to identify epistemic uncertainty in the estimated seismic hazard and the degree of uncertainty in the CanSHMs. In the present study, we developed seismic source models using spatial smoothing and historical earthquake catalogue. We quantified the differences in the estimated Canadian seismic hazard by considering the delineated source model and spatially smoothed source models. For the development of the spatially smoothed seismic source models, we considered spatial kernel smoothing techniques with or without adaptive bandwidth. The results indicate that the use of the delineated seismic source model could lead to under or over-estimation of the seismic hazard as compared to those estimated based on spatially smoothed seismic source models. This suggests that an epistemic uncertainty caused by the seismic source models should be considered to map the seismic hazard.