Urban Seismic Risk Research Articles

High-Resolution 3D Shallow S-Wave Velocity Structure Revealed by Ambient-Noise Double Beamforming with a Dense Array in Guangzhou Urban Area, China

Abstract Shallow velocity structure surveys are very important for urban seismic hazard monitoring and risk assessment. Ambient-noise tomography provides an ideal way to obtain urban fine structure. In this study, we obtained a high-resolution 3D VS model of the metropolitan areas of the Pearl River Delta (PRD) using the ambient-noise double-beamforming method with a dense nodal array. The new model reveals shallow structures that correlate well with surface geological features, with low-velocity anomalies in fault depressions and high-velocity anomalies in fault uplifts. Our findings reveal detailed fault geometries and basin characteristics of the PRD. The Guangzhou–Conghua fault emerges as a prominent velocity boundary, playing a significant role in controlling the development and subsidence of the Longgui basin. The Xinhui–Shiqiao fault and Shougouling fault are identified as major faults that control the formation and evolution of depressions in the PRD. The basin structures in the PRD are classified as semigraben basins controlled by synsedimentary faults. The long axes of the sub-basins align with the strike of the major faults, and the deposit centers are located in close proximity to these faults. Furthermore, our investigation reveals low-velocity anomalies along the faults, suggesting the existence of pre-existing faults facilitating heat transfer and fluid/melt migration from the deep crust. Our results provide new constraints on the geometric structure of the sedimentary basins and fault systems in the PRD area, thereby contributing to urban seismic hazard assessment and offering valuable insights into potential geothermal resources.

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

Abstract Understanding 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.

Extending urban seismic risk assessment to open spaces for the 2011 Lorca earthquake scenario

Extending urban seismic risk assessment to open spaces for the 2011 Lorca earthquake scenario

Improving urban seismic risk estimates for Bishkek, Kyrgyzstan, through incorporating recently gained geological knowledge of hazards

Many cities are built on or near active faults, which pose seismic hazard and risk to the urban population. This risk is exacerbated by city expansion, which may obscure signs of active faulting. Here, we estimate the risk to Bishkek city, Kyrgyzstan, due to realistic earthquake scenarios based on historic earthquakes in the region and an improved knowledge of the active fault sources. We use previous literature and fault mapping, combined with new high-resolution digital elevation models to identify and characterise faults that pose a risk to Bishkek. We then estimate the hazard (ground shaking), damage to residential buildings and distribution of losses (economical cost and fatalities) using the Global Earthquake Model OpenQuake engine. We model historical events and hypothetical events on a variety of faults that could plausibly host significant earthquakes. This includes proximal, recognised, faults as well as a fault under folding in the north of the city that we identify using satellite DEMs. We find that potential earthquakes on faults nearest to Bishkek—Issyk Ata, Shamsi Tunduk, Chonkurchak and the northern fault—would cause the most damage to the city. An Mw 7.5 earthquake on the Issyk Ata fault could potentially cause 7900 ± 2600 completely damaged buildings, a further 16,400 ± 2000 damaged buildings and 2400 ± 1500 fatalities. It is vital to properly identify, characterise and model active faults near cities to reduce uncertainty as modelling the northern fault as a Mw 6.5 instead of Mw 6.0 would result in 37% more completely damaged buildings and 48% more fatalities.

Urban seismic scenario-based risk analysis using empirical fragility curves for Kerend-e-gharb after Mw 7.3, 2017 Iran earthquake

Urban seismic scenario-based risk analysis using empirical fragility curves for Kerend-e-gharb after Mw 7.3, 2017 Iran earthquake

Urban Seismic Risk Assessment and Damage Estimation: Case of Rif Buildings (North of Morocco)

The interest in assessing seismic risk in earthquake-prone regions in Morocco has been increasing over recent decades, to a large extent due to the substantial amount of damage imposed by recent events and because the population in these regions has grown significantly. In this context, the present study is aimed to contribute to the understanding of seismic risk in the urban areas of the Rif region, one of the most seismically active zones of Morocco, through the development and analysis of 36 building models representative of this area. Two earthquake scenarios were considered for the assessment of the seismic hazard, based on the national seismic code and the European code adapted to local seismic parameters. The performance points, determined following generated response and capacity spectra, made it possible to establish damage probability matrices. Obtained results corroborate those of previous reports, confirming that the damage is more significant in Imzouren due to the nature of the soil. It has also been shown that the credibility of the response spectra drawn from the national code is questioned, given the extreme damage estimated. The adapted European spectrum proved to be a more reliable probabilistic earthquake scenario for damage estimation.

A Hybrid Intelligent Model for Urban Seismic Risk Assessment from the Perspective of Possibility and Vulnerability Based on Particle Swarm Optimization

Assessing seismic risk is an essential element of urban risk management and urban spatial security work. In response to the issues posed by the complexity and openness of urban systems, the nonlinearity of driving factors, and sudden changes in geological processes that affect urban seismic research, this paper is based on a variety of intelligent algorithms to develop a hybrid intelligent model that integrates probability and vulnerability to evaluate and quantify the difference in the urban spatial units distribution of earthquake risk. We applied this model to Hefei, one of the few superlarge provincial capital cities on the “Tancheng-Lujiang” fault zone, one of the four major earthquake zones in China, which suffers frequent earthquakes. Our method combined the genetic algorithm (GA), particle swarm optimization (PSO), and backpropagation neural network methods (BP) to automatically calculate rules from inputted data on known seismic events and predict the probability of seismic events in unknown areas. Then, based on the analytic hierarchy process (AHP), spatial appraisal and valuation of environment and ecosystems method (SAVEE), and EMYCIN model, an urban seismic vulnerability was evaluated from the four perspectives of buildings, risk of secondary disasters, socioeconomic conditions, and urban emergency response capabilities. In the next step, the overall urban seismic risk was obtained by standardizing and superimposing seismic probability and vulnerability. Using the hybrid intelligent model, earthquake probability, seismic vulnerability, and overall seismic risk were obtained for Hefei, and the spatial characteristics of its overall seismic risk were examined. This study concludes that areas with very high, high, low, and very low earthquake risk in Hefei account for 8.10%, 31.90%, 40.94%, and 19.06% of its total area, respectively. Areas with very high earthquake risk are concentrated in the old city, the government affairs district, Science City, and Xinzhan District. This study concludes that government authorities of Hefei should target earthquake safety measures consisting of basic earthquake mitigation measures and pre- and postearthquake emergency measures. In the face of regional disasters such as earthquakes, coordinating and governing should be strengthened between cities and regions.

Fault-Source-Based Probabilistic Seismic Hazard and Risk Analysis for Victoria, British Columbia, Canada: A Case of the Leech River Valley Fault and Devil’s Mountain Fault System

This study develops a fault-source-based seismic hazard model for the Leech River Valley Fault (LRVF) and the Devil’s Mountain Fault (DMF) in southern Vancouver Island, British Columbia, Canada. These faults pose significant risks to the provincial capital, Victoria, due to their proximity and potentially large earthquake magnitudes. To evaluate the effects of including these faults in probabilistic seismic hazard analysis and city-wide seismic loss estimation for Victoria, a comprehensive sensitivity analysis is conducted by considering different fault rupture patterns and different earthquake magnitude models, as well as variations in their parameters. The aim is to assess the relative contributions of the LRVF-DMF system to the overall seismic hazard and risk in Victoria at different return periods. The consideration of the LRVF-DMF system as a potential seismic source increases the seismic risk assessment results by 10 to 30%, especially at the high return period levels. The sensitivity analysis results highlight the importance of determining the slip rate for the fault deformation zone and of specifying the earthquake magnitude models (e.g., characteristic versus truncated exponential models). From urban seismic risk management perspectives, these nearby faults should be considered critical earthquake scenarios.

A Multilevel Procedure at Urban Scale to Assess the Vulnerability and the Exposure of Residential Masonry Buildings: The Case Study of Pordenone, Northeast Italy

More than the 60% of the Italian residential building stock had already been built by 1974, when seismic codes were enforced on a minimal part of the country. Unreinforced masonry buildings represent most of that share, but they are typical for each region, in terms of both materials and structural configurations. The definition of ‘regional’, i.e., more specific, vulnerability and exposure models are required to improve existing forecast models. The research presents a new geographic information system (GIS)-based multilevel procedure for earthquake disaster prevention planning at urban scale; it includes multicriteria analysis, such as architectural types, structural vulnerability analysis, microzonation studies, and socio-economic aspects. The procedure has been applied to the municipality of Pordenone (PN), a district town of the Friuli–Venezia–Giulia region, in Northeast Italy. To assess the urban seismic risk, more than 5000 masonry residential buildings were investigated and common types within sub-municipal areas and exposure data were collected. Simplified mechanical analysis provided a ‘regional’ vulnerability model through typological fragility curves. The integration of results into GIS tool permitted the definition of cross-mapping among vulnerability, damage scenarios (conditional and unconditional) and exposure (seismic losses, casualties, impact), with respect to various earthquake intensities expected in the town. These results are presented at different scales: from the single building, to submunicipal area and to the entire town.

Urban Seismic Risk Assessment by Integrating Direct Economic Loss and Loss of Statistical Life: An Empirical Study in Xiamen, China.

The growing densities of human and economic activities in cities lead to more severe consequences when a catastrophe such as an earthquake occurs. This study on urban seismic risk evaluation is carried out from the perspective of the direct loss caused by disasters in urban areas, including the measurement of both the expected direct economic loss and loss of life in the face of characteristic earthquakes. Aiming to estimate, quantify and visualize the earthquake risk in each unit of urban space, this research proposes to assess urban seismic risk by integrating the direct economic loss and the loss of statistical life in a disaster, with consideration of diverse earthquake frequencies. Empirical research of the proposed assessment framework and corresponding models is then conducted to measure urban seismic risk in Xiamen, China. Key findings of the case study include the expected direct economic losses and the expected number of deaths in three characteristic earthquakes, their estimated spatial distributions, the average loss of the value of a statistical life (VSL) of one average local resident and the overall seismic risk distributions in Xiamen.

Proactive Actions Based on a Resilient Approach to Urban Seismic Risk Mitigation

Background: Seismic risk mitigation is an important issue in earthquake-prone countries, and needs to be solved in those complex communities governed by complex processes, where urban planning, socioeconomic dynamics, and, often, the need to preserve cultural assets are present simultaneously. In recent years, due to limited financial resources, mitigation activities have often been limited to post-earthquake events, and only a few in periods of inactivity, particularly in urban planning. At this point, a significant change in point of view is necessary. Methods: The seismic risk mitigation (and more generally, natural risk mitigation) must be considered as the main topic in urban planning and in the governance of communities. In fact, in several recent earthquakes, significant socioeconomic losses have been caused by the low or lack of resilience of the communities. This is mainly due to the high vulnerability of private buildings, in particular, housing units. Results: Therefore, in recent years, several studies have been conducted on the seismic resilience of communities. However, significant improvements are still needed for the resilience assessment of the housing stock, both qualitatively and quantitatively. In this study, which is applied to the housing system, a proposal regarding a change in urban planning and emergency management tools based on the concept of resilience is reported. As a first application, a case study in Italy is considered. Conclusion: The proposal is focused on defining and quantifying the improvement of the resilience of the communities and this must be obtained by modifying the current Civil Protection plan. New tools are based on a new resilience community plan by encompassing urban planning tools, resilient mitigation strategies, and consequently, emergency management planning.

An approximate procedure for estimating the member demands in mid-rise reinforced concrete buildings

Seismic assessment of mid-rise reinforced concrete buildings is important for urban seismic risk reduction. Nonlinear time history analysis is the state-of-the-art analysis tool for this purpose. However, the number of such buildings may reach to several tens of thousands in metropolitan cities of earthquake prone countries. This necessitates faster yet sufficiently accurate assessment methods to mitigate the seismic risk. In this study, a simple and efficient approach is developed and validated for the assessment of such buildings. The proposed method relies on estimating the reduced secant stiffness values for structural members based on elastic analysis. Afterwards, subsequent elastic analyses with the reduced stiffness values is conducted employing the equal displacement rule. The procedure is tested for twelve buildings with and without shear walls, and torsional irregularity. The member end chord rotation results obtained with the proposed procedure are compared with the mean results of eleven nonlinear time history analyses. It is found that the proposed procedure can estimate column and beam chord rotation demands with reasonable accuracy, significantly reducing the computational time.

Urban seismic risk model for resilient cities. The case of Thessaloniki

Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses at local, urban, national and even continental scale. In this study we present a preliminary model for the probabilistic seismic risk assessment at urban scale. The studied model will be applied to the residential building stock of Thessaloniki, Greece, for which detailed building inventory and very good knowledge of the soil conditions are available. The applied model comprises three main components, i.e., seismic hazard, building exposure model and physical - socioeconomic vulnerability models. Seismic hazard for rock site conditions is properly amplified to account for site effects of Thessaloniki city, considering the available detailed data of the soil conditions. Exposure model for residential buildings of Thessaloniki is developed based on the results from the 2011 Population and Housing Census. Both physical and socioeconomic losses were considered. For the assessment of the physical and socioeconomic losses we applied the fragility and vulnerability models developed for Greece by GEM. The work has been conducted in the framework of SERA European project (http://www.sera-eu.org/en/home/), which aims at developing a pan-European seismic risk model, applicable at both urban and national risk assessment. The model developed in this work will contribute to the efforts towards increasing the resilience of cities.

ER2-Earthquake: Interactive web-application for urban seismic risk assessment

An interactive user-friendly web-based application for urban seismic risk assessment referred to as rapid risk evaluator (ER2) is presented. It combines three major input components: seismic hazard, exposed buildings and respective vulnerabilities. Intended primarily for application by the larger public-safety community, ER2 intuitively guides non-expert users with step-by-step prompts and on-screen instructions through otherwise complex risk scenarios. Open-source software is used to offer the application free of all financial cost for users. The analyses are based on parameters of the well-known FEMA's Hazus method. To accelerate the computation and rapidly obtain estimates of the negative impacts, ER2 employs pre-populated inventory and vulnerability databases. The standard displacement-based structural fragility curves and iterative nonlinear static analyses are replaced with fragility curves determined as direct functions of the shaking intensity. Comparison of damage probability results, economic and social losses concur with Hazus estimates for individual buildings and for aggregated inventory at urban scale. An example of seismic risk assessment for Quebec City, Canada, is shown to illustrate the effectiveness of ER2.

Performance-based Seismic Risk Assessment of Urban Systems

ABSTRACTDisaster risk mitigation has become a urgent global need. Similar to other natural hazards, earthquakes may cause significant damage on a large scale. In Europe and in other regions with dense urbanization, seismic events can heavily impact historical city centers due to the several structural fragilities. These centers are often part of the worldwide cultural heritage and their preservation is considered a strategic issue. Furthermore, earthquakes may have severe negative short-term economic effects on the impacted communities and adverse longer-term consequences for economic growth. For this reason, the development of an efficient approach for urban seismic risk assessment becomes essential. An original approach is proposed, based on performance concepts and multidisciplinary perspectives. The procedure is applied for validation to the city center of Concordia Sulla Secchia (Italy), damaged by the 2012 Pianura Padana Earthquake (PPE), comparing predicted damage scenarios with the actual post-seismic survey data.

Classical Temples and Industrial Stores: Survey Analysis of Historic Unreinforced Masonry (URM) Precincts to Inform Urban Seismic Risk Mitigation

ABSTRACTOamaru, Winton, and Invercargill feature some of New Zealand’s most intact heritage precincts that are confronted by ongoing threats of seismic activity. The 2010/2011 Canterbury earthquake sequence and Canterbury Earthquakes Royal Commission of 2012, identified a nationwide trend through the proportion of deaths that occurred in public places as a result of the prevalent historic unreinforced masonry (URM) building stock. The reported study was undertaken to address urban safety and seismic risk mitigation through the lens of heritage conservation. The range of classically designed public buildings and industrial warehouses in the South Island of New Zealand were often produced by singular architectural practices, using locally sourced materials and construction techniques. It is vital to incorporate an examination of unique architectural qualities within urban seismic risk assessment and mitigation. Historic urban layout, architectural deployment of masonry, and extent of retrofits were recorded through onsite visual surveys via Geographical Information Systems and three-dimensional representation technologies. Extending the scope of information collected for engineering seismic risk assessment by focusing on the historical architectural context informs the selection of future mitigation measures. Oamaru, Winton, and Invercargill present intriguing case studies for multidisciplinary analysis, prior to testing urban-scale survey approaches within comparable historic centers across New Zealand.

Seismic vulnerability assessment at urban scale: Case of Algerian buildings

The main purpose of risk reduction methodological and operational approaches is to protect lives and properties against the impact of natural or industrial disaster. Although it is unrealistic to expect to live in a risk free environment, it is possible to reduce this risk through appropriate prediction and management strategies.This work presents an integrated framework for seismic damage assessment at urban scale in Algeria. Its main objective is the proposal of simplified methodological and operational approaches to assess urban vulnerability and socio-economic losses. It relies on the performance of probable seismic scenarios in urban areas exposed to earthquakes. This will enable decision makers to take adequate preventive measures and develop appropriate mitigation strategies, i.e. crisis prevention and management plans to reduce the losses.It deals with the assessment of building seismic risk of urban areas in Algeria by using the RADIUS Model (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) after a prior adaptation to the Algerian context. It estimates also the expected number of victims and their spatial distributions.This concept is adopted to estimate the urban seismic risk of the Great-Blida region (consisting of 4 cities, namely Blida, Ouled-Yaïch, Bouarfa and Beni-Mered), west of Algiers region, by performing an earthquake scenario. The region of Blida has experienced strong earthquakes during the last centuries generating seismic intensities ranging between X and XI, of which that most significant, occurred on Mars 2, 1825. It represents an important administrative, military, economic and scientific pole, and features a high concentration of population (1390 inhabitants/km2). In order to draw reliable results, an extensive survey was carried out concerning the buildings (approximately 46,000 units). The data were mapped and stored in databases using GIS tools. The results of this earthquake scenario show that serious damages would be observed in the studied area.The results reported in this study will drive the decision-making, by the local authorities, adapted to the specific socio-environmental vulnerability context at the Great-Blida urban scale. For this purpose, the paper proposes a list of operational measures contributing to the seismic risk reduction, relying on the resilience-building demand.A complementary study, i.e. a separate paper (second part), deals about assessment of seismic risk related to road infrastructures and lifelines devoted to the Algerian urban context.

An Assessment of Earthquake Risk in Thecho of Kathmandu Valley Nepal: Scenario and Reality

Natural disaster cannot be stopped but its effect can be minimized or avoided by adopting technology and necessary human adjustment. Earthquake is a natural event which occurs without early warning signs. Computer based earthquake scenarios are used worldwide to describe and estimate the damage from potential earthquakes. The current study is an attempt to explore potential risk with respect to physical infrastructure and assess modeled and actual physical damage and human loss caused by different earthquake scenario and actual 2015 earthquake event in Thecho of Kathmandu valley. The earthquake scenario is based on two nearest fault lines. Risk Assessment Tools for the Diagnosis of Urban Seismic Risk (RADIUS) method has been applied for estimation of potential building damage and casualties..The research has adopted integrated approach using secondary and primary data sources such as field observation, key informant survey and building survey through purposive random sampling.The study found that potential building damage estimated by RADIUS for Gorkha 2015 earthquake scenario and North-west (Khokana) are lower than the actual post-earthquake assessment whereas North earthquake scenario resulted higher loss. Actual damage caused by 2015 earthquake compared to modeled damage from RADIUS is found higher because additional damaged were made by successive aftershocks. Spatial distribution of potential building damage for earthquake scenarios and actual 2015 earthquake event is also variable. North-Nuwakot Earthquake Scenario resulted more hazardous than the North-Khokana scenario though the location of epicenter is relatively farther with high intensity. The study concluded that though earthquake occurrence and disaster is still less predictable risk assessment tools like RADIUS and mitigation measures based on such is important for reducing risk of earthquake disaster.The Geographical Journal of NepalVol. 11: 127-136, 2018

Assessment of earthquake-induced liquefaction hazard in urban areas of Hanoi city using LPI-based method

Assessment of earthquake-induced liquefaction hazard in urban areas of Hanoi city using LPI-based method

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics