Earthquake Loss Research Articles

Hybrid posttensioned rocking (HPR) frame buildings: Low-damage vs low-loss paradox

The 2010-11 Canterbury Earthquake Sequence inflicted seismic losses worth more than $40B, which is about 25% of the GDP of New Zealand (as per 2011 data). More than 80% of these losses were insured, which comprised of more than $10B covered by the Earthquake Commission (a New Zealand crown entity providing insurance to residential property owners) and more than $22B (comprising of roughly equal split between domestic and commercial claims) by private insurers [1]. The scale of financial impact has been perceived to be disproportionately large given the building regulatory regime in New Zealand is relatively stringent and the earthquakes and aftershocks were of moderate magnitude. As it is well known that some of the major faults spread in the Wellington region and the subduction boundary passing through the centre of New Zealand can generate much bigger earthquakes (upwards of magnitude 8), people are left pondering whether New Zealand is able to cope with the financial impact of larger earthquakes. This fearful realisation gradually led to people being dissatisfied with merely life-safe buildings and demanding more resilient buildings that meet the objectives of performance based design; i.e. suffer less damage, incur less loss, and can remain functional after earthquakes.
 In light of the extensive building damage resulting in high financial loss in recent earthquakes, practicing engineers and researchers in New Zealand have been advocating for revising the current design approach to improve performance of new structures and infrastructure in future earthquakes [2-5]. As a result, large proportion of buildings constructed in the last decade (including those built to replace earthquake-damaged buildings) have shied away from the traditional damage-friendly ductile structural systems and instead adopted one of the new and emerging structural systems claimed to be “low-damage”. In many cases, the adopted structural systems are not covered by existing design standards and are approved as alternate solutions through expert peer review. The “low-damage” attribute of most structural systems has been validated by component (or sub-assembly) level experimental tests, but their interactions with other building components and implications of their use in buildings have not been rigorously scrutinised. Hence, the rushed adoption of some of these systems in buildings can surprise the engineering community in future earthquakes with mismatch between the expected and real performances of the buildings; akin to what New Zealand engineering fraternity is currently going through due to realisation of poor seismic performance of precast hollow-core flooring system that has been widely used in New Zealand buildings without rigorous scrutiny.
 One such “low-damage” structural system is precast post-tensioned rocking frames with supplemental energy dissipaters. This paper summarises the development of this structural system, critically reviews the literature reporting the seismic performance of this system, and qualitatively evaluates system-level implications of its use in buildings. This paper is intended to better inform engineers of the likely seismic performance of buildings with this structural system so that they can optimise its benefits by giving due consideration to its effect on other building components.

Earthquake loss and Solvency Capital Requirement calculation using a fault-specific catastrophe model

Earthquake loss and Solvency Capital Requirement calculation using a fault-specific catastrophe model

Estimation of Seismic Economic Loss and Downtime of Precast Concrete Frames with “Dry” Connections

The seismic loss of buildings comes not only from the damaged structural components. Much more loss may be induced by non-structural components, the demolition loss and social impacts associated with excessive downtime. One of the main characteristics of a resilient city is that the buildings in the city should be able to recover to their pre-earthquake functionalities with minimized economic loss and downtime. For this purpose, a comparative study regarding seismic economic loss and downtime is conducted between the conventional cast-in-situ reinforced concrete frames (RCFs) and precast concrete frames (PCFs) with "dry" connections. The results show that the PCFs with prestressed tendons (PTs) can effectively reduce demolition loss given their extraordinary self-centering capacity provided by PTs. By adding web friction devices at the beam ends, the economic loss of structural components and drift-sensitive non-structural components can be effectively reduced. The downtime of PCFs is reduced at given hazard levels compared with RCF given their rapid repair speed and easy assemblage. In view of the rapid post-earthquake repair and lower earthquake loss, the PCFs are worth further investigation and application to develop resilient cities.

A computational framework for selecting the optimal combination of seismic retrofit and insurance coverage

AbstractEconomic earthquake losses can be mitigated through either building retrofit strategies and/or, to some extent, risk‐transfer to the (re)insurance market. This paper proposes a computational framework to select the optimal combination of seismic retrofit and insurance policy parameters for buildings. First, a designer selects a suitable retrofit strategy. This is implemented incrementally to define interventions with increasing retrofit performance levels. The cost of each intervention is calculated, along with the cost of property rental while the retrofit is implemented. Alternative insurance options are considered. For each retrofit‐insurance combination, the insured and uninsured economic losses within a given time horizon are estimated. The optimal retrofit and insurance combination minimizes the tail value at risk of the life cycle cost. The selected confidence level for this metric depends on the homeowner's risk aversion. The proposed framework is illustrated for a case‐study archetype Italian reinforced concrete frame building retrofitted with concrete jacketing, also considering the Italian retrofit tax incentives/rebates called “Sismabonus.”

Toward a uniform earthquake loss model across Central America

This study presents a probabilistic earthquake loss model for Central America, which is used to evaluate the indicators of the Sendai Framework for Disaster Risk Reduction (SFDRR). The exposure, vulnerability, and hazard components of the model were established using a uniform methodology for all the countries. Earthquake risk is expressed according to three indicators: mortality (A-1), population affected (B-1), and economic losses (C-1). Exposure results indicate that over 9.1 million structures (with an economic value of US$635 billion) are exposed to seismic hazard in the region. The risk results indicate an average annual human loss of 0.7 fatalities per 100,000 inhabitants, an average number of 35 people affected per 100,000 inhabitants, and an average annual economic loss of US$990 million. This represents 0.43% and 0.16% of the regional gross domestic product (GDP) and total replacement value, respectively. Guatemala, Nicaragua, and El Salvador present the highest risk, contributing with 75% of the absolute economic losses and 84% of the average annual fatalities in the region.

Impacts on catastrophe risk assessments from multi-segment and multi-fault ruptures in the UCERF3 model

The Uniform California Earthquake Rupture Forecast Version 3 (UCERF3) relaxes fault segmentation, allowing multi-segment and multi-fault ruptures through fault-to-fault “jumps,” with lengths up to ∼1200 km along the San Andreas Fault. Local faults are also highly interconnected, including ruptures on the order of hundreds of kilometers. These prescribed long ruptures did not exist in older models. Longer ruptures produce larger aggregate loss estimates for geographically dispersed assets (portfolios) due to the wider areas that are affected by strong ground shaking. In this study, we model probabilistic earthquake losses of a hypothetical state-wide building portfolio in California. We develop risk deaggregation methods to identify multi-segment and multi-fault ruptures that contribute significantly to high portfolio-wide risks. Three risk measures that are commonly used in risk management decisions are examined: Average Annual Loss (AAL), Return Period Loss (RPLα), and Tail Conditional Expectation (TCEα), for an annual exceedance probability “α,” or corresponding return period “1/α.” Our results show that while the super long ruptures (>500 km) contribute modestly (∼7%) to the portfolio AAL estimate, they contribute more significantly to portfolio catastrophe risk estimates. Specifically, at a 250 year return period, these long ruptures contribute about 26% and 32% to RPL250 and TCE250 estimates, respectively. At a 500-year return period, the corresponding contributions reach about 35% and 39%. Ruptures that connect complex fault systems are also found to be highly influential to estimated portfolio risks. At a 500-year return period, a mere six rupture groups contribute nearly 70% to the RPL500 estimate. Due to the importance of the UCERF3 model to many risk management and public policy decisions, a critical examination of the limit and uncertainty of fault connectivity and rupture lengths of future earthquakes, as well as their impacts on catastrophe risk assessments, is warranted in future model updates.

Rapid earthquake loss assessment based on machine learning and representative sampling

This article proposes a new framework for rapid earthquake loss assessment based on a machine learning damage classification model and a representative sampling algorithm. A random forest classification model predicts a damage probability distribution that, combined with an expert-defined repair cost matrix, enables the calculation of the expected repair costs for each building and, in aggregate, of direct losses in the earthquake-affected area. The proposed building representation does not include explicit information about the earthquake and the soil type. Instead, such information is implicitly contained in the spatial distribution of damage. To capture this distribution, a sampling algorithm, based on K-means clustering, is used to select a minimal number of buildings that represent the area of interest in terms of its seismic risk, independently of future earthquakes. To observe damage states in the representative set after an earthquake, the proposed framework utilizes a local network of trained damage assessors. The model is updated after each damage observation cycle, thus increasing the accuracy of the current loss assessment. The proposed framework is exemplified using the 2010 Kraljevo, Serbia earthquake dataset.

The US Geological Survey ground failure product: Near-real-time estimates of earthquake-triggered landslides and liquefaction

Since late 2018, the US Geological Survey (USGS) ground failure (GF) earthquake product has provided publicly available spatial estimates of earthquake-triggered landslide and liquefaction hazards, along with the qualitative hazard and population exposure-based alerts for M > 6 earthquakes worldwide and in near real time (within ∼30 min). Earthquake losses are oftentimes greatly aggravated by the impacts due to ground failure, yet those particular events with dramatic additional losses have not, heretofore, been rapidly identifiable. The GF product now provides situational awareness about the potential extent and severity of ground failure in the crucial time period before direct observations are available. We describe our implementation of the GF product and the lessons learned from the earthquakes that have occurred since the GF product was released. We describe the product design process, the underlying GF models, the methods we have developed for modeling uncertainty, and the development of the alert levels. The GF product has been produced in near real time for 320 events over the 2-year period since its public implementation in late 2018 through early 2021. The majority of these events yielded the lowest level (green) alerts for all ground-failure types, with 25 resulting in elevated hazard or exposure to landslides and 47 for liquefaction. In a qualitative comparison between the GF product alerts and GF occurrence information, we found that the product succeeds at assigning appropriate alert levels in the majority of cases. Based on our experience with the product, we have identified the following priorities for future improvements: (1) refinements of the underlying probabilistic models to incorporate severity and explicitly model the type of landslide/liquefaction; (2) development of models for fatalities and economic losses due to ground failure; and (3) estimation of the impacts of ground failure on infrastructure.

Impact of exposure spatial resolution on seismic loss estimates in regional portfolios

The spatial resolution of exposure data has a substantial impact on the accuracy and reliability of seismic risk estimates. While several studies have investigated the influence of the geographical detail of urban exposure data in earthquake loss models, there is also a need to understand its implications at the regional scale. This study investigates the effects of exposure resolution on the European loss model and its influence on the resulting loss estimates by simulating dozens of exposure and site models (630 models) representing a wide range of assumptions related to the geo-resolution of the exposed asset locations and the associated site conditions. Losses are examined in terms of portfolio average annual loss (AAL) and return period losses at national and sub-national levels. The results indicate that neglecting the uncertainty related to asset locations and their associated site conditions within an exposure model can introduce significant bias to the risk results. The results also demonstrate that disaggregating exposure to a grid or weighting/relocating exposure locations and site properties using a density map of the built areas can improve the accuracy of the estimated losses.

The Impact of a Government Risk Pool and an Opt-Out Framing on Demand for Earthquake Protection

This paper describes the design and analysis of a web-based choice experiment that examines how the demand for earthquake protection in Quebec and British Columbia is influenced by the default option and the structure of the insurance plan. Homeowners in both provinces were given the opportunity to purchase protection against earthquake losses when presented with one of the following options: the current private insurance plan, a high deductible private insurance plan, and a proposed public-private risk pool. The default frame was changed so the homeowner could either opt-in by purchasing this coverage or opt-out of being given this protection and receiving a premium discount. Assigning participants to a public-private risk pool rather than the current private insurance plan increases the likelihood of purchasing earthquake protection by 151%. The opt-out frame leads to a likelihood greater than 1.6 of purchasing coverage relative to the opt-in frame when given the same plan structure. The policy implications of this finding are discussed.

Using non-structural mitigation measures to maintain business continuity: a multi-stakeholder engagement strategy

Encouraging property owners and individuals to adopt mitigation measures to improve the resilience of their buildings and equipments to seismic hazard has been a major challenge in many earthquake- prone countries. Few business leaders are aware of the fragility of their supply chains or other critical systems due to earthquake hazard. Bridging the gap between research production and research use is another crucial challenge for the earthquake risk research process. The KnowRISK project outcome is aimed at encouraging the proactive engagement of multi- stakeholders (community at large, schools, business community and local govern-ment groups) undertaking non-structural mitigation measures that will minimize earthquake losses to individuals and communities. Engaging stakeholders, taking into account their needs and inputs to maintain critical and urgent business activities, can contribute to the research findings and ensure that our data collection is thorough and complete. Engagement with stakeholders, during the whole process can lead to improved outcomes and for the development of viable solutions, for business and society, because of stakeholder’s role and influence within the organizations.

SEISMIC ASSESSMENT OF CONTEMPORARY VERSUS OLD URBAN FRAME BUILDINGS

This comparative study probabilistically assesses the relative safety margins of code-compliant and pre-seismic code RC buildings with different heights in a region of medium seismicity. Detailed structural design and fiber-based modeling of six benchmark structures, namely two code-compliant buildings and two pre-code structures before and after retrofit, are undertaken to develop fragility functions using several earthquake records representing the most critical seismic scenario in the study area. Several inelastic dynamic analyses are performed to assess the seismic response and derive a range of fragility functions for the six benchmark buildings. Compared with contemporary structures, the study highlights the vulnerability of pre-code buildings due to the insufficient stiffness, strength, and ductility provided by their lateral force resisting systems. A practical retrofit solution for pre-code structures is subsequently assessed using the methodology adopted for other modern and old buildings. The probabilistic assessment results confirmed the comparable seismic performance of the retrofitted and code-conforming buildings. The comparative study, which provided insights into the differences between code-compliant versus pre-seismic code buildings before and after retrofit, contributes to reducing earthquake losses and improving community seismic resilience in earthquake-prone regions.

Earthquake loss analysis and assessment of group buildings in Songyuan area

To study the earthquake damage and loss of group buildings in towns and urban areas of Songyuan, the simulation analysis of earthquake damage of group buildings in some areas of Chaganhua town and urban areas of Songyuan was conducted. In this paper, based on the building performance evaluation method in FEMA-P58 and the Standard for seismic resilience assessment of buildings (GB/T 38591-2020), the different methods between China and the US were eliminated. Firstly, the distribution of earthquake damage of various buildings was analyzed. The economic losses of the two regions are analyzed and compared by using PACT software to evaluate the repair costs and repair time of buildings under different earthquake levels.

A case study for probabilistic seismic risk assessment of earthquake-prone old urban centers

The study focuses on the probabilistic seismic risk assessment of earthquake prone old urban centers. This issue becomes even more complex if the considered area is a highly populated, cultural or commercial center. Hence it is an important task to estimate regional earthquake losses and to develop strategies for earthquake mitigation through seismic risk prioritization among such vulnerable populated old urban areas. For this purpose, a sub-district with six neighborhoods in Beyoglu, Istanbul has been selected as the study area, which is located in a high-seismicity region. This is one of the most attractive cultural places in the city as well as a commercial center with a high population. Building stock is dense and composed of many old and deficient buildings located within close vicinity of active faults. For risk assessment, site-specific hazard curves are obtained first. Then reinforced concrete and masonry buildings in the region are classified by using the results of a recent walk down survey data and fragility curve sets that reflect local structural characteristics of the buildings in the area are attained to each class. In the last step, probabilistic seismic risk assessment approach is utilized to obtain the estimated damage state distributions at the considered neighborhoods for a 50-year time interval. The results reveal the urgency in order to take precautions to mitigate earthquake losses in vulnerable old urban centers. This study is deemed to propose a potential approach by carrying out site-specific hazard, vulnerability and risk assessments as an assistance to risk mitigation efforts.

Fragility Assessment of Beam-Slab Connections for Informing Earthquake-Induced Repairs in Composite-Steel Moment Resisting Frames

Earthquake loss estimation in composite-steel moment resisting frames (MRFs) necessitates a proper estimation of the level of damage in steel beam-to-slab connections. These usually feature welded headed shear studs to ensure the composite action between the concrete slab and the steel beam. In partially composite steel beams, earthquake-induced damage in the shear studs and the surrounding concrete occurs due to shear stud slip demands. Within such a context, this paper proposes shear slip-based fragility functions to estimate the probability of being or exceeding four damage states in steel beam-slab connections. These damage states include cracking and crushing of the concrete slab in the vicinity of the shear studs, as well as damage in the shear studs themselves. The developed fragility functions are obtained from a gathered dataset of 42 cyclic push-out tests. They incorporate uncertainty associated with specimen-to-specimen variability, along with epistemic uncertainty arising from the finite number of available experimental results. An application of the proposed fragility functions is conducted on a six-story building with composite-steel MRFs. It is shown that steel beam-slab connections along the building height only exhibit light cracking (i.e., crack sizes of 0.3 mm or less) at design basis seismic events. At seismic intensities associated with a low probability of occurrence seismic event (i.e., return period of 2475 years) the nonlinear building simulations suggest that the 25% reduction of the shear stud resistance in steel beam-slab connections with beam depths of 500 mm or less is not imperative to maintain the integrity of the shear stud connectors.

Optimal Choice between CAT Bond and Debt to Cover the Risks of Natural Disasters

This article analyses the choice between non-contingent bonds and catastrophe (CAT) bonds to cover the risk of earthquakes. A dynamic stochastic optimization model with frictions was developed and shows under which conditions it may be advantageous for a government to issue a CAT bond instead of a standard non-contingent bond. The authors show how friction costs, such as the illiquidity premium associated with non-contingent debt issuance when a catastrophe occurs, increase the opportunity to issue CAT bonds. The calibration of the proposed model to real data allows us to estimate the price of CAT bonds to insure against earthquake losses in Quebec. <b>TOPICS:</b>Fixed income and structured finance, tail risks <b>Key Findings</b> ▪ This article proposes a dynamic stochastic optimization model with frictions to analyse the choice between non-contingent bonds and catastrophe (CAT) bonds to cover the risk of earthquakes. ▪ Friction costs, such as the illiquidity premium associated with non-contingent debt issuance when a catastrophe occurs, increase the opportunity to issue CAT bonds. ▪ The calibration of the proposed model to real data allows us to estimate the price of CAT bonds to insure against earthquake losses in Quebec.

Earthquake loss estimation for an educational reinforced concrete building by using FEMA P-58 methodology

The costs of damages in both social and economic aspects are increased as a result of several significant earthquakes worldwide, the economic and social losses are a function of damage of the buildings because the buildings are vulnerable to earthquake damage [1]. In this study a probabilistic methodology FEMA P-58 is applied for seismic performance assessment for Iraqi educational reinforced concrete building in order to calculate the performance in terms of two aspects, the first one is the direct economic losses which include repair costs and repair time and the second one is social losses which include casualties and injuries. This methodology is prepared by ATC, the American Applied Technology Council and its prepared for Federal Emergency Management Agency (FEMA) in 2012. The study is a continuation of other research papers related to applying the same method to the same building that the researcher undertook for the purpose of evaluating the performance of the building when exposed to earthquake and calculating the losses resulting from these damages by choosing different aspects of each research in terms of the method of simplified analysis or the calculation of damages and losses.

REVIEW OF ESTIMATION METHODS AND SYSTEMS USED TO PREDICT EARTHQUAKE CASUALTIES

Earthquake casualty estimation is key to earthquake resistance and hazard prevention planning prior to earthquakes and emergency rescue efforts after earthquakes. Scholars in the fields of earthquake engineering, geophysics, sociology, public health etc. have performed multi-perspective studies on this issue. Earthquake casualty assessment models are divided into global/regional models and local models. According to their relevant factors, they are categorized based on the appropriate seismic parameters and building fragility factors, and some researchers additionally consider the influence of secondary disasters and population characteristics. Following an introduction to the importance of earthquake casualty assessment work, traditional casualty estimation methods, and emerging methods combined with artificial intelligence, big data and spatial information technology are summarized in this review. The framework, technical foundation and application of earthquake loss estimation systems are introduced, and future development trends are envisioned.

Seismic zoning of Tabriz area by stochastic finite fault model considering site-specific soil effects

Abstract Tabriz, as one of the most earthquake-prone cities in the Iran plateau, has experienced enormous earthquakes that have even destroyed the city altogether. Considering this seismological background and the vicinity of Tabriz's northwestern fault, reducing the possible earthquake losses can be highly useful by scrutinizing the strong ground motion resulting from the fault activation. To this end, a stochastic finite-fault ground motion simulation (EXSIM) method was applied as an important means for predicting the ground motion near the epicenter of the earthquake. EXSIM is an open-source stochastic finite-fault simulation algorithm that generates the time-series of the earthquake's ground motion. Based on the findings, the peak horizontal acceleration reached 0.83 g in the northern parts by creating artificial accelerograms and Tabriz's seismic zonation. In comparison, it reduced by 0.48 g by departing from the fault in the city's southern parts. Additionally, providing a seismic zonation map in Tabriz revealed that stopping the construction in the north parts while extending the settlement construction to the south part of the city are considered vital and unavoidable. Also, by applying the magnification and effects of the soil layers above the bedrock, it was further found that the existence of the loose layer with low strength and compaction intensify the application of seismic acceleration on the near-surface structures in the central, west, and southwest parts of the target area.

Comparing Short-Term Seismic and COVID-19 Fatality Risks in Italy

Abstract Risks assessment and risks comparison are basic concepts for emergency management. In the fields of earthquake engineering and engineering seismology, the operational earthquake loss forecasting (OELF) is the research frontier for the assessment of short-term seismic risk. It combines seismicity models, continuously updated based on ground-motion monitoring (i.e., operational earthquake forecasting), with large-scale vulnerability models for the built environment and exposure data. With the aim of contributing to the discussion about capabilities and limitations of OELF, the study presented aims at comparing the OELF results and the fatality risk (based on fatality data) related to coronavirus 2019 (COVID-19) that, at the time of writing, is perceived as very relevant and required unprecedented risk reduction measures in several countries, most notably Italy. Results show that, at a national scale in Italy, the COVID-19 risk has been higher than the seismic risk during the two pandemic waves even if, at the end of the so-called lockdown, the evolution of the pandemic suggested the possibility (not realized) of reaching a situation of comparable seismic and COVID-19 risks in a few weeks. Because the two risks vary at a local scale, risks comparison was also carried out on a regional basis, showing that, before the beginning of the second wave, in some cases, the seismic risk, as assessed by means of OELF, was larger than the pandemic one.