Critical Issues on Probabilistic Earthquake Loss Assessment

Probabilistic loss modeling can be used to develop risk reduction measures, such as the identification of regions more prone to human and economic losses, or to develop financial mechanisms to transfer the earthquake risk from local governments to the private sector. This study addresses several critical issues in probabilistic loss modeling, and provides recommendations depending on the intended final use of the risk results. Modeling issues related to convergence in probabilistic event-based analysis; consideration of epistemic uncertainties within a logic tree; generation of different types of loss exceedance curves; and derivation of risk maps are thoroughly investigated. The Metropolitan Area of Lisbon is used to explore these issues, and it is demonstrated that different assumptions in the loss modeling process can lead to considerably different risk results. Furthermore, the findings and recommendations of this study are also relevant for institutions that promote the assessment of earthquake hazard and risk, such as the Global Earthquake Model Foundation.     

Regional Seismic Risk Assessment of Bridge Network in Charleston,South Carolina

This article presents the results of a seismic risk assessment of the bridge network in Charleston, South Carolina and the surrounding counties to support emergency planning efforts, and for prioritization of bridge retrofit. This study includes an inventory analysis of the approximately 375 bridges in the Charleston area, and convolution of the seismic hazard with fragility curves analytically derived for classes of bridges common to this part of the country. State-of-the-art bridge fragility curves and replacement cost estimates based on region-specific data are used to obtain economic loss estimates. The distribution of potential bridge damage and economic losses are evaluated for several scenario events in order to aid in the identification of emergency routes and assess areas for investment in retrofit. This article also evaluates the effect of uncertainty on the resulting predicted economic losses. The findings reveal that while the risk assessment is very sensitive to both the assumed fragility curves and damage ratios, the estimate of total expected economic losses is more sensitive to the vast differences in damage ratio models considered.     

Can Earthquake Loss Models be Validated Using Field Observations?

The occurrence of a damaging earthquake provides an opportunity to compare observed and estimated damage, provided that detailed observations of the earthquake effects are made in the field. A question that arises is whether such comparisons can provide the basis for validation of an earthquake loss model. In order to explore this issue, a case study loss model for the northern Marmara region has been set up and the losses have been calculated for various ground-motion fields that arise when different assumptions are made about the ground-motion variability. In particular, the influence of removing the inter-event variability for a scenario earthquake and modeling spatial correlation among ground motions is studied. Further analyses are conducted assuming that a number of accelerograms are available within the region and that knowledge of spatial correlations among ground motions can therefore be used to better predict the motions at sites in the vicinity of the recording stations. The results demonstrate that unless one has a dense network of accelerographs (commensurate with the geographical resolution of exposure), then the variability in the losses cannot be sufficiently reduced to allow validation of the loss model.     

Stochastic Modeling of Earthquake Scenarios in Greater Tehran

Tehran, the capital of Iran, with millions of inhabitants, has been affected several times by historical and recent earthquakes that confirm the importance of seismic hazard assessment for the area. The main objective of this article is to present a probabilistic procedure to construct time series compatible with the source-path and site reflecting the influence of different magnitude events at different distances that may occur during a specified time period. A Monte Carlo approach is used to generate numerous synthetic catalogs for the evaluation of the probabilistic seismic hazard in greater Tehran over hard rock site for a return period of 475 years. The disaggregation of the seismic hazard is carried out to identify hazard-dominating events and to associate them with one or more specific faults, rather than a given distance. The stochastic finite-fault technique based on region specific seismic parameters is used to generate time series of earthquake scenario.     

Sustainability of Highway Bridge Networks Under Seismic Hazard

In order to evaluate the seismic risk of transportation networks, it is necessary to develop a methodology that integrates the probabilities of occurrence of seismic events in a region, the vulnerability of the civil infrastructure, and the consequences of the seismic hazard to the society, environment, and economy. In this article, a framework for the time-variant seismic sustainability and risk assessment of highway bridge networks is presented. The sustainability of the network is quantified in terms of its social, environmental, and economic metrics. These include the expected downtime, expected energy waste and carbon dioxide emissions, and the expected loss. The methodology considers the probability of occurrence of a set of seismic scenarios that reflect the seismic activity of the region. The performance of network links is quantified based on individual bridge performance evaluated through fragility analyses. The sustainability and risk depend on the damage states of both the links and the bridges within the network following an earthquake scenario. The time-variation of the sustainability metrics and risk due to structural deterioration is identified. The approach is illustrated on a transportation network located in Alameda County, California.     

Cost-Benefit Analysis of Alternative Retrofit Strategies for RC Frame Buildings

Monetary losses induced by earthquakes in Reinforced Concrete (RC) buildings are mainly due to damage to non-structural elements (infills, partitions, finishes, etc.). In this study, alternative retrofit strategies for reducing monetary losses in RC frame buildings are examined. They include local strengthening of infills (and partitions) and seismic isolation. The Expected Annual Loss (EAL) of a number of RC frame buildings, pre- and post-rehabilitation, is evaluated, following the time-based assessment approach proposed in the FEMA P-58 guidelines. The breakeven time of each retrofit intervention is then computed, considering the initial cost of the intervention and the expected benefit in terms of EAL reduction.     

SEISMIC HAZARD ASSESSMENT OF METROPOLITAN TEHRAN,IRAN

This paper presents a probabilistic seismic hazard assessment of Tehran, the capital of Iran. Two maps have been prepared to indicate the earthquake hazard of Tehran and its vicinity in the form of iso-acceleration contour lines. They display the probabilistic estimate of Peak Ground Acceleration (PGA) over bedrock for the return periods of 475 and 950 years. Tehran is a densely populated metropolitan in which more than 10 million people live. Many destructive earthquakes happened in Iran in the last centuries. It comes from historical references that at least 6 times, Tehran has been destroyed by catastrophic earthquakes. The oldest one happened in the 4th century BC. A collected catalogue, containing both historical and instrumental events and covering the period from the 4th century BC to 1999 is then used. Seismic sources are modelled and recurrence relationship is established. For this purpose the method proposed by Kijko [2000] was employed considering uncertainty in magnitude and incomplete earthquake catalogue. The calculations were performed using the logic tree method and three weighted attenuation relationships; Ramazi [1999], 0.4, Ambraseys and Bommer [1991], 0.35, and Sarma and Srbulov [1996], 0.25. Seismic hazard assessment is then carried out for 12×11 grid points using SEISRISK III. Finally, two seismic hazard maps of the studied area based on Peak Ground Acceleration (PGA) over bedrock for 10% probability of exceedance in two life cycles of 50 and 100 years are presented. The results showed that the PGA ranges from 0.27(g) to 0.46(g) for a return period of 475 years and from 0.33(g) to 0.55(g) for a return period of 950 years. Since population is very dense in Tehran and vulnerability of buildings is high, the risk of future earthquakes will be very significant.     

Statistical Characterization of Structural Demand under Earthquake Loading. Part 2: Robust Estimation of the Dispersion of the Data

Performance-based earthquake engineering methodologies often require a probabilistic model of structural demand. Since observations masking the probability distribution of the majority of the data are frequently found, robust estimation methods are proposed to estimate the probabilistic model parameters (i.e., central value and dispersion). The performance of thirty-three robust dispersion estimators is evaluated, for different sample sizes, using the chord rotation, curvature, shear force, and inter-story drift demands obtained after analyzing five reinforced concrete structures under real earthquake records scaled to several intensities. Based on the results, combinations involving dispersion and central value (defined in a companion article) estimators are proposed.     

Developing Direct Displacement-Based Procedures for Simplified Loss Assessment in Performance-Based Earthquake Engineering

Various loss assessment methodologies have been proposed and developed over the past decades to provide risk assessment on a regional scale. There is an increasing need, however, to provide engineers with practical tools for building-specific loss assessment. Recently, progress has been made towards probabilistic loss models such as the PEER framework. However, as comprehensive probabilistic methodologies could be too complex for practicing engineers, this article presents a simplified probabilistic loss assessment methodology that builds on a direct displacement-based framework. The methodology is tested via examination of two RC frame buildings and encouragingly shows similar results to the PEER methodology.     

FRAGILITY OF STANDARD INDUSTRIAL STRUCTURES BY A RESPONSE SURFACE BASED METHOD

National and international regulatory standards require industrial risk assessment, taking into account natural hazards including earthquakes, in the framework of Quantitative Risk Analysis (QRA). Seismic fragility analysis of industrial components may be carried out similarly as what has been done for buildings, even though some peculiar aspects require the development of specific tools. In the present paper a contribution to the definition of a rational procedure for seismic vulnerability assessment of standardised industrial constructions in a probabilistic framework is given. The method covers a range of components of the same structural type. Seismic reliability formulation for structures is used. Both seismic capacity and demand are considered probabilistic with the latter assessed by dynamic analyses. The application example refers to shell elephant foot buckling of unanchored sliding tanks. A regression-based method is applied to relate fragility curves to parameters varying in the domain of variables for structural design.     

An Applied Method for General Regional Seismic Loss Assessment—With A Case Study in Los Angeles County

We describe the formulation and application of an integrated general regional seismic loss assessment (RSLA) method for buildings in seismic regions. An efficient method for RSLA is valuable for engineers involved in city planning, risk management, and insurance dealings. In contrast to previously reported methods, the framework presented herein is hazard-based and utilizes a regional rapid seismic hazard deaggregation tool that allows regional assessment to be conducted more efficiently. The proposed technique is implemented as an example to assess general regional seismic loss in Los Angeles County for a ground motion hazard with 10% probability of exceedance in 50 years.     

An exploration of regional climate change scenarios for Scotland

Based on a high resolution regional climate model (RCM) experiment, a climate change scenario for Scotland for the end of this century is constructed with the aim of exploring the added value of utilising a regional rather than a global model (GCM) for climate change scenario construction. Spatial variations in regional seasonal average temperature and precipitation change are analysed and the local response of ‘extreme’ weather events to climate warming is assessed using daily model output. The analyses suggest that in comparison with the GCM, the RCM does not provide fundamentally different patterns of seasonal climate change and daily weather response over Scotland, although it does capture more subtle spatial variations in these changes. The RCM also simulates more realistic daily weather events than the GCM, although the relative changes in the frequencies of daily extremes are not greatly different. However, with the limited length of the single model simulation analysed here, it is not easy to establish how robust and significant are the sub‐national patterns of climate response across Scotland. To improve the quality and comprehensiveness of regional climate change scenario information, a number of research issues remain to be addressed.     

Seismic Hazard Analysis Using Discrete Faults in Northwestern Pakistan: Part II – Results of Seismic Hazard Analysis

This article is the second of two companion articles that evaluate seismic hazard in northwestern (NW) Pakistan. Using the properties and characteristics of discrete faults in NW Pakistan described in the first article, probabilistic and deterministic seismic hazard analyses for 11 major cities in NW Pakistan were conducted. The results from both probabilistic and deterministic seismic hazard analyses exhibit good agreement. Median deterministic spectra compare favorably with uniform hazard spectra (UHS) for 475- or 975-year return periods, while the 84^th-percentile deterministic spectra compare favorably with the UHS for a 2475-year return period. Peak ground accelerations (PGAs) for 2475-year return periods exceed 1.0 g for the cities of Kaghan and Muzaffarabad, which are surrounded by major faults. The PGAs for a 475-year return period for these cities are approximately 0.6g — 3 to 4 times greater than estimates by previous studies using diffuse areal source zones. The PGAs for some cities located farther from faults (including Astor, Malakand, Mangla, Peshawar, and Talagang) are similar to those predicted using diffuse areal source zones. Seismic hazard maps for PGA and spectral accelerations at periods of 0.2 s and 1.0 s corresponding to three return period (2475, 975, and 475 years) were produced. Based on deaggregation results, a discussion of the conditional mean spectra for engineering applications is presented.     

Managing the risk of climatic variability in late prehistoric northern Chile

The concept of risk management encompasses the diverse strategies employed in preventing and mitigating losses associated with social and environmental calamities. Building on the growing literature on risk, we use archaeological data from the Tarapacá Valley, located in northern Chile, to document the risk-reduction tactics mobilized by the valley’s inhabitants to navigate the increasingly volatile environmental and social conditions of the Late Intermediate Period (AD 1000–1450). With the onset of exceptionally unpredictable environmental conditions after AD 1100, residents of the Tarapacá Valley chose strategies such as increased trade and agricultural diversification and extensification to minimize shortages in staple resources. Threats of raiding and intra-community strife exacerbated the risks associated with subsistence shortfalls. Valley communities elected a number of strategies to curtail conflict-induced risk, including movement of settlements and field systems to defensible locations, construction of walls and other defensive features, and the introduction of plazas. Rock art data suggest that trade was increasingly embedded in ritually sanctioned events involving groups from different ecological zones. While studies of risk have focused disproportionately on environmental hazards, subsistence-related crises are often compounded by social hazards that require their own risk-mitigating strategies, further constraining options for coping with subsistence stress.     

A Survey of Soil Erosion in Australia using Caesium‐137

A survey of soil erosion was conducted in Australia using the fallout radioisotope caesium‐137 as an indicator of topsoil redistribution. Two hundred and six sites were sampled, 100 within rotational cropping and horticultural use, 52 within uncultivated permanent pasture and forest, and 54 in rangelands. Average net soil losses were approximately equal for cultivated cropping lands and rangelands (ca. 5.5 t ha^?1 yr^?1), and just over 1 t ha^?1 yr^?1 for pasture and forest. The Mann Whitney U Test revealed that losses under cropping and rangeland conditions were significantly higher (p < 0.05) than under uncultivated pasture and forest. Soil loss was negatively correlated with mean annual rainfall and slope gradient, and positively correlated with slope length (Spearman's rank correlation). There was no correlation between rates of soil loss and a rainfall erosi‐vity index. An assessment of erosional events was provided by landholders for 104 sites, with their ranking being weakly but significantly correlated with soil loss estimates (r =+0.35). Sixty percent of sites had net soil losses greater than 1 t ha^?1 yr^?1, and 74% of sites had losses of more than 0.5 t ha^?1 yr^?1. This latter rate may be regarded as a limit for a tolerable level of soil loss. These high rates of soil loss have occurred since the mid‐1950s despite there being significant landholder awareness of the soil erosion hazard.     

Probabilistic Calibration and Experimental Validation of the Seismic Design Criteria for One-Story Concrete Frames

This article investigates the seismic performance of one-story reinforced concrete structures for industrial buildings. To this aim, the seismic response of two structural prototypes, a cast-in-situ monolithic frame and a precast hinged frame, is compared for four different levels of translatory stiffness and seismic capacity. For these structures an incremental nonlinear dynamic analysis is performed within a Monte Carlo probabilistic simulation. The results obtained from the probabilistic analysis prove that precast structures have the same seismic capacity of the corresponding cast-in-situ structures and confirm the overall goodness of the design criteria proposed by Eurocode 8, even if a noteworthy dependency of the actual structural behavior from the prescribed response spectrum is pointed out.

The experimental verification of these theoretical results is searched for by means of pseudodynamic tests on full-scale structures. The results of these tests confirm the overall equivalence of the seismic behavior of precast and cast-in-situ structures. Moreover, two additional prototypes have been designed to investigate the seismic behavior of precast structures with roof elements placed side by side. The results of these further tests show that an effective horizontal diaphragm action can be activated even if the roof elements are not connected among them, and confirm the expected good seismic performance of these precast systems. Finally, the results of the experimental tests are compared with those obtained from nonlinear structural analyses. The good agreement between numerical and experimental results confirms the accuracy of the theoretical model and, with it, the results of the probabilistic investigation.     

Playing with matches: An assessment of accuracy in linked historical data

This article evaluates linkage quality achieved by various record linkage techniques used in historical demography. The author creates benchmark, or truth, data by linking the 2005 Current Population Survey Annual Social and Economic Supplement to the Social Security Administration's numeric identification system by social security number. By comparing simulated linkages to the benchmark data, she examines the value added (in terms of number and quality of links) from incorporating text-string comparators, adjusting age, and using a probabilistic matching algorithm. She finds that text-string comparators and probabilistic approaches are useful for increasing the linkage rate, but use of text-string comparators may decrease accuracy in some cases. Overall, probabilistic matching offers the best balance between linkage rates and accuracy.     

Performance-based Seismic Design of a Pendulum Tuned Mass Damper System

The study implements the performance-based analysis and design methodology to assess the seismic vulnerability of a coal-fired power plant and to optimally design its equivalent pendulum-type tuned mass damper system such that the direct losses are minimized. A building-specific total loss ratio is developed to link the component level losses with the total repair cost of the original structure. The optimal system configuration is finally derived for cases with the minimum loss. The study demonstrates a systematic way of achieving the optimal pendulum-type tuned mass damper design with considerations of uncertainties in earthquake inputs and the combined component level damages.     

Seismic Hazard Assessment of the NW Himalayan Fold-and-Thrust Belt,Pakistan, Using Probabilistic Approach

The Seismic Hazard Assessment (SHA) based on probabilistic approach has been carried out for the entire seismically active NW Himalayan Fold and Thrust Belt in Pakistan. Additional information in the form of earthquake catalog, delineation of 41 active faults in a structural map, their relationship to the seismicity, and establishment of seismotectonic zones has also been undertaken.

From the distribution of the 813 events within the study area, it appears that seismicity (≥4.0 M_w) is associated with both surface and blind faults. The clustering of events in specific parts along the surface faults shows that some fault segments, especially in the hinterland zone, are more active. In parts of the active deformational front, like the Salt Range, southern Potwar and Bannu, lesser seismic activity (≥4.0 M_w) could be due to damping effect of the thick Precambrian salt.

A majority of the earthquakes (86%) range in magnitude from 4.0 to 4.9 M_w, followed by 107 events (13%) ranging from 5.0 to 5.9 M_w. The remaining 1% range from 6.0 to 6.7 M_w. There is a predominance of shallow seismicity (<50 km focal depth). Larger magnitudes events are more in the hinterland zone. In contrast, based on distribution of 683 (≥4.0 M_w) events, a deeper level of seismicity (50 to 200 km) prevails especially in the adjoining Hindukush Range of Afghanistan.

Four seismotectonic zones have been established in the area. The b value is highest for the Peshawar-Hazara Seismic Zone (PHSZ) at 1.27, followed by 1.12 for the Surghar-Kurram Seismic Zone (SKSZ). The Swat-Astor Seismic Zone (SASZ) and Kohat-Potwar-Salt Range Seismic Zone (KPSZ) have b values of 0.99 and 1.03, respectively, thereby indicating the occurrence of more events of relatively higher magnitude as compared to the other two zones. The mean activity rate of the earthquakes (λ) ranges from 4.26 to 1.73. In decreasing order, the values are 4.26, 2.62, 2.07, and 1.73 for PHSZ, SASZ, KPSZ, and SKSZ, respectively. Using four regression relationships, the maximum potential magnitude (m₁) has been determined for the 4 Quaternary faults. The highest value within each seismic zone represents its m₁. Our calculations show that m₁ is 7.8 in the hinterland (SASZ and PHSZ) and 7.4 in the foreland part (KPSZ and SKSZ).

SHA, incorporating probabilistic approach, has been undertaken at 10 sites, along with disaggregation at the assigned amplitude of 0.2g. Pakistan does not have an attenuation equation of its own. The two equations of Ambraseys et al. (1996) Ambraseys, N. N., Simpson, K. A. and Bommer, J. J. 1996. Prediction of horizontal response spectra in Europe. Earthquake Engineering and Structural Dynamics, 25: 371–400. [Crossref], [Web of Science ®] , [Google Scholar] and Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been used and the results obtained using the equation of Boore et al. (1997) Boore, D. M., Joyner, W. B. and Fumal, T. E. 1997. Equations from estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68: 128–153. [Crossref] , [Google Scholar] have been preferred. In the Probabilistic seismic hazard assessment (PSHA), the PGA values with 10% probability of exceedance in the 50 years, i.e., the return period of 475, have been determined using the EZ-FRISK (6.2 beta version) software. Best-estimated seismic hazard parameters (λ, m₁, m₀, and the β value) of the four seismic zones were used as the input. Results were generated in the form of total hazard curves. Values obtained range from 0.08g (for Bannu) to 0.21g (for Malakand and Kohat). For the other seven sites they are: Astore (0.082g), Kaghan (0.12g), Muzaffarabad (0.13g), Islamabad and Peshawar (0.15g), Talagang (0.16g), and Mangla (0.18g). High population density and more poorly constructed structures in Rawalpindi (twin city of Islamabad) and Peshawar make them more hazardous.