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The impact of liquefaction on a regional scale is not well understood or modeled with traditional approaches. This paper presents a method to quantitatively assess liquefaction hazard and risk on a regional scale, accounting for uncertainties in soil properties, groundwater conditions, ground-shaking parameters, and empirical liquefaction potential index equations. The regional analysis is applied to a case study to calculate regional occurrence rates for the extent and severity of liquefaction and to quantify losses resulting from ground shaking and liquefaction damage to residential buildings. We present a regional-scale metric to quantify the extent and severity of liquefaction. A sensitivity analysis on epistemic uncertainty indicates that the two most important factors on output liquefaction maps are the empirical liquefaction equation, emphasizing the necessity of incorporating multiple equations in future regional studies, and the ground motion model, highlighting the same necessity for the peak ground acceleration input. Furthermore, the disaggregation of seismic sources reveals that triggering earthquakes for various extents of liquefaction originate from multiple sources, though primarily nearby faults and large magnitude ruptures. This finding indicates the value of adopting regional probabilistic analysis in future studies to capture the diverse sources and spatial distribution of liquefaction. [ABSTRACT FROM AUTHOR]

When solving the performance‐based earthquake engineering (PBEE) integral, the engineering demand parameters (EDPs) are assumed to be independent of the "upstream" parameters used in ground motion models (e.g., magnitude and source‐to‐site distance) after conditioning on the intensity measure (IM). This paper formulates a methodology for evaluating this conditional independence assumption through the lens of causal inference (CI). From a causal perspective, the effect of an upstream parameter on the EDP of interest is partially mediated by the IM with the remainder having a direct influence on the EDP. An IM is judged to be desirable (from a conditional independence standpoint) if the mediated effect of the upstream parameter is maximized, which implies that the direct effect is minimized. In the language of causal inference (CI), the IM, EDP and upstream parameters are described as the "treatment", "outcome" and "confounding" variables, respectively. It then follows that the best performing IM is the one that maximizes the effect on the EDP after controlling for the upstream parameters. A semi‐parametric model that employs double machine learning is used to estimate the causal effect. The methodology is demonstrated through a case study application utilizing the responses from five special steel moment frames analyzed using 240 site‐agnostic ground motions. Compared to sufficiency‐based assessments, the casual inference method produces findings that are more explainable using structural dynamics principles and invariant to the number of ground motions used in the evaluation. [ABSTRACT FROM AUTHOR]

This article investigates the correlation coefficients of ground-motion intensity measures for ground motions containing near-fault directivity velocity pulses. These correlation coefficients are necessary to quantify conditional multivariate intensity measure distributions and generate realizations from them for ground-motion selection. The empirical correlations between intensity measures representing ground-motion amplitude, frequency content, duration, and cumulative effects are calculated using the RotD50 definition and compared with published models. The impact of intensity measure definition as in RotD50, RotD100, and the geometric mean is also scrutinized. The sensitivity of the results to the considered ground motion set and the reference ground motion model are addressed in the computations. The results are compared with those from only non-directivity and mixed data sets based on the NGA-West2 database. The results indicate that the adopted data set has the largest influence on the variability of the empirically computed correlation coefficients. Given the multiple sources that contribute to uncertainty in these calculations, the authors conclude that existing models for predicting median correlation coefficients based on mixed data sets are sufficient for use with directivity, non-directivity, and mixed ground motions. [ABSTRACT FROM AUTHOR]

Large earthquakes cause widespread damage and can result in substantial direct and indirect economic losses. Previous researchers have proposed separate models for predicting region-wide direct and indirect losses due to future earthquakes; however, comprehensive simulation approaches that include both remain underdeveloped. In particular, the propagation of uncertainty along the various modeling steps has not been previously considered. This article addresses that gap by proposing a three-stage model to assess economic impacts of possible future earthquakes, consisting of regional ground motion simulation, damage and direct loss modeling, and macroeconomic recovery modeling. In this model, economic indicators such as direct asset losses and changes in economic sectors' value added and employment are quantified. The model also captures uncertainty in the spatial distribution of earthquake shaking and damage patterns, which in turn is reflected in post-disaster economic indicators. The results show that considering uncertainty leads to a wide range of possible economic outcomes and high variance in direct and indirect losses. A cross-model sensitivity analysis is performed to evaluate the effect of different model parameters on the quantification of economic consequences. [ABSTRACT FROM AUTHOR]

The choice of spectral targets for ground motion selection has a strong impact on structural demands resulting from nonlinear time history analysis. In particular, the conditional mean spectrum (CMS) has been recognized as an appealing alternative to the uniform hazard spectrum (UHS) as a spectral target due to the former's more realistic shape and reduced conservatism. Using a tall building case study in a high-seismicity region, this paper evaluates the building demands generated by UHS- and CMS-based selection procedures. Theoretically rigorous implementation of CMS-based selection using 17 different conditioning periods is shown to reduce maximum considered earthquake (MCE)–level demands on the case study building by 9%–35% relative to UHS-based selection. Furthermore, the simplified CMS-based procedure in the building code with apt choice of only two conditioning periods is found to satisfactorily capture the demands generated by the theoretically rigorous approach. Findings also highlight the degree of sensitivity of CMS-based results to the choice of conditioning periods and to enforcement of lower bounds on spectral targets, such as 75% of the UHS. The presented analysis procedure can be replicated in future studies for explicit evaluation of simplified CMS ground motion selection in other structural systems or analysis cases. Since its introduction to the building code, the alternative, conditional mean spectrum-based method for ground motion selection has gained traction among practitioners due to its reduced conservatism relative to traditional selection methods. To simplify the implementation of conditional mean spectra in practice, the building code alternative method requires a minimum of only two target spectra be used, so long as their envelope satisfies a lower bound within a specified period range. However, there are few quantitative studies of the impacts of these simplifications on the resulting building demands. In this study, we demonstrate how building demands vary when a tall building in a high-seismicity region is analyzed using either a traditional or a conditional mean spectrum-based selection approach. We find that using two reasonable target spectra in accordance with the alternative method produces acceptable building demands as compared to the demands obtained from performing exhaustive nonlinear analysis with a large number of target spectra. Furthermore, we illustrate how different choices of conditional mean spectrum targets maximize different types of building demands (e.g., interstory drift, base shear, floor acceleration) and how some types of demands are more sensitive to this choice than others. This work provides a procedure for evaluating conditional mean spectrum-based ground motion selection that can be replicated in the future for other buildings or structural systems. [ABSTRACT FROM AUTHOR]

The widely used incremental dynamic analysis (IDA) offers attractive efficiencies to organize and conduct nonlinear dynamic structural analyses under earthquake ground motions. However, its use of a fixed ground motion set limits its ability to resolve ground motion characteristics that vary based on location and intensity. To overcome this limitation and utilize IDA in site-specific seismic risk analysis, a new method is proposed, called the site-specific adjustment framework for incremental dynamic analysis (SAF-IDA), which involves two modifications to conventional IDA. The first is a process to select input ground motions for the IDA over a distributed grid of ground motion characteristics that influence structural response. The second is a post-processing procedure to develop a surrogate model from the raw IDA data to adjust the structural response results based on site- and intensity-specific ground motion hazard parameters. The proposed SAF-IDA method is illustrated in case study analyses of archetype building structures and validated through comparison with analysis results based on more computationally intensive multiple stripe analysis (MSA), which employs site-specific selection of ground motions for each intensity level. [ABSTRACT FROM AUTHOR]

A framework is proposed to assess the impact of safety cordons on the recovery of community functions after an earthquake, using high-resolution geospatial information to simulate the damage, cordons, and recovery trajectories for buildings in the affected area. Ground motion maps are developed to characterize shaking intensities for regional building-level engineering assessments of damage, repair times, and recovery times to quantify the impact of access restrictions associated with cordons around tall buildings with impaired collapse safety. The results are presented as recovery curves that quantify the cumulative loss in building functionality across the community as a function of time following an earthquake. A case study considers recovery of office space in Downtown San Francisco, following a Mw 7.2 event on the San Andreas Fault. For this scenario, an average of 219 community days of office functionality are lost in the first year, representing about 60% of the total office space capacity. About one-third of the loss is attributed to access restrictions associated with cordons around older tall buildings. The proposed framework can be used to investigate the efficacy of various mitigation strategies to expedite recovery. While the most effective strategy for mitigating the overall impact of cordon restrictions is to seismically retrofit older tall buildings that trigger cordons, other less expensive preparedness measures are shown to be effective, depending on the recovery time frame of interest. Specifically, recovery preparedness measures are generally more effective when evaluated for longer-term recovery targets (e.g. recovery of function after 12 months) compared with short-term targets (e.g. recovery after 4 months). [ABSTRACT FROM AUTHOR]

This paper presents new techniques for quantifying nonstationary spatial variations in strong ground motion, using data from recent well‐recorded earthquakes in New Zealand. The data set is unique in that many recording stations are relatively densely spaced, and multiple strong ground motions have been recorded at the same stations. This allows calculation of site‐specific and region‐specific correlations in ground‐motion amplitude for Wellington and Christchurch, and the results are compared to a model assuming stationary correlations at all locations. Strong nonstationarity in spatial correlation is observed in the Wellington and Christchurch regions. Heterogeneous geologic conditions appear to be associated with the nonstationary spatial correlation. Several factors influencing nonstationary spatial correlation were studied: (a) site‐specific residuals indicate deviation of correlation from a stationary model; (b) most earthquakes have no systematic effect on spatial correlations and there is no indication of a trend in correlations with magnitude; (c) rupture complexity is related to the variation of spatial correlations in ground‐motion residuals; (d) variation of site‐specific correlations cannot be resolved by using VS,30 terms in Ground‐Motion Models. The nonstationary correlation approach provides an opportunity to incorporate the site‐specific effects in future correlation models. [ABSTRACT FROM AUTHOR]

This manuscript describes a subset of CyberShake numerically simulated ground motions that were selected and vetted for use in engineering response-history analyses. Ground motions were selected that have seismological properties and response spectra representative of conditions in the Los Angeles area, based on disaggregation of seismic hazard. Ground motions were selected from millions of available time series and were reviewed to confirm their suitability for response-history analysis. The processes used to select the time series, the characteristics of the resulting data, and the provided documentation are described in this article. The resulting data and documentation are available electronically. [ABSTRACT FROM AUTHOR]

This study examines the influence of ground motion duration on the collapse capacities of a modern five-story steel moment frame and a reinforced concrete bridge pier. The effect of duration is isolated from the effects of ground motion amplitude and response spectral shape by assembling sets of "spectrally equivalent" long and short duration records and employing them in comparative nonlinear dynamic analyses. For the modern steel moment frame, the estimated median collapse capacity is 29% lower when using the long duration set, as compared to the short duration set. For the concrete bridge pier, the collapse capacity is 17% lower. A comparison of commonly used duration metrics indicates that significant duration is the most suitable metric to characterize ground motion duration for structural analysis. Sensitivity analyses to structural model parameters indicate that structures with high deformation capacities and rapid rates of cyclic deterioration are the most sensitive to duration. [ABSTRACT FROM AUTHOR]

Chapter 16 of ASCE 7 governs the selection of ground motions for analysis of new buildings and requires recordings that meet specified criteria. If a sufficient number of recordings cannot be found, it allows the use of "appropriate simulated ground motions," but does not provide further guidance. This paper outlines a procedure for generating and selecting a set of "appropriate" hybrid broadband simulations and a comparable set of recordings. Both ground motion sets are used to analyze a building in Berkeley, California, and the predicted structural performance is compared. The structural behavior resulting from recordings and simulations is similar, and most discrepancies are explained by differences in directional properties such as orientation of the maximum spectral response. These results suggest that when simulations meet the criteria outlined for recordings in ASCE 7 and properties such as directionality are realistically represented, simulations provide useful results for structural analysis and design. [ABSTRACT FROM AUTHOR]

Estimation of fragility functions using dynamic structural analysis is an important step in a number of seismic assessment procedures. This paper discusses the applicability of statistical inference concepts for fragility function estimation, describes appropriate fitting approaches for use with various structural analysis strategies, and studies how to fit fragility functions while minimizing the required number of structural analyses. Illustrative results show that multiple stripe analysis produces more efficient fragility estimates than incremental dynamic analysis for a given number of structural analyses, provided that some knowledge of the building's capacity is available prior to analysis so that relevant portions of the fragility curve can be approximately identified. This finding has other benefits, given that the multiple stripe analysis approach allows for different ground motions to be used for analyses at varying intensity levels, to represent the differing characteristics of low-intensity and high-intensity shaking. The proposed assessment approach also provides a framework for evaluating alternate analysis procedures that may arise in the future. [ABSTRACT FROM AUTHOR]

The NGA-West2 project is a large multidisciplinary, multi-year research program on the Next Generation Attenuation (NGA) models for shallow crustal earthquakes in active tectonic regions. The research project has been coordinated by the Pacific Earthquake Engineering Research Center (PEER), with extensive technical interactions among many individuals and organizations. NGA-West2 addresses several key issues in ground-motion seismic hazard, including updating the NGA database for a magnitude range of 3.0–7.9; updating NGA ground-motion prediction equations (GMPEs) for the "average" horizontal component; scaling response spectra for damping values other than 5%; quantifying the effects of directivity and directionality for horizontal ground motion; resolving discrepancies between the NGA and the National Earthquake Hazards Reduction Program (NEHRP) site amplification factors; analysis of epistemic uncertainty for NGA GMPEs; and developing GMPEs for vertical ground motion. This paper presents an overview of the NGA-West2 research program and its subprojects. [ABSTRACT FROM AUTHOR]

The NGA-West2 research program, coordinated by the Pacific Earthquake Engineering Research Center (PEER), is a major effort to produce refined models for predicting ground motion response spectra. This study presents new models for ground motion directionality developed as part of that project. Using a database of recorded ground motions, empirical models have been developed for a variety of quantities related to direction-dependent spectra. A model is proposed for the maximum spectral acceleration observed in any orientation of horizontal ground motion shaking (Sa RotD 100), which is formulated as a multiplicative factor to be coupled with the NGA-West2 models that predict the median spectral accelerations over all orientations (Sa RotD 50). Models are also proposed for the distribution of orientations of the Sa RotD 100 value, relative to the fault and the relationship between Sa RotD 100 orientations at differing periods. Discussion is provided regarding how these results can be applied to perform seismic hazard analysis and compute realistic target spectra conditioned on different parameters. [ABSTRACT FROM AUTHOR]

The 2009 NEHRP Provisions modified the definition of horizontal ground motion from the geometric mean of spectral accelerations for two components to the peak response of a single lumped mass oscillator regardless of direction. These maximum-direction (MD) ground motions operate under the assumption that the dynamic properties of the structure (e.g., stiffness, strength) are identical in all directions. This assumption may be true for some in-plan symmetric structures, however, the response of most structures is dominated by modes of vibration along specific axes (e.g., longitudinal and transverse axes in a building), and often the dynamic properties (especially stiffness) along those axes are distinct. In order to achieve structural designs consistent with the collapse risk level given in the NEHRP documents, we argue that design spectra should be compatible with expected levels of ground motion along those principal response axes. The use of MD ground motions effectively assumes that the azimuth of maximum ground motion coincides with the directions of principal structural response. Because this is unlikely, design ground motions have lower probability of occurrence than intended, with significant societal costs. We recommend adjustments to make design ground motions compatible with target risk levels. [ABSTRACT FROM AUTHOR]

Dynamic structural analysis often requires the selection of input ground motions with a target mean response spectrum. The variance of the target response spectrum is usually ignored or accounted for in an ad hoc manner, which can bias the structural response estimates. This manuscript proposes a computationally efficient and theoretically consistent algorithm to select ground motions that match the target response spectrum mean and variance. The selection algorithm probabilistically generates multiple response spectra from a target distribution, and then selects recorded ground motions whose response spectra individually match the simulated response spectra. A greedy optimization technique further improves the match between the target and the sample means and variances. The proposed algorithm is used to select ground motions for the analysis of sample structures in order to assess the impact of considering ground-motion variance on the structural response estimates. The implications for code-based design and performance-based earthquake engineering are discussed. [ABSTRACT FROM AUTHOR]

A common goal of dynamic structural analysis is to predict the response of a structure subjected to ground motions having a specified spectral acceleration at a given period. This is important, for example, when coupling ground-motion hazard curves from probabilistic seismic hazard analysis (PSHA) with results from dynamic structural analysis. The prediction is often obtained by selecting ground motions that match a target response spectrum and using those ground motions as input to dynamic analysis. The commonly used uniform hazard spectrum (UHS) is shown here to be an unsuitable target for this purpose, as it conservatively implies that large-amplitude spectral values will occur at all periods within a single ground motion. An alternative, termed a conditional mean spectrum (CMS), is presented here. The CMS provides the expected (i.e., mean) response spectrum, conditioned on occurrence of a target spectral acceleration value at the period of interest. It is argued that this is the appropriate target response spectrum for the goal described above and is thus a useful tool for selecting ground motions as input to dynamic analysis. The CMS is described, its advantages relative to the UHS are explained, and practical guidelines for use in ground-motion selection are presented. Recent work illustrating the impact of this change in target spectrum on resulting structural response is briefly summarized. [ABSTRACT FROM AUTHOR]

One of the challenges of assessing structural collapse performance is the appropriate selection of ground motions for use in the nonlinear dynamic collapse simulation. The ground motions should represent characteristics of extreme ground motions that exceed the ground-motion intensities considered in the original building design. For modern buildings in the western United States, ground motions that cause collapse are expected to be rare high-intensity motions associated with a large magnitude earthquake. Recent research has shown that rare high-intensity ground motions have a peaked spectral shape that should be considered in ground-motion selection and scaling. One method to account for this spectral shape effect is through the selection of a set of ground motions that is specific to the building's fundamental period and the site hazard characteristics. This selection presents a significant challenge when assessing the collapse capacity of a large number of buildings or for developing systematic procedures because it implies the need to assemble specific ground-motion sets for each building. This paper proposes an alternative method, whereby a general set of far-field ground motions is used for collapse simulation, and the resulting collapse capacity is adjusted to account for the spectral shape effects that are not reflected in the ground-motion selection. The simplified method is compared with the more direct record selection strategy, and results of the two approaches show good agreement. [ABSTRACT FROM AUTHOR]

Ground motion models (or "attenuation relationships") describe the probability distribution of spectral acceleration at an individual period, given a set of predictor variables such as magnitude and distance, but they do not address the correlations between spectral acceleration values at multiple periods or orientations. Those correlations are needed for several calculations related to seismic hazard analysis and ground motion selection. Four NGA models and the NGA ground motion database are used here to measure these correlations, and predictive equations are fit to the results. The equations are valid for periods from 0.01 seconds to 10 seconds, versus similar previous equations that were valid only between 0.05 and 5 seconds and produced unreasonable results if extrapolated. Use of the new NGA ground motion database also facilitates a first study of correlations from intra- and inter-event residuals. Observed correlations are not sensitive to the choice of accompanying ground motion model, and intra-event, inter-event, and total residuals all exhibit similar correlation structure. A single equation is thus applicable for a variety of correlation predictions. A simple example illustrates the use of the proposed equations for one hazard analysis application. [ABSTRACT FROM AUTHOR]

Analysis of the seismic risk to a structure requires assessment of both the rate of occurrence of future earthquake ground motions (hazard) and the effect of these ground motions on the structure (response). These two pieces are often linked using an intensity measure such as spectral acceleration. However, earth scientists typically use the geometric mean of the spectral accelerations of the two horizontal components of ground motion as the intensity measure for hazard analysis, while structural engineers often use spectral acceleration of a single horizontal component as the intensity measure for response analysis. This inconsistency in definitions is typically not recognized when the two assessments are combined, resulting in unconservative conclusions about the seismic risk to the structure. The source and impact of the problem is examined in this paper, and several potential resolutions are proposed. This discussion is directly applicable to probabilistic analyses, but also has implications for deterministic seismic evaluations. [ABSTRACT FROM AUTHOR]

In this paper, we propose a community detection method to find regions in spatial data with higher correlations. We construct a 'correlation deviation graph' that considers the influence of global correlation caused by the node's geographical location. We compare the performance of the correlation deviation graph to conventional correlation graph construction approaches for community detection, using synthetic data, and show that the proposed method has the best performance in the presence of a global correlation structure. We also compare the performance of signed spectral clustering and the signed Louvain algorithm for community detection on the correlation graphs, and find that the signed spectral clustering algorithm performs best. We apply our algorithms to simulated earthquake ground motion data in the Los Angeles region. The results suggest that communities of high correlation in ground shaking tend to be associated with common geological conditions and relative location along the rupture strike direction. • We propose a community detection method to find higher spatial correlation regions. • We propose a 'correlation deviation graph' to consider the effect of node distance. • The proposed method outperforms traditional approaches on synthetic data. • We apply the proposed method to earthquake ground motion data. • We find geological condition and geometry relative to rupture influence correlations. [ABSTRACT FROM AUTHOR]