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Most traditional passive friction dampers are limited to the design of single activated energy dissipation mechanism; therefore, when the seismic intensity is not strong enough to activate the mechanism, traditional friction dampers can only increase stiffness of the structure just like braces; only when the mechanism is activated will the energy dissipation elements perform energy absorption and assist the structure to absorb received seismic energy. The objective of this study is to improve this defect of traditional friction dampers, developing a Multi–Level Friction Damper (MFD) with a two‐stage energy dissipation mechanism, helping building structures (e.g., hospitals, high‐tech plants) reduce the acceleration responses of the superstructure. MFDs are proven to provide more comprehensive protection and have higher energy dissipation benefits than traditional friction dampers by the validation of numerical analysis and shaking table test. The study in turn performed parameter fitting with the results of the numerical simulation analysis and shaking table test, and the experimental results turned out to be satisfactory, validating the accuracy of the theoretical formulas. [ABSTRACT FROM AUTHOR]

Current seismic design codes for bridge structures do not account for the influence of aftershock sequences, which, to some extent, overestimate the seismic performance for bridges subjected to mainshock‐aftershock (MS‐AS) scenarios. To address the great need for ground motion sequences tailored to specific research sites for fragility analysis, this study proposes a method for generating artificial MS‐AS ground motion sequences based on the evolutional bimodal Kanai–Tajimi model and the Epidemic–Type Aftershock Sequence model. We establish a framework for MS‐AS fragility analysis using an input–output Hidden Markov Model (IOHMM), where the damage states (DS) of bridge piers are considered unobservable and are inferred statistically through damage indices in an unsupervised manner. Model parameters are trained using intensity measure (IM) sequences and damage index (DI) sequences. Fragility curves for both the mainshock and state‐dependent aftershocks considering multiple aftershocks are formulated based on the initial state probability and state transition probabilities of the proposed IOHMM. The fragility analysis results reveal that as the initial seismic damage level increases, the probability of aftershocks causing higher damage levels in the structure also increases, highlighting the significant impact of aftershocks on structural damage increments. Furthermore, we extend the proposed model to a bivariate seismic intensity measure and develop fragility surfaces. The proposed framework provides a novel approach and insights for tackling seismic fragility under multiple aftershocks. [ABSTRACT FROM AUTHOR]

This paper aims at assessing the failure time of a 7‐story reinforced concrete (RC) frame in a post‐earthquake fire (PEF) event probabilistically. Cumulative distribution functions (CDF) of the studied frame's failure time in various seismic load intensities have been calculated and presented with the aid of Monte Carlo analysis. Seismic load intensity, failure time, and failure probability are three parameters that are correlated through probabilistic analysis. The effects of cracking, spalling, and residual deformations resulted from the seismic load are considered in the strength of structure against the fire load. Seismic load intensity, materials properties, gravity load, and geometry are considered as random variables and one probabilistic analysis has been carried out for each seismic load intensity. The results have illustrated that in low seismic load intensities, probabilistic values of failure time in a structure subjected to pure fire load are equal to the one exposed to PEF. With the increase of seismic load intensity, the effects of cracking, spalling, and residual deformations would lead to a decline in the strength of structural elements against PEF scenario. The failure time in 50% failure probability for Sa = 0.2 g, Sa = 1 g, and Sa = 2 g intensities has been calculated as 14,300, 12,200, and 5100 s, respectively. The analysis results have shown that in an unspecified seismic load intensity, the failure time of the 7‐story RC frame for the 50% occurrence probability is equal to 9750 s. [ABSTRACT FROM AUTHOR]

The seismic resilience of cities plays a crucial role in achieving the United Nations Sustainability Development Goal. However, despite the occurrence of elevator passenger entrapment in numerous earthquakes, there is a notable lack of studies addressing this sophisticated issue. This study aims to bridge this gap by proposing a novel urban risk assessment model designed to evaluate city‐scale earthquake‐induced elevator passenger entrapment. The model integrates big data and physics‐based approaches. A novel mapping method was developed to estimate city‐scale elevator traffic level based on population heatmap data and deep learning. A process‐based parallel computing scheme was designed to accelerate the assessment. The applicability was demonstrated based on a real‐world urban area comprising 619 buildings. The findings reveal that as the time of the earthquake varies, the risk exhibits significant fluctuations. Additionally, this study highlights that a simplistic correspondence between seismic intensity and passenger entrapment risk can lead to erroneous estimations. [ABSTRACT FROM AUTHOR]

Numerous studies have reported anomalous ultralow frequency (ULF) electromagnetic fields preceding earthquakes. In this paper, we estimate the current intensity responsible for generating the earthquake‐related ULF fields under the assumption that the origin is a current flowing at the hypocenter and that it has the same frequency dependence for all cases. To estimate current intensity, we perform ULF electromagnetic field simulations with an absorbing boundary condition developed in this study, taking into account the conductivity distribution of the Earth's crust. We analyze 11 earthquakes, including those that occurred in Loma Prieta, Spitak, Guam, Biak, Kagoshima, Iwateken Nairiku Hokubu, Izu swarm, Jammu and Kashmir, Alum Rock, Wenchuan, and L'Aquila. Our results show that, for nine out of the 11 events, there is a positive correlation between current intensity and earthquake magnitude, suggesting that the measured ULF fields originate from seismic activity and supporting our assumptions. Key Points: A positive correlation between current intensity causing ULF emissions associated with earthquakes and earthquake magnitude is indicatedThe ULF emissions are successfully computed by using the weighted Laguerre polynomial‐finite difference time domain method [ABSTRACT FROM AUTHOR]

A devastating earthquake with moment magnitude 7.5 occurred in the Noto Peninsula in central Japan on 1 January 2024. We estimate the rupture evolution of this earthquake from teleseismic P‐wave data using the potency‐density tensor inversion method, which provides information on the spatiotemporal slip distribution including fault orientations. The results show a long and quiet initial rupture phase that overlaps with regions of preceding earthquake swarms and associated aseismic deformation. The following three major rupture episodes evolve on segmented, differently oriented faults bounded by the initial rupture region. The irregular initial rupture process followed by the multi‐scale rupture growth is considered to be controlled by the preceding seismic and aseismic processes and the geometric complexity of the fault system. Such a discrete rupture scenario, including the triggering of an isolated fault rupture, adds critical inputs on the assessment of strong ground motion and associated damages for future earthquakes. Plain Language Summary: On 1 January 2024, a moment magnitude 7.5 earthquake occurred in the northern Noto Peninsula, Japan. The strong ground motion and tsunami associated with the earthquake caused severe damage to buildings and infrastructure, resulting in at least 245 causalities in the affected areas. The Noto Peninsula is affected by northwest‐southeast compression, and active reverse faults are known along the northern coast of the peninsula and its offshore region. Before the 2024 earthquake, the source region experienced long‐lasting earthquake swarm activity, which is a set of seismic events without an obvious mainshock‐aftershock pattern. Our seismological analysis found that there was a 10‐s‐long initial rupture episode around the hypocenter that overlapped with the earthquake swarm region. The initial rupture was followed by a series of three different rupture episodes on differently oriented fault segments. This earthquake highlights a multi‐scale rupture growth across a segmented fault network after a very quiet initial rupture process that was controlled by the preceding earthquake swarms and associated aseismic deformation related to fluid injection from depth. The rupture process advances our understanding of earthquake source physics and can lead to a better assessment of future earthquake hazards. Key Points: The 2024 Mw 7.5 Noto Peninsula earthquake involves a multi‐segmented rupture sequence on differently oriented faultsThe long and quiet initial rupture domain coincides with the preceding earthquake swarm regionFluid‐induced earthquake swarms and a segmented fault network control the complex earthquake rupture growth [ABSTRACT FROM AUTHOR]

Past major earthquakes have demonstrated that a significant proportion of existing residential buildings are vulnerable to seismic hazards, resulting in economic and social losses. The assessment of earthquake‐induced losses is crucial for devising strategies aimed at enhancing seismic resilience through mitigation plans and emergency response measures. This study intends to provide an analytical methodology for evaluating economic losses for existing residential concrete shear wall buildings in Eastern Canada seismic zones based on Canadian‐compatible seismic capacity parameters. A sampled data set related to residential buildings in Montreal was analyzed and statistical distributions were developed that represent the proportion of buildings in different seismic design code levels and number of stories. Vulnerability analyses were performed, which involved estimating buildings' response under seismic hazard inputs according to the 2020 National Building Code of Canada and conducting loss assessment for structural components, nonstructural displacement‐sensitive components, nonstructural acceleration‐sensitive components, and contents. The results of vulnerability analyses in terms of loss ratio curves showed that the seismic performance varies between mid‐rise and high‐rise concrete shear wall buildings with different seismic design code levels, and nonstructural displacement‐sensitive components exerted the most significant influence on overall economic losses among building components. In addition, a comparison was conducted between Canadian‐compatible economic loss ratio curves and those developed based on the standard seismic capacity parameters in the Hazus technical manual and differences in predicted loss ratios were discussed. The developed loss ratio curves can be integrated into regional scale loss assessment tools for rapid estimation of earthquake‐induced economic losses for concrete shear wall buildings as a function of seismic intensity. [ABSTRACT FROM AUTHOR]

Human perception in high‐rise buildings during far‐field long‐period earthquake ground motions often induces psychological discomfort, including fear and anxiety. A comprehensive understanding on human perception of seismic events is vital for city planning and emergency management, facilitating effective evacuation plans and minimizing stampede risks. This study addresses a gap by employing the seismic fragility analysis method to delineate how human perception in high‐rise buildings is affected during far‐field long‐period ground motions. The methodology involves several key steps. First, the far‐field long‐period earthquake ground motion was identified by detecting the later‐arriving surface waves, and a series of records were selected from the next generation attenuation (NGA) West‐2 ground motion database of the Pacific Earthquake Engineering Research center. Then, a high‐rise building in Shanghai, China was modeled using ETABS 20. Through the linear‐elastic time history analysis, the structural seismic response at each floor was computed. Furthermore, human perception thresholds to vibration were introduced to assess the degree of human perception at each floor, illustrating the difference of human perception to seismic tremor at different floors. Finally, a novel earthquake intensity measure (IM), namely average response spectrum intensity (ARSI) within the vibration period ranging from 0.1 s to 10 s was introduced to generate seismic fragility curves for human perception. According to the investigation, it was found that the corner frequency and the associated energy ratio are useful indicators to identify the far‐field long‐period earthquake ground motions. The ARSI is an effective parameter to assess human perception to seismic tremor compared to the spectral acceleration at a given fundamental period. The generated seismic fragility analysis can provide a complete and thorough understanding on the probability of people that should be evacuated under different earthquake intensity levels. The probability of human perception at different floors varies along the building height, demonstrating the difficulty to make crowd evacuation plan in practice. This insight is vital for understanding and mitigating seismic concerns in high‐rise buildings, particularly in low‐to‐moderate seismicity regions. [ABSTRACT FROM AUTHOR]

The Walker Lane (WL) in the western Great Basin (GB) is an active plate boundary system accommodating 10%–20% of the relative tectonic motion between the Pacific and North American plates. Its neotectonic framework is structurally complex, having hundreds of faults with various strikes, rakes, and crustal blocks with vertical axis rotation. Faults slip rates are key parameters needed to quantify seismic hazard in such tectonically active plate boundaries but modeling them in complex areas like the WL and GB is challenging. We present a new modeling strategy for estimating fault slip rates in complex zones of active crustal deformation using data from GPS networks. The technique does not rely on prior estimates of slip rates from geologic studies, and only uses data on the surface trace location, dip, and rake. The iterative framework generates large numbers of block models algorithmically from the fault database to obtain many estimates of slip rates for each fault. This reduces bias from subjective choices about how discontinuous faults connect and interact to accommodate strain. Each model iteration differs slightly in block boundary configuration, but all models honor geodetic and fault data, regularization, and are kinematically self‐consistent. The approach provides several advantages over bespoke models, including insensitivity to outlier data, realistic uncertainties, explicit mapping of off‐fault deformation, and slip rates that are more objective and independent of geologic slip rates. Comparisons to the U.S. National Seismic Hazard Model indicate that ∼80% of our geodetic slip rates agree with their geologic slip rates to within uncertainties. Plain Language Summary: The Walker Lane (WL) is a complex zone of faults in the western Great Basin of the western United States that experiences frequent earthquakes driven by active plate tectonics. Ground networks of very sensitive GPS stations deployed over the last few decades have collected data showing where the ground deforms most quickly, and hence where earthquakes are more likely to occur. Data on how fast faults slip over time is used to inform the public about the distribution and intensity of the seismic hazard. In this study we present improved data and modeling that resolve with unprecedented detail the rates, patterns, and styles of active crustal motion, resulting in better estimates of fault slip rates in the WL. This work brings the picture of earthquake potential derived from GPS networks into sharper focus, provides new information about how plate tectonics works, and will lead to more accurate estimates of seismic hazard that can help reduce the loss of life and property from earthquakes. Key Points: We estimate Walker Lane fault slip rates using a dense filtered and gridded geodetic velocity field and a robust multi‐block model approachThe geodetic slip rates are independent of geologic slip rates, but 80% agree with them to within uncertaintiesThe method images off‐fault deformation and vertical axis rotations providing more insight into how crustal motion drives earthquakes [ABSTRACT FROM AUTHOR]

In the probabilistic seismic performance assessment of structures, intensity measures (IMs) represent seismic characteristics and variations. Traditional fragility analysis method based on the assumption of linear regression requires selecting an optimal IM as input variable. By introducing machine learning (ML) techniques, nonparametric fragility analysis theoretically allows for considering all potential IMs as inputs. Nevertheless, to reduce input dimensionality and improve training efficiency, the feature selection of IMs remains imperative. This paper proposes a method to select optimal ground motion IMs for data‐driven surrogate modeling of structures. Specifically, the elastic net algorithm is employed to select the optimal multiple IMs based on the coefficient of determination and regression coefficient, differing from the efficiency and practicality emphasized in the traditional method. Using the optimal multiple IMs as input variables, several ML techniques are employed to construct surrogate models for seismic damage assessment of structures, thereby developing fragility functions, that is, the conditional probability of exceeding a damaged state given seismic intensity. A 3‐span, 6‐storey, reinforced concrete frame is utilized to illustrate the proposed methodology. The predictive performance of all ML models with the optimal multiple IMs outperforms that of the models with the commonly used IM (e.g., peak ground acceleration, PGA) as sole input and all candidate IMs as inputs. Additionally, the surrogate models with the optimal multiple IMs enable a more comprehensive seismic fragility modeling of structures under two or more IMs simultaneously, such as the fragility surface under spectral acceleration at 1.0s (Sa‐1.0s) and velocity spectrum intensity (VSI). [ABSTRACT FROM AUTHOR]

Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of seismology, their occurrence has been identified as a possible mechanism leading to further crustal destabilization, hence, to major failures. However, several cases occurred without any previous anomalous seismic activity, so that the hypothesis of foreshocks as reliable seismic precursors fails to pass statistical tests. Here, we perform an all‐round statistical comparative analysis of seismicity in Southern California to assess whether any differences can be identified between swarms and foreshocks. Our results suggest that extremely variable seismic patterns can forerun mainshocks, even though they tend to be preceded by clusters with more numerous events spread over larger areas than swarms and with a wider range of magnitudes. We provide a physical explanation of such dissimilarity and conclude, despite it, that foreshocks can hardly be reliable short‐term precursors of large earthquakes in California. Plain Language Summary: Large earthquakes can be preceded by a wide range of different seismic anomalies. Among these, seismicity has been reported to increase both in magnitude and frequency, but, on the other hand, it can also undergo a short period of reduced intensity before major events. The first pattern corresponds to the occurrence of foreshocks, that is, small to moderate quakes forewarning an upcoming larger one, while the second behavior is called seismic quiescence. In our research, we focus on foreshock activity. We perform an analysis of seismicity in Southern California, for which a well‐provided relocated earthquake catalog is available. While several studies have been conducted so far about what happens before large earthquakes after their occurrence and also there are some works about foreshocks discrimination, a systematic analysis comparing properties of clusters of "swarms", seismicity without a major event, and "foreshocks" before their mainshock is missing. Are foreshocks different from swarms before the occurrence of the main event? Are foreshocks fore‐shocks? Our results suggest that foreshocks can hardly be distinguished from swarms until the largest event takes place. On the base of this analysis and theoretical modeling, we think that foreshocks have limited reliability, if considered alone, for short‐term forecasts. Key Points: The occurrence of mainshocks can be preceded by a wide range of seismic patternsForeshocks slightly differ from swarms in Southern California, but they can be hardly distinguished before mainshocksForeshocks are not reliable precursors of large seismic events [ABSTRACT FROM AUTHOR]

Traditional seismic evaluations for high‐voltage switchgear equipment, the critical power facilities, consider only structural failure mode and may underestimate the actual seismic risk. By additionally introducing a probable functional failure mode caused by the excessive deformation of the switchable blade of equipment, a novel copula‐based framework is proposed to utilize limited samples to generate simulation data and evaluate the joint failure probability (JFP). The correlation index and Akaike Information Criterion are employed to optimize the Copula function. For illustration, a disconnector, representative switchgear equipment, was selected as an example and modeled with the experiment validation. Model analysis results demonstrate the Clayton type is the most competent for evaluation. Neglecting functional failure can significantly underestimate the actual failure probability at various seismic intensities, up to 50%. Furthermore, it was found that the current equipment material strength level already meets the requirements, and enhancing strength alone does not effectively improve reliability under strong earthquakes. For PGA intensities ≥0.7 g, the blade deformation capacity plays the primary reliability constraint, independent of material stress. A cost‐effective seismic design should optimize the combination of allowable material stress and blade deformation based on the JFP considering seismic intensity and targeted reliability. [ABSTRACT FROM AUTHOR]

The behavior of short‐period reinforced concrete (RC) shear wall structures is often complicated and hard to predict accurately, even when the structure behaves in the elastic region, due to significant uncertainties in the material and the environment. Modeling assumptions used in finite element (FE) analyses often influence the accuracy of the dynamic response predictions. This paper discusses the numerical modeling of shaking table tests of a 3‐story RC shear wall specimen, which was carried out by Korea Atomic Energy Research Institute in July 2020. The experimental program is briefly introduced in this paper. Through nonlinear time history analyses using ABAQUS, the effect of modeling assumptions on the accuracy of the FE methods in predicting the linear and moderately nonlinear behavior of the RC structure is presented. Two commonly used modeling/model updating assumptions are considered: concrete Young's modulus and foundation flexibility. Influences of such modeling assumptions in predicting beyond design dynamic behavior (i.e., nonlinear responses and damage development) of the testing structure are also studied. The results showed that the accuracy of the dynamic response prediction of the structure could be improved significantly after calibrating the models against the white noise test results. Nevertheless, models established with different modeling assumptions can only capture the behavior of the structure at certain seismic intensity levels. Different models give results with a considerable variation in the structure's peak acceleration, floor response spectrum, acceleration amplification profile, damage pattern, and damage severity. [ABSTRACT FROM AUTHOR]

To investigate the isolation effect of the friction pendulum system (FPS) horizontal isolation bearing and the air spring‐FPS three‐dimensional (3D) isolation bearing in truss structure and the influences of long‐period ground motions on the isolated structure, the shaking table test of a truss structure is designed and conducted. The ordinary ground motions, near‐fault pulse‐like ground motions, and far‐field long‐period ground motions with different spectral characteristics are chosen to input into the structure, and the dynamic characteristics such as the acceleration, displacement, and stress of the truss are compared and analyzed. The horizontal frequency of the horizontal isolated structure is reduced after the horizontal isolation, while the vertical frequency is further reduced after 3D isolation. The isolation effect of nodal acceleration, nodal displacement, and member stress under 3D isolation is better than that of horizontal isolation, especially the vertical seismic response is significantly improved. When the ground motion intensity is small, the FPS horizontal isolation bearing slides little, and reducing the seismic response of the structure is limited. There is a better isolation effect of 3D isolated structure. The vertical frequency ratio Rf under ordinary ground motions is far away from 1 and close to 3, basically avoiding the main energy segment of the ground motions. The advantage of 3D isolated structure is relatively reduced under long‐period ground motions, which lies in the rich low‐frequency components of long‐period ground motions which are difficult to isolate effectively. [ABSTRACT FROM AUTHOR]

There has been no consensus on post‐earthquake operating plan for high‐speed railway trains. In this paper, two three‐dimensional coupling model of track‐bridge system without and with trains for high‐speed railways were developed, and their performance were verified based on shaking table tests. The equivalent method of design seismic track irregularity for random structures was discussed, and the amplitude response spectra of design seismic track irregularity for all levels of seismic intensity were proposed. In addition, the rationality of design seismic track irregularity was evaluated based on engineering case analysis, providing a theoretical foundation of formulating post‐earthquake contingency plans for high‐speed railways. The results show that when span number increases, the design seismic track irregularity amplitude increases and then tends to be stable; when the span number reaches 9, the train dynamic response gradually becomes stable; the random structures with arbitrary span numbers are equivalent to a specific 9‐span structure when constructing design seismic track irregularity. When the seismic intensity is low, there is no significant difference in shape and amplitude between the measured pre‐earthquake and post‐earthquake track alignment irregularities, and the train can normally run with no significant deceleration required. The train dynamic response under the design post‐earthquake track irregularity is greater than that under the measured post‐earthquake track irregularity, indicating that the design seismic track irregularity has a reasonable safety margin and a good feasibility in engineering practice. [ABSTRACT FROM AUTHOR]

The Southern San Andreas Fault (SSAF) in California is one of the most thoroughly studied faults in the world, but its configuration at seismogenic depths remains enigmatic in the Coachella Valley. We use a combination of space geodetic and seismic observations to demonstrate that the relatively straight southernmost section of the SSAF, between Thousand Palms and Bombay Beach, is dipping to the northeast at 60–80° throughout the upper crust (<10 km), including the shallow aseismic layer. We constrain the fault attitude in the top 2–3 km using inversions of surface displacements associated with shallow creep, and seismic data from a dense nodal array crossing the fault trace near Thousand Palms. The data inversions show that the shallow dipping structure connects with clusters of seismicity at depth, indicating a continuous throughgoing fault surface. The dipping fault geometry has important implications for the long‐term fault slip rate, the intensity of ground shaking during future large earthquakes, and the effective strength of the southern SAF. Plain Language Summary: The San Andreas Fault (SAF) is capable of large, destructive earthquakes and poses significant seismic hazard in California. In the Coachella Valley, the geometry of the SAF beneath the Earth's surface has been the subject of much debate. Here, we present new constraints on the fault's structure in the uppermost 2–3 km of the crust from several new sets of observations. We measure slow movement of the fault at the surface using satellite‐based radar and perform simulations of what fault geometry is most likely to produce the observed motion. We also installed an array of sensors across the SAF to measure seismic waves that travel through or reflect off the fault. Analysis of both data sets indicates that the shallow portion of the SAF dips to the northeast in the Coachella Valley. Precise locations of small earthquakes at greater depths exhibit a similar trend—we thus suggest the fault dips throughout the Earth's crust. Better understanding the geometry of this section of the SAF has implications for earthquake hazards in Southern California, as well as the fault's geologic history. Key Points: InSAR measurements and models of shallow creep on the southernmost San Andreas Fault indicate a moderate‐to‐steep northeast fault dipSeismic imaging using data from a dense array deployed near Thousand Palms reveal northeast dipping fault damage zonesA joint interpretation of available data suggests that the northeast dip persists throughout the upper 10 km of the crust [ABSTRACT FROM AUTHOR]

Precariously balanced rocks (PBRs) are a type of naturally occurring freestanding structure that provides valuable information to constrain seismic hazard at return periods which are important for critical facilities such as nuclear power plants and nuclear repositories. Exposure ages have been established to be in excess of 10,000–30,000 years, which is why precarious rocks are one of the only available means to validate seismic hazard associated with long return periods. One critical component for constraining seismic hazard in this way is the overturning estimate of a given precarious rock as a function of earthquake intensity. However, current state‐of‐the‐art methods for modeling the seismic response of precarious rocks involve significant sources of uncertainty. One of the main sources of uncertainty stems from the interface of the rock, which is usually occluded during surveying and assumed during modeling. Through extensive shake table testing, this study analyzes the uncertainty in the overturning response of a granite precarious rock specimen incorporating various degrees of interface contact. The results indicate that a small variation in the contact geometry could result in a substantial increase in the stability of the specimen, which is significant given the difficulty of surveying the interface of PBRs in the field. Repeatability tests indicate that the overturning demand can vary up to nearly ±50%. The probabilistic overturning responses are compared across the interface changes to bound uncertainty; and, the effect of modeling parameters, namely the contact normal stiffness, is evaluated through a parametric study and comparison with experimental results. [ABSTRACT FROM AUTHOR]

Past earthquakes have highlighted the impact of prolonged downtime on community recovery. The introduction of performance objectives expressed in terms of recovery time has been identified as a key goal for the next generation of building codes. Recent development of downtime estimation frameworks now allows for the discussion of how to use recovery time estimates to (1) establish recovery‐targeted performance and (2) assess the functional recovery performance of buildings designed with modern code provisions. In this paper, we employ methods adapted from life‐safety provisions to evaluate building functional recovery performance using downtime simulation outputs. A scenario‐based, an intensity‐based and a risk‐targeted analysis of functional recovery performance objectives are presented. The functional recovery performance of a series of modern residential reinforced concrete shear wall archetype buildings, ranging from eight to 24 stories in height, at a site in downtown Seattle, Washington, are then assessed. Results of the scenario‐based assessment of an M9 Cascadia Subduction zone earthquake, comparable to an intensity‐based assessment at the 975‐year intensity level, show that the probability of achieving functional recovery within four months is close to zero, while the likelihood of achieving functional recovery by one year is approximately 60%. The results of the risk‐targeted assessment of the archetype buildings show a 50% probability in 50 years of the building downtime to functional recovery exceeding one month, a 43% in 50‐year probability of the downtime exceeding four months and an 8% in 50‐year probability of downtime exceeding one year. Finally, the expected annual downtime is approximately three days for all building heights considered. Disaggregation was used to identify intensity levels that contribute most of the downtime risk. The risk of downtime exceeding one month to one year is dominated by frequent, low‐intensity earthquakes (e.g., 100‐year return period). The risk of exceeding longer recovery times is dominated by less frequent, higher intensity earthquakes (i.e., return periods greater than 975 years). While the results of the analysis are sensitive to assumed damage thresholds and impeding factor delays triggered at low intensity levels, the findings suggest that reinforced concrete shear wall buildings designed following current building codes have a high risk of lengthy downtimes. Ultimately, the proposed methods and results illustrate the importance of introducing recovery‐based provisions into the next generation of building codes. [ABSTRACT FROM AUTHOR]

Efficient regional seismic risk assessment including ground motion prediction and damage risk estimation is needed for emergency response planning. However, a conventional regional assessment suffers from low data‐ and time‐ efficiency as it generally involves a large number of locations and infrastructure systems that have specific soil conditions, and geometric, material, and structural properties, requiring access to large data and massive individual calculations with complicated procedures. To achieve efficient regional seismic risk assessment, this work presents a deep generative learning framework to construct input–output surrogate models of regional seismic risk by learning the underlying complex relation between earthquake source parameters and regional seismic risk involving many locations and structures from data. The learned deep surrogate models directly output the ground motion intensity map and the risk map of a region given earthquake source parameters, circumventing massive individual calculations and data access to individual locations and structures. The presented framework is validated on the bridge network risk assessment using simulated scenario earthquakes of the San Francisco Bay Area. We observe that the obtained deep surrogate models perform well without the need of data access to locations and structures and are time‐efficient. We also discuss the applicability and limitations of the presented framework. [ABSTRACT FROM AUTHOR]

Physics‐based simulations of earthquake ground motion are useful to complement recorded ground motions. However, the computational expense of performing numerical simulations hinders their applicability to tasks that require real‐time solutions or ensembles of solutions for different earthquake sources. To enable rapid physics‐based solutions, we present a reduced‐order modeling approach based on interpolated proper orthogonal decomposition (POD) to predict peak ground velocities (PGVs). As a demonstrator, we consider PGVs from regional 3D wave propagation simulations at the location of the 2008 MW 5.4 Chino Hills earthquake using double‐couple sources with varying depth and focal mechanisms. These simulations resolve frequencies ≤1.0 Hz and include topography, viscoelastic attenuation, and S‐wave speeds ≥500 m/s. We evaluate the accuracy of the interpolated POD reduced‐order model (ROM) as a function of the approximation method. Comparing the radial basis function (RBF), multilayer perceptron neural network, random forest, and k‐nearest neighbor, we find that the RBF interpolation gives the lowest error (≈0.1 cm/s) when tested against an independent data set. We also find that evaluating the ROM is 107–108 times faster than the wave propagation simulations. We use the ROM to generate PGV maps for 1 million different focal mechanisms, in which we identify potentially damaging ground motions and quantify correlations between focal mechanism, depth, and accuracy of the predicted PGV. Our results demonstrate that the ROM can rapidly and accurately approximate the PGV from wave propagation simulations with variable source properties, topography, and complex subsurface structure. Plain Language Summary: Computer simulations can be used to predict the intensity of ground shaking caused by earthquakes. However, these simulations require significant amounts of computing time to obtain accurate results, making them too slow for real‐time systems. In this work, we apply a technique that allows us to obtain instantaneous and accurate approximations of a scenario earthquake simulation using simplified models. The simplified models are fast enough to evaluate this earthquake scenario on demand. We use the simplified models to predict shaking intensities for 1 million different fault planes at the location of the 2008 Chino Hills earthquake. By analyzing the predicted shaking intensities from these earthquakes, we identify possible areas of strong shaking, areas that might otherwise be unidentified if fewer earthquake scenarios were examined. These results suggest that these types of simplified models could be considered to assess regional earthquake hazards and to inform shaking intensity predictions in earthquake early warning. Key Points: Physics‐based simulations are useful for seismic hazard assessment and ground motion prediction but are computationally expensiveOur reduced‐order model accurately predicts simulated peak ground velocities (PGVs) for scenarios, including 3D wavefield and topographic effectsThe reduced‐order model produces physics‐based ground motion maps in milliseconds for variable source depths and focal mechanisms [ABSTRACT FROM AUTHOR]

A bidirectional rocking isolation bearing system (Bi‐RIBS) is proposed to provide seismic protection for bridge structures. By using the 3‐D rocking motion of the Bi‐RIBS, this system acts as a mechanical fuse to limit the maximum force transmitted to the bridge piers and as a restoring component to control an excessive girder response. Possible applications in bridge structures were discussed. A simple analytical model was established to characterize the dynamics of an example bridge featuring such a Bi‐RIBS. A series of dynamic analyses were performed by using the proposed model to investigate the effects of several factors on controlling the seismic responses of the bridge, for example, the design parameters of Bi‐RIBS including inclined angle and size, the damping property at the support interface, and the mass ratio. The peak ground accelerations of the bidirectional ground motion record were scaled to various levels to evaluate the maximum performance indices of the bridge structure and the response control effectiveness of the Bi‐RIBS compared to the uncontrolled counterparts. The simulation results demonstrated that the proposed Bi‐RIBS could effectively control the maximum pier displacement while keeping the bearing from overturning if suitable parameters were selected. In particular, the control effectiveness on the maximum pier response becomes more significant as the seismic intensity increases, due to its distinctive negative stiffness property. [ABSTRACT FROM AUTHOR]

The hybrid self‐centering braced frames (HSBFs) with shape memory alloy‐based braces (SMABs) and viscous dampers (VDs) are an emerging structural system developed for improving the seismic resilience of traditional braced frames (e.g., buckling restrained braced frames [BRBFs]) and self‐centering braced frames (SCBFs) by reducing residual inter‐story drifts (RIDs) and floor acceleration responses simultaneously. Nevertheless, the excellent performance of HSBFs is captured by introducing high initial construction costs. This paper aims to highlight the benefits of HSBFs compared with BRBFs and SCBFs by investigating the earthquake‐induced life‐cycle costs. To this end, 6‐story BRBF, SCBF, and HSBF are designed separately to achieve the same maximum inter‐story drifts under design basis earthquakes (DBE) for a fair comparison. The advanced numerical models of the considered systems were developed, and nonlinear dynamic analyses were conducted to obtain the structural seismic responses under various intensities. Monte Carlo simulation (MCS) was adopted for considering the modeling uncertainty. The life‐cycle costs were subsequently estimated based on the revised HAZUS loss estimation method. The influence of RIDs, initial construction costs of SMABs and VDs, and values of contents inside buildings were comprehensively investigated. It has been found that HSBF can achieve better performance in reducing seismic loss than BRBF and SCBF due to its excellent capability of controlling structural and nonstructural damage. SCBF may show higher seismic loss than BRBFs, given high RID limits for demolition or high building contents' value, highlighting the importance of controlling floor acceleration responses of SCBFs. The life‐cycle benefits of BRBFs, SCBFs, and HSBFs are highly influenced by the RIDs, initial construction costs of SMABs and VDs, building contents' values, and building's lifetime. HSBFs show better life‐cycle benefits than SCBFs when the building's lifetime is not lower than 50 years. Compared to BRBF, the life‐cycle cost effectiveness of SCBF can be only achieved when the initial cost of SMABs is lower than 1.21 times that of BRBs for the building with 50 years' lifetime; the life‐cycle cost effectiveness of HSBF6 can be only achieved when the initial cost of SMABs or VDs is lower than 1.84 times that of BRBs for the building with 50 years' lifetime. It has been concluded that reducing the initial costs of SMABs and VDs is critical and essential for increasing the life‐cycle economic benefits of SCBFs and HSBFs and promoting their real‐world applications. [ABSTRACT FROM AUTHOR]

This study experimentally investigates a dynamic behavior of an end‐anchored floating bridge under the joint actions of earthquakes and water waves. A truncated model with a geometrical scale of 1:100 was utilized for the hydrodynamic test, and an actuator was used to generate the earthquake input. A series of trials were conducted for the floating bridge model under the combined action of two different sea states and three earthquake inputs with increasing intensity based on the concept of the incremental dynamic analysis method. For comparison, the dynamic responses of the floating bridge model under earthquake action in still water and pure wave action were also conducted. Based on the test data, the dynamic responses, particularly focused on the sway, heave, roll, and pitch motions of the pontoons, of the test model were experimentally analyzed. The experimental results showed that earthquake excitation along the longitudinal axis of the bridge girder would induce noticeable oscillation of the bridge pontoons in still water. The magnitude of the coupled effects of earthquakes and water waves is dependent on the intensity of the earthquake inputs and the sea state. [ABSTRACT FROM AUTHOR]

Lessons from recent earthquakes have provided a tough reality check of the traditional seismic design approach and technologies, highlighting the urgent need for a paradigm shift of performance‐based design criteria and objectives toward low‐damage design philosophy and technologies for the whole building system. Modern society is asking for "earthquake proof" resilient buildings that are able to withstand seismic events without compromising their functionality. The EU‐funded SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe Project) project discussed in this paper provided the opportunity to develop and validate within the European context an integrated seismic low‐damage prototype, including main structure and non‐structural elements, for the next generation of high‐performance buildings. This paper presents an overview of the research, involving three‐dimensional shake table tests of a two‐storey 1:2 scaled timber‐concrete post‐tensioned dissipative low‐damage structure "dressed" by earthquake‐resistant gypsum/masonry partitions and glass/concrete facades. Specimen details, construction and assembly phases, test setup, and experimental results are discussed. After many cycles of input motions at increasing levels of seismic intensity (higher than Collapse Prevention Limit State), the integrated building system exhibited a very high seismic performance. The experimental campaign carried out at the National Laboratory of Civil Engineering in Lisbon confirmed the unique potential of low‐damage technologies and the opportunity for their widespread implementation into design practice. [ABSTRACT FROM AUTHOR]

Site‐structure cluster interaction (SSCI) has a significant effect on the seismic response of densely distributed buildings, and rationally and effectively quantifying its effect when modelling the urban seismic damage can provide more optimal decisions to mitigate earthquake disasters. This paper focuses on the input motion of the structures, by extracting the main influential parameters of SSCI and adopting the loosely typed wavelet packet neural network to rapidly simulate the spatially varying ground motion in the urban environment. In the proposed framework, the wavelet packet energy ratio is presented to describe the variation of ground motion characteristics and used as the sole output to carry out the multi‐resolution spectral modulation, and the training samples were accumulated by a validated finite element simulation method. The developed surrogate model considers the effects of a series of factors, including the earthquake intensity, site condition, configuration of structure cluster, structural dynamic characteristics and spacing, and is superior to the one using conventional artificial neural network. It is verified by a virtual test that the waveshape and spectral features of the predicted ground motion agree well with the target result with an error of peak acceleration being only 1.23%. The suggested approach has the advantages of better modulation precision and lower sample size requirement. Moreover, it is almost zero cost to use the developed surrogate model to correct the ground motion of urban buildings and to consider the influence of SSCI, and the structural seismic response can be more factually displayed in the time and space domains. These specialties make it a promising technique in the rapid assessment of urban seismic damage. [ABSTRACT FROM AUTHOR]

In the context of performance‐based earthquake engineering (PBEE), response‐history analysis is currently considered an analytical tool for developing fragility curves. Typically, this involves subjecting a structural system to a large number of ground motion records (GMRs) representing seismic hazards at a site of interest and may be a time‐consuming task. To address this computational challenge, this study proposes a method for selecting a representative subset of GMRs that enables the reproduction of the fragility curve of the general GMR set. In this method, dimension reduction techniques are used to preferentially extract the principal features of earthquake intensity measures, which are applied to construct the feature space. Then, the divisive hierarchical clustering technique is applied to the feature space to obtain a subset of GMRs from the general set until the fragility curve converges. The performance of the proposed method is successfully demonstrated through various numerical examples that include a wide class of single‐degree‐of‐freedom systems and two steel‐frame buildings. The results confirm that the seismic hazard at a given site represented by a general GMR set can be covered in structural fragility estimation using a representative subset of GMRs selected based on the proposed method. The proposed method could contribute to significantly reducing the computational costs for structural fragility estimation without compromising the accuracy. [ABSTRACT FROM AUTHOR]

In the network‐based on‐site earthquake early warning system (EEWS), the 'blind zone', namely the zone where the issued warning arrives later than the destructive S and surface waves, is one of the challenges affecting its effectiveness. The 'blind zone' is determined by the interstation distance, or equivalently the density of seismic stations, of the network. In this paper, we suggest a practical approach according to which, when in a region a temporary increase of seismic hazard is declared, additional stations are deployed in such a way that the blind zone is temporarily reduced. In the procedure, the time‐dependent neo‐deterministic seismic hazard assessment (TD‐NDSHA) plays a vital role in the identification of the regions potentially exposed to high macroseismic intensities. As a showcase example, we consider the scenario of year 2014 at the Sichuan‐Yunnan border of southwest China. The TD‐NDSHA is based on the standard NDSHA procedure at regional scale (bedrock conditions), with the 'controlling earthquakes' defined on the basis of the Annual Consultation. We show that the 'blind zone' can be reduced in the identified areas of interest (e.g., MMI ≥ VI), by deploying a limited number of additional seismic stations. In the case where false alarms can be tolerated, significant reduction of the 'blind zone' can be implemented by moving from a network‐based EEWS to a single‐sensor‐based EEWS and skipping the process of location and magnitude‐determination/prediction procedures. [ABSTRACT FROM AUTHOR]

Using results from 57 large‐scale physics‐based fault‐rupture and wave propagation simulations, this research aims to evaluate the seismic risk, loss, and resilience of more than 16,000 reinforced concrete buildings in the Zeytinburnu district of Istanbul, Turkey. For each building and under each earthquake scenario, the spatially varying site‐specific simulated ground motions were used for performing three‐dimensional nonlinear time‐history analyses. The resulting structural responses—such as peak story drift ratios (PSDR) and peak floor accelerations (PFAs)—were utilized to conduct three region‐scale tasks: (i) building‐ and site‐specific seismic fragility analysis for both structural and nonstructural components of each building; (ii) intensity‐based seismic loss assessment using the FEMA P58 methodology and Monte Carlo simulations; and (iii) resilience evaluation based on the expected time of recovery predicted through FEMA P58. Moreover, both inertial and kinematic soil–structure interaction (SSI) effects were considered using a substructuring method for all three tasks. Site‐specific soil properties were utilized to compute the coefficients of soil springs and dashpots, as well as the foundation input motions. The SSI effects were investigated by comparing the fragility, loss, and resilience indices obtained with and without considering SSI. [ABSTRACT FROM AUTHOR]

This paper presents a new hybrid energy dissipation device and investigates experimentally its capability to improve the seismic response of an inherently very flexible structural system: a reinforced concrete waffle‐flat plate structure. The new device combines in parallel within a single device a low‐cost viscoelastic (VE) component and a metallic yielding (MY) component. The device has a gap that prevents deformations on the MY component in the range of displacements caused by wind or low intensity earthquakes, to avoid high‐cycle fatigue damage. The MY component is expected to activate under the design or the maximum credible earthquake, providing the main structure with lateral stiffness, and a reliable and large source of energy dissipation capacity. Six new hybrid energy dissipation devices (energy dissipation system) were installed in a scaled two‐story portion of a prototype RC waffle‐flat plate structure (main structure) designed only for gravity loads, without considering special ductility detailing or capacity design rules for the columns. The VE component of the hybrid energy dissipation devices reduced the translational periods with largest effective modal mass along the horizontal directions X and Y to 60%, and increased the fraction of damping to about 12%. The main structure with the energy dissipation system was subjected to bidirectional shake table tests that represented frequent, design and maximum credible earthquakes. In the tests, the main structure remained basically undamaged under the frequent and the design earthquakes, whereas it suffered minor (reparable) damage under the maximum credible earthquake. The MY component remained undeformed under low intensity earthquakes. [ABSTRACT FROM AUTHOR]

Application of Buckling Restrained Braces (BRBs) with Truss Moment Frames (TMFs) results in a robust seismic force‐resisting system, herein referred to as Buckling Restrained Knee Braced Truss Moment Frame (BRKB‐TMF), which utilizes the advantages of both BRBs and TMFs. Although steel is commonly used to make the core of BRBs, previous studies have demonstrated the efficacy of annealed aluminum as a preferred core material because of its high ductility and high over‐strength. However, the deformation compatibility of the truss members with the aluminum‐core BRB in BRKB‐TMFs at high drifts is not well studied in the literature. Hence, an experimental study is performed on a scaled sub‐assemblage of a BRKB‐TMF frame designed using the Performance‐Based Plastic Design method. Cyclic tests are performed on 1:3 scale models of aluminum‐core BRB and BRKB‐TMF to evaluate their performance at drifts corresponding to Maximum Considered Earthquake intensity. Also, to further compare the performance of steel and aluminum as suitable BRB core materials, cyclic tests are performed on BRBs with steel and aluminum cores designed using a consistent criterion. The experiments demonstrated the superior performance of aluminum core BRB over steel core BRB. The experimental studies on the BRKB‐TMF concluded that per the design intent, the BRB acted like a fuse for the frame by restricting all the inelastic deformations to itself and the study frame could successfully meet the target drift criteria. [ABSTRACT FROM AUTHOR]

Empirical cross‐hazard analysis and prediction of disaster vulnerability, resilience, and risk requires a common metric of hazard strengths across hazard types. In this paper, the authors propose an equivalent intensity scale for cross‐hazard evaluation of hazard strengths of events for entire durations at locations. The proposed scale is called the Murphy Scale, after Professor Colleen Murphy. A systematic review and typology of hazard strength metrics is presented to facilitate the delineation of the defining dimensions of the proposed scale. An empirical methodology is introduced to derive equivalent intensities of hazard events on a Murphy Scale. Using historical data on impacts and hazard strength indicators of events from 2013 to 2017, the authors demonstrate the utility of the proposed methodology for computing the equivalent intensities for earthquakes and tropical cyclones. As part of a new area of research called hazard equivalency, the proposed Murphy Scale paves the way toward creating multi‐hazard hazard maps. The proposed scale can also be leveraged to facilitate hazard communication regarding past and future local experiences of hazard events for enhancing multi‐hazard preparedness, mitigation, and emergency response. [ABSTRACT FROM AUTHOR]

Estimates of the earthquake ground motion intensity over a geographical area have multiple uses, that is, emergency management, civil protection and seismic fragility assessment. In particular, with reference to fragility assessment, it is of interest to have estimates of the values of different ground‐motion intensity measures in order to correlate them with the observed damage. To this purpose, the present paper uses a procedure recently proposed in the literature to estimate the ground‐motion intensity for the 2012 Emilia mainshocks, considering different ground motion intensity measures and directionality effects. Ground motion prediction equations based on different site effect models, and spatial correlation models are calibrated for the Emilia earthquakes. The paper discusses the accuracy of the shakemaps obtained using the different soil effect models considered and presents the obtained shakemaps as supplementary material. The procedure presented in the paper is aimed at providing ground motion intensity values for seismic fragility assessment and is not intended as a tool to estimate shakemaps for rapid emergency assessment. [ABSTRACT FROM AUTHOR]

This paper aims to assess the seismic fragility of vehicle‐bridge‐interaction (VBI) systems considering the effects of vehicle types, traffic conditions, and road surface qualities. A stochastic nonlinear mechanical model for the earthquake‐VBI system is developed, and the fragility functions for the proposed VBI model are derived by considering the relevant probabilistic seismic demand parameters. On the basis of a typical four‐span continuous prestressed concrete highway bridge in China, a complete numerical model for the VBI system is built considering multiple uncertainties from bridge and vehicle parameters, as well as the road surface qualities. A total of 120 real ground motion records with different combinations of magnitude‐source‐to‐site distance (M‐R) and earthquake intensity characteristics are selected. Meanwhile, 80 scenarios in terms of different combinations of vehicle types, vehicle speeds, and road surface irregularities are defined. In this context, 96,000 nonlinear time‐history analyses are performed, and the developed fragility models are applied to the VBI system at both component and system levels. Results indicate that the fragilities of pier drift, bearing shear strain, and the overall VBI system increase with the increase of the vehicle weight or the decrease of the vehicle speed, while the vertical deck displacement is dominated by the vehicle weight. It is also found that the road surface quality has a negligible effect on both component and system fragilities. [ABSTRACT FROM AUTHOR]

This paper explores the use of sliding friction dampers (SFDs) as dissipative floor connectors to mitigate higher mode effects and earthquake‐induced absolute acceleration demands on steel concentrically braced frame (CBF) buildings. The dampers connect each floor of the steel CBF system to the diaphragms of the gravity framing system (GFS) and they allow for a relative in‐plane movement between the two systems. For this purpose, a design methodology is first proposed to define the activation forces in the SFDs so as to ensure damage‐free seismic performance in the steel CBF and the diaphragms of the GFS. The efficiency of the design methodology is demonstrated through nonlinear response history analyses on a low‐ and high‐ductility six‐story steel CBF building. The simulation results suggest that (a) the determined activation forces of the SFDs are effective in mitigating higher mode effects and in preventing story drift concentrations regardless if capacity design is employed for the CBF system; (b) the absolute acceleration demands are reduced by approximately 50% relative to those in the rigid diaphragm counterpart. Similar reductions are achieved in the lateral drift demands of the GFS at seismic intensities with return periods of 475 and 2475 years. The reduction in the variability of seismic response, both in terms of absolute floor acceleration demands and story drift ratios (SDRs) in the CBF system, is noteworthy. Limitations as well as suggestions for future work are discussed. [ABSTRACT FROM AUTHOR]

The interstory drift‐based scaling procedure (IDS) developed recently by the authors for plane frames under single component horizontal ground motions, has been extended to three‐dimensional structures possessing torsional coupling under bi‐axial ground motions which are represented by their geometric mean spectrum. The ground motion‐scaling factor is defined as the ratio of average interstory drift along building height under target spectrum versus that under the associated ground motion spectrum. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. IDS for 3D systems is applied to 20‐story and 3‐story concrete space frames with mass and stiffness eccentricity, respectively. Accuracy and efficiency of the IDS procedure is assessed under a set of near‐fault strong motion pairs from large magnitude events. The results revealed that the proposed procedure is accurate and noticeably more efficient as compared to conventional procedures suggested in seismic codes and in literature. Further, the intensity measure employed in the IDS procedure is proved as a good predictor of fundamental demand measures (maximum interstory drift ratio and maximum plastic rotations) obtained from nonlinear dynamic analyses under individual ground motion pairs. Hence, employing the intensity measure of IDS for ground motion scaling in intensity‐based evaluation of structures is proposed for reliable estimation of structural performance under code‐prescribed seismic hazard. [ABSTRACT FROM AUTHOR]

Seismic risk assessment of new and existing structures has a long history, which is based on the development of specific methods for seismic hazard and vulnerability analyses. Performance‐based earthquake engineering is the natural evolution and integration of all these aspects that is nowadays implemented in several precodes. However, some critical aspects are not yet completely clarified. As a matter of fact, the vulnerability analysis suffers the so‐called record‐to‐record variability, which is usually controlled through different parameters used as seismic intensity measures (IMs), whose significance is still under discussion. Moreover, this variability represents an additional source of uncertainty, which is added to the dispersion derived from the ground motion prediction equation (GMPE), leading to an overconservatism. For these reasons, the present paper aims to propose a novel framework for the seismic risk assessment of structures, which is found on the idea to control the response variability in evaluating seismic hazard curves without taking into account the randomness (ε) of the GMPE, which instead is transferred to fragility curves. These latter are built by using groups of accelerograms, whose median and 84% fractile spectra fit well, for different return periods, the uniform hazard spectra for ε= 0 and 1, respectively. For this purpose, a new search algorithm for selecting natural records is formulated. The proposed method offers considerable advantages as it is no longer necessary to refer to a specific IM, and allows to select pairs of spectrum‐compatible natural records, which is enable to solve the problem of the seismic assessment of three‐dimensional structures. The procedure is then applied to assess seismic risk of a typical reinforced concrete frame, whose results demonstrate the robustness of the method and the practical independence from the record set used. [ABSTRACT FROM AUTHOR]

Exhumed fossil subduction zones are archives of the deformation conditions and mechanisms from depths not directly accessible. Microstructural analysis of samples exhumed therefrom offers insights into the micromechanics and deformation processes associated with subduction such as earthquakes, slow earthquakes, and aseismic creep. Subducted and exhumed continental metasediments of the Tuscan Metamorphic Units of the Italian Northern Apennines contain a mylonitic foliation and quartz and carpholite dilational hydroshear veins with crack‐and‐seal textures, both developed at blueschist facies conditions (350–400°C, ∼1 GPa). As shown by overprinting relationships and mineral assemblages, these two structure types formed broadly coeval within the stability field of carpholite. Metaconglomerates and metaquartzarenites deformed mainly by dissolution‐precipitation creep and secondary by dislocation creep. Microstructural and electron backscatter diffraction analyses of the veins suggest only limited recrystallization of quartz fibers by subgrain rotation recrystallization, with adjacent metapelite bands acting as decollement horizons, likely by slip on the basal plane of phyllosilicates. We estimated differential stresses of 43–55 MPa and strain rates between 10−13 and 10−14 s−1 from the vein recrystallized quartz fibers. We propose these microstructures and deformation mechanisms to represent a geological evidence of deep episodic tremor and slow slip events in subducted continental metasediments. Pore pressure cyclically reached supralithostatic values triggering tremors causing fracturing of all involved lithotypes. Likely, slow slip was accommodated preferentially by slip on phyllosilicate bands. Aseismic creep occurred mainly by dislocation creep with subgrain rotation recrystallization in vein quartz, slip on the basal plane of phyllosilicates, and dissolution and precipitation creep in the host rock. Plain Language Summary: Rocks exhumed from great depth can help us to investigate processes otherwise non directly accessible. The Italian Northern Apennines comprise exhumed continental sediments that were deformed and metamorphosed at depths of 30–40 km and temperatures of 350–400°C. Broadly coeval continuous and discontinuous deformation is documented as highly deformed zones (shear zones) and veins. We used microstructural analyses and electron microscopy techniques to reconstruct how these rocks deformed and the structures formed. Quartz‐rich metasediments deformed mainly by dissolution and precipitation processes. Weak phyllosilicate‐rich bands accommodated deformation likely by slip on their platy basal planes. Fluid pressure cyclically reached high values that caused failure of the metasediments, with subsequent migration of portion of the fluid and formation of the veins. Veins display only a limited amount of crystal plastic deformation. Quartz paleopiezometry and flow law suggest low differential stresses and average geological strain rates for the deformation of veins. We propose that these structures can be seen as a possible geological record of deep episodic tremor and slow slip events, low intensity and long lasting seismic events associated with slip transients faster than average plate motion. Key Points: Coeval dilational hydroshear veins and mylonites may shed light on deformation mechanisms of deep episodic tremor and slow slip eventsDilational hydroshear veins formed by incremental crack‐seal at supralithostatic pore pressure values and deformed by dislocation creepBlueschist facies mylonites formed mainly by a combination of dissolution‐precipitation creep and slip along phyllosilicate bands [ABSTRACT FROM AUTHOR]

Electrical substations are critical elements of a power grid, enabling the transmission and distribution of electric power from power generators to the end‐users. Experiences from previous earthquakes have shown that electrical substations can be damaged due to ground shaking, reducing their functionality and potentially preventing the generated electric power from reaching end‐users. To assess the seismic vulnerability of a substation, a modular quantitative assessment method is proposed. In this method, the relation between the functionality state of a substation and the damage state of its components was established through the connection matrix technique. A substation is viewed as a network system, whose topology is defined by the connections among various pieces of electrical equipment (i.e., the components), represented in the connection matrix. The maximum allowable power transmission capacity of the substation after an earthquake is adopted as the system functionality metric, which is jointly determined by the power input, transform, and output capacity of the substation. The seismic vulnerability of an electrical substation is quantified by probabilistically calculating its postearthquake functionality when exposed to various earthquake intensities using Monte Carlo sampling. Finally, the risk of substation functionality loss is quantified by integrating the seismic hazard curve with the seismic vulnerability model of the substation. Two realistic case studies on a distribution substation and a transmission substation, with the same equipment configuration but different power delivery paths, were performed using the proposed method. Furthermore, a sensitivity analysis regarding the equipment fragility parameters is conducted, providing a risk‐informed basis for improving the seismic performance of the substation system. [ABSTRACT FROM AUTHOR]

Steel moment resisting frames (MRFs) are drift‐sensitive structures and their design is largely influenced by code requirements to limit the lateral displacements and to control the second order effects. Current and next generation of Eurocode 8 recommend different rules to verify the lateral rigidity and resistance of steel MRFs that lead to structures that are substantially different in terms of size of members and overall performance. In order to investigate the influence of the design rules on the seismic behaviour of ductile steel MRFs a parametric numerical study was carried out on 48 structures designed according to Eurocodes as well as US codes, the latter analysed as benchmark, varying the number of storeys, moment resisting spans and seismic intensity. The results of non‐linear static and dynamic analyses show that the structures complaint with current Eurocode 8 are the most expensive and characterised by the greater lateral rigidity and resistance, while MRFs designed in accordance with ASCE7 rules have the smaller profiles and the lower overstrength. The frames designed with rules of the latest version of next generation of Eurocode 8 have an intermediate behaviour even if closer to ASCE7‐compliant structures. These results are also confirmed by the probability of collapse that is smaller than the minimum value specified by EN1990 for the considered consequence class of the examined buildings. [ABSTRACT FROM AUTHOR]

A regional seismic risk assessment requires the estimation of ground‐motion intensities at multiple locations for a given event simultaneously. In this context, the spatial correlation of ground‐motion residuals plays an important role in characterizing the probability distribution of the field of shaking intensities. Over the last 20 years, the spatial correlation of ground‐motions has been widely studied and different models have been developed. In general, these models vary from each other depending on the ground‐motion database used to generate them, on the adopted intensity measure, on the selected ground‐motion model, and on the estimation methods, among others. This paper proposes a spatial correlation model for within‐event residuals of peak ground acceleration and spectral pseudo‐acceleration ordinates in the Chilean subduction zone. Although the database considered for this study has only a few well‐recorded earthquakes, it contains a large number of station pairs sharing several common events. Therefore, we compute non‐stationary correlations between station pairs and then fit a stationary spatial correlation model. Results of this paper are compared with previous models, concluding that, in general, subduction models show higher spatial correlations than those for active shallow crust events for long‐period spectral ordinates. Moreover, no evidence was found for a systematic effect of earthquake magnitude or site conditions on spatial correlation. Finally, the proposed model is compared with a model obtained assuming stationarity in spatial correlations, showing more reliable estimates when using the proposed model. [ABSTRACT FROM AUTHOR]

This paper proposes a new displacement‐based methodology for the design of concentric steel‐brace retrofitting systems for RC framed buildings. It relies on deformation control for different levels of seismic intensity and explicitly considers the interaction between both structural systems. When dealing with the seismic assessment and strengthening of existing RC buildings, practitioners are likely to resort to the q‐factor approach, due to its simplicity and popularity for the design of new structures. However, in non‐seismically designed RC structures, the uncertainties associated to the nonlinear behaviour are relevant, making it therefore very difficult to define a direct correlation between the real internal forces that develop in structural members during the seismic excitation, and those experienced by an equivalent indefinitely elastic structure. Consequently, several authors have argued that the force‐based seismic assessment and retrofitting of existing RC structures will not yield, in general, satisfactory results. The design methodology proposed herein thus addresses this limitation, offering a solution which is intuitive and fit to be used in practical applications, while providing retrofitted structures with adequate and more predictable seismic performance. [ABSTRACT FROM AUTHOR]

In the last decades, high priority has been given to community disaster resilience owing to seismic events with a particular focus on the post‐disaster restoration. Therefore, damage reduction of structural and non‐structural elements after a disaster is fundamental for costs and for functionality aspects. In this context, the European RFCS project DISSIPABLE was funded with the aim to perform large demonstration tests of steel frames equipped with easily repairable seismic dissipative devices. In this paper, the experimental tests performed according to dynamic substructuring are described. The capacity of withstanding seismic actions as well as the energy dissipation relies on the Dissipative Replaceable Link Frame system, composed of two rigid columns connected by weakened beams. Two different configurations of frames equipped with DRLF systems were tested: i) frames made of only mild steel and ii) frames made of both mild and high‐strength steel. Bidimensional frames were tested under different seismic intensity levels: Damage Limitation, Significant Damage and Near Collapse. [ABSTRACT FROM AUTHOR]

Seismic hazards in subduction settings typically arise from megathrust, intraslab and crustal earthquake sources. Despite the frequent occurrence of intraslab earthquakes in subduction zones and their potential threat to communities, their long‐term recurrence behaviour is barely studied. Sedimentary sequences in lakes may register ground shaking from different seismic sources. This study investigates two long sediment cores (13 m and 16 m) from Skilak Lake, a proglacial lake in south‐central Alaska, to evaluate whether different seismic sources leave a distinct imprint. The sedimentary record shows a continuously varved sediment sequence, occasionally interrupted by turbidites, slump deposits and tephra beds. Turbidites and slump deposits were objectively identified using a statistical outlier analysis on varve thickness. The earthquake origin of these deposits was ascertained by resemblance with deposits induced by instrumentally recorded earthquakes (for example, 1964 ce Mw 9.2 megathrust and 1954 ce Mw 6.4 intraslab earthquakes) and correlation with multiple coeval landslide deposits on sub‐bottom profiles. The Skilak Lake record chronicles 19 earthquakes with moderate to very high confidence level in the past 1350 years. The sedimentary evidence of instrumentally‐recorded intraslab and megathrust earthquakes within the past 70 years demonstrates that not only megathrust earthquakes, but also past intraslab events are recorded. Although reported seismic intensities at Skilak Lake are comparable for the 1964 ce megathrust and the 1954 ce intraslab earthquakes, the long duration and low frequency content of seismic ground motion during megathrust earthquakes facilitate the triggering of multiple, voluminous landslides and the generation of megaturbidites. In contrast, the shorter duration and higher frequency source spectrum of intraslab earthquakes may only induce surficial slope remobilization and the generation of thinner turbidites. This study demonstrates that the sedimentary record of Skilak Lake has the potential to decipher multiple seismic sources, which opens possibilities for a comprehensive seismic hazard analysis for south‐central Alaska. [ABSTRACT FROM AUTHOR]

The evaluation of a bridge's structural damage state following a seismic event and the decision on whether or not to open it to traffic under the threat of aftershocks (ASs) can significantly benefit from information about the mainshock (MS) earthquake's intensity at the site, the bridge's structural response, and the resulting damage experienced by critical structural components. This paper illustrates a Bayesian network (BN)‐based probabilistic framework for updating the AS risk of bridges, allowing integration of such information to reduce the uncertainty in evaluating the risk of bridge failure. Specifically, a BN is developed for describing the probabilistic relationship among various random variables (e.g., earthquake‐induced ground‐motion intensity, bridge response parameters, seismic damage, etc.) involved in the seismic damage assessment. This configuration allows users to leverage data observations from seismic stations, structural health monitoring (SHM) sensors and visual inspections (VIs). The framework is applied to a hypothetical bridge in Central Italy exposed to earthquake sequences. The uncertainty reduction in the estimate of the AS damage risk is evaluated by utilising various sources of information. It is shown that the information from accelerometers and VIs can significantly impact bridge damage estimates, thus affecting decision‐making under the threat of future ASs. [ABSTRACT FROM AUTHOR]

Mature faults with large cumulative slip often separate rocks with dissimilar elastic properties and show asymmetric damage distribution. Elastic contrast across such bimaterial faults can significantly modify various aspects of earthquake rupture dynamics, including normal stress variations, rupture propagation direction, distribution of ground motions, and evolution of off‐fault damage. Thus, analyzing elastic contrasts of bimaterial faults is important for understanding earthquake physics and related hazard potential. The effect of elastic contrast between isotropic materials on rupture dynamics is relatively well studied. However, most fault rocks are elastically anisotropic, and little is known about how the anisotropy affects rupture dynamics. We examine microstructures of the Sandhill Corner shear zone, which separates quartzofeldspathic rock and micaceous schist with wider and narrower damage zones, respectively. This shear zone is part of the Norumbega fault system, a Paleozoic, large‐displacement, seismogenic, strike‐slip fault system exhumed from middle crustal depths. We calculate elastic properties and seismic wave speeds of elastically anisotropic rocks from each unit having different proportions of mica grains aligned sub‐parallel to the fault. Our findings show that the horizontally polarized shear wave propagating parallel to the bimaterial fault (with fault‐normal particle motion) is the slowest owing to the fault‐normal compliance and therefore may be important in determining the elastic contrast that affects rupture dynamics in anisotropic media. Following results from subshear rupture propagation models in isotropic media, our results are consistent with ruptures preferentially propagated in the slip direction of the schist, which has the slower horizontal shear wave and larger fault‐normal compliance. Plain Language Summary: Earthquake faults that separate geologic materials with different elastic properties are referred to as bimaterial faults. Elastic contrast across bimaterial faults can modify rupture dynamics including rupture propagation direction and earthquake intensity and is therefore important for understanding potential earthquake hazards. The effects of elastic contrast between elastically isotropic materials (same elastic properties in all directions) on rupture propagation are reasonably well understood. However, rocks separated by natural faults are typically elastically anisotropic (having different elastic properties in different directions), and we know relatively little about the effects of this anisotropy on rupture propagation. To better understand the effects of elastic anisotropy, we analyze anisotropic rocks with different mica proportions collected from both sides of an ancient strike‐slip earthquake fault, in which mica grains are aligned sub‐parallel to the fault. We calculate the velocities of seismic waves in these rocks and their elastic contrast. We find that analysis of the horizontal shear wave propagating parallel to the sub‐vertical fault plane gives results that are consistent with rupture propagation theory for isotropic materials. Thus, the shear‐wave propagation direction should be considered when measuring seismic velocities and calculating elastic contrasts to investigate rupture along natural faults in anisotropic rocks. Key Points: Seismic properties are analyzed for two anisotropic rocks with different mica content across a strike‐slip fault showing asymmetric damageHorizontally polarized shear wave propagating parallel to the fault is important in determining elastic contrast between these rocksCalculating elastic contrast from the horizontal shear wave in these rocks leads to results consistent with models in isotropic media [ABSTRACT FROM AUTHOR]

Locating the epicenters and quantifying the magnitudes of historical earthquakes are important, yet difficult, tasks. These tasks often entail estimating seismic intensities based on written documentation, which suffers from biases and uncertainties that are difficult to evaluate. However, past strong earthquakes may trigger numerous landslides that remain in the landscape to the present day, whose number and distribution are correlated with the magnitude and location of the earthquakes. Thus, mapping historical coseismic landslides may provide a useful tool for re‐evaluating the magnitudes of historical earthquakes. We use remote sensing images to map landslides in the southern Loess Plateau, China. We suggested that c. 5000 preserved landslides are related to the 734 ce Tianshui earthquake. These landslides are densely distributed along a c. 70‐km‐long section of the West Qinling Fault. Based on the assumption that the length of the zone in which substantial landslides occurred is equal to the fault rupture length, we estimated a Mw of 7.2 for the 734 ce Tianshui event, which is similar to previous estimates (Mw = 6.8–7.5). We confirmed that the 1920 ce Haiyuan, 1718 ce Tongwei, and 1654 ce Lixian earthquakes did not contribute to the historical landslides observed in the study area by combination of the mapping and Chinese related literature. We estimated an Mw of 7.0 for the 1654 ce Lixian earthquake, which is lower than previous estimates (Mw = 8.0). We suggest that coseismic landslide of medium and large sizes with areas > 104 m2 can be used as a criterion to locating and quantifying historical earthquakes, thereby reducing uncertainties in the estimated magnitudes of historical earthquakes that lack instrument records. [ABSTRACT FROM AUTHOR]

Fault zone complexities contain important information about factors controlling earthquake dynamic rupture. High‐resolution fault zone imaging requires high‐quality data from dense arrays and new seismic imaging techniques that can utilize large portions of recorded waveforms. Recently, the emerging Distributed Acoustic Sensing (DAS) technique has enabled near‐surface imaging by utilizing existing telecommunication infrastructure and anthropogenic noise sources. With dense sensors at several meters' spacing, the unaliased wavefield can provide unprecedented details for fault zones. In this work, we use a DAS array converted from a 10‐km underground fiber‐optic cable across Ridgecrest City, California. We report clear acausal and coda signals in ambient noise cross‐correlations caused by surface‐to‐surface wave scattering. We use these scattering‐related waves to locate and characterize potential faults. The mapped fault locations are generally consistent with those in the United States Geological Survey Quaternary Fault database of the United States but are more accurate than the extrapolated ones. We also use waveform modeling to infer that a 35 m wide, 90 m deep fault with 30% velocity reduction can best fit the observed scattered coda waves for one of the identified fault zones. These findings demonstrate the potential of DAS for passive imaging of fine‐scale faults in an urban environment. Plain Language Summary: Fault zones are complex networks of fractures that can host earthquakes. The fractured rock surrounding the faults in the top hundreds of meters can amplify earthquake shaking intensity. Therefore, locating and characterizing faults is important for evaluating seismic hazards, especially in urban settings. But it is challenging to identify small hidden faults in the absence of surface evidence or cataloged seismicity. High resolution, high frequency seismic experiments may provide a solution. Distributed acoustic sensing (DAS) is an emerging technique that can turn existing fiber‐optic cables into cost‐effective seismic networks with meter‐scale spacing. In this work, we show how we image the fault zones at shallow depth using seismic noise generated by traffic along a DAS cable in Ridgecrest City, CA. The results can detect and distinguish faults at sub‐kilometer scales. We also show we can use DAS data to characterize fault zone properties. These results demonstrate the potential of DAS in fine‐scale fault imaging without needing earthquakes. Key Points: Ambient noise interferometry with distributed acoustic sensing captures scattered surface waves from fault zonesThe fault locations mapped with scattered surface waves are generally consistent with previous models but with higher resolutionWe constrain the fault zone geometry and velocity reduction using the amplitudes of the scattered surface waves [ABSTRACT FROM AUTHOR]

Nominated for Eurosteel 2021 Best Paper Award In recent decades, innovative seismic‐resilient structural systems have been proposed to reduce the direct and indirect losses related to seismic events. Among others, steel moment‐resisting frames (MRFs) equipped with damage‐free self‐centring column bases (SC‐CBs) represent a promising solution. Although several configurations of SC‐CBs have been proposed in literature, only a few research studies investigated how the significant parameters (e. g. number of storeys, frame layout, seismic mass, seismic intensity) affect the seismic performance of MRFs with SC‐CBs. To further investigate this aspect, the present work focuses on the influence of an additional parameter (i. e. the combination of seismic mass and acceleration) on their self‐centring capability. Three 5‐bay steel MRFs with 4, 6 and 8 storeys are considered as case‐study frames and designed based on two different values of the seismic mass (i. e. M1 and M2). Numerical models are developed in OpenSees, incremental dynamic analyses (IDAs) are performed to monitor global engineering demand parameters (EDPs), and fragility curves are derived to evaluate the seismic performance of the structures. It is observed that the inclusion of SC‐CBs produces beneficial effects in terms of increased self‐centring capability on all the investigated case studies. Moreover, the parametric analysis allows some preliminary observations to be drawn regarding the influence of the number of stories and seismic mass. [ABSTRACT FROM AUTHOR]

Rapid urban growth has been paired with a rapid increase in the demand for high‐rise buildings, and has accelerated the need for developing more resilient high‐rise buildings in earthquake‐prone regions. Current best practices for the seismic design of high‐rise buildings follow a performance‐based design approach that allows the designer to use innovative structural systems, select performance objectives, and verify seismic performances targeted at multiple levels of seismic intensity. As shortcomings in conventional code‐designed high‐rise buildings continue to be revealed by strong earthquakes, the importance of more resilient high‐rise systems is increasingly evident. Several high‐performance systems have been proposed to limit the excessive seismic demands attributed to higher‐mode effects in high‐rise buildings. However, these systems still face design challenges associated with distributed damage and residual deformations. This paper proposes a novel self‐centering base mechanism for high‐rise buildings that independently limits both shear forces and overturning moments at the base to mitigate higher‐mode effects, while eliminating residual deformations and controlling concentrated stresses within the structure that otherwise would need to be designed for. The schematic overview of the proposed system is first introduced, followed by the detailed design of a physical embodiment developed based on a reference 42‐story RC core wall building. Results of a numerical case‐study comparison confirm that an enhanced seismic performance is achieved through the proposed system with minimum damage and negligible residual deformations even following major seismic loading. The proposed system, with further investigations, also has the potential to be applied to a wider range of structural systems. [ABSTRACT FROM AUTHOR]

This paper is motivated by the renewed interest in space exploration and the need to provide structurally sound and resource‐efficient shielding solutions for valuable assets and future habitable modules. We present, implement and test a methodology for the preliminary design and assessment of optimal arch forms subjected to self‐weight as well as seismically induced loads. The numerical framework, built around a limit thrust‐line analysis, previously published by the authors, is summarized first. This is followed by a detailed account of the form‐finding algorithm for arches of variable thickness. Special attention is placed on the physical feasibility of our assumptions and the justification of the engineering inputs adopted. The newly form‐found arches achieve material efficiencies between 10% and 50% in comparison with their constant minimum‐thickness circular or elliptical counterparts, depending on the relative intensity of the seismic action. The influence of the initial input geometry and the stabilising presence of additional shielding material against extreme radiation are also evaluated with emphasis on the effects of low‐gravity conditions. Finally, a case study is presented and Discrete Element Models of constant and varying thickness arches (VTAs) are assessed under a set of representative ground‐motions on a lunar setting. The significant over‐conservatism of constant thickness arches (CTAs) is made manifest and potential improvements of the optimally found arch shape are highlighted. Although developed with extraterrestrial applications in mind, the results and methods we present herein are also applicable to terrestrial conditions when material efficiency is of utmost concern. [ABSTRACT FROM AUTHOR]