Earthquake Spectra

Journal: Earthquake Spectra

Abbreviation

Earthq. Spectra

Publisher

SAGE

ISSN

8755-2930
1944-8201

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Publications1 - 10 of 20

Systematic assessment of nonlinear soil behavior at KiK-net sites in Japan: Thresholds and controlling site factors
Loviknes, Karina; Bergamo, Paolo; Fäh, Donat; et al. (2025)
Earthquake Spectra
We address two open questions concerning nonlinear soil behavior in a seismic hazard and risk context; (1) which site proxies can be used to predict and map nonlinear site amplification? (2) At which level of ground-motion intensity should such nonlinear models be considered? To answer these questions, we use the KiK-net network in Japan, which includes stations with instruments at both surface and depth, considering events recorded between 1997 and 2024. Using the surface-to-borehole ratio, we systematically capture the empirical effects of nonlinear soil response as the amplitude change and frequency shift between individual events and the linear site response. We then derive station-specific parameters for degree of nonlinearity and threshold for onset of nonlinear behavior. The statistical correlation between nonlinearity and a selection of geotechnical and geological site parameters shows that although parameters characterizing the depth to bedrock and the shallowest part of the soil layer have a promising potential for capturing nonlinear site amplification, the correlation is generally low, suggesting that a single site parameter is not sufficient. As a consistent reference for ground-motion intensity, we empirically calculate PGAemp.rock, as an approximation for PGA recorded on a standard outcropping rock site with VS30 = 760 m/s (average shear-wave velocity of upper 30 m). When analyzing the nonlinear behavior for all recorded events, we define the nonlinear soil behavior as significant when the amplitude change, and frequency shift are greater than 10% for the majority (50%) of the records. We find that in the PGAemp.rock-range 1−3 m/s2 nonlinear soil behavior is significant only for soft soil stations (VS30 < 250 m/s) with intermediate sediment thickness (<30 m). While, according to the mean behavior of all sites, regardless of grouping, nonlinearity is significant only at PGAemp.rock > 3 m/s2. These results show that for nonlinear site-amplification modeling, the onset of nonlinearity is strongly related to the site conditions.
Fragility-based methodology for evaluating the time-dependent seismic performance of post-tensioned timber frames
Granello, Gabriele; Broccardo, Marco; Palermo, Alessandro; et al. (2020)
Earthquake Spectra
Since 2010, the construction of post‐tensioned wooden buildings (Pres‐Lam) has been growing rapidly worldwide. Pres‐Lam technology combines unbonded post‐tensioning tendons and supplemental damping devices to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. In low seismic areas, designers may choose not to provide additional damping, relying only on the post‐tensioning contribution. However, post‐tensioning decreases over time due to creep phenomena arising in compressed timber members. As a consequence, there is a reduction of the clamping forces between the elements. This reduction affects the seismic response of Pres‐Lam buildings in the case of low‐ and high‐intensity earthquakes. Therefore, understanding and accounting for the post‐tensioning losses and their uncertainty are paramount for a robust assessment of the safety of Pres‐Lam constructions. So far, however, there have been no comprehensive studies which tackle the overall seismic performance of such systems in the presence of time‐varying post‐tension losses and the associated uncertainty. This study tackles this research gap by introducing a comprehensive seismic evaluation of Pres‐Lam systems based on time‐dependent fragility curves. The proposed fragility analysis is specifically designed to account systematically for time‐varying post‐tension losses and the related uncertainty. The method is applied to two case studies, designed, respectively, with and without supplemental damping devices. In terms of structural performance, results show that the use of additional dissipaters mitigates the effect of post‐tensioning loss for earthquakes of high intensity. Conversely, performance under low‐intensity earthquakes is strongly dependent on the post‐tensioning value, as the reduction of stiffness due to the anticipated rocking motion activation would lead to damage to non‐structural elements.
Impact assessment of earthquake early warning systems in Central America
Orihuela Gonzales, Benazir Ioana; Papadopoulos, Athanasios N.; Clinton, John Francis; et al. (2025)
Earthquake Spectra
Earthquake Early Warning (EEW) systems aim to alert users in advance of imminent shaking, enabling them to take action. In collaboration with local seismic agencies, the Swiss Seismological Service (SED), has developed national EEW systems across Central America. Public EEW alerts are now available, considering the frequent seismic activity and the vulnerability of the building stock, EEW has the potential to reduce casualties (i.e. fatalities and injuries). In this study, we build upon a probabilistic framework to quantify the potential benefits of EEW systems in reducing casualties. For each event generated in the stochastic catalog (100,000 event sets), we estimate the number of casualties in the absence of EEW. The framework evaluates the potential casualty reduction attributable to an operational EEW system, considering the expected warning times in each event at the target site, the subsequent actions taken upon receiving the alert, and system performance. For a return period of 475 years, the fatality reduction could reach ∼14% to 17% corresponding to hundreds fewer fatalities in Costa Rica and Nicaragua, and thousands fewer fatalities in El Salvador and Guatemala. From this baseline scenario, we explore strategies to improve casualty reduction: (1) increase warning time by densifying the seismic network; and (2) compare the effectiveness of Drop, Cover, And Hold On (DCHO) versus evacuation as recommended protective actions. Our results suggest that evacuation is a suitable strategy for reducing fatalities in this region, given the prevalence of single-story structures. Given the available warning time, evacuation is advised for occupants on the first floor, and those on upper floors should adopt DCHO. Our findings indicate that the implementation of EEW leads to a ∼10% reduction in average annual fatalities. A cost–benefit analysis reveals that the economic benefits of public EEW systems significantly outweigh the associated costs, making EEW a cost-effective mitigation strategy.
Sharing data and code facilitates reproducible and impactful research
Baker, Jack W.; Crowley, Helen; Wald, David; et al. (2024)
Earthquake Spectra
Modern research often involves the collection or analysis of data and the use of specialized computer algorithms. Traditional text articles thus provide only partial documentation of a research study. Readers have limited ability to reproduce or utilize work if the source data are not available or if it relies on an algorithm that is described, but code is not provided. Fortunately, a wide variety of tools are now available to support the publication of research data and code. The effort required to publish data is now relatively small, and the benefits can be immense. This opinion article discusses trends toward increased sharing in academic publishing. It describes opportunities and resources to support data and code sharing and describes the benefits for both authors and readers. Finally, it discusses how Earthquake Spectra is providing resources and enhancing its policies to establish the sharing of data as the default procedure when publishing in the journal, and encourage the sharing of code and other resources.
Accounting for ground-motion uncertainty in empirical seismic fragility modeling
Bodenmann, Lukas; Baker, Jack W.; Stojadinovic, Bozidar (2024)
Earthquake Spectra
Seismic fragility models provide a probabilistic relation between ground-motion intensity and damage, making them a crucial component of many regional risk assessments. Estimating such models from damage data gathered after past earthquakes is challenging because of uncertainty in the ground-motion intensity the structures were subjected to. Here, we develop a Bayesian estimation procedure that performs joint inference over ground-motion intensity and fragility model parameters. When applied to simulated damage data, the proposed method can recover the data-generating fragility functions, while the traditionally used method, employing fixed, best-estimate, intensity values, fails to do so. Analyses using synthetic data with known properties show that the traditional method results in flatter fragility functions that overestimate damage probabilities for low-intensity values and underestimate probabilities for large values. Similar trends are observed when comparing both methods on real damage data. The results suggest that neglecting ground-motion uncertainty manifests in apparent dispersion in the estimated fragility functions. This undesirable feature can be mitigated through the proposed Bayesian procedure.
Dataset from the shake table tests of a rocking podium structure
Vassiliou, Michalis F.; Cengiz, Cihan; Dietz, Matt; et al. (2021)
Earthquake Spectra
Conventional validation of analytical and numerical models in Earthquake Engineering involves the comparison of numerically simulated response time histories to experimentally obtained benchmark responses to the same earthquake excitations. As the seismic design problem is inherently stochastic, an alternative, statistical, and easier-to-pass validation procedure has been suggested. As an example, numerical and analytical models may fail to predict the planar rocking response of a rigid block to a specific ground motion, but they can be proven quite successful in predicting the statistical distribution of the maxima of that response to an ensemble of ground motions. This article describes the publicly available data obtained from a series of 226 shake table tests of a 3D rocking podium structure, designed at ETH Zurich and carried out at EQUALS Lab, University of Bristol. This well-documented dataset is the largest one involving a shake table and can be used to statistically validate analytical and numerical models of rocking structures.
Database of rocking shallow foundation performance: Slow-cyclic and monotonic loading
Hakhamaneshi, Manouchehr; Kutter, Bruce L.; Gavras, Andreas G.; et al. (2020)
Earthquake Spectra
Many physical model tests have examined the performance of rocking foundations during cyclic and seismic loading. These tests varied in model size, testing equipment, superstructure properties, footing shape, supporting soil environment, and loading protocol. “FoRCy, Foundation Rocking database of Cyclic and Monotonic Loading” is a new database (published at https://datacenterhub.org/), summarizing the results of monotonic and slow-cyclic loading tests of rocking foundations. The database consists of columns identifying testing equipment and facility, soil, superstructure, and system properties, as well as loading protocol and results. The database contains 456 records (rows), each one being unique in either model configuration or loading amplitude. To illustrate its value, this article shows correlations between (1) settlement, rotation, and factor of safety with respect to bearing capacity and (2) moment and cumulative rotation for shallow footings. Data indicate that the rotation required to mobilize the moment capacity is surprisingly constant (about 0.01 radians) for a wide range of experiments.
Assessment of urban seismic resilience of a town in Eastern Turkiye: Turkoglu, Kahramanmaras before and after 6 February 2023 M 7.8 Kahramanmaras earthquake
Askan, Aysegul; Altindal, Abdullah; Aydin, Mehmet Firat; et al. (2025)
Earthquake Spectra
On 6 February 2023, two earthquakes occurred approximately 9 h apart, with Mw 7.8 and 7.5, and epicenters located in Pazarcık and Elbistan districts of Kahramanmaras province, respectively. As part of a national project team which was funded by the Disaster and Emergency Management Presidency of Turkiye (AFAD) between June 2021 and June 2023, the authors of this article had proposed a framework to assess the seismic resilience of an urban region. The pilot area of this national project was a small-scale industrial town named Turkoglu located to the south of Kahramanmaras, at the intersection of Amanos and Pazarcik segments of the East Anatolian Fault zone. The proposed framework encompasses the assessment of active faults in the region, construction of regional velocity models, ground motion simulations of potential earthquakes, structural vulnerability, and study of seismic resilience indicators. The Pazarcik earthquake occurred 4 months before the end of the project on the exact fault system, which was modeled in ground motion simulations within the project in 2022. The objective of this article is multifold: first, to present our findings before the earthquake (2021–2022) in the region, including regional velocity models, ground motion simulations, street survey-based building classifications, and vulnerability classes; and second, to compare the after-event modeling of damage distributions in comparison with the observed damages as well as resilience evaluations of the region from multiple perspectives. A third objective is to assess the seismic resilience framework used in the project, as there are multiple seismically active areas in Turkiye and the world where similar large events are anticipated. This study constitutes a significant case study in the Turkoglu region, which involves critical evaluations of seismic resilience from before and after event data.
The 2018 version of the Global Earthquake Model: Hazard component
Pagani, Marco (2020)
Earthquake Spectra
In December 2018, at the conclusion of its second implementation phase, the Global Earthquake Model (GEM) Foundation released its first version of a map outlining the spatial distribution of seismic hazard at a global scale. The map is the result of an extensive, joint effort combining the results obtained from a collection of probabilistic seismic hazard models, called the GEM Mosaic. Together, the map and the underlying database of models provide an up-to-date view of the earthquake threat globally. In addition, using the Mosaic, a synopsis of the current state-of-practice in modeling probabilistic seismic hazard at national and regional scales is possible. The process adopted for the compilation of the Mosaic adhered to the maximum extent possible to GEM’s principles of collaboration, inclusiveness, transparency, and reproducibility. For each region, priority was given to seismic hazard models either developed by well-recognized national agencies or by large collaborative projects involving local scientists. The version of the GEM Mosaic presented herein contains 30 probabilistic seismic hazard models, 14 of which represent national or sub-national models; the remainder are regional-scale models. We discuss the general qualities of these models, the underlying framework of the database, and the outlook for the Mosaic’s utility and its future versions.
Large-scale experimental investigation of a low-cost PVC ‘sand-wich’ (PVC-s) seismic isolation for developing countries
Tsiavos, Anastasios; Sextos, Anastasios; Stavridis, Andreas; et al. (2020)
Earthquake Spectra
This study presents a large-scale experimental investigation on the seismic performance of an innovative, low-cost seismic isolation system for developing countries. It is based on the beneficial effect of the encapsulation of sand grains between two PVC surfaces on the initiation of sliding and the dissipation of seismic energy between the surfaces. A three-times scaled-down, idealized, seismically isolated model of a prototype single-story structure located in Nepal is subjected to an ensemble of recorded earthquake ground motion excitations. The experimentally derived response of the seismically isolated structure is compared with the response of the corresponding fixed-base structure. This system is part of a wider hybrid design approach where the structure is designed to resist the seismic forces at the design acceleration level. The seismic isolation system sets an upper bound to the response of the structure for ground motion excitations exceeding the design level.

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