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Continuous data streams from translational and rotational seismometers installed in TAIPEI 101 enable monitoring of the natural frequencies on different time scales. Using the 2014 seismic data recorded on the 90th floor of this high-rise building and the meteorological data from a weather station located just 1 km away, we explored the characteristics and controlling factors of the ambient vibrations in TAIPEI 101. Using the random decrement technique, the three modal frequencies in translation were identified as 0.15 Hz (F1), 0.43 Hz (F2), and 0.78 Hz (F3). For rotation around the vertical axis, the modal frequencies were 0.23 Hz (R1), 0.59 Hz (R2), and 0.93 Hz (R3). In translation, TAIPEI 101 exhibits a trend of increasing modal frequency with increasing temperature but decreasing modal frequency with increasing wind velocity. The trend with temperature is reversed in rotation motion. The different frequency versus temperature relationship seen for rotational and translational motion demonstrates the importance of introducing rotational motion analysis into structural health monitoring. The change in modal frequencies were also found to decrease with growing amplitude. It is intriguing that F1 exhibits a weaker dependency with amplitude with respect to the higher modes, which may be associated with the suppression of F1 vibration caused by the damper installed in TAIPEI 101. Other than long-term (seasonable) variation, we also highlight the hourly variation of the first-mode amplitude throughout a day by comparing with weather and mobility data. Other than the atmospheric conditions that strongly influence the modal frequencies in long-term behavior, we found that human activities may play an important role in the short-term vibration characteristics of the building.

Influence of seismic strain rates on the co- and post-seismic response of civil engineering buildings

Assessing or forecasting seismic damage to buildings is an essential issue for earthquake disaster management. In this study, we explore the efficacy of several machine learning models for damage characterization, trained and tested on the database of damage observed after Italian earthquakes (DaDO). Six regression- and classification-based machine learning models were considered: random forest, gradient boosting and extreme gradient boosting. The structural features considered were divided into two groups: all structural features provided by DaDO or only those considered to be the most reliable and easiest to collect (age, number of storeys, floor area, building height). Macroseismic intensity was also included as an input feature. The seismic damage per building was determined according to the EMS-98 scale observed after seven significant earthquakes occurring in several Italian regions. The results showed that extreme gradient boosting classification is statistically the most efficient method, particularly when considering the basic structural features and grouping the damage according to the traffic-light based system used, for example, during the post-disaster period (green, yellow and red). The results obtained by the machine learning-based heuristic model for damage assessment are of the same order of accuracy as those obtained by the traditional Risk-UE method. Finally, the machine learning analysis found that the importance of structural features with respect to damage was conditioned by the level of damage considered.

Pulse-wave propagation velocity and resonance frequency measured in civil engineering structures are both related to structural design. Monitoring their variation following seismic strong shaking provides information about the immediate building capacity. Joint-interpretation of frequency and velocity variation requires a better understanding of the processes controlling seismic structural health. In this study, we analysed 8 years of earthquake data recorded by the vertical array installed in the Te Puni building in Wellington, New Zealand, as part of the GeoNet building instrumentation programme. Co-seismic variations of pulse wave velocity and fundamental frequency are analysed and interpreted through a Timoshenko beam-like building model. This study shows that even though no structural damage was visually reported over the considered time of monitoring, co- and post-seismic variation of both parameters’ values are observed for almost all earthquakes, including a permanent shift following strong ground shaking. Variations of pulse-wave velocity and resonance frequency are cross-interpreted in terms of the building model. They reflect a time variant building response, correlated with the seismic loading. In addition, time delay of the pulse-wave velocity as a function of the building height provides relevant information on the location of the changes and confirms the efficient cross-interpretation of both methods for seismic Structural Health monitoring.

This work presents the implementation of a high standards dataset of earthquake ground motions recorded in Metropolitan France between 1996 and 2016. This dataset is intended to serve the scopes of a large seismological community; however, its primary aims are engineering seismology and earthquake engineering applications. The dataset includes records from broadband and accelerometric sensors provided by permanent and temporary seismic networks operated by French research institutions and partners grouped within the Réseau Sismologique et géodésique Français (RESIF) consortium (see Data and Resources). All the waveforms are first homogenized to acceleration units and underwent a full quality control process including: (1) visual verification and manual phase picking, (2) processing scheme, and (3) consistency check by residual analysis. These make the dataset fully compliant with international standards. Finally, the RESIF dataset includes more than 6500 quality-checked records from 468 earthquakes recorded at 379 stations. Over the 379 stations included in the dataset, 177 are permanent stations (RA and FR networks) and 202 are temporary stations (YP and X7 networks). The dataset is complete down to magnitude ML 3.5 over the whole French territory and less (about ML 2.5) in the eastern part. Magnitudes range from ML 2.4 to 5.6 and from Mw 2.0 to 5.2, whereas distances range from less than 1 to 600 km. The disseminated dataset is constituted of (1) a versioned flatfile containing the metadata and main intensity measures computed on each processed record, (2) time histories, and (3) response spectra for several damping values and Fourier spectra.

We apply interferometry by deconvolution to compute the shear-wave velocity in shallow sediments (0–83.4 m) based on earthquake records from a vertical accelerometric array (ARGOstoli Network [ARGONET]) on Cephalonia Island, Greece. Analysis of the time variation of measured values reveals a cyclical pattern, which correlates negatively to rainfall and a soil moisture proxy. The pattern includes a sharp reduction in velocity at the beginning of rainy seasons and a gradual rise toward dry periods, the overall variation being around 20%–25% within the shallowest depth interval examined (0–5.6 m) and estimated to reach 40% within the top 2 m. The variation itself and its amplitude are verified by surface-wave dispersion analysis, using ambient vibration data. Synthetic standard spectral ratios suggest that this seasonal effect leaves an imprint on soil response, causing differences in the level of high-frequency ground motion between dry and rainy seasons, and this is verified by earthquake records. Furthermore, the near-surface velocity decrease due to soil saturation can be of the same order of magnitude as the nonlinear coseismic variation, masking the physical process of the nonlinear response of the site due to weak-to-strong-motion shaking. Thus, seasonal variations of seismic-wave velocities in shallow sediments may be important for a number of site-effect related topics, such as high-frequency ground-motion variability, soil anisotropy, kappa measurements, nonlinear site response, and so on.

ORFEUS (Observatories and Research Facilities for European Seismology, http://orfeus-eu.org/) is a non-profit organization founded in 1986 with the chief goal to promote seismology in the Euro-Mediterranean area through the collection, archival and distribution of seismic waveform data, metadata, and closely related services and products. ORFEUS also supports the coordination and implementation of large scale community initiatives and experiments in observational seismology, and provides community support through software and travel grants, editorial initiatives and training activities. ORFEUS data and services are collected or developed at national level by more than 60 contributing Institutions (see https://orfeus-eu.org/organization/corporate_founders/ and https://orfeus-eu.org/organization/participation/) in the greater European region, and further developed, integrated, standardized, homogenized and promoted through ORFEUS. Within EPOS, ORFEUS represents the seismological waveform services as one of three sub-domains of EPOS Seismology. ORFEUS data and services are open, FAIR, and accompanied by clear policies and licensing information. Two Service Management Committees (SMCs) are established within ORFEUS, devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated waveform Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); and (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/). A new SMC is being formed to represent the community of European mobile instrument pools, including also amphibian instrumentation. Products and services for computational seismologists are also possible candidates for integration in the ORFEUS domain. Overall, ORFEUS services currently provide access to waveforms acquired by ~ 16,000 stations, including dense temporary experiments, with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on web services that allow automated user access to data gathered and/or distributed by the various ORFEUS institutions (see https://orfeus-eu.org/data/eida/webservices/ and https://esm-db.eu/#/data_and_services/web_services). Particular attention is paid to acknowledging the crucial role played by data providers, who are part of the ORFEUS community. ORFEUS strongly encourages the use of international network codes, seismic network digital object identifiers, and full network citations. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal (https://www.ics-c.epos-eu.org/). Documentation on ORFEUS data and services is provided on the ORFEUS website and is complemented by a large archive of ORFEUS community workshops and seminars / webinars (https://orfeus-eu.org/other/workshops/). ORFEUS data and services are assessed and improved with the help of technical and scientific feedback from a User Advisory Group (UAG), which comprises European Earth scientists with expertise on a broad range of observational seismology topics. ORFEUS is a key participant in EC-funded projects and collaborates with global and international organizations with similar scope, like the FDSN (https://fdsn.org/), IRIS (https://www.iris.edu/), and COSMOS (https://strongmotion.org/)., EGUsphere

International audience; In 2017-2019, a seismic swarm was triggered in the Maurienne valley (French Alps), with more than 5000 events detected by the regional SISmalp network. The population, who asked SISmalp to provide information on the processes and the associated risk, felt many earthquakes. In a post-L'Aquila trial context, we conducted a reflection on the scientific and social operational management of the crisis. The geological and tectonic analysis, the deployment of a temporary seismic network, an automatic double-difference relocation procedure (HypoDD) after clustering earthquakes, as well as the interactions with the population and the risk managers, have been carried out jointly. The length and unpredictability of the sequence complicated crisis management and the relations between local authorities and civil protection. The involvement of SISmalp, beyond its main scientific and observation prerogatives, has contributed to moderate the fears of the population by providing scientific explanations.

The presence of multiscale interactions means that the complex urban wavefield must be observed and analyzed in order to understand seismic ground motion in urban environments. Originally called site–city interaction, the interactions between soil and structures, structures and soil, and between structures contribute to the modification of urban seismic ground motion. This may affect the lateral variability of the ground motion observed in relation to earthquake damage, the characterization of site effects in urban areas, and also the response of civil engineering structures designed without consideration of the immediate urban environment. The METACity‐Quito experiment was designed to take accurate measurements of the effects of the resonator array formed by structures in the seismic wavefield, in the manner of an urban metamaterial. Current applications in the fields of physics, acoustics and, more recently, geophysics have shown the existence of forbidden bands, that is, frequencies at which seismic energy vanishes. This concept could help to understand the heterogeneous distribution of damage in urban areas as well as to imagine the future design of seismic‐proof cities.

In this article, we propose an interpretation of the propagation velocities of the pulse wave obtained in vertical structures through seismic interferometry by deconvolution. The novelty of this article is to propose a parametric study applied to canonical finite‐element models of fixed‐base buildings from pure‐shear to pure‐bending beam‐like buildings, adjusted to equivalent Timoshenko beam‐like structures. For given input seismic motions, the time histories of the horizontal displacement at each floor are obtained and used to estimate the propagation velocity of the pulse wave by deconvolution. A frequency–wavenumber technique is used to highlight the dispersive characteristics of the pulse wave. The obtained velocity is compared with the theoretical dispersion curve of the Timoshenko beam‐like structure and interpreted according to the nature of the structure. We propose a corrective coefficient to link the first resonance frequency of the building to the velocity obtained by deconvolution, according to the shear‐to‐bending ratio. Finally, we compare specific Timoshenko beam models with a number of previously published studies on the experimental interpretation of velocity in real‐case buildings for which soil–structure interaction conditions are different from the fixed‐base conditions of the Timoshenko beam‐like structure.

International audience; The Résif project, which started in 2008, aims at gathering under a common research infrastructure the French seismological, Global Navigation Satellite Systems and gravimeter permanent networks, as well as the mobile instrument pools. A central part of Résif is its seismological information system, Système d'Information de Résif (Résif‐SI) (started in 2012), which is in charge of collecting, validating, archiving, and distributing seismological data and metadata from seven national centers. Résif‐SI follows a distributed architecture, in which the six data collection and validation centers (A‐nodes) send validated data and metadata to a national data center (Résif Data Center [Résif‐DC]), which is the central point for data archiving and distribution. Résif‐SI is based on international standard formats and protocols, and is fully integrated into European and international data exchange systems (European Integrated Data Archive, European Plate Observing System [EPOS], Incorporated Research Institutions for Seismology, International Federation of Digital Seismograph Networks). In this article, we present the organization of Résif‐SI, the technical details of its implementation, and the catalog of services provided to the end users. The article is aimed both at seismologists, who want to discover and use Résif data, and at data center operators, who might be interested in the technical choices made in the implementation of Résif‐SI. We believe that Résif‐SI can be a model for other countries facing the problem of integrating different organizations into a centralized seismological information system.; Le Système d'Information sismologique de Résif (Résif-SI), dont la construction a commencé en 2012, est chargé de collecter, valider, archiver et distribuer les données et métadonnées des stations sismologiques opérés par les établissements de recherche français et leur partenaires. Il a été construit par l'intégration des infrastructures de données issues des réseaux permanents français, qui se sont fédérés au sein de Résif et ont harmonisé leurs pratiques et leurs formats d’archivage, de description et de distribution des séries temporelles sismologiques. Le résultat est une architecture distribuée organisée en six centres de collecte et de validation qui envoient les données et métadonnées validées à un centre national (Résif Data Center) qui archive et distribue l'ensemble des séries temporelles. Résif-SI est basé sur des formats et des protocoles standard internationaux, à la définition et développement desquels il participe activement. Il est entièrement intégré dans les systèmes d'échange de données européens et internationaux et constitue l’un des douze nœuds de l’archive européenne Eida (European Integrated Data Archive de l’European plate observing system – Epos,).L'article de SRL présente notamment l'organisation de Résif-SI, les détails techniques de sa mise en œuvre et le catalogue des services fournis aux utilisateurs finaux.

We analyse the spatio-temporal variations of the seismicity recorded during the Maurienne swarm. The Maurienne swarm occurred between 2017 and 2018 in the French Alps in the central part of the external crystalline massif of Belledonne. This massif extends for more than 120km in N30 direction, it is bounded to the west by the wide topographic depression of the Isère valley and the Combe de Savoie, and it is crosscut by the Maurienne valley. The location and the 3D shape of the seismic swarm are consistent with an outcroping N80 vertical fault zone. The seismic activity is interpreted as a result of the reactivation of this inherited vertical fault system. The largest event had a magnitude of 3.5.We used a catalog of 58000 events that were detected using template-matching and relocated with a double-difference method. We show that the swarm is characterised by short-term (days) and long-term (months) migrations that may be related to the presence of fluids. We also observe that the b-value decreases with depth and we discuss how this variation may due to shallow fault systems whose geometry differs from the one of the main fault system. Part of the events occurred when only one station was active. This study shows that, by grouping earthquakes into groups of similar events (clusters), it is possible to study spatio-temporal variations in such conditions.

In this article, we analyze the rotation rates in a building derived from a network of translation sensors and recorded by a rotation sensor. The building is Grenoble city hall, a reinforced concrete structure with permanent accelerometric translation sensors at the top and bottom of the building. A temporary experiment was conducted, consisting in installing a BlueSeis-3A rotation sensor for more than 24 h at the top of the structure. The ambient vibrations were analyzed. The amplitudes of translation accelerations and rotation rates at the top and bottom of the building, along with their variations over time, were analyzed. The acceleration/rotation ratios were then compared with the impulse wave velocities derived from seismic interferometry by deconvolution between the top and bottom. Perspectives with regard to building imaging, time monitoring of structural integrity and understanding the contribution of rotations to the structure’s response are discussed, offering new suggestions for research projects.

In this article, we analyze the rotation rates in a building derived from a network of translation sensors and recorded by a rotation sensor. The building is Grenoble city hall, a reinforced concrete structure with permanent accelerometric translation sensors at the top and bottom of the building. A temporary experiment was conducted, consisting in installing a BlueSeis-3A rotation sensor for more than 24 h at the top of the structure. The ambient vibrations were analyzed. The amplitudes of translation accelerations and rotation rates at the top and bottom of the building, along with their variations over time, were analyzed. The acceleration/rotation ratios were then compared with the impulse wave velocities derived from seismic interferometry by deconvolution between the top and bottom. Perspectives with regard to building imaging, time monitoring of structural integrity and understanding the contribution of rotations to the structure’s response are discussed, offering new suggestions for research projects.

Temporal changes of seismic velocities generated at the subsurface by the 2011 Mw 9 Tohoku earthquake in Japan are analyzed using interferometry and autocorrelation of waveforms recorded by surface and borehole sensors at the KiK-net station IBRH16. Spectral ratios and interferometry of data recorded in moving time windows at the surface and a depth of 300 m exhibit clear time delays and reduction of the predominant frequency during the strong ground motion followed by partial recovery in the waveform coda. Converting the time-delay evolution to velocity changes implies about 30% velocity reduction in the structure between the two sensors. Calculating temporal evolution with autocorrelation of data at the surface sensor in the moving time window indicates about 50% velocity reduction, reflecting changes of shallower material below the station. Computing autocorrelations of data recorded by the surface sensor with the Stockwell transform allows monitoring temporal changes with higher resolution that approaches the sampling rate of the waveforms. Using this technique, we estimate about 60% drop of seismic velocity below the surface sensor during strong ground motion followed again by partial recovery in the coda. These results provide fundamental information on in situ dynamic properties of soils and damaged shallow rocks that complement laboratory measurements, with important implications for constitutive equations of material degradation and healing and nonlinear site effects.

Elastic properties of civil engineering structures change when subjected to a dynamic excitation. The modal frequencies show a rapid decrease followed by a relaxation, or slow recovery, that is dependent on the level of damage. In this article, we analyze the slow recovery process applying three relaxation models to fit real earthquake data recorded in a Japanese building that shows variant structural state over 20 years. Despite the differences in conditions, the different scales and the complexity of a real-scale problem, the models originally developed for laboratory experiments are well adapted to real building data. The relaxation parameters (i.e. frequency variation, recovery slope, characteristic times and their amplitudes, and range of relaxation times) are able to characterize the structural state, given their clear connection to the degree of fracturing and mechanical damage to the building. The recovery process following strong seismic deformation, could, therefore, be a suitable proxy to monitor structural health.

Since 2017, the Maurienne Valley (French Alps) has been affected by an episode of seismic unrest. In this study we focused on the seismic swarm that occurred in 2017 and 2018, which was characterized by 8 events with ML > 3 and a maximum magnitude of 3.7. The goal was to extend the existing SISmalp catalog, and also to provide accurate locations and magnitude estimations.The employed data was recorded by a local seismic network composed of 6 broadband stations. The use of template matching allowed us to detect more than 70000 events, increasing the detection rate by more than ten times compared to the original catalog. We obtained high resolution locations applying a double difference relocation method, providing as input differential times calculated by cross-correlating templates with their respective detections. Finally, we estimated magnitudes using template-family-based linear regression analysis, in order to include even the weakest events. The seismic locations will be discussed in the tectonic and geological setting of the Maurienne Valley.

Over the last two decades, seismic ground motion prediction has been significantly improved thanks to the development of shared, open, worldwide databases (waveform and parametric values). Unlike seismic ground motion, earthquake data recorded in buildings are rarely shared. However, their contribution could be essential for evaluating the performance of structures. Increasing interest in deploying instrumentation in buildings gives hope for new observations, leading to better understanding of behavior. This manuscript presents a flat-file containing information on earthquake responses of instrumented buildings. Herein, we present the structure of the NDE1.0 flat-file containing site and earthquake characteristics (vs30, Magnitude, Distance...), structural response parameters (i.e. drift ratio, peak top values of acceleration, velocity and displacement, pre- and co-seismic fundamental frequencies) computed for several intensity measures characterizing ground motion (peak and spectral values, duration...). The data are from real earthquake recordings collected in buildings over the years. This 1.0 version contains 8,520 strong motion recordings that correspond to 118 buildings and 2,737 events, providing useful information for analyses related to seismic hazard, variability of building responses, structural health monitoring, nonlinear studies, damage prediction, etc. Some specific analysis will be presented concerning seismic structural health monitoring and damage prediction, with a special focus on the engineering demand parameter versus intensity measures variability.

Despite California being a highly seismic prone region, around 85% of people are not covered against this risk. This situation results from more than 100 years of evolution since the first earthquake insurance cover after the 1906 San Francisco earthquake. To understand this evolution, two analyses have been performed: the first one at the market level and the second one at the insured people level.At the market level, as many variables as the premium amount, the risk monitoring, the funding sources of prevention plans, the insurance company’s solvency and the attractiveness of earthquake insurance solutions, have been investigated. By cross-analysing data collected and analysing the evolution with time, three different phases have been identified in the earthquake insurance market history.At insured people level, a database is built from 18 different data sources about earthquake insurance, gathering data since 1921. Next, a new model is developed to assess the rate of homeowners insured against this risk, according to their risk awareness and the average annual insurance premium amount.These two analyses are finally used to investigate in which extent the California earthquake insurance market could reach again 40% of people insured, like in 1993 and 1996. Even if results show that a widespread belief that a devastating earthquake is imminent could bring such a situation, only a new earthquake insurance model will allow to achieve this goal in a sustainable way. In that respect, the efficiency of two current initiatives to bring more people to get an earthquake insurance: "Earthquake Brace and Bolt" and "JumpStart Recovery", is assessed at the light of the analyses performed previously in this paper.

In moderate-to-low seismic hazard regions, estimating the socio-economic consequences of an earthquake on the urban scale is a costly and difficult task. This study analyses existing global earthquake databases to build a loss flat file of 445 earthquakes since 1967 with a magnitude greater than 4.5. The flat file includes information on the social consequences (fatalities, etc.) and economic losses (direct and indirect costs, number of buildings destroyed or damaged, etc.) of each earthquake. In this study, exposed population and GDP at the date of the earthquake complete the flat file information, estimated in relation to the ground motion footprint provided by USGS ShakeMap. TThe completeness of our catalog of social and economic losses is tested thanks to the creation of a synthetic database of losses of the 22 856 earthquakes between 1967 and 2015 affecting at least one country from the ISC-gem database. From these data, we propose a more realistic loss models. Then, occurrence models of human and direct economic losses relative to the exposed population and GDP per capita are derived showing that, although the number of casualties and the absolute magnitude of losses increase as a consequence of urban concentration, global losses relative to exposure decrease. Finally, the projection of future losses is discussed.

The damping ratio and the resonance frequency represent relevant health indicators in structural health monitoring, and they are key parameters in the design of buildings. The combination of two modal parameters (i.e., damping, frequency) is reported to vary in time due to changes in environmental conditions, and with damage to the structure and dynamic loading. Amplitude dependence of the damping and frequency parameters has also been reported for strong loading, such as strong winds. However, none of these reasons can explain the much higher fluctuations of the damping values compared to the resonance frequency in the amplitude range of natural ambient vibrations. The objective here is to investigate if any amplitude dependence in this lower range of loading can explain the observed differences in the scattering of these two modal parameters. To do so, the first approach consists of a study of vertical clamp-free beams made out of different materials. Secondly, the observations and interpretations obtained are scaled up to buildings under continuous monitoring. Finally, we consider the fluctuation–dissipation theorem to explain these uncommon results.

Application of seismic interferometry in buildings gained interest in the recent years for structural health monitoring. It allows us to derive the shear wave velocity for an equivalent homogeneous medium representing the structure. Previous authors suggested using a shear beam model to compute the fundamental frequency of the structure out of this velocity. This model is however not adapted to a large part of existing buildings having different behaviors. In this paper, we propose a correction factor from shear beam and based on the Timoshenko beam to link the fundamental frequencies with the observed pulse velocity and the relative effects of shear and bending. This factor provides corrections up to 60% in frequency with respect to the shear beam model. The proposed correction factor shows that the higher velocities observed in the literature for shear wall buildings compared to frame buildings is compensated by their bending flexibility, resulting in resonance frequencies scaling similarly with building height. This model is applied to an 18-story reinforced concrete shear wall building (Ophite tower). The observed pulse velocity obtained by seismic interferometry in this building was about 500 m/s correlated to the resonance frequency by the correction factor. We show that variations of velocity in this structure and the well-studied Factor building (California), related to non-linear behavior at low-strains (down to 10−5), can be retrieved with seismic interferometry, demonstrating that this method is sensitive enough for structural health monitoring.

This study presents centrifuge tests analysis of nonlinear soil–structure interactions and the reciprocal influence of the soil and the structure. Weak and strong motions were considered and applie...

We performed large-scale earthquake economic loss estimations for France and cost–benefit analyses for several French cities by developing a semiempirical, intensity-based approach. The proposed methodology is inexpensive and easily applicable in case of a paucity of detailed information regarding the specific regional seismic hazard and the structural characteristics of the building stock, which is of particular importance in moderate-to-low seismic hazard regions. The exposure model is derived from census datasets, and the seismic vulnerability distribution of buildings is calculated using data mining techniques. Several hypothetical, large-scale retrofit scenarios are proposed, with increasing levels of investment. These cities, in their respective reinforced states, are then subjected to a series of hazard scenarios. Seismic hazard data for different return periods are calculated from regulatory accelerations from French seismic zoning. Loss estimations for the original (non-reinforced) configuration show high levels of expected building repair and replacement costs for all time spans. Finally, the benefits in terms of damage avoidance are compared with the costs of each retrofit measure. Relatively limited strengthening investments reduce the probability of building collapse, which is the main cause of human casualties. However, the results of this study suggest that retrofitting is, on average, only cost-effective in the parts of France with the highest seismicity and over the longest time horizons.

In this study, we analyze the acceleration time histories data at the Belleplaine (Guadeloupe, French West Indies) vertical array, recorded between 2008 and 2014, to evaluate the seismic response of sediments. First, we apply seismic interferometry by deconvolution method to compute the in-situ shear wave velocity between the sensor at the surface and the two shallow sensors located at GL-15m and GL-39m depth. The efficiency of this method is discussed by studying the variability of the velocity profile obtained and comparing with the in-situ geophysical survey of the site. Computed strains between sensors remain very weak, lower than 10 −5 , meaning that nonlinearities are not expected for these events. Moreover, the small dispersion of shear wave velocities values deduced from seismic interferometry may be related to the elastic behavior of the soil column. Furthermore, the transfer functions between each sensor combination are inverted to obtain a new velocity profile compatible with the geological knowledge of the site. The lag times calculated by seismic interferometry are then used to constrain random perturbations of the inverted velocity profile, allowing to study the variability of the 1D soil response. Since recorded motion has a PGA less than 10 cm/s2 in the dataset, we numerically predict the nonlinear response of the site using strong motion from a worldwide dataset. Furthermore, we study the ratio between the PGV and the medium shear velocity as a proxy showing the development of shear deformation during strong motion. Finally, using strong motion events from a worldwide dataset, we numerically predict the nonlinear response of the site based on shear wave velocity variation and the strain proxy computed by the particle velocity versus shear wave velocity ratio. We conclude that seismic interferometry by deconvolution is a robust and accurate solution to help extracting the shear wave velocity profile and to monitor the soil nonlinear response. This technique can be used when strong earthquakes will be recorded at this experimental site in order to track and assess nonlinear effects in the soil column.

International audience; In this study focused on France, we explore the uncertainties related to choices made while building a source model for hazard assessment and we quantify the impact on probabilistic hazard estimates. Earthquake recurrence models are initially built from the French Seismic CATalog (FCAT, Manchuel et al. in Bull Earthq Eng, 2018. https://doi.org/10.1007/s10518-017-0236-1). We set up a logic tree that includes two alternative seismogenic source models (ESHM13 and Baize et al. in Bull Soc Géol Fr 184(3):225–259, 2013), two versions of FCAT catalog, two alternative declustering algorithms, and three alternative minimum magnitudes for earthquake recurrence modeling. We calculate the hazard for six cities (i.e. Nantes, Lourdes, Clermont-Ferrand, Briançon, Nice and Strasbourg) that are located in source zones with a minimum amount of data to work with. Results are displayed for the PGA and spectral period 0.2 s, at return periods 475 and 5000 years. Exploration of the logic tree shows that the parameters with the most impact on hazard results are the minimum magnitude used in the recurrence modeling (up to 31%) and the selection of the seismogenic source model (up to 30%). We also use the SHARE European Earthquake Catalog (SHEEC, Woessner et al. in Bull Earthquake Eng, 2015. https://doi.org/10.1007/s10518-015-9795-1) to build earthquake recurrence models and compare hazard values obtained with the FCAT logic tree. Comparisons are limited because of the low number of events available in some sources in SHEEC; however, results show that, depending on the site considered, the earthquake catalog selection can also strongly impact the hazard estimates (up to 50%). The FCAT logic tree is combined with four ground-motion models (Bindi et al. in Bull Earthq Eng 12(1):391–430, 2014; Boore et al. in Earthq Spectra 30(3):1057–1085, 2014; Cauzzi et al. in Bull Earthq Eng 13(6):1587–1612, 2015. https://doi.org/10.1007/s10518-014-9685-y; Drouet and Cotton in Bull Seismol Soc Am 105(4):1883–1902, 2015) to account for the epistemic uncertainty on the prediction of ground-motion. Exploration of the logic tree shows that the contribution of ground-motion model uncertainties can be larger than, equivalent to, or lower than the contribution of the source-model uncertainties to the overall hazard variability. Which component controls overall uncertainty depends on the site, spectral period and return period. Finally, exploring the logic tree provides a distribution for the ratios between hazard levels at 5000 and 475 years return periods, revealing that the ratios only slightly depend on source-model uncertainties, vary strongly from site to site, and can take values between 3 and 5, which is significantly higher than what is commonly assumed in the engineering community.

Under strong seismic excitation, the resonance frequencies of civil engineering structures rapidly decrease, followed by slow recovery back to their initial values if there is no damage. In this study, we show that as for laboratory trials with rock samples, the properties of the slow recovery characterise the level of heterogeneities, and in this case, the damage rate. First, we validate this concept with laboratory tests applied to continuous beam-like structures in damaged and undamaged states. One recent model is used to fit the observed recoveries, and we show that its parameters (i.e., frequency variation, recovery slope, characteristic times) change with the health of the equivalent structure. In a second step, this concept is applied to two civil engineering structures that experience earthquakes: the first (Factor Building, USA) without observed damage; and the second (Geophysics Institute building, Ecuador) that experienced a fore/ main/ after-shock sequence with apparent damage that was characterised by a permanent drop in resonance frequency. The efficiency of the proposed model is confirmed for monitoring and for the fit of the frequency recovery. We conclude that the recovery process is a clear proxy of the structural state, and that this could be helpful for seismic monitoring of structural health during earthquake sequences.

The city of İznik (ancient Nicaea), located on the middle strand of the North Anatolian fault zone (MNAF), presents outstanding archeological monuments preserved from the Roman and Ottoman periods (first to fifteenth centuries A.D.), bearing deformations that can be linked to past seismic shaking. To constrain the date and intensity of these historical earthquakes, a systematic survey of earthquake archeological effects (EAEs) is carried out on the city’s damaged buildings. Each of the 235 EAEs found is given a quality ranking, and the corresponding damage is classified according to the European Macroseismic Scale 1998 (EMS-98). We show that the walls oriented north–south were preferentially damaged, and that most deformations are perpendicular to the walls’ axes. The date of postseismic repairs is constrained with available archeological data and new C14 dating of mortar charcoals. Three damage episodes are evidenced: (1) between the sixth and late eighth centuries, (2) between the nineth and late eleventh centuries A.D., and (3) after the late fourteenth century A.D. The repartition of damage as a function of building vulnerability points toward a global intensity VIII on the EMS-98. The 3D modeling of a deformed Roman obelisk shows that only earthquakes rupturing the MNAF can account for this deformation. Their magnitude can be bracketed between Mw 6 and 7. Our archeoseismological study complements the historical seismicity catalog and confirms paleoseismological data, suggesting several destructive earthquakes along the MNAF, since the first century A.D. We suggest the fault might still have accumulated enough stress to generate an Mw 7+ rupture.

The METAFORET experiment was designed to demonstrate that complex wave physics phenomena classically observed at the meso- and micro-scales in acoustics and in optics also apply at the geophysics scale. In particular, the experiment shows that a dense forest of trees can behave as a locally resonant metamaterial for seismic surface waves. The dense arrangement of trees anchored into the ground creates anomalous dispersion curves for surface waves, which highlight a large frequency band-gap around one resonant frequency of the trees, at ∼45 Hz. This demonstration is carried out through the deployment of a dense seismic array of ∼1000 autonomous geophones providing seismic recordings under vibrating source excitation at the transition between an open field and a forest. Additional geophysical equipment was deployed (e.g. ground-penetrating radar, velocimeters on trees) to provide essential complementary measurements. Insights and interpretations on the observed seismic wavefield, including the attenuation length, the intensity ratio between the field and the forest and the surface wave polarization, are validated with 2D numerical simulations of trees over a layered halfspace.