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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.

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.

Nonlinear elasticity has been observed in different materials and at different scales (from laboratory tests to the crust of the Earth). This behavior is evidenced by nonlinear response accompanied by slow dynamics, a process in which elastic properties recover (fully or partially) values previous to the excitation. In this study we show that nonlinear elasticity also occurs at buildings scale, where nonlinear signatures can be observed even for low levels of strain, and slow dynamics is seen at both short and long-term monitoring. Although the physics behind this response remains unknown, it is believed that this fascinating behavior is controlled by the presence of cracks, heterogeneities and dislocations; and therefore, it might be linked to the level of structural damage. By using data from Japan, we analyze the dynamic response of 24 buildings facing strong motions. The objective is to monitor variations of fundamental frequency over time and correlate them with different levels of structural drift and loading. Analyzing nonlinear elastic behavior might become a very useful and valuable way to monitor the time evolution of structural health, and hopefully, a predictive method to estimate deterioration and likely structural damage over time.

Analyzing the integrity of a structure and implementing a process to estimate the level of damage in real time increase the safety of people and goods and reduce economic losses associated with the production interruption or operation of the structure. The appearance of damage to a building changes its dynamic response (frequency, damping and/or modal shape) and, therefore, one of the most effective methods for continuous assessment of integrity is based on the use of ambient vibrations. However, if the resonance frequency can be used as indicator of changes, a misinterpretation can be due to the fact that frequency is not only affected by the occurrence of damage, but also by certain operating conditions and especially certain atmospheric conditions. In this study, after analyzing the correlation of the resonance frequency values with temperature for one building, we used the data mining method called "association rule learning" (ARL) to predict the future frequency depending on the measured temperature. We then propose an interpretation strategy of anomalies using the method called "traffic-light".

A primary school in Rotonda was monitored during an on-going seismic sequence in the Pollino area, Southern Italy. The Reinforced Concrete (RC) building is a typical three story building with a concrete frame, bearing pre-cast slab flooring, concrete block internal walls and pre-cast external infill slabs. The monitoring began in September 2011 with a single station on top of the building, and after the M L = 5 mainshock occurred in October 2012 a network was completed with accelerometers on each floor and real-time streaming data was transmitted to the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (Udine-Northern Italy). The school suffered no visible damage during the sequence. The real-time monitoring of the Rotonda school proved to be important for two reasons: (1) the large range of magnitudes and recorded peak accelerations allowed the study of the non-stationary frequency response; (2) the results also show how a simple, real-time monitoring system using cost-effective accelerometers could be used as a tool to provide information on the damage state and usability of the school.

In this paper, a relationship proxy for predicting the nonlinear soil responses is proposed by mean of monitoring the variation of shear wave velocity along vertical array. The recent seismic interferometry by deconvolution method is applied to extract the shear-wave velocity profile throughout the soil column. Using synthetic modeling, this method is shown to be a relevant and an efficient solution for assessing the Vs profile along a vertical seismic array. The ratio between particle velocity and the equivalent linear shear-wave velocity, v*/Vs*, is computed between two successive sensors, and is assumed to be a proxy for strain. The particle acceleration, a*, versus v*/Vs* is proposed as a stress-strain representation for nonlinear analysis of soil response. Using centrifuge tests, v*/Vs* is shown to be a good representation for soil strain, and analysis of the variation of v*/Vs* as a function of a* allows the nonlinear soil response to be determined in an earthquake situation. These relationship proxies are finally applied to the Japanese K-NET and KiK-net in-situ data, where Vs30 is used instead of Vs* for practical purposes related to site classification recommendations.

Safety assessment of structures and/or critical infrastructures is a key factor in post-seismic decision-making. In this context we present a performance-based framework for modeling time-variant vulnerability of reinforced concrete buildings during aftershock sequences. Structural damage is associated with first eigenperiod elongation, a performance metric whose measurement can complement visual inspection and assessment of structural health as a post-seismic operative tool. The proposed framework is applied for a series of reinforced concrete building models and two aftershock sequences. Damage states are defined using thresholds of period elongation. Numerical models of the buildings in each damage state are considered and their fragility curves are computed. The time-variant vulnerability is modeled with Markov chain as a function of the characteristics of the aftershocks sequence. Finally, the probabilities of the damage states are computed as a function of time during two real aftershock sequences.

The seismic damage to buried pipelines could be disruptive in terms of safety, life quality, and socioeconomic impacts. In this paper, we investigate the extensive list of available buried pipelines fragilities: we select a series of typical and interesting fragilities in terms of different ground motions, diverse pipeline and soil types typologies and nature (i.e. empirical, analytical); and then we compare the seismic damage results. The aim is to have a palpable overview of the variability of damage results while using different selected buried pipelines fragilities, various ground motion parameters and different hazard scenarios. To achieve this comparative study, the buried pipeline wastewater network of Byblos, Lebanon, is used as a case study. The methodology used to assess damage to the waste-water network encompasses hazard assessment, wastewater network inventory, wastewater damage functions, and model development. The Ergo platform was especially updated by implementing the list of selected fragilities to achieve the damage to wastewater comparison in this article. Results and recommendations are offered; first for a more adequate usage of those fragilities; second, for improvement of existing and future developed buried pipelines fragility functions; and third, for the Byblos wastewater pipelines network, allowing the establishment of a resilient earthquake preparedness strategy and recovery plan for infrastructure network in Byblos.

International audience; Rapid post-earthquake damage assessment is critical to short-term earthquake crisis management. Reinforced concrete buildings may accumulate damage during an aftershock sequence, and short-term damage forecasts after the mainshock can aid in decision-making (in particular, on whether to allow immediate occupancy) before further damage actually occurs. This paper presents an operative damage forecasting and building tagging procedure for reinforced concrete buildings during synthetic aftershock sequences near Thessaloniki, Greece, for two hypothetical earthquake scenarios. The synthetic aftershock sequences are simulated, and the time-variant seismic vulnerability is modeled based on fragility curves for the damage state thresholds in terms of period elongation. Period elongation is chosen as a damage proxy because it is available for rapid damage assessment in buildings with permanent monitoring systems or for city-scale post-earthquake surveys. Time-variable damage state probabilities owing to aftershocks are estimated, and a building tagging scheme is proposed based on a trafficlight concept (red-orange-green) to assist in seismic crisis management during aftershock sequences.

Environmental seismology consists in studying the mechanical vibrations that originate from, or that have been affected by external causes, that is to say causes outside the solid Earth. This includes for instance the coupling between the solid Earth and the cryosphere, or the hydrosphere, the anthroposphere and the specific sources of vibration developing there. Environmental seismology also addresses the modifications of the wave propagation due to environmental forcing such as temperature and hydrology. Recent developments in data processing, together with increasing computational power and sensor concentration have led to original observations that allow for the development of this new field of seismology. In this article, we will particularly review how we can track and interpret tiny changes in the subsurface of the Earth related to external changes from modifications of the seismic wave propagation, with application to geomechanics, hydrology, and natural hazard. We will particularly demonstrate that, using ambient noise, we can track 1) thermal variations in the subsoil, in buildings or in rock columns; 2) the temporal and spatial evolution of a water table; 3) the evolution of the rigidity of the soil constituting a landslide, and especially the drop of rigidity preceding a failure event.

H/V noise spectral ratio (HVSR), standard spectral ratio (SSR), and receiver functions (RF) techniques have been used in the Quito (Ecuador) urban area to estimate the frequency dependence of soil response. Two amplified frequencies obtained by the HVSR method appear on about 60 sites. Taking into account the most amplified frequency rather than considering only the first amplified frequency, generally associated with the fundamental frequency, we find that iso-frequency curves tightly fit the surface geology. The second amplified frequency is interpreted as the fundamental frequency of the soft thin topmost layer, which in some cases amplifies the surface ground motion more than the rest of the soil column. This hypothesis is further supported by the results provided from the SSR and RF studies at a station located on top of a solid waste landfill, and by a study of known thickness of a waste landfill, using the HVSR method.

The 28 March 1996 earthquake ( Mw =5.7) produced extensive damage in Pujili, a small town located in the central part of the Inter-Andean valley of Ecuador. Variations in the damage rate of adobe constructions throughout the city let us suppose a ground motion amplification related to site effects. A site effect study using the H / V spectral ratio confirmed the good agreement with geological formations and showed that a second peak in some soil response appears at sites that are located over a zone of alluvial deposits, in the most damaged area of the city. This second peak is in the frequency range 5–7 Hz, close to the natural response of adobe building frequency. Thus, the second peak seems to increase the damage rate of adobe buildings and may be related to superficial alluvial deposits of a river, acting independently of the rest of the soil column.