Search

A source of ground-motion recordings in urban Los Angeles that has seen limited prior application is the Community Seismic Network (CSN), which uses low-cost, micro–electro–mechanical system (MEMS) sensors that are deployed at much higher densities than stations for other networks. We processed CSN data for the 29 earthquakes with M > 4 between July 2012 and January 2023 that produced CSN recordings, including selection of high- and low-pass corner frequencies (fcHP and fcLP, respectively). Each record was classified as follows: (1) Broadband Record (BBR)—relatively broad usable frequency range from fcHP < 0.5 to fcLP > 10 Hz; (2) Narrowband Record (NBR)—limited usable frequency range relative to those for BBR; and (3) Rejected Record (REJ)—noise-dominated. We compare recordings from proximate (within 3 km) CSN and non-CSN stations (screened to only include cases of similar surface geology and favorable CSN instrument housing). We find similar high- to medium-frequency ground motions (i.e. peak ground acceleration (PGA) and Sa for T < 5 s) from CSN BBR and non-CSN stations, whereas NBRs have lower amplitudes. We examine PGA distributions for BBR and REJ records and find them to be distinguished, on average across the network, at 0.005 g, whereas 0.0015 g was found to be the threshold between usable records (BBR and NBR) and pre-event noise. Recordings with amplitudes near or below these thresholds are generally noise-dominated, reflecting environmental and anthropogenic ground vibrations and instrument noise. We find nominally higher noise levels in areas of high-population density and lower noise levels by a factor of about 1.5 in low-population density areas. By applying the 0.0015 g threshold, limiting distances for the network-average site condition, based on the expected fifth-percentile ground-motion levels, are 89, 210, 280, and 370 km for M 5, 6, 7, and 8 events, respectively. [ABSTRACT FROM AUTHOR]

Highlights: We used array-based ambient vibration modal analysis and eigenfrequency modeling to characterize the dynamic behavior and structural conditions of a partly collapsed lava tube roof. Multiple resonance modes were identified from spectral and cross-correlation analyses, and used to calibrate a heterogeneous numerical model of the lava tube. Our study shows that the combination of experimental and numerical modal analysis is a valuable tool for mapping and structural characterization of underground cavity roofs. [ABSTRACT FROM AUTHOR]

While geodetic measurements have long been used to assess landslides, seismic methods are increasingly recognized as valuable tools for providing additional insights into subsurface structures and mechanisms. This work aims to characterize the subsurface structures of the deep-seated gravitational slope deformation (DSGSD) at Heinzenberg through the integration of active and passive seismic measurements. Seismic techniques can hereby deliver additional information on the subsurface structure and mechanisms involved, e.g., the degree of rock mass degradation, the resonant frequencies of the potentially unstable compartments, and the local fracture network orientations that are influenced by wavefield polarization. By employing advanced methods such as H/V analysis, site-to-reference spectral ratios, polarization analysis, surface wave analysis, and the joint multizonal transdimensional Bayesian inversion of velocity structures, we establish a comprehensive baseline model of the landslide at five selected sites. This baseline model shall help identify potential changes after the refilling of Lake Lüsch, which started in 2021. Our results reveal the rupture surface of the DSGSD at various depths ranging from 30 m at the top to over 90 m in the middle of the slope. Additionally, we estimate key parameters including the shear wave velocities of the different rock masses. The 2D geophysical profiles and rock mass properties contribute to the understanding of the subsurface geometry, geomechanical properties, and potential water pathways. This study demonstrates the significance of integrating seismic methods with traditional geodetic measurements and geomorphologic analysis techniques for a comprehensive assessment of landslides, enhancing our ability to monitor and mitigate hazardous events. [ABSTRACT FROM AUTHOR]

This paper reports on a series of experimental tests and a numerical study carried out on the historic masonry bridge of Santa Teresa of Bitonto, located in Bari (Southern Italy). A systematic working technique was planned and carried out with the final objective of defining the dynamic properties of the bridge and verifying the seismic repose by means of a response spectrum analysis. Initial stages were carried out including historical research, visual inspection, and geometric integrated aerial and ground survey on-site using UAV technique for the identification of the geometric details of the structural and non-structural elements of the bridge. An experimental campaign was scheduled and executed by performing free and forced-vibration tests using uniaxial and biaxial accelerometers placed at 22 monitoring points to retrieve the main vibration modes of the bridge with their corresponding frequencies and damping ratios. Although the free vibration tests detected only the main mode of vibration due to the squat nature of the structure, the forced-vibration tests help to confirm the findings and identify further modes of vibration. The consistency of the experimental frequencies was statistically confirmed by varying the conditions of the forced-vibration tests. A Finite-Element (FE) model was constructed and calibrated qualitatively (i.e., order of vibration modes) with respect to the experimental ones, based on both the geometric survey and the visual inspection outputs. Then, a second phase of calibration was undertaken by tuning the remaining free parameters to match the numerical values of all the detected modes. The calibrated model, capable of producing the experimental results, was adopted for performing a response spectrum analysis for the global response evaluation of the bridge. The results showed a globally acceptable level of stress, while excessive values were limitedly observed in a few critical zones. [ABSTRACT FROM AUTHOR]

Copyright of Multidiszciplináris Tudományok is the property of University of Miskolc and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Scour is the prevailing cause of bridge failure worldwide, leading not only to traffic disruption, but also to social and economic losses and even to casualties. Many vibration-based monitoring techniques have been proposed for identifying the scour location and extent, based on the evaluation of the changes of the bridge modal properties due to scour. This study describes the experimental and numerical research carried out to investigate the effects of scour on the dynamic properties of structures with shallow foundations. Although these are the most vulnerable ones, they have received less attention compared to structures founded on pile foundations. To fill some existing knowledge gaps, field experiments were carried out on EuroProteas, a structural prototype with shallow foundation that was subjected to increasing levels of scour. The changes of the dynamic properties of the system are evaluated by postprocessing the ambient vibration recordings and by developing various models of the soil–foundation–structural system with different descriptions of the soil–structure interaction problem. The study results shed light on the effects of scour on systems with shallow foundations and on the accuracy of alternative modelling approaches. They are presented here to inform the development and validation of vibration-based techniques and modelling strategies for bridge scour identification. [ABSTRACT FROM AUTHOR]

Abstract In this study, we determine the properties of the maar volcanic structure using ambient vibration analysis. We performed several ambient vibrations surveys at Mýtina maar (West-Bohemia, Czechia) to map amplification by site-to-reference spectral ratios and to estimate average shear wave velocities by array methods. As the maar diatreme is formed by a deep concave body of broken rock, strong 3D resonances develop. The site-to-reference amplification factors reach a value of 20 in the central part of the maar. Using the noise data, we demonstrate possibility of mapping the lateral dimensions of the maar infills by ambient noise measurements. To understand these observations, we developed a simplified 3D viscoelastic velocity model and simulated synthetic ambient vibrations by the finite difference method. The simulated response fitted both, measured fundamental frequencies and the amplification levels. The maximum depth of the crater was estimated to be at least 800 m. Graphical Abstract

Modal parameter evaluation is widely used for structural health monitoring, damage detection, and numerical model calibration. This study benchmarks two methods for modal identification under controlled laboratory conditions using operational modal analysis to compare dynamic parameters from ambient vibrations and shaker tests. A 2‐storey 3D spatial steel frame equipped with 3‐axial accelerometers is used as a case study. The identified dynamic parameters are benchmarked against a preliminary finite element model by computing Auto‐MAC and MAC matrices. It can be concluded that the preliminary FEM approach performs better in the prediction of modes shapes than natural frequencies. It was found that analysing the structural response to both ambient and artificially induced excitations provide a more complete understanding of a structure's dynamic characteristics. An additional mode shape was identified from the artificially induced excitation that was not previously captured from the ambient excitation. [ABSTRACT FROM AUTHOR]

In this study, we determine the properties of the maar volcanic structure using ambient vibration analysis. We performed several ambient vibrations surveys at Mýtina maar (West-Bohemia, Czechia) to map amplification by site-to-reference spectral ratios and to estimate average shear wave velocities by array methods. As the maar diatreme is formed by a deep concave body of broken rock, strong 3D resonances develop. The site-to-reference amplification factors reach a value of 20 in the central part of the maar. Using the noise data, we demonstrate possibility of mapping the lateral dimensions of the maar infills by ambient noise measurements. To understand these observations, we developed a simplified 3D viscoelastic velocity model and simulated synthetic ambient vibrations by the finite difference method. The simulated response fitted both, measured fundamental frequencies and the amplification levels. The maximum depth of the crater was estimated to be at least 800 m. [ABSTRACT FROM AUTHOR]

The goal of the multi-year seismic microzonation mapping project for Greater Vancouver, British Columbia, Canada, is to produce seismic hazard maps inclusive of local site effects, in particular seismic hazard specific to one-dimensional site response and three-dimensional Georgia sedimentary basin amplification, as well as liquefaction and landslide hazard potential. We explore the variability in key seismic site characterization measures most often used for seismic microzonation mapping to evaluate the impact on mapping and communication of seismic microzonation of Greater Vancouver. This study focuses on the comparison of seismic microzonation maps of Greater Vancouver based on up to three seismic site term parameters and their associated classification schemes: 1) the time-averaged shear-wave velocity (Vs) of the upper 30 m (Vs30) and associated Canadian National Building Code (NBC) site class; 2) Vs30-based site classification proposed for the updated Eurocode 8; 3) site period (T0) determined from microtremor site amplification spectra; and 4) a hybrid site classification based on T0 and the average Vs and thickness of soil. 810 Vs30 and 2,200 T0 values are determined to evaluate sub-regional differences in these important seismic site parameters in Greater Vancouver. We find that the seismic microzonation of Greater Vancouver depends on the chosen seismic site parameter (Vs30, T0, or a combination of parameters) and that classification schemes with greater class divisions are beneficial to communicating the great variability in seismic site conditions in Greater Vancouver. We recommend that either one hybrid classification map or two classification maps of Vs30 and T0 together are required for effective communication of the seismic microzonation of Greater Vancouver.

One of the main strategies of disaster risk reduction policies in seismic-prone areas is to assess a building's susceptibility to critical structural behaviour, which could induce and aggravate seismic damage. Subsequently, it is important to implement structural upgrading interventions to remove or reduce such critical issues. For existing buildings, this strategy is a core aspect of vulnerability assessment methods, and it is usually inferred by analysing specific features of site and building conditions. Both vulnerability assessments and structural upgrading interventions would benefit from a rapid check aimed at verifying, through on-site measurements, if the presumed structural behaviour (before and/or after the interventions) corresponds to the actual situation. This paper presents an integrated methodology, conceived to account for the above-mentioned issues, based on the acquisition and interpretation of ambient vibrations. The paper illustrates the use of the proposed methodology in different applications, first, for a preliminary characterisation of the situations, then, as a support in the assessment and definition of actions to reduce the structural vulnerability, and finally, for a-posteriori effectiveness control of the upgrading interventions being implemented. To conclude, the paper provides some considerations on the strengths and limitations concerning the use of the methodology for seismic risk reduction purposes. [ABSTRACT FROM AUTHOR]

Corrosion directly affects the structural stiffness of a steel element, reducing the thickness, thus inertia, due to the gradual deterioration of the material. Quickly identifying corrosion damage to the stiffness of a steel structure is a challenge in coastal environments since corrosion progresses rapidly, and traditional methods of inspection and diagnosis are time-consuming and costly. This is an important issue; therefore, characterization of the corrosion level represents a key element in making decisions regarding maintenance or structural integrity. This work estimates the relationship between the corrosion level in steel structures and their dynamic parameters using ambient vibration records. It comprises the characterization of the dynamic behavior and corrosion state of three full-scale pedestrian bridges with similar geometry, material, and structural configuration characteristics but with significant differences in the degree of deterioration. The structures were instrumented with piezoelectric sensors connected to a portable data acquisition system; the recorded information was analyzed with optimization algorithms in Python based on the power spectral density (PSD) of the vibrations of each bridge. The parameters obtained related to the degree of corrosion determine the incidence of the level of deterioration in the structural behavior, thus involving changes in its stiffness and mass. [ABSTRACT FROM AUTHOR]

An experimental study of the fundamental period of vibration of geologic strata above multiple impedance contrasts is presented for the Canterbury Plains, a deep, complex sedimentary basin on the South Island of New Zealand. Microtremor Horizontalto-Vertical Spectral Ratio (mHVSR) analysis was used at 152 locations to investigate the fundamental period of the strata above three significant impedance contrasts in the region: the Riccarton Gravel, the Banks Peninsula volcanic (BPV) rock, and the deep gray-wacke basement bedrock. Up to three mHVSR peaks were observed in many of the mHVSR curves, with the long-period (2-7 s) peaks controlled by the BPV and/or the underlying bedrock. As the thickness of the BPV increases, the response of the geologic strata above the basement bedrock was masked by the shallower BPV, effectively changing the definition of what constitutes the reference condition (i.e. engineering bedrock) for site response analyses. The mHVSR peaks matched the long-period amplification peaks observed in the response spectra calculated from ground motions recorded during the Canterbury Earthquake Sequence events, underscoring the importance of the identification and consideration of deep impedance contrasts in site classification. [ABSTRACT FROM AUTHOR]

We introduce non-invasive seismic methods for identifying and characterizing maar sedimentary infills. We conducted a dense ambient vibration survey and employed state-of-the-art 3D resonance analysis techniques to map the lateral extent and depths of the sedimentary layers, a challenge with traditional geophysical methods due to unfavorable aspect ratios (depth > lateral dimension). The ambient vibrations of maars are predominantly driven by normal mode motions due to 3D resonance of crater infills. Dense station coverage enabled detailed images of the normal mode shapes revealing infill symmetries. The resonance results in extreme ground motion amplification, with factors reaching up to 30 on the vertical component, challenging conventional beliefs about site effects and methodologies based on widely used horizontal-to-vertical spectral ratios. These results are supported by numerical simulations of the maar's seismic response. The observed response is so specific that it can be used to identify partly eroded maar structures in the field. • 3D resonance in the maar infill with amplification of ground motion of factor 30. • Ambient vibration used to constrain depth, width, and internal structure of the maar. • The widely used HVSR does not work in the case of deep maar sediments. [ABSTRACT FROM AUTHOR]

While geodetic measurements have long been used to assess landslides, seismic methods are increasingly recognized as valuable tools for providing additional insights into subsurface structures and mechanisms. This work aims to characterize the subsurface structures of the deep-seated gravitational slope deformation (DSGSD) at Heinzenberg through the integration of active and passive seismic measurements. Seismic techniques can hereby deliver additional information on the subsurface structure and mechanisms involved, e.g., the degree of rock mass degradation, the resonant frequencies of the potentially unstable compartments, and the local fracture network orientations that are influenced by wavefield polarization. By employing advanced methods such as H/V analysis, site-to-reference spectral ratios, polarization analysis, surface wave analysis, and the joint multizonal transdimensional Bayesian inversion of velocity structures, we establish a comprehensive baseline model of the landslide at five selected sites. This baseline model shall help identify potential changes after the refilling of Lake Lüsch, which started in 2021. Our results reveal the rupture surface of the DSGSD at various depths ranging from 30 m at the top to over 90 m in the middle of the slope. Additionally, we estimate key parameters including the shear wave velocities of the different rock masses. The 2D geophysical profiles and rock mass properties contribute to the understanding of the subsurface geometry, geomechanical properties, and potential water pathways. This study demonstrates the significance of integrating seismic methods with traditional geodetic measurements and geomorphologic analysis techniques for a comprehensive assessment of landslides, enhancing our ability to monitor and mitigate hazardous events.

The reliability of non-invasive shear wave velocity (Vs) profiling techniques is assessed for four Ontario highway sites in comparison to invasive methods (N60, su, laboratory bender element Vs, borehole geology). Our non-invasive Vs profiles are obtained from joint inversion of surface wave dispersion and microtremor horizontal to vertical spectral ratio peak(s). The overall inter-method average relative difference in soil Vs is 15%. Non-invasive and invasive methods provide consistent Vs30 and earthquake site classification. Multi-method site classification demonstrates greater success of non-invasive and invasive methods to determine the Vs profile and soil properties respectively. [ABSTRACT FROM AUTHOR]

The Middle-Chelif basin, in northwestern Algeria, is located in a seismically active region. In its western part lies the El-Asnam fault, a thrust fault responsible for several strong earthquakes. The most important being the El-Asnam earthquake (Ms = 7.3) of 1980. In the present study, ambient vibration data with single-station and array techniques were used to investigate the dynamic properties of the ground and to estimate the V s 30 structure in the main cities of the basin. Soil resonance frequencies vary from 1.2 to 8.3 Hz with a maximum amplitude of 8.7 in. Collapsing behavior has also been demonstrated west of the city of El-Attaf, reflecting a strong potential for liquefaction. A V s 30 variation map and a soil classification for each city were obtained mainly by inversion of the HVSR and Rayleigh wave dispersion curves. Finally, an empirical prediction law of V s 30 for the Middle-Chelif basin was proposed. [ABSTRACT FROM AUTHOR]

The paper presents a survey of the historic Arch-cathedral bell tower in Vilnius induced by the appearance of cracks in the structure after a new bell system installation. An attempt is undertaken to identify the reason for the crack occurrence and to check a possible crack influence on global structural behaviour. The research is based on dynamic measurements made in the tower during ambient vibrations and during vibrations caused by swinging bells. The amplitudes of the accelerations and the spectral peaks due to the ambient and excited vibrations are compared. Magnification of the first spectral peak due to bells swinging points at resonance. The root-mean-square analysis is conducted to detect the tower section most vulnerable to swinging bells. The modal curvature approach applied to the first mode shape serves as the damage indicator. The algorithm locates damage in the region of the cracks observed in the tower; thus, the cracks are considered structural. The research proves the necessity of a dynamic survey in similar cases before important decisions are undertaken regarding the replacement of the bell system. [ABSTRACT FROM AUTHOR]

This paper presents the experimental analysis on the "Municipal Headquarters" of Palagianello Town. This is a strategic building with a high complexity at planimetric and altimetric level, so it is interesting the evaluation of its structural dynamic performance in case of seismic emergency management. To this aim, environmental vibrations have been acquired in situ and accelerometers have been positioned in well-defined points. The data were analyzed with an easy and accurate process that includes the Operational Modal Analysis (OMA), to identify the natural frequencies, the mode shapes and the damping ratios with non-destructive testings. Subsequently, the experimental results were compared with those of two numerical models (with and without infill walls) defined by means of the finite element method (FEM); this allowed for better calibration of the model and to arrive at more realistic conclusions about the behavior of the structure. The paper discusses the influence of the stiffness contribution of masonry infills on the dynamic properties of the building. Moreover, it shows that the adoption of ad hoc chosen locations of the sensors could influence the accuracy of the experimental results, especially for structures characterized by irregularities. [ABSTRACT FROM AUTHOR]

Corrosion directly affects the structural stiffness of a steel element, reducing the thickness, thus inertia, due to the gradual deterioration of the material. Quickly identifying corrosion damage to the stiffness of a steel structure is a challenge in coastal environments since corrosion progresses rapidly, and traditional methods of inspection and diagnosis are time-consuming and costly. This is an important issue; therefore, characterization of the corrosion level represents a key element in making decisions regarding maintenance or structural integrity. This work estimates the relationship between the corrosion level in steel structures and their dynamic parameters using ambient vibration records. It comprises the characterization of the dynamic behavior and corrosion state of three full-scale pedestrian bridges with similar geometry, material, and structural configuration characteristics but with significant differences in the degree of deterioration. The structures were instrumented with piezoelectric sensors connected to a portable data acquisition system; the recorded information was analyzed with optimization algorithms in Python based on the power spectral density (PSD) of the vibrations of each bridge. The parameters obtained related to the degree of corrosion determine the incidence of the level of deterioration in the structural behavior, thus involving changes in its stiffness and mass.

Seismic stations are usually used to record seismic event and, therefore, they are recommended to be installed far from railways and traffic roads in order to avoid the superposition of ambient noise signals to those provoked by an earthquake. In this paper, instead, seismic stations, placed intentionally in areas near railway and traffic roads, are used to characterize the subsoil spectral properties and to assess the effect of vibrations due to trains and vehicles. A cemetery in the green countryside near Florence is chosen as a reference case study to deal with this topic. Most of the buildings in the cemetery area are affected by an extensive crack pattern. In January 2020 five seismic stations were installed in order to evaluate if the trains running in the tunnels of the regional and high-speed railway lines located below and in the vicinity of the cemetery and the vehicles traveling on the nearby A1 highway and regional road can produce vibrations in the ground that justify the observed damage pattern.Collected data are analyzed using the Nakamura technique in order to estimate the dynamic properties of the ground and compared to the limits provided by the current regulations. Furthermore, the trend of the Root Mean Square average over the entire recording period is computed as well.From the obtained results, it is possible to highlight that the average daily oscillation level increases from early morning until 7 p.m. and then it decreases, and also that the highest amplitudes of transients are concentrated in the late evening and during the night, when the background noise is lower.Furthermore, the computed values of the maximum and average amplitudes are lower than those that can cause damage to buildings as defined by the guidelines, the eigenfrequency of the ground falls in a range far from that ascribable to the cemetery buildings, so that the resonance effects can be excluded. In order to confirm these results, the amplitude of ground shaking due to recorded transients is compared to that produced by two earthquakes (a 3.4 Mw local earthquake at more than 100 km and a Mw 6.6 teleseism from Turkey) which occurred during the monitoring period. One can conclude that it seems unlikely that the shaking produced by nearby vehicles and trains could be responsible for the observed damage.

Operational Modal Analysis (OMA) is becoming a mature and widespread technique for Structural Health Monitoring (SHM) of engineering structures. Nonetheless, while proved effective for global damage assessment, OMA-based techniques can hardly detect local damage with little effect upon the modal signatures of the system. In this context, recent research studies advocate for the use of wave propagation methods as complementary to OMA to achieve local damage identification capabilities. Specifically, promising results have been reported when applied to building-like structures, although the application of Seismic Interferometry to other structural typologies remains unexplored. In this light, this work proposes for the first time in the literature the use of ambient noise deconvolution interferometry (ANDI) to the structural assessment of long bridge structures. The proposed approach is exemplified with an application case study of a multi-span reinforced-concrete (RC) viaduct: the Chiaravalle viaduct in Marche Region, Italy. To this aim, ambient vibration tests were performed on February 4 th and 7 th 2020 to evaluate the lateral and longitudinal dynamic behaviour of the viaduct. The recorded ambient accelerations are exploited to identify the modal features and wave propagation properties of the viaduct by OMA and ANDI, respectively. Additionally, a numerical model of the bridge is constructed to interpret the experimentally identified waveforms, and used to illustrate the potentials of ANDI for the identification of local damage in the piers of the bridge. The presented results evidence that ANDI may offer features that are quite sensitive to damage in the bridge substructure, which are often hardly identifiable by OMA. [ABSTRACT FROM AUTHOR]

Seismic behavior of masonry walls has been heavily investigated, especially by means of laboratory experiments employing cyclic tests to determine the mechanical parameters and seismic capacity. Nevertheless, the dynamic properties of the tested walls often remain unknown, even though the nature of the seismic response is dynamic and profoundly affected by the structure's dynamic properties. This paper presents an investigation on the dynamic properties of three different masonry wall panels in healthy and damaged states, and examines if damage quantification via tracking the changes in dynamic properties is feasible. Ambient vibration and impact measurements are used for the dynamic identification of wall panels, before and after they are tested in reversed-cyclic in-plane shear-compression tests. The natural frequencies, damping ratios, and mode shapes of the walls are determined and compared to each other. Moreover, the damage progression and its effect on the dynamic features of the URM wall panel is investigated using a discrete element model of the benchmark wall that is validated in terms of the force-displacement response and damage pattern of the wall. The results of the study indicate that changes in natural frequencies and mode shapes are traceable, although it is difficult to infer damage quantification relationships from these changes. The outcomes of this study also highlight that numerical models verified with the nonlinear quasi-static behavior do not necessarily match the wall's dynamic behavior, and that more research is required to update nonlinear numerical models. Overall, the results contribute to the knowledge regarding the dynamic characteristics of masonry walls in healthy and damaged conditions, and to quantify the damage in masonry walls as well as the changes in their dynamic properties. • Cyclic shear-compression tests on three stone masonry wall panels. • Dynamic identification in healthy state and after damage. • Effects of damages on the dynamic properties of the walls. • Effects of strengthening on the dynamic properties of the walls. • Numerical investigation of modal properties in healthy and damaged states. [ABSTRACT FROM AUTHOR]

The Middle-Chelif basin, in northwestern Algeria, is located in a seismically active region. In its western part lies the El-Asnam fault, a thrust fault responsible for several strong earthquakes. The most important being the El-Asnam earthquake (Ms = 7.3) of 1980. In the present study, ambient vibration data with single-station and array techniques were used to investigate the dynamic properties of the ground and to estimate the Vs30 structure in the main cities of the basin. Soil resonance frequencies vary from 1.2 to 8.3 Hz with a maximum amplitude of 8.7 in. Collapsing behavior has also been demonstrated west of the city of El-Attaf, reflecting a strong potential for liquefaction. A Vs30 variation map and a soil classification for each city were obtained mainly by inversion of the HVSR and Rayleigh wave dispersion curves. Finally, an empirical prediction law of Vs30 for the Middle-Chelif basin was proposed.

This paper presents results from the dynamic monitoring of a reinforced concrete school building located in Camerino (central Italy) during the seismic swarm following the first main shock of the Central Italy earthquake that occurred in August 2016. After the main shock of August 24th, ambient vibration tests were executed on the building to identify its modal dynamic behavior, which was assumed as benchmark to study changes in the structural response because of the subsequent events. A three-day dynamic monitoring was then performed with the aim of investigating changes in the dynamic behavior of the building subjected to ambient and seismic excitations. A procedure to identify the nonlinear response of the structure subjected to seismic events is presented, starting from an optimization methodology that permits the identification of the structure dynamics within time windows in which the building dynamic behavior can be considered linear time-invariant. Data show the variability of the modal properties, resonance frequencies, and damping ratios of the building, with the earthquake intensity. [ABSTRACT FROM AUTHOR]

The ambient vibration horizontal-to-vertical spectrum method (HVSR) is widely used in microzonation and structural studies, assuming stability and reproducibility of HVSR frequency peaks. A 35-day continuous HVSR monitoring performed in the suburbs of Algiers (Algeria) reveals that HVSR peaks are not always stable and reproducible both in frequency and amplitude. HVSR curves show a first peak, which varies from 0.9 to 1.8 Hz with amplitudes from 0.9 to 3.3, and a second peak from 5 to 7.7 Hz with amplitudes from 1.4 to 4. These results show that HVSR peak frequencies and amplitudes are highly sensitive to nearby anthropogenic sources. [ABSTRACT FROM AUTHOR]

In the present work, the extension of the Seismic Model from Ambient Vibrations (SMAV) to historical masonry buildings is presented. The probabilistic simplified model, which has already been validated for ordinary building, is able to predict their seismic behaviour on the basis of its experimental modal parameters, taking into account the dependence between the resonance frequencies and the vibration amplitude, through a linear-equivalent analysis. The SMAV model is based on the definition of a Structural Serviceability Index (IOPS), expressing the probability of the building to preserve its structural functionality after an earthquake occurrence. As the dynamic parameters are extracted from the vibrations which occur during the normal operating conditions, this methodology is particularly in accordance with the non-invasiveness requirements of monumental buildings, both in terms of service maintaining and structural interventions. The different phases provided for by the methodology and the feasibility of their application to real cases are illustrated with reference to the town hall of Sansepolcro, "Palazzo delle Laudi", an Italian renaissance building of XIII century. [ABSTRACT FROM AUTHOR]

Twenty-nine single-station noise measurements, processed through the Horizontal to Vertical Spectral Ratio (HVSR) technique, a Multichannel Analysis of Surface Waves (MASW) survey, and two 2D array measurements were performed in Durrës to provide useful elements for a geophysical subsoil characterisation. Results from noise measurements defined a zone eastwards of the historical centre, where the characteristics of shallow soil layers are responsible for modification to the seismic response. In particular, HVSR curves in this area showed amplitude higher than 3.4 at a period higher than 1 s. From the analysis of the collected data, four different groups of HVSR curves were recognised, whereas noise measurements were also used to retrieve a preliminary bedrock depth map. These results are potentially useful for correlating construction typologies and vibration period of the buildings with the site amplification and with the damages observed during the seismic sequence for which the highest magnitude event was the MW 6.2, 26 November 2019 earthquake. Moreover, two shear waves velocity VS profiles were obtained from a joint inversion of Rayleigh curves with ellipticity. In one case, it revealed the presence of a soil of very poor mechanical properties, which was classified as D soil according to the international codes (EC8, NEHRP); in the other case, the VS profile allowed us to retrieve important information about the seismic bedrock to be used in numerical modelling for the third level of seismic microzonation. [ABSTRACT FROM AUTHOR]

The rise of human activities and the constant increase of vehicles traffic in the cities, and in particular of heavy vehicles such as buses and trucks, causes continues ambient vibrations that can detrimentally affect the conservation of built artifacts, especially historical constructions. The effects of urban vibrations on buildings and monuments are far from being fully investigated. In general, peak levels of traffic-induced vibrations are rarely high enough to be the main cause of heavy structural damages. On the other hand, they contribute to the process of deterioration by adding extra stresses—through fatigue damage accumulation occurring as a result of long periods of exposure to low levels of vibration—or by contributing to soil densification—which can lead to the settlement of building foundations. As such, the estimation of threshold levels above which traffic-induced vibrations may cause damages to monumental buildings requires specific studies including long-time monitoring campaigns. Data from experimental campaign can, indeed, be used to extract information on the variation of dynamic properties of buildings, thus providing valuable pieces of information for a complete knowledge to plan effective preservation interventions. The present work aims to identify the effects of traffic induced urban vibrations on the two Towers of Bologna, particularly prone to fatigue-related damages and close to a high transit of vehicles, through a preliminary analysis of data from several dynamic monitoring campaigns conducted during the last years.

This paper presents the experimental analysis on the “Municipal Headquarters” of Palagianello Town. This is a strategic building with a high complexity at planimetric and altimetric level, so it is interesting the evaluation of its structural dynamic performance in case of seismic emergency management. To this aim, environmental vibrations have been acquired in situ and accelerometers have been positioned in well-defined points. The data were analyzed with an easy and accurate process that includes the Operational Modal Analysis (OMA), to identify the natural frequencies, the mode shapes and the damping ratios with non-destructive testings. Subsequently, the experimental results were compared with those of two numerical models (with and without infill walls) defined by means of the finite element method (FEM); this allowed for better calibration of the model and to arrive at more realistic conclusions about the behavior of the structure. The paper discusses the influence of the stiffness contribution of masonry infills on the dynamic properties of the building. Moreover, it shows that the adoption of ad hoc chosen locations of the sensors could influence the accuracy of the experimental results, especially for structures characterized by irregularities.