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Current in situ methods used to geotechnically characterize the ground are predominantly based on invasive mechanical techniques (e.g. CPT, SPT, DMT). These techniques are localized to the tested area thus making it quite time consuming and costly to extensively cover large areas. Hence, a study has been initiated to investigate the use of the non-invasive Multichannel Analysis of Surface Waves (MASW) and Multichannel Simulation with One Receiver (MSOR) techniques to provide both an evaluation of compacted ground and a general geotechnical site characterization. The MASW technique relies on the measurement of active ambient vibrations generated by sledgehammer hits to the ground. Generated vibrations are gathered by interconnected electromagnetic geophones set up in the vertical direction and in a linear array at the ground surface with a constant spacing. The MSOR technique relies on one sensor, one single geophone used as the trigger, and multiple impacts are delivered on a steel plate at several distances in a linear array. The main attributes of these non-invasive techniques are the cost effectiveness and time efficiency when compared to current in situ mechanical invasive methods. They were applied to infer the stiffness of the ground layers by inversion of the phase velocity dispersion curves to derive the shear wave velocity (Vs) profile. The results produced by the MASW and the MSOR techniques were verified against independent mechanical Cone Penetration Test (CPT) and Standard Penetration Test (SPT) data. This paper identifies that the MASW and the MSOR techniques could be potentially useful and powerful tools in the evaluation of the ground compaction and general geotechnical site characterization.

A parametric study on synthetic microtremors is proposed to compare the suitability of two ground models estimated from two surface wave inversions. Synthetic microtremors for array stations are calculated by controlling the magnitude of input sources applied on the ground surface, through the parameter “ratio of forces” R F . The value for R F is determined by the minimum misfit between synthetic vertical/horizontal component dispersion curves and, by quantitative comparison of the value of synthetic H / V spectral ratio predominant frequency and its spectral amplitude, with the experimental ones obtained at a Swiss site.

The citadel of Machupicchu is probably the most famous Inca heritage site in Peru. Considering the seismically active region, this research is an attempt to perform a seismic risk analysis of the heritage structures at Machupicchu. A systematic approach is adopted for this purpose. Characteristic seismicity of the region, where these historical constructions are located, is discussed based on the seismic hazard analysis. Evaluation of the vulnerability of the structures under the prevalent earthquake hazard is another important aspect essential for risk analysis. As a first step to proper understanding of the seismic behavior of these heritage structures, typical elements of Inca construction are studied by simple analytical models to verify basic aspects of structural integrity. The possibility that peak ground acceleration corresponding to even relatively low hazard may produce instability in some structural components like gable walls was noted. In view of this preliminary result, attempt was made to identify the dynamic characteristics of typical buildings units from more detailed investigation. This forms part of the outcome from the field study program, which included microtremor measurement of free field as well as typical constructions, planned and undertaken by the authors. The results of the microtremor measurements are utilized to estimate the dynamic characteristics of the Inca stone structures. That is, the analytical results are compared with the measurements to calibrate the analytical model. Since microtremor measurements involve very small displacements, the characteristics of stones structures thus obtained correspond to elastic behavior applicable to small strain condition. Based on this scheme, an approach has been proposed to evaluate the seismic behavior and hence the seismic vulnerability of these structures. The procedure also permits identification of the probable mode of failure of the structures concerned.

The evaluation of the natural frequency of random Vs profiles before analyzing the fundamental Rayleigh-wave dispersion characteristics is proposed in this paper. The inclusion of this parameter optimizes the effectiveness of random inverse searching to estimate Vs profiles. To demonstrate this method, a numerical test was performed using the "experimental" Rayleigh-wave dispersion curve obtained for a fictitious TEST site.

During the Meiji period (by the end of the 19 th century) many brick masonry buildings were constructed in Japan. However, due to the lack of reinforcement, these structures collapsed during the great Kanto earthquake, which occurred in the year 1923. Since then, this type of structure is not used for buildings and only a few historical constructions remain from that era. In Akita Prefecture, in the northeastern part of Japan, some of these buildings have been declared as local culture heritages. One of them is located in Ani village and was constructed in 1879 to serve as the residence for a German engineer who was working for a local mining company. As an initial step to evaluate the seismic vulnerability of this historical building, dynamic characterization has been undertaken. For that purpose, measurements of the micro vibration of the building was planned and undertaken by the authors. For the analytical modeling, mechanical parameters were estimated from a series of laboratory tests on masonry brick units obtained from the stock that are conserved near the building under study. The results of the microtremor measurements are discussed in relation to the analytical procedure adopted to estimate the dynamic characteristics of this historical brick structure. The structure shows intricate modes of vibration that are reflected in the multiple peaks observed in the transfer functions of microtremor records. With the analytical simulation considering only the effect of the brick walls, the multiple predominant frequencies are obtained for a certain range. With this good agreement of the analytical procedure and the measurement results, the reliability of the employed methodology was verified.

This paper presents an interesting and unique case study of a composite compacted site where the upper section of dynamically compacted material achieved in the first stage of compaction was subsequently removed, reinstated, and recompacted in lifts in the second stage using conventional roller compaction. Dynamic compaction was employed initially in this area because of the need to densify deep fill materials. Although a number of mechanical methods are already available for assessing deep compaction, it has been particularly rare to find a costeffective method that can be applied to a deep and extensive compacted site. Noninvasive techniques based on measurement of the horizontalto- vertical spectral ratio (HVSR) of ambient vibrations (microtremors) are proposed in this paper to assist in a pilot appraisal of this area, which occupies a part of a deep and laterally extensive compacted site. First, the key features of the measured HVSR curves were interpreted to give a preliminary insight into the quality of compaction achieved. Second, a trial-and-error forward modeling procedure fitting the theoretical HVSR curve to the measured HVSR curve then allowed the shear-wave velocity (Vs) profile conveying the compaction quality of the compacted ground to be inferred. An initial calibration was carried out to match the inferred Vs profile in a relative sense against the conepenetration- test (CPT) data at a test location. Verification was further made by comparing the inferred Vs profiles against independent CPT, dialatometer-test (DMT), and dry-density data at two other locations. The HVsR technique was then applied to appraise the consistency and quality of compaction at grid points not covered by the localized mechanical and other independent tests.

This paper proposes a HVSR (horizontal to vertical spectral ratio)-based approach to assess a deep and dynamically compacted fill area in Western Sydney. In addition to recognizing that the predominant resonance peak of the HVSR curve is a reflection of the impedance contrast between the surface layers and bedrock, the present paper recognizes that the secondary resonance peaks of the curve at higher frequencies may reflect strong impedance contrast within surface layers. This concept has been applied to develop a methodology of HVSR-based approach relying on the measurement of the HVSR of microtremors at measuring stations, and calibration and verification by independent mechanical and MSOR (multichannel simulation with one receiver) tests. The use of MSOR tests is introduced in this paper to facilitate the calibration of the HVSR forward model, particularly in terms of providing information for the initial guess of the shear wave velocity, Vs, profile in the HVSR forward modelling. The present paper demonstrates the effective use of the HVSR-based approach to assess dynamic compaction in the gaps away from and not covered by the mechanical tests. The mapping between the depth of bedrock and the predominant resonance frequency is also extended to include the mapping of the depths of layers with strong impedance contrasts to the secondary resonance peaks, after the data have been verified by independent mechanical tests.

In the last decade, the H/V Spectral Ratio (HVSR) inversion has been explored as a low cost technique for estimating the Vs ground profile (shear wave velocity – thickness) of a site, since the HVSR curve can be obtained easily from 3 component microtremor records carried out at the ground surface. Recently, some researchers suggested that more detailed estimation of near surface layers might be inverted when the HVSR curve contains information on high predominant frequencies too. In this paper, the correlation between the experimental HVSR predominant frequencies and the minimum fundamental and/or higher mode theoretical Rayleigh H/V elliptical frequencies is discussed using available Vs ground profiles and microtremor records gathered at 19 Akita Kik-net stations in Japan. The fair correlation obtained in this case study suggests us that the assessment of theoretical Rayleigh H/V elliptical frequencies of fundamental and higher modes should be carried out to select the potential ground models before the inversion process.

Ground improvement works are commonly required to overcome poor underlying soils in conjunction with infrastructure and housing development. An extensively employed and popular improvement technique is to impart mechanical compaction to the ground in an effort to achieve adequate strength and favourable load-deformation behaviour (stiffness) for the construction of civil infrastructure, including buildings and roads. This paper describes the study of a passive ambient vibration (often also known as microtremors) HVSR based method for assessing compacted ground. Two methods to control this compaction process at a very large site were employed: (a) strictly controlled rolling compaction (b) visually monitored (by naked eye) rolling compaction. The key features of the measured HVSR curves have been studied and analysed to infer useful insights about the compaction achieved by the two methods. Furthermore, the fitting of these measured HVSR curves by trial-and-error forward modelling forms the basis for inferring the shear wave velocity (V s) profile and layer thicknesses of the compacted ground. It is shown in this paper that the process of analysing and interpreting the HVSR curves, as well as the forward modelling of the HVSR curves reveal useful information about the quality and consistency of the compacted ground. © 2012 Elsevier Ltd.

In the last decades, geophysicists and seismologists have focused their attention on the inversion of empirical surface-waves’ dispersion curves from microtremor measurements for estimating the S-wave velocity structure at a site. This procedure allows a fast and convenient investigation without strong active sources, which are difficult to deploy especially in urban areas. In this study we report on a 2D seismic noise array experiment carried out at Bevagna (central Italy) near the station BVG of the Italian Accelerometric Network (RAN). The site was investigated within the DPC-INGV S4 Project (2007-2009). The Rayleigh- and Love-waves dispersion characteristics were estimated using different methods. The inversion of the dispersion curves was then performed independently, obtaining two estimations for the S-wave velocity profiles. The results of cross-hole logging near the seismic station are used for a comparison. The shear-wave velocity profiles estimated by microtremor analyses range up to 150 m depth. The two independent procedures provide consistent shear-wave velocity profiles for the shallow part of the model (20–30 m in depth) in agreement with the results of the cross-hole logging. Some problems arise between 30–40 m in depth in the profile estimated by surface waves. In this range cross-hole logging evidences an inversion of the S-wave velocity. Although the cross-hole logging stops at 40 m of depth, we are confident about the results provided by the Rayleigh-wave analysis below 40–50 m. This case study suggests that greater efforts should be devoted to exploit the potential of a coupled analysis of Rayleigh and Love waves from microtremor array measurements.

International audience; In the study of rock avalanche phenomena, numerical modelling makes use of back analyses of the rock avalanche propagation for calibration of the modelling assumptions and parameters. The back analyses require knowledge of the run-out area boundaries and the thickness distribution of the deposit. Geophysical methods can be applied to retrieve the thickness distribution, but, due to strong heterogeneities and logistic problems they are seldom applied. The aim of this work is to assess the potential of integrated geophysical methods to recognise and characterise a deposit created by two rock avalanches which occurred in the Sandalp valley (Switzerland) in 1996. The topography of the site before and after the rock avalanche is known and can be used as a benchmark. Resistivity tomography, seismic P-wave tomography, and active and passive surface wave analysis have been applied on several profiles deployed both on the rock avalanche deposit and in the surrounding area. Innovative approaches for surface wave analysis based on laterally constrained inversion and multimodal inversion have been applied to the data. A comparison of the results of the geophysical investigations with the topographic benchmark has shown the capability of the geophysical methods to locate the bottom of the deposit in the areas where the contrast with the host sediments properties is significant. In these areas, the deposit has higher resistivities and lower seismic velocities than the underlying materials. In the areas where the deposit is thicker and richer in fine-grained materials the geophysical parameters are not able to discriminate between the rock avalanche deposit and the underlying sediments. As a secondary task, the geophysical methods also allowed the bedrock pattern to be outlined.

An attempt to discuss and/or verify the suitability of subsoil velocity models estimated from Monte-Carlo inversion using synthetic microtremors is performed. In the last 2 decades, experimental Rayleigh dispersion curve from passive microtremor measurements has been explored as a tool for estimating subsoil velocity profiles. The Monte Carlo inversion is one of the most popular methods to estimate them. However, it is also known that the Monte Carlo method gives non-uniqueness solutions. In this paper, the suitability of one of the solutions (the bad case) of soil profiles estimated from experimental surface wave dispersion curves at one site is discussed using the simulation method proposed by the authors in 2009. The simulation is carried out by controlling the magnitude of input sources at the ground surface, through the parameter: ratio of forces RF. As case study, microtremor measurements from an Alpine site are analyzed and compared with the synthetic ones. The synthetic vertical/horizontal dispersion curves and the synthetic classical/modified H/V spectral ratios for certain values of RF are compared with the experimental one. According to this comparison, the tested subsoil profile should be discarded. The proposed method would be a promising tool to resolve the problem of non-uniqueness.

Old traditional wooden constructions in Japan are declared as buildings of cultural interest and therefore efforts are made to preserve these kinds of buildings. In this study, a traditional wooden structure is investigated to determine its dynamic characteristics and evaluate its seismic performance. The structure corresponds to a framed wooden construction with traditional connections between columns and beams. In general, nails are not used in these joints, and instead, the beam is narrowed at each end to be inserted into a hole cut in the column. This joint is known as a mortise-tenon joint. The end narrowed member of the beam is called the tenon, and the hole in the column is called the mortise. The joints are wedged to lock them in place. The modeling of this joint becomes a challenge since it does not correspond to a rigid joint of a common frame or to a hinge. The stiffness of this joint varies from the hinge to the perfect rigid joint. Therefore, the model used in this study is called a half rigid joint where the moment rotation relationship is specified for each beam end. Then, the dynamic analysis is performed to obtain the modes of vibration, and the results are compared with those obtained by means of the microvibration measurements. In general, good agreement was obtained between both results.