
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

The Journal of the Acoustical Society of America

Cours d'economie politique

Today, surface-wave analysis is widely adopted for building near-surface S-wave velocity models. The surface-wave method is under continuous and rapid evolution, also thanks to the lively scientific debate among different disciplines, and interest in the technique has increased significantly during the last decade. A comprehensive review of the literature in the main scientific journals provides historical perspective, methodological issues, applications, and most-promising recent approaches. Higher modes in the inversion and retrieval of lateral variations are dealt with in great detail, and the current scientific debate on these topics is reported. A best-practices guideline is also outlined.

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Surface-wave analysis for building near-surface velocity models — Established approaches and new perspectives

With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions along different hydro-mechanical paths.

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

The N-S trending T. Traversola Deformation Zone (TTDZ), developing on the western edge of the Asti Reliefs, represents one of the most relevant geological features of the Piedmont hilly area, in northwestern Italy. Morphologically this deformation zone corresponds to an evident scarp with, a rectilinear trend in map view, an height up to a hundred meters and a length of about 30 km, delimiting a hilly area (Asti Reliefs) from a plain area (Poirino Plateau) developed at averagely higher altitudes. In the western side of the Asti Reliefs some local differences between the “villafranchian succession” (Pliocene-Pleistocene) occur across the scarp, together with soft sediment deformations. Close to TTDZ the sediments (Piacenzian and Calabrian) are also widely fractured and locally show cataclastic structure. New morphological, stratigraphic, micro-palontological, structural and geophysical data reported in this study better highlight how the TTDZ is structurally organized in several N-S trending, sub-vertical right faults with horizontal displacement. In the southern slope of the Turin Hill the deformation zone probably continues in the Moncucco Torinese quarry area where it strongly deforms the Messinian sediments. The TTDZ represents the shallow evidence of a deep right structure that separates the Poirino Plateau, showing a significant northward shift, from the Asti Reliefs, where such a shift is less evident. This structure exhibits different deformation magnitude in sediments of different age, suggesting that the tectonic activity took place throughout a long time during post-Messinian periods. The TTDZ could be also interpreted as part of a structural context related to north-thrusting of the Piedmont Hills over the Po foreland basin.

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The involving of the pliocene-pleistocene succession in the T. traversola deformation zone (NW Italy)

A new seismic dilatometer (SPDMT) has been developed to combine the measurements of the flat dilatometer (DMT) geotechnical parameters with both P- and S- waves velocities. This new SPDMT is composed of the traditional mechanical DMT and four sensors for measuring the body waves velocities placed above the DMT blade. This SPDMT device is presented here, and the test procedure and the interpretation of P- and S-wave measurements are discussed. Results of the application of this new instrument are reported in a test site located in Bondeno (Emilia Romagna, Italy). Here, challenging water table conditions offer the opportunity to evaluate the advantage of a combined measure of the two propagation velocities, together with DMT geotechnical parameters, with the same apparatus for the porosity evaluation and a more calibrated liquefaction assessment.

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Combined P- and S-Wave Measurements by Seismic Dilatometer Test (SPDMT): A Case History in Bondeno (Emilia Romagna, Italy)

Building accurate initial models for FWI is a very challenging task in near surface contexts. This is due to the complex behavior of the surface waves (SW) while interacting with the highly heterogeneous geophysical properties distribution. The geometrical dispersion of SW can be exploited to estimate the subsurface seismic velocity model. Commonly, SW dispersion curves (DCs) are used to retrieve the S-wave velocity (Vs) profiles, but recent studies (Socco et al., 2017; Socco and Comina, 2017) have proposed a method based on the concept of SW skin depth to estimate also P-wave velocity (Vp) profiles. An integrated DCs clustering and data-transform approach, based on SW data only, suggests the possibility of building accurate enough Vp and Vs initial models for FWI application. Here we perform a synthetic test where the estimated model is compared with the true synthetic model using a spectral element full-waveform modeling code. Results on a synthetic example with local high variations of heterogeneities motivate us to future more complex tests and real applications.

Building initial models for full-waveform Inversion of shallow targets by surface waves dispersion curves clustering and data transform

Study of the Mechanical Properties of a Conglomerate

The paper summarises the experimental data collected by in-situ and laboratory tests on the soils in the Aterno valley, with the aim to characterize the seismic response of the sites selected for the emergency houses (C.A.S.E.), built few months after the April 6, 2009 L’Aquila earthquake. The results reported in the paper are relevant to the experimental activity coordinated by the Italian Geotechnical Society (AGI), and carried out by a network of advanced soil dynamics laboratories. The in situ tests consisted of MASW tests; the shear wave velocity profiles in some sites were successfully compared against DH and SDMT tests and instrumentally recorded HVSR amplification. The laboratory investigation included cyclic/dynamic simple/torsional shear tests on undisturbed samples. The results, summarised in terms of variation of stiffness and damping with shear strain, highlighted some peculiar properties of the soils in the Aterno valley, which can significantly affect the non-linear seismic response of the sites.

Cesare Comina

Papers

The involving of the pliocene-pleistocene succession in the T. traversola deformation zone (NW Italy)

Combined P- and S-Wave Measurements by Seismic Dilatometer Test (SPDMT): A Case History in Bondeno (Emilia Romagna, Italy)

Building initial models for full-waveform Inversion of shallow targets by surface waves dispersion curves clustering and data transform

Study of the Mechanical Properties of a Conglomerate

Geotechnical Characterization of the C.A.S.E. project sites