HVSR

This book bridges the gap between theory and practice, showing how a detailed definition of the shear-wave velocity (Vs) profile can be efficiently obtained using limited field equipment and following simple acquisition procedures. It demonstrates how surface waves (used to define the Vs profile) and vibration data (used to describe the dynamic behaviour of a building) can be recorded using the same equipment, and also highlights common problems, ambiguities and pitfalls that can occur when adopting popular methodologies, which are often based on a series of simplistic assumptions. Today, most national and international building codes take into account a series of parameters aimed at defining the local seismic hazard. Sites are characterised based on the local Vs profile, and the dynamic behaviour of existing buildings is defined through the analysis of their eigenmodes. The book includes a series of case studies to help readers gain a deeper understanding of seismic and vibration data and the meaning (pros and cons) of a series of techniques often referred to as MASW, ESAC, SPAC, ReMi, HVSR, MAAM and HS. It also provides access to some of the datasets so that readers can gain a deeper and more concrete understanding of both the theoretical and practical aspects.

Software para análisis de ondas superficiales (MASW, ReMi, ESAC, MFA y RPM), modelamiento e inversión de dispersion de ondas Rayleigh y Love, análisis de atenuación de las ondas Rayleigh para estimar factores de calidad QS, determinación de la frecuencia de resonancia a partir del análisis de microtremors (HVSR, método Nakamura) y modelamiento del cociente espectral H/V para mejorar el perfil VS hacia capas más profundas.
Sismograma sintético e inversion de Espectro de Velocidad Completo (FVS) (no necesita de picking o interpretacion de las curvas de dispersión).
Análisis (inversión conjunta con dispersión de data) de Superficie RPM frecuencia - offset (Movimiento de Partícula de ondas Rayleigh “Rayleigh-wave Particle Motion”).
Análisis Back-scattering. Análisis de data MASW con espaciamiento no constante.

The present study illustrates a series of technical aspects regarding the holistic acquisition and analysis of Rayleigh waves acquired by a single multi-component geophone.
Compared with the common multi-channel and multi-offset active and passive methodologies, this approach requires simple and straightforward acquisition procedures and takes advantage of the joint analysis of the group-velocity spectra of both the vertical and radial components together with the Radial-to-Vertical Spectral Ratio (RVSR), i.e. the ratio between the amplitude spectra of the radial and vertical components.
In this way we can fully describe the Rayleigh-wave propagation both in terms of velocities (group-velocity spectra) and relative amplitudes (RVSR) and jointly invert the data by means of a three-objective optimization scheme based on the Pareto optimality.
Since the group-velocity spectra of the vertical and radial components are analyzed according to the Full Velocity Spectrum (FVS) approach, data inversion is performed without interpreting the velocity spectra in terms of dispersion curves.
The results of the described methodology are assessed by considering two case studies and by comparing the retrieved shear-wave velocity profiles with the ones obtained through the analysis of the dispersion retrieved from standard active and passive multi-channel and multi-offset data also considering the Horizontal-to-Vertical Spectral Ratio (HVSR).
Eventually, through a synthetic dataset, the effect of significant lateral variations is discussed with respect to the group-velocity spectra and the RVSR and RPM (Rayleigh-wave Particle Motion) curves.

Ambient noise Horizontal-to-Vertical Spectral Ratio (HVSR) technique is commonly used approach to obtain 1D models of the shear-wave velocity in the shallow surface of an investigated area. However, obtained models can have a wide margin of uncertainty if inversions have not been appropriately constrained by detailed strati-graphic information. An application of HVSR inversion constrained by lithostrati-graphic data is presented in order to verify the effectiveness of this technique for purposes of geological and geophysical reconstruction of a sedimentary basin in a densely urbanized area. This is often the case of seismic microzonation studies, in which almost all the information derives from near surface stratigraphic drillings, since other geophysical methods are logistically difficult to carry out. In our work, we used stratigraphic constraints derived from 93 superficial boreholes whose depth rarely exceeds 30 m. In an area called "La Bandita", located in Palermo Plain (Sicily, Italy), a geophysical survey was performed by means of 55 microtrem-or recordings. Part of these was distributed randomly, while others very close to the available stratigraphic perforations. The reconstruction of the stratigraphy in the studied area has been obtained by a review of the main stratigraphic sequences and by a consequent stratigraphic three-dimensional modelling. HVSR curves have been interpreted taking care the thicknesses of the near surface successions derived by the stratigraphic 3-D model. The results , in terms of vertical profiles of the shear-wave velocity, have been interpolated to obtain a 3D seismic model. This has been used to extract basic information to identify and reconstruct the seismic bed-rock and the main geological boundaries that were not directly identifiable by means of only stratigraphic logs. It results that the bedrock is affected by a fault system that generated adjacent depressions where Quaternary successions deposited.

Determinazione del profilo Vs dall'analisi congiunta delle velocità di gruppo delle componenti Z e R (HoliSurface®) e HVSR: caso studio con commenti

Determination of the Vs profile from the joint analysis of group velocities of the Z and R components (HoliSurface®) and the HVSR: commented case study [in Italian]

Surface Wave (SW) dispersion and Horizontal-to-Vertical Spectral Ratio (HVSR) are known as tools able to provide possibly complementary information useful to depict the vertical shear-wave velocity profile. Their joint analysis might then be able to overcome the limits which inevitably affect such methodologies when they are singularly considered.When a problem involves the optimization (i.e. the inversion) of two or more objectives, the standard practice is represented by a normalized summation able to account for the typically different nature and magnitude of the considered phenomena (thus objective functions). This way, a single cost function is obtained and the optimization problem is performed through standard solvers.This approach is often problematic not only because of the mathematically and physically inelegant summation of quantities with different magnitudes and units of measurements. The critical point is indeed represented by the inaccurate performances necessarily obtained while dealing with problems characterized by several local minima and the impossibility of a rigorous assessment of the goodness and meaning of the final result.In the present paper joint analysis of both synthetic and field SW dispersion curves and HVSR datasets is performed via the Pareto front analysis. Results show the relevance of Pareto's criterion not only as ranking system to proceed in heuristic optimization (Evolutionary Algorithms) but also as a tool able to provide some insights about the characteristics of the analyzed signals and the overall congruency of data interpretation and inversion.Possible asymmetry of the final Pareto front models is discussed in the light of relative non-uniqueness of the two considered objective functions.A tool for retrieving the Vs profile while also evaluating correctness of data interpretation and overall consistency of the analyses.►Joint analysis of surface wave dispersion curves and Horizontal-to-Vertical Spectral Ratio (HVSR) is performed in the framework of a Multi-Objective optimisation scheme based on an evolutionary algorithm. ►Symmetry of the final Pareto front models is a distinctive feature validating overall consistency of the inversion. ►Possible data interpretation errors and/or inadequate modelling criteria are put in evidence by such a (a)symmetry. ►Contribution of body waves to observe HVSR is thus discussed while analyzing a field dataset.

In questo articolo vengono sintetizzati una serie di problemi relativi all'acquisizione ed analisi delle onde di superficie secondo una serie di tecniche (attive e passive) utili a definire le proprietà dispersive del mezzo e poter poi ricavare un modello del sottosuolo in termini di velocità delle onde di taglio (Vs). L'obiettivo è chiarire come dietro ad una nutrita serie di abusati acronimi (MASW, ReMi, ESAC, SPAC, MFA/FTAN, HS, MAAM eccetera) si possano celare significative ambiguità e differenze che solamente un approccio fondato sulla consapevolezza di alcuni snodi teorici può risolvere e superare.
Analogamente, vengono anche ribaditi alcuni aspetti riguardanti il rapporto spettrale H/V (HVSR) e l'analisi di dati di sismica di pozzo (VSP, Vertical Seismic Profiling), troppo spesso utilizzati in modo acritico dando per scontate una serie di assunzioni che la teoria insegna non essere sempre e comunque applicabili.
Viene inoltre puntualizzata la profonda differenza concettuale (e quindi pratica) tra analisi congiunta (pratica puntuale e quantitativa) e integrazione di dati (modalità del tutto qualitativa e approssimativa).

The present study illustrates a series of technical aspects regarding the holistic acquisition and analysis of Rayleigh waves acquired by a single multi-component geophone. Compared with the common multi-channel and multi-offset active and passive methodologies, this approach requires simple and straightforward acquisition procedures and takes advantage of the joint analysis of the group-velocity spectra of both the vertical and radial components together with the Radial-to-Vertical Spectral Ratio (RVSR), i.e. the ratio between the amplitude spectra of the radial and vertical components. In this way we can fully describe the Rayleigh-wave propagation both in terms of velocities (group-velocity spectra) and relative amplitudes (RVSR) and jointly invert the data by means of a three-objective optimization scheme based on the Pareto optimality. Since the group-velocity spectra of the vertical and radial components are analyzed according to the Full Velocity Spectrum (FVS) approach, data inversion is performed without interpreting the velocity spectra in terms of dispersion curves. The results of the described methodology are assessed by considering two case studies and by comparing the retrieved shear-wave velocity profiles with the ones obtained through the analysis of the dispersion retrieved from standard active and passive multi-channel and multi-offset data also considering the Horizontal-to-Vertical Spectral Ratio (HVSR). Eventually, through a synthetic dataset, the effect of significant lateral variations is discussed with respect to the group-velocity spectra and the RVSR and RPM (Rayleigh-wave Particle Motion) curves.

The 2006 Yogyakarta earthquake caused an extensive damage to various areas of Yogyakarta regions. The damage distribution indicates the role of local site effects during the earthquake as the damage extended from Bantul Regency in Yogyakarta Province to Klaten Regency in Central Java. Microzonation based on the damage distribution is then carried out using Horizontal-to-Vertical Spectral Ratio (HVSR) technique. From this technique, amplification factor and predominant frequency can be obtained and then spatially mapped. Inversion can also be conducted to the HVSR curves to infer the geological condition of the study area.