TY  - JOUR
A1  - Wathelet, Marc
A1  - Guillier, B.
A1  - Roux, P.
A1  - Cornou, C.
A1  - Ohrnberger, Matthias
T1  - Rayleigh wave three-component beamforming
BT  - signed ellipticity assessment from high-resolution frequency-wavenumber processing of ambient vibration arrays
JF  - Geophysical journal international
N2  - The variation of Rayleigh ellipticity versus frequency is gaining popularity in site characterization. It becomes a necessary observable to complement dispersion curves when inverting shear wave velocity profiles. Various methods have been proposed so far to extract polarization from ambient vibrations recorded on a single three-component station or with an array of three-component sensors. If only absolute values were recovered 10 yr ago, new array-based techniques were recently proposed with enhanced efficiencies providing also the ellipticity sign. With array processing, higher-order modes are often detected even in the ellipticity domain. We suggest to explore the properties of a high-resolution beamforming where radial and vertical components are explicitly included. If N is the number of three-component sensors, 2N x 2N cross-spectral density matrices are calculated for all presumed directions of propagation. They are built with N radial and N vertical channels. As a first approach, steering vectors are designed to fit with Rayleigh wave properties: the phase shift between radial and vertical components is either -Pi/2 or Pi/2. We show that neglecting the ellipticity tilt due to attenuation has only minor effects on the results. Additionally, we prove analytically that it is possible to retrieve the ellipticity value from the usual maximization of the high-resolution beam power. The method is tested on synthetic data sets and on experimental data. Both are reference sites already analysed by several authors. A detailed comparison with previous results on these cases is provided.
KW  - Fourier analysis
KW  - Time-series analysis
KW  - Site effects
KW  - Surface waves and free oscillations
KW  - Wave propagation
Y1  - 2018
U6  - https://doi.org/10.1093/gji/ggy286
SN  - 0956-540X
SN  - 1365-246X
VL  - 215
IS  - 1
SP  - 507
EP  - 523
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Garofalo, F.
A1  - Foti, S.
A1  - Hollender, F.
A1  - Bard, Pierre-Yves
A1  - Cornou, C.
A1  - Cox, B. R.
A1  - Ohrnberger, Matthias
A1  - Sicilia, D.
A1  - Asten, M.
A1  - Di Giulio, G.
A1  - Forbriger, T.
A1  - Guillier, B.
A1  - Hayashi, K.
A1  - Martin, A.
A1  - Matsushima, Satoru
A1  - Mercerat, D.
A1  - Poggi, V.
A1  - Yamanaka, H.
T1  - InterPACIFIC project: Comparison of invasive and non-invasive methods for seismic site characterization. Part I: Intra-comparison of surface wave methods
JF  - Soil Dynamics and Earthquake Engineering
N2  - The main scope of the InterPACIFIC (Intercomparison of methods for site parameter and velocity profile characterization) project is to assess the reliability of in-hole and surface-wave methods, used for estimating shear wave velocity. Three test-sites with different subsurface conditions were chosen: a soft soil, a stiff soil and a rock outcrop. This paper reports the surface-wave methods results. Specifically 14 teams of expert users analysed the same experimental surface-wave datasets, consisting of both passive and active data. Each team adopted their own strategy to retrieve the dispersion curve and the shear-wave velocity profile at each site. Despite different approaches, the dispersion curves are quite in agreement with each other. Conversely, the shear-wave velocity profiles show a certain variability that increases in correspondence of major stratigraphic interfaces. This larger variability is mainly due to non-uniqueness of the solution and lateral variability. As expected, the observed variability in V-s,V-30 estimatesis small, as solution non-uniqueness plays a limited role. (C) 2015 Elsevier Ltd. All rights reserved.
KW  - Surface-wave methods
KW  - Dispersion curve
KW  - Inversion
KW  - V-s,V-30
KW  - Site characterization
KW  - MASW
KW  - Microtremors
KW  - Rayleigh waves
KW  - Geophysical methods
Y1  - 2016
U6  - https://doi.org/10.1016/j.soildyn.2015.12.010
SN  - 0267-7261
SN  - 1879-341X
VL  - 82
SP  - 222
EP  - 240
PB  - Elsevier
CY  - Oxford
ER  -