Diffuse elastic wavefield within a simple crustal model. Some consequences for low and high frequencies

Abstract

[1] The reliability of usual assumptions regarding the wavefield composition in applications of the Diffuse Field Approach (DFA) to passive seismic prospecting is investigated. Starting from the more general formulation of the DFA for full wavefield (FW), the contribution of each wave to the horizontal-and vertical-component power spectra at surface are analyzed for a simple elastic waveguide representing the continental crust-upper mantle interface. Special attention is paid to their compositions at low and high frequencies, and the relative powers of each surface wave (SW) type are identified by means of a semianalytical analysis. If body waves are removed from the analysis, the high-frequency horizontal asymptote of the H/V spectral ratio decreases slightly (from 1.33 for FW to around 1.14 for SW) and shows dependence on both the Poisson's ratio of the crust and the S wave velocity contrast (while FW-H/V asymptote depends on the former only). Experimental tests in a local broadband network provide H/V curves compatible with any of these values in the band 0.2-1 Hz, approximately, supporting the applicability of the DFA approximation. Coexistence of multiple SW modes produces distortion in the amplitudes of vertical and radial component Aki's coherences, in comparison with the usual predictions based on fundamental modes. At high frequencies, this effect consists of a decrement by a constant scaling factor, being very remarkable in the radial case. Effects on the tangential coherence are severe, including a À π/4 phase shift, slower decay rate of amplitude versus frequency, and contribution of several velocities for large enough distances.Citation: Garcı´a-Jerez, A., F. Luzo´n, F. J. Sa´nchez-Sesma, E. Lunedei, D. Albarello, M. A. Santoyo, and J. Almendros (2013), Diffuse elastic wavefield within a simple crustal model. Some consequences for low and high frequencies,

Antarctic ice sheet thickness estimation using the horizontal-to-vertical spectral ratio method with single-station seismic ambient noise

“…No strong evidence supports that the peak amplitude indicates the amplification factor of the site and there is some controversy about the nature of the ambient noise wave field and its sources (Sánchez-Sesma et al, 2011). During the past few decades, two research branches have formed to interpret the ambient noise wave field: Rayleigh wave ellipticity (Fäh et al, 2001;Wathelet et al, 2004) and the full wave-field assumptions, including distributed surface sources (DSSs, Lunedei and 798 P. Yan et al: Antarctic ice sheet thickness estimation Albarello, 2009Albarello, , 2010 and diffuse field assumption (DFA, Shapiro and Campillo, 2004;Sánchez-Sesma and Campillo, 2006;Sánchez-Sesma et al, 2011;García-Jerez et al, 2013. To calculate the H / V spectrum, a specialized GEOPSY program was developed by the European SESAME team, and widely used to investigate sediment structures (Bard and SESAME Team, 2005).…”

A Review and Some New Issues on the Theory of the H/V Technique for Ambient Vibrations

“…In this frame, the displacement power can be linked with the source filed power via the Green's function, which, in turn, depends on the subsoil configuration. About the DFA model, very recently García-Jerez et al (2013) have shown some consequence, at low and high frequencies, of its application to a simple crustal model. The most recent development of this model is its application to a case where a lateral variation exists, by Matsushima et al (2014).…”

The inversion of spectral ratio H/V in a layered system using the diffuse field assumption (DFA)

“…One possible approach is to apply Bouchon's (2007) Discrete Wavenumber Method, instead the focus of this research is to isolate the contributions of the various waves. To this end, the expressions obtained by García-Jerez et al (2013;2016) are used. The kernels in the ( , ) domain, where = horizontal (radial) component of the wave vector, are extended to the complex -plane.…”

“…As shown in García-Jerez et al (2013;2016) the expressions of the imaginary part of the Green's function, for the special case when source and receiver coincide at the top of the layered media, can be written in a very compact form. It is clear that the contributions from surface and body waves can be isolated:…”