Statistical properties of the seismic noise field: influence of soil heterogeneities

Pilz, Marco; Parolai, Stefano

doi:10.1093/gji/ggu273

Cited by 13 publications

(6 citation statements)

References 86 publications

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“…The fact that the intrinsic attenuation is likely to dominate at higher frequencies in all the cases, is also in line with the results of the detrended fluctuation analysis (cf. Pilz & Parolai 2014) which shows mainly ballistic (i.e. less diffusive and less scattering) behaviour for most of the sites (the scattering redistributed energy is anyway correlated in the noise wavefield analysis).…”

Section: Discussionmentioning

confidence: 99%

Shear wave velocity versus quality factor: results from seismic noise recordings

Boxberger¹,

Pilz²,

Parolai

2017

Geophysical Journal International

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S U M M A R YThe assessment of the shear wave velocity (v s ) and shear wave quality factor (Q s ) for the shallow structure below a site is necessary to characterize its site response. In the past, methods based on the analysis of seismic noise have been shown to be very efficient for providing a sufficiently accurate estimation of the v s versus depth at reasonable costs for engineering seismology purposes. In addition, a slight modification of the same method has proved to be able to provide realistic Q s versus depth estimates. In this study, data sets of seismic noise recorded by microarrays of seismic stations in different geological environments of Europe and Central Asia are used to calculate both v s and Q s versus depth profiles. Analogous to the generally adopted approach in seismic hazard assessment for mapping the average shear wave velocity in the uppermost 30 m (v s30 ) as a proxy of the site response, this approach was also applied to the quality factor within the uppermost 30 m (Q s30 ). A slightly inverse correlation between both parameters is found based on a methodological consistent determination for different sites. Consequently, a combined assessment of v s and Q s by seismic noise analysis has the potential to provide a more comprehensive description of the geological structure below a site.

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Section: Discussionmentioning

confidence: 99%

Shear wave velocity versus quality factor: results from seismic noise recordings

Boxberger¹,

Pilz²,

Parolai

2017

Geophysical Journal International

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“…Because H/V is more commonly estimated on noise than on seismic coda, we test is it would be possible to replace for the mode identification the H/V ratio measured on coda by the one measured on noise. Even if equipartition cannot be proved, recent work on the statistical properties of seismic noise shows that, under a wide variety of circumstances, the emergency of Green's function is effective after an adequate averaging process is performed (Pilz & Parolai 2014).…”

Section: Identifying the Dominant Mode Of Surface Waves Using H/v Spectral Ratiosmentioning

confidence: 99%

Identification of surface wave higher modes using a methodology based on seismic noise and coda waves

Rivet¹,

Campillo

Sánchez‐Sesma

et al. 2015

Geophys. J. Int.

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Dispersion analysis of Rayleigh waves is performed to assess the velocity of complex structures such as sedimentary basins. At short periods several modes of the Rayleigh waves are often exited. To perform a reliable inversion of the velocity structure an identification of these modes is thus required. We propose a novel method to identify the modes of surface waves. We use the spectral ratio of the ground velocity for the horizontal components over the vertical component (H/V) measured on seismic coda. We then compare the observed values with the theoretical H/V ratio for velocity models deduced from surface wave dispersion when assuming a particular mode. We first invert the Rayleigh wave measurements retrieved from ambient noise cross-correlation with the assumptions that (1) the fundamental mode and (2) the first overtone are excited. Then we use these different velocity models to predict theoretical spectral ratios of the ground velocity for the horizontal components over the vertical component (H/V). These H/V ratios are computed under the hypothesis of equipartition of a diffuse field in a layered medium. Finally we discriminate between fundamental and higher modes by comparing the theoretical H/V ratio with the H/V ratio measured on seismic coda. In an application, we reconstruct Rayleigh waves from cross-correlations of ambient seismic noise recorded at seven broad-band stations in the Valley of Mexico. For paths within the soft quaternary sediments basin, the maximum energy is observed at velocities higher than expected for the fundamental mode. We identify that the dominant mode is the first higher mode, which suggests the importance of higher modes as the main vectors of energy in such complex structures.

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“…In one such effort, Pilz and Parolai (2014) recently analyzed statistical properties of microtremors as time-evolutionary characteristics of the squared average displacement and found that over very short durations (< 0:1 s) microtremors show a highly correlated (ballistic) nature but that over longer durations (> 1:0 s) they show a weakly correlated nature with diffusive characteristics. They also reported that, at all of their target sites in Tajikistan, they cannot reject the hypothesis of directional isotropy based on the same procedure as in Mulargia and Castellaro (2008) and Mulargia (2012).…”

Section: Introductionmentioning

confidence: 99%

Applicability of Theoretical Horizontal-to-Vertical Ratio of Microtremors Based on the Diffuse Field Concept to Previously Observed Data

Kawase¹,

Matsushima²,

Satoh³

et al. 2015

Bulletin of the Seismological Society of America

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Horizontal-to-vertical spectral ratios of microtremors (MHVRs) have been interpreted as representing either the Rayleigh-wave ellipticity or the amplitude ratio of the sum of Rayleigh and Love waves in a horizontally layered structure. However, based on the recently established diffuse field concept, the theoretical form of MHVR has been proposed to be the square root of the ratio between the imaginary part of the horizontal Green's function on the surface and that of the vertical one. The theory assumes that the energy of a wavefield inside the earth will be equipartitioned among the various states in 3D space. In the case of microtremors, this may occur for randomly applied point-force loadings on the surface after sufficient lapse time to allow multiple scattering. Recent works on diffuse fields suggest that equipartition may arise in several ways, but understanding the emergence of equipartition in realistic settings requires further scrutiny. In the meantime, the resulting formula is quite simple, and its meaning has theoretical support from deterministic exact solutions. As references, we use observed microtremor data from several sites that were reported previously and validate the diffuse field method (DFM) as an alternative method to explain observed MHVR. We use only sites with reliable velocity structures to compare different methods quantitatively. As a result, we found that the DFM solutions with the corresponding 1D layered structures well explain the observed MHVRs for most of the sites. Thus, we believe that MHVR can be used to invert a 1D velocity structure by using DFM as a theoretical tool.

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Statistical properties of the seismic noise field: influence of soil heterogeneities

Cited by 13 publications

References 86 publications

Shear wave velocity versus quality factor: results from seismic noise recordings

Shear wave velocity versus quality factor: results from seismic noise recordings

Identification of surface wave higher modes using a methodology based on seismic noise and coda waves

Applicability of Theoretical Horizontal-to-Vertical Ratio of Microtremors Based on the Diffuse Field Concept to Previously Observed Data

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