Estimation of the coda quality factor for the Romanian territory

Oancea, Victoria; Bazacliu, Olivia; Mihalache, Georgeta

doi:10.1016/0031-9201(91)90062-m

Cited by 9 publications

(3 citation statements)

References 3 publications

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“…Several extensive studies of Q 0 can be found in the literature (e.g. Singh & Herrmann 1983; Jin & Aki 1988; Oancea, Bazacliu & Mihalache 1991) that show large variations of Q 0 depending on the geological environment.…”

Section: Effect Of a Strong Mean Free Path Contrast On The Codamentioning

confidence: 99%

Radiative transfer and diffusion of waves in a layered medium: new insight into coda Q

Margerin¹,

Campillo

Tiggelen

1998

Geophysical Journal International

141

163

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S U M M A R Y This paper is devoted to the study of the seismic coda in inhomogeneous media exhibiting a discontinuity of physical properties at a given depth, We focus on the problem of a layer overlying a half-space and analyse the precise effect of a contrast of wave velocities and/or scattering strengths between them. In order to model S-codawave envelopes, we solve the Radiative Transfer Equation by the Monte Carlo method, thereby neglecting the polarization (i.e. the acoustic approximation). We pay special attention to the transition towards the diffusion regime. Under the assumption of an almost isotropic intensity field, a Diffusion Equation can be derived from the Radiative Transfer Equation and we accurately determine the boundary conditions associated with our models. Analytical solutions of the Diffusion Equation have been obtained and systematically compared to the numerical solutions of the Radiative Transfer Equation.We identify the domain of validity of the diffusion approximation which provides a simple analytical form for the decay in the late coda.We apply our theoretical investigations to the continental lithosphere. If the scattering strengths of the mantle and the crust are assumed to be of the same order, a velocity contrast at the Moho will-according to our theory-amplify the coda signal, since part of the energy is trapped in the crust. An amplification factor is defined and given explicitly as a function of the reflection coefficients and the velocity contrast at the Moho. The shape of the long time decay is of the algebraic form f(-3/2), like that of a uniform half-space.On the other hand, if the scattering strength of the mantle is small with respect to that of the crust, the decay in the diffusive regime is predicted to be of the form r-I exp (-2nft/ Qa, where Q: is a function of the reflection coefficients at the Moho, the mean free path of waves in the crust, and frequencyf. The coefficient Q;quantifies the rate at which the partially trapped energy leaks from the crust into the mantle. This formula has the same form as that proposed by Aki & Chouet (1975) to fit coda observations, which has since been widely used to deduce the Qc parameter. With realistic model parameters, we find that Q : roughly equals the parameter Qc deduced from observations. This shows that the effect of partial trapping of energy in the crust may be significant. Consequently, seismic albedos of the crust may have been underestimated in previous studies. In our theory, the energy decay of seismic coda waves is determined by the layered structure of the Earth, that is a highly heterogeneous crust overlying a rather homogeneous mantle. Such structure is confirmed by geological and geochemical studies.

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Section: Effect Of a Strong Mean Free Path Contrast On The Codamentioning

confidence: 99%

Radiative transfer and diffusion of waves in a layered medium: new insight into coda Q

Margerin¹,

Campillo

Tiggelen

1998

Geophysical Journal International

141

163

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“…Coda Q studies include Rautian and Khalturin (1978), Roecker et al (1982), Rodriguez et al (1983), Singh and Herrmann (1983), Biswas and Aki (1984), Pulli (1984), Rhea (1984), Jin et al (1985), Del Pezzo et al (1985), Jin and Aki (1988), van Eck (1988), Kvamme and Havskov (1989), Matsumoto and Hasegawa (1989), Baskoutas and Sato (1989), Oancea et al (1991), Tsuruga et al (2003), Giampiccolo et al (2004), and Goutbeek et al (2004).…”

Section: Scattering Observationsmentioning

confidence: 99%

Deep Earth Structure: Seismic Scattering in the Deep Earth

Shearer

2015

Treatise on Geophysics

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“…Coda Q studies include Rautian and Khalturin (1978), Roecker et al (1982), Rodriquez et al (1983), Singh and Herrmann (1983), Biswas and Aki (1984), Pulli (1984), Rhea (1984), Jin et al (1985), Del Pezzo et al (1985), Jin and Aki (1988), van Eck (1988), Kvamme and Havskov (1989), Matsumoto and Hasegawa (1989), Baskoutas and Sato (1989), Oancea et al (1991), Tsuruga et al (2003), Giampiccolo et al (2004), and Goutbeek et al (2004).…”

Section: S Codamentioning

confidence: 99%

Deep Earth Structure – Seismic Scattering in the Deep Earth

Shearer¹

2007

Treatise on Geophysics

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Most seismic analyses of Earth structure rely on observations of the traveltimes and waveforms of direct seismic waves that travel along ray paths determined by Earth's large-scale velocity structure. These observations permit inversions for radially averaged P wave and S wave velocity profiles as well as three-dimensional (3-D) perturbations. However, smaller-scale velocity or density perturbations cause some fraction of the seismic energy to be scattered in other directions, usually arriving following the main phase as incoherent energy over an extended time interval. This later-arriving wavetrain is termed the coda of the direct phase. Given the number of different scattering events and the complexity of the scattered wavefield, it is generally impossible to resolve individual scatterers. Instead, coda-wave observations are modeled using random media theories that predict the average energy in the scattered waves as a function of scattering angle, given the statistical properties of the velocity and density perturbations. In this way, it is possible to characterize Earth's heterogeneity at much smaller scales than can be imaged using tomography or other methods.The fact that direct seismic waves can be observed in the Earth indicates that this scattering must be relatively weak so that a significant fraction of the seismic energy remains in the primary arrivals. In contrast, scattering on the Moon is proportionally much stronger than in the Earth, preventing the easy observation of direct P and S waves at global distances (at least at the recorded frequencies of the available data) and complicating inversions for lunar structure. In addition to facilitating observations of direct arrivals, weak (as opposed to strong) scattering can also simplify modeling by permitting use of single-scattering theory (i.e., the Born approximation). However, it is now clear that accurate modeling of scattering in the lithosphere, and possibly deeper in the mantle as well, requires calculations based on multiple scattering theories. Fortunately, increased computer power makes these calculations computationally feasible.Although both body waves and surface waves exhibit scattering, the emphasis in this review is on observations and modeling of deep-Earth scattering, 695

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Estimation of the coda quality factor for the Romanian territory

Cited by 9 publications

References 3 publications

Radiative transfer and diffusion of waves in a layered medium: new insight into coda Q

Radiative transfer and diffusion of waves in a layered medium: new insight into coda Q

Deep Earth Structure: Seismic Scattering in the Deep Earth

Deep Earth Structure – Seismic Scattering in the Deep Earth

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