Breakdown of equipartition in diffuse fields caused by energy leakage

Margerin, Ludovic

doi:10.1140/epjst/e2016-60165-6

Cited by 14 publications

(14 citation statements)

References 43 publications

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“…Margerin (2017) derived an equation to calculate Q l −1 :

Q_{l}^{- 1} = \frac{c}{ω \times l^{*} \times ((), 1 - g) \times τ_{l} ((), H / l^{*})}

where c is the medium velocity, ω is the angular frequency, l ∗ is the mean free path which is the inverse of scattering coefficient ( g ∗ ), g is the anisotropy factor, and τ l is the mean free time which is a function of Moho depth ( H ) normalized by l ∗ . τ l can be approximated using the plot of τ l versus H/l ∗ for rough surfaces provided in Margerin (2017) and g is set to 0 for isotropic scattering. Q l −1 can provide leakage coefficient ( b lk ) as

b_{lk} = Q_{l}^{- 1} \times ω

…”

Section: Methodsmentioning

confidence: 99%

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

Ranjan

Konstantinou

2020

JGR Solid Earth

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We applied sensitivity kernels based on perturbation theory to map the crustal intrinsic and scattering attenuation of S wave envelopes in the southern Aegean. The southern Aegean crust is under extension due to the rollback of the Nubian plate, which is subducting beneath the Aegean plate. The waveforms of 104,531 crustal events (<40 km) were used to calculate S wave envelopes in four frequency bands. The S wave envelopes were modeled using the 3-D isotropic solution of the radiative transfer equation with a factor for energy leakage. A two-stage grid search with linear least squares was applied to estimate the attenuation parameters from each S wave envelope. Then we calculated the 2-D scattering and absorption sensitivity kernels for each wave path based on perturbation theory. These kernels and the envelope attenuation parameters were inverted using the Markov chain Monte Carlo algorithm to obtain maps of intrinsic and scattering attenuation (Q i −1 and Q sc −1). High Q i −1 has thermal origin associated with fluids while high Q sc −1 stems from velocity contrasts caused by deformed structure such as faults, folds, or fractures. The Corinth rift, the Santorini-Amorgos zone, and the Gulf of Gökova show strong extensional deformation, which may produce high Q sc −1. The deformed oceanic material accreted below the continental crust and fractures generated by large thrust earthquakes likely produce high Q sc −1 in Crete. The Corinth rift with its repeated earthquake swarms demonstrates fluid activity, which can explain high Q i −1. Thermal contrasts generated by metamorphic core complexes are a potential source of Q i −1 in Cyclades and Crete. The envelopes of seismograms provide joint estimates of Q sc −1 and Q i −1 in the region surrounding their wave paths. Separate estimates of Q sc −1 and Q i −1 for a half-space model from the envelopes of both early and late coda S waves were first made using multiple lapse time window analysis (MLTWA) (Fehler et al., 1992; ©2020. American Geophysical Union. All Rights Reserved.

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“…Margerin (2017) derived an equation to calculate Q l −1 :

Q_{l}^{- 1} = \frac{c}{ω \times l^{*} \times ((), 1 - g) \times τ_{l} ((), H / l^{*})}

b_{lk} = Q_{l}^{- 1} \times ω

…”

Section: Methodsmentioning

confidence: 99%

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

Ranjan

Konstantinou

2020

JGR Solid Earth

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“…But other studies confirmed analytically or numerically that the P -to-S energy ratio is shifted in the presence of intrinsic attenuation (Margerin et al, 2001;Trégourès and van Tiggelen, 2002a), interfaces (Trégourès and van Tiggelen, 2002a) or sub-surface layering (Margerin et al, 2009). Based on a radiative transfer model for scalar waves in a wavguide geometry, Margerin (2017) shows that the energy flux at the free surface is never isotropic, even at long lapse-time. Hence, while a key concept, the conditions of application of equipartition to seismological data needs to be carefully examined.…”

Section: Introductionmentioning

confidence: 92%

“…Therefore, even without absorption the crustal energy can only decrease over time, a phenomenon called energy leakage (Korn, 1990;Margerin et al, 1998). As shown in Margerin et al (1998) and Margerin (2017), one can distinguish two regimes for leakage. In the case of strong scattering in the crust (l * /H 1), the typical leakage time scales like H 2 /(cl * ) (Margerin et al, 1999;Wegler, 2004).…”

Section: Model Presentation and Important Scale Lengthsmentioning

confidence: 99%

Revisiting Multiple-Scattering Principles in a Crustal Waveguide: Equipartition, Depolarization and Coda Normalization

Heller

Margerin

Sèbe

et al. 2022

Pure Appl. Geophys.

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When comparing different shear dislocation mechanisms, we find that the energy level in the coda can differ by up to 60 percent. While equipartition, depolarization and coda normalization remain fundamental guides to our understanding of the coda, their application requires a good a priori knowledge of the attenuation properties of the crust. Keywordscoda waves • polarized waves • crustal waveguide • radiative transfer • scattering • energy partition • seismic source

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“…Thus, even being presented general interpretations, we do not discard limitations of the techniques and dataset used, neither the methods implemented, which could inhibit a precise identification of underlying processes. Future works should board these issues, including the proper mapping of the multiple scattering, depth-dependence of the seismic scattering, anisotropy, and depth/thickness of the main seismic discontinuities on the thermal estimations (Margerin, 2017;De Siena et al, 2017;Del Pezzo et al, 2018;Sanborn and Cormier, 2018).…”

Section: Uncertainties and Other Considerationsmentioning

confidence: 99%

Estimation of the Thermal Structure Beneath the Volcanic Arc of the Northern Andes by Coda Wave Attenuation Tomography

2019

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In the Northern Andes, the magmatic arc rises from a broad area of active volcanism in the South, at the border between Ecuador and Colombia, to a linear north-directed trend of active and inactive volcanic cones. A ∼240-km-long west-east-striking slab tear (Caldas Tear) located approx. 5.5 • N creates an offset in the volcanic arc. This tear looks like a significant controller of volcanic activity: its quasi-WE structure separates inactive magmatic bodies of late Miocene age or older in the North from Quaternary magmatic activity in the South. Coda wave attenuation tomography applied on seismic waveforms recorded between 1993 and 2018 illuminates the volcanic arc, which appears as a segmented structure derived from the complex process of subduction of the Nazca and Caribbean plates under the South America Continent. The attenuation measurements are transformed into thermal measurement using standard rock physics relationships, supported by thermal estimations and geothermal gradient observations measured in wells. Active and inactive magmatic belts are associated with a range of relatively low temperatures (∼640 to ∼810 • C in the depth range of 25-100 km), which may be a consequence of the fluid content in hydrous minerals. Along the volcanic arc, the isotherms become shallower from South to North and are interrupted by a cold structure; this structure may reflect a lateral change of the mantle viscosity that prevents the continuity of the volcanic arc. Our estimations show an irregular depth-geometry of the isotherms, probably associated with recent slip events that have perturbed the thermal state along the study area. The isotherms also deepen to the West, probably due to the subduction process of the Nazca Plate (∼0-5 • N). In some areas, the isotherms follow a trend similar to that of a thrust fault-related folding geometry, which suggests a recent process of regional perturbation. We hypothesize that the Panama Arc collision at the north and the effect that imprint the Carnegie Ridge against the continent at the South are responsible for these thermal effects. The northern anomaly suggests thickening of the lithospheric system that prevents the development of the volcanic arc at the north of the Caldas Tear.

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Breakdown of equipartition in diffuse fields caused by energy leakage

Cited by 14 publications

References 43 publications

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

Revisiting Multiple-Scattering Principles in a Crustal Waveguide: Equipartition, Depolarization and Coda Normalization

Estimation of the Thermal Structure Beneath the Volcanic Arc of the Northern Andes by Coda Wave Attenuation Tomography

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