ORCID Profile
0000-0002-0998-4670
Current Organisation
Ecole Normale Supérieure de Lyon
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Publisher: American Geophysical Union (AGU)
Date: 10-2021
DOI: 10.1029/2021JB022322
Abstract: Seismic anisotropy in the Earth's mantle inferred from seismic observations is usually interpreted in terms of intrinsic anisotropy due to crystallographic preferred orientation (CPO) of minerals, or extrinsic anisotropy due to shape preferred orientation (SPO). The coexistence of both contributions confuses the origins of seismic anisotropy observed in tomographic models. It is thus essential to discriminate CPO from SPO. Homogenization/upscaling theory provides means to achieve this goal. It enables computing the effective elastic properties of a heterogeneous medium, as seen by long‐period waves. In this work, we investigate the effects of upscaling an intrinsically anisotropic and heterogeneous mantle. We show analytically in 1‐D that the observed radial anisotropy parameter is approximately the product of the intrinsic and the extrinsic components: This law is verified numerically in the case of a homogenized 2‐D marble cake model of the mantle in the presence of CPO obtained from a micro‐mechanical model of olivine deformation. Our numerical findings predict that for wavelengths smaller than the scale of deformation patterns, tomography may overestimate intrinsic anisotropy due to significant extrinsic anisotropy. At longer wavelengths, intrinsic anisotropy is always underestimated due to spatial averaging. Therefore, we show that it is imperative to homogenize a CPO model first before drawing comparisons with tomographic models. As a demonstration, we use our composite law with a homogenized CPO model of a plate‐driven flow underneath a mid‐ocean ridge, to estimate the SPO contribution to an existing tomographic model of radial anisotropy.
Publisher: Oxford University Press (OUP)
Date: 22-09-2017
DOI: 10.1093/GJI/GGX389
Publisher: Geological Society of America
Date: 2007
DOI: 10.1130/G23240A.1
Publisher: Springer Science and Business Media LLC
Date: 21-10-2020
Publisher: Research Square Platform LLC
Date: 27-06-2023
DOI: 10.21203/RS.3.RS-3071456/V1
Abstract: Subduction zones are home to the world’s largest and deepest earthquakes. Recently, large-scale interactions between shallow (0-60 km) and intermediate (80-150km) seismicity have been evidenced before megathrust earthquakes along with large-scale changes in surface motion. Large-scale deformation transients following major earthquakes have also been observed possibly due to a change in slab pull or to a bending/unbending of the plates, which suggests the existence of interactions between the deep and shallow parts of the slab. In this study, we analyze the spatio-temporal variations of the Japanese seismicity before and after the 2011/3/11 Mw9.0 Tohoku-oki earthquake. We observe that the rate of the intermediate to deep (150-450km) seismicity underwent a deceleration of 55% south of the rupture zone and an acceleration of 30% north of it, coherent with the GPS surface displacements. This shows for the very first time how a megathrust earthquake can affect the stress state of the slab over a 2500 km lateral-range and a large depth range, demonstrating that earthquakes interact at a much greater scale than the surrounding rupture zone usually considered. Our vision of subduction zones must consequently be renewed as a whole, from shallow to large depths.
Publisher: Elsevier BV
Date: 06-2009
Publisher: Springer Science and Business Media LLC
Date: 19-01-2021
No related grants have been discovered for yanick ricard.