A quantitative evaluation of the contribution of crustal rocks to the shear-wave splitting of teleseismic SKS waves

Barruol, Guilhem; Mainprice, David

doi:10.1016/0031-9201(93)90161-2

Cited by 189 publications

(108 citation statements)

References 36 publications

(39 reference statements)

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“…Crustal anisotropy may account for delay times up to 0.2^0.3 s [15,16], consistent with values predicted from rock physics [16]. According to Barruol and Mainprice [17], maximum delay times up to 0.2 s per 10 km of pervasively structured crust might be expected. Major wrench faults in the Ribeira belt are marked by wide (up to 10 km) mylonitic structures with pervasive vertical foliations and subhorizontal lineations [8].…”

Section: Lithospheric Origin Of the Anisotropysupporting

confidence: 67%

Shear wave splitting in SE Brazil: an effect of active or fossil upper mantle flow, or both?

Heintz

Vauchez

Assumpção

et al. 2003

Earth and Planetary Science Letters

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We investigated the structure of the upper mantle beneath southeastern Brazil using teleseismic shear wave splitting measurements. Measurements were performed on seismic data recorded in the Ribeira and Brasilia Neoproterozoic belts, which wrap around the southern termination of the Sa ‹o Francisco craton and disappear westward under the Parana ¤ basin. In the northern Ribeira belt, dominated by thrust tectonics, the fast shear wave polarization planes trend on average N080 ‡E, whereas in the central domain, dominated by strike-slip tectonics, fast shear waves are polarized parallel to the structural trend (N065 ‡E). Stations located above the main transcurrent fault display large delay times ( s 2.5 s). Such values, among the largest in the world, require either an unusually large intrinsic anisotropy frozen within the lithosphere, or a contribution from both the lithospheric and asthenospheric mantle. Within the southern Brasilia belt, fast split shear waves are polarized parallel to the structural trend of the belt, at a high angle from the APM. Although part of our data set strongly favors an origin of anisotropy related to a fabric frozen in the lithospheric mantle since the Neoproterozoic, a contribution of the asthenospheric flow related to the present day plate motion is also required to explain the observed splitting parameters.

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Section: Lithospheric Origin Of the Anisotropysupporting

confidence: 67%

Shear wave splitting in SE Brazil: an effect of active or fossil upper mantle flow, or both?

Heintz

Vauchez

Assumpção

et al. 2003

Earth and Planetary Science Letters

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“…For all stations beneath Germany, we found delay times greater than 1 s. Since it is generally assumed that crustal anisotropy generates delay times only up to 0.4 s (e.g. Barruol & Mainprice 1993), we conclude that the sources of the observed SKS splitting is mainly located in the mantle below the crust.…”

Section: Geodynamic Implicationsmentioning

confidence: 72%

Automated analysis of SKS splitting to infer upper mantle anisotropy beneath Germany using more than 20 yr of GRSN and GRF data

Walther¹,

Plenefisch²,

Rümpker

2013

Geophysical Journal International

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S U M M A R YUpper mantle anisotropy beneath Germany is investigated through the measurements and analysis of shear-wave splitting using SKS phases. We analysed teleseismic events recorded by 24 broadband stations of the German Regional Seismic Network (GRSN) and three broadband stations of the Gräfenberg-Array (GRF). These permanent German networks cover an area extending from the Alps in the south up to the Northern German basin towards north. In comparison to several former studies that are based either on short observation periods or that are restricted to limited areas of Germany, we resort to 22 yr of the GRSN (1991GRSN ( -2012 and 34 yr of GRF data archive . Due to the huge amount of data, we applied a fully automatic procedure to determine SKS splitting parameters from archived recordings and also applied strong quality constraints to obtain reliable solutions. From our analysis, two main features are obvious: For the stations in the middle and southern part of Germany we found homogeneous E-W to ENE-WSW fast-axis directions. In contrast, stations in NE-Germany exhibit a NW-SE oriented fast axis. Both findings can be correlated to major tectonic features in Central Europe. The E-W to ENE-WSW orientations in the middle and southern part of Germany are nearly parallel to the strike of the Variscan mountain belts, whereas the NW-SE direction in NE-Germany corresponds to the orientation of the nearby Tornquist-Teisseyre suture zone. For the southern part of Germany, there are indications for an alignment of the fast axis parallel to the curvature of the nearby Alps. Apart from the more large-scale features there are two stations (BFO and CLZ) which seem to have an imprint related to the regional geodynamic setting, namely the rifting in the Southern Rhine Graben and the formation of the Harz Mountains, respectively. We conclude that the observed regional variations of splitting parameter over Germany advocate for a mostly lithospheric route of the anisotropy. Furthermore, variations of the splitting parameters with respect to the azimuths of the incoming waves, as observed at some stations, point to vertical varying anisotropy. For some stations (BFO, RUE) the inversions for two anisotropic layers revealed directions of the fast axes that are similar to the strike directions of the surrounding tectonic units. For other stations, the confidence regions are too large for a tectonic interpretation.

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“…We summarize in Table 5 the calculated Rc for the various interfaces. The eclogite/crustal rocks interfaces as well Barruol and Mainprice (1993b); as the peridotite/''mean crust'' interface systematically display very high reflection coefficient (higher than 0.1). This strong reflectivity is primarily due to the density contrast between eclogite (density of 3487 kg/ m 3 on average) or peridotite (density of 3310 kg/m 3 ) and the crustal rocks (mean density of 2700 kg/m 3 ).…”

Section: Discussionmentioning

confidence: 99%

EBSD-measured lattice-preferred orientations and seismic properties of eclogites

Bascou¹,

Barruol²,

Vauchez³

et al. 2001

Tectonophysics

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102

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measured lattice-preferred orientations and seismic properties of eclogites. Tectonophysics, Elsevier, 2001, 342, pp.61 -80. <10.1016/S0040-1951 AbstractWe investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities (Alps, Norway, Mali and eastern China) through the analysis of their microstructures and lattice-preferred orientations (LPO). These samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions. Omphacite and garnet LPO were determined from electron backscatter diffraction (EBSD) technique. Garnet appears to be almost randomly oriented whereas omphacite develops strong LPO, characterized by the [001]-axes concentrated sub-parallel to the lineation, and the (010)-poles concentrated sub-perpendicular to the foliation. In order to analyze the deformation mechanisms that produced such omphacite LPO, we compare our observations to LPO simulated by viscoplastic selfconsistent numerical models. A good fit to the measured LPO is obtained for models in which the dominant slip systems are 1/2h110i{110}, [001] {110} and [001] (100). Dominant activation of these slip systems is in agreement with TEM studies of naturally deformed omphacite. Seismic properties of eclogite are calculated by combining the measured LPO and the single crystal elastic constants of omphacite and garnet. Although eclogite seismic anisotropies are very weak (less than 3% for both P-and S-wave), they are generally characterized by a maximum P-wave velocity sub-parallel to the lineation and by a minimum velocity approximately normal to foliation. The mean P-and S-wave velocities are high (respectively, 8.6 and 4.9 km/s). The S-wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation. Calculated reflection coefficients show that an eclogite/crust interface is generally a good reflector (Rc > 0.1), whereas an eclogite body embedded in the upper mantle would be hardly detectable. D

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A quantitative evaluation of the contribution of crustal rocks to the shear-wave splitting of teleseismic SKS waves

Cited by 189 publications

References 36 publications

Shear wave splitting in SE Brazil: an effect of active or fossil upper mantle flow, or both?

Shear wave splitting in SE Brazil: an effect of active or fossil upper mantle flow, or both?

Automated analysis of SKS splitting to infer upper mantle anisotropy beneath Germany using more than 20 yr of GRSN and GRF data

EBSD-measured lattice-preferred orientations and seismic properties of eclogites

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