Models of seismic anisotropy in the deep continental lithosphere

Babuška, Vladislav; Plomerová, Jaroslava; Šı́lený, Jan

doi:10.1016/0031-9201(93)90154-2

Cited by 135 publications

(57 citation statements)

References 31 publications

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“…This variation could result from a single layer of anisotropy with a dipping fast axis [Chevrot and van der Hilst, 2003], spatially variable anisotropy within the station Fresnel zone [Alsina and Snieder, 1995;Rümpker and Ryberg, 2000], or more complicated anisotropy [Babuška et al, 1993;Saltzer et al, 2000]. This visualization reveals trends in f at several stations (bold) where strong complexity was identified in Figure 4 (shaded circles).…”

Section: Variations As a Function Of Back Azimuthmentioning

confidence: 93%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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[1] East Africa is a tectonically complex region owing to the presence of a rigid craton, paleothrust belts and shear zones, active magmatism and rifting, and possibly even a mantle plume. We present new splitting results of teleseismic shear phases recorded by 21 broadband seismic stations in Tanzania, seven broadband stations in Kenya, and three permanent broadband Global Seismic Network stations in Kenya and Uganda. Inconsistent apparent splitting is observed beneath the craton and along its southern and southeastern flank in Tanzania. Splitting at stations elsewhere in the rifts and orogenic belts is more consistent. We test between different models of anisotropy for stations with inconsistent splitting (single layer with horizontal fast axis, single layer with dipping fast axis, and two layers with horizontal fast axes). However, we show that these more complicated models do not reasonably explain the data. The data are explained better by a laterally (and/or in some places vertically) varying single-layer model with a horizontal fast axis. We arrive at a conceptual model of anisotropy in Tanzania and Kenya that is controlled by (1) active shear along the base of the plate associated with asthenospheric flow beneath and around the moving craton keel, (2) asthenospheric flow from a plume north of central Kenya, (3) fossilized anisotropy in the lithosphere due to past orogenic events, and possibly (4) aligned magma-filled lenses beneath the rifts. Our most robust conclusion is that we can rule out an extension-induced lattice preferred orientation of olivine as a dominant factor, which is surprising given the long history of extension in the region. This indicates that mantle-lithospheric extension in East Africa occurs via dikeintrusion and/or ductile thinning within narrow rift zones and is possibly facilitated by a mechanical lithospheric anisotropy imparted by fossilized north/south structural or mineralogical fabrics.

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Section: Variations As a Function Of Back Azimuthmentioning

confidence: 93%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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“…Models of anisotropic P and/or S velocity have been made for parts of Europe [e.g., Babuska et al, 1993;Bormann et al, 1996], but not with the same spatial resolution and covering the same area as the isotropic velocity models used in this study. Because of the many uncertainties still associated with anisotropic seismic velocity models and because forward modeling of anisotropic seismic velocity (including temperature and pressure effects) still needs further experimental and theoretical developments, the effect of anisotropy will be neglected in this study.…”

Section: Forward Modeling Of Seismic Velocitiesmentioning

confidence: 99%

Shallow mantle temperatures under Europe from P and S wave tomography

Goes¹,

Govers²,

Vacher³

2000

J. Geophys. Res.

532

640

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Abstract. Temperature is one of the key parameters controlling lithospheric and mantle dynamics and rheology. Using recent experimental data on elastic parameters and anelasticity, we obtain models of temperature at 50 to 200 km depth beneath Europe from the global P wave velocity model of Bijwaard et al. [ 1998] and the regional S wave velocity model of Marquering and Snieder [1996]. Forward modeling of seismic velocity allows us to assess the sensitivity of velocity to various parameters. In the depth range of interest, variations in temperature (when below the solidus) yield the largest effects. For a 100øC increase in temperature, a decrease of 0.5-2% in Vp and 0.7-4.5% in Vs is predicted, where the strongest decrease is due to the large effect of anelasticity at high temperature. The effect of composition is expected to give velocity anomalies <1% for the shallow mantle and would therefore be difficult to resolve. At depths >80 km the relative amplitudes of the European Vp and Vs anomalies are consistent with a thermal origin. At shallower depths, variations in crustal thickness and possibly the presence of partial melt appear to have an additional effect, mainly on S wave velocity. In regions where both P and S anomalies are well-resolved, Vp-and Vs-derived thermal models agree well with each other and with temperatures determined from surface heat flow observations. Furthermore, the thermal models are consistent with known tectonics. The inferred temperatures vary significantly, from around 400øC below an average mantle adiabat at 100 km depth under the Russian Platform and a 300øC increase from east to west across the Tornquist-Teisseyre zone to temperatures around the mantle adiabat in the depth range 50-200 km under areas with present surface volcanism. In spite of the uncertainties in the calculation of temperatures due to uncertainties in the experimental elastic parameters and anelasticity and uncertainties associated with tomographic imaging, we find that the tomographic models of the shallow mantle under Europe can yield useful estimates of the thermal structure.

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“…1). The observation of dependence of splitting parameters on azimuth of phase arrival can be interpreted in several ways: as departures of the anisotropy from the simple hexagonally symmetric horizontal axis model commonly used to interpret splitting results, such as plunging symmetry axis [38], as two superposed layers of anisotropy [32], or as lateral variability of anisotropy at sublithospheric depths [39]. Because the data at TKK are limited to arrivals from only two narrow back-azimuth ranges, it is impossible to determine which, if any, of these possibilities is valid.…”

Section: Discussion Of Splitting Resultsmentioning

confidence: 99%

Evidence for a rheologically strong chemical mantle root beneath the Ontong–Java Plateau

Klosko

Russo

Okal

et al. 2001

Earth and Planetary Science Letters

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Shear wave splitting measurements, in conjunction with studies of shear wave velocity structure, indicate that the Ontong^Java Plateau (OJP) large igneous province (LIP) has a thick, compositionally distinct root that diverts asthenospheric mantle flow beneath the Pacific plate. The OJP, the largest of Earth's LIPs, stands 2 km above adjacent Pacific abyssal plains and is composed of mantle plume derived volcanics erupted at 122 and 90 Ma. Surface wave tomography of the Plateau reveals a seismically slow upper mantle root that extends approximately to 300 km depth. The thickness and juxtaposition of the Plateau and the mantle root imply that the OJP is the preserved`head' of a rising mantle plume formed in situ when the LIP erupted. Thus, it is a far-traveled body currently moving northwestwards with the Pacific plate. Shear wave splitting at four seismic stations along the northern margin of the OJP varies systematically: the fast axis of seismic anisotropy at three stations on the NE OJP margin trend NW, parallel to hotspot-defined Pacific absolute plate motion; at a fourth station, on the NW margin of the Plateau, the fast shear wave trend is NE. Upper mantle flow directions delineated by the shear wave splitting could thus represent mantle flow diverted around the leading, northwestern face of the rheologically strong, chemically distinct OJP root. In sum, the Plateau and its deep root appear to be similar to continental tectosphere, except for contrasting seismic velocities. ß

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Models of seismic anisotropy in the deep continental lithosphere

Cited by 135 publications

References 31 publications

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

Shallow mantle temperatures under Europe from P and S wave tomography

Evidence for a rheologically strong chemical mantle root beneath the Ontong–Java Plateau

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