Velocity variations in the upper mantle beneath central Europe and the East European platform

Hurtig, E.; Grässl, S.; Oesberg, R. P.

doi:10.1016/0040-1951(79)90027-1

Cited by 20 publications

(2 citation statements)

References 16 publications

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“…A number of studies have shown that upper-mantle shear-wave seismic velocities beneath the Precambrian EEP are between 7 and 12 per cent higher than those beneath central and western Phanerozoic Europe (e.g. Hurtig et al 1979;Snieder 1988;Spakman et at. 1993;Zielhuis & Nolet 1994;Lomax & Snieder 1995;Marquering & Snieder 1995).…”

Section: Why Refractions?mentioning

confidence: 99%

Constraints on the velocity structure beneath the Tornquist-Teisseyre Zone from beam-forming analysis

Alsina

Snieder

1996

Geophysical Journal International

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S U M M A R YThe primary indicators of lateral heterogeneity in the Earth are the slowness and azimuth of incoming seismic signals. On a regional scale, surface waves in the upper mantle and crust are often scattered and/or refracted, which results in deviations from the great-circle azimuth. The slowness and direction of propagation of an arriving wave packet provides information about the lateral heterogeneity, and can be measured by performing beam-forming on the recordings across an array of stations. The azimuthal deviation gives a constraint on the transverse velocity gradient along the path. In addition, its frequency dependence gives information on the depth dependence of the heterogeneity.We have performed beam-forming of fundamental-mode Rayleigh waves in the period range of 20 to 100 s travelling from the south-east of Europe to the NARS-NL array in the Netherlands. The purpose of this study is to obtain new information about the velocity structure beneath the Tornquist-Teisseyre Zone (TTZ). The TTZ is known to be a transition between the higher seismic velocities in the thicker and older Precambrian crust of the East European Platform (EEP), and the lower velocities in the thinner and younger Palaeozioc crust of central and western Europe (tectonic Europe, TE). However, the lateral velocity gradient and the depth extent of this transition are not very well constrained. We have used events located at both sides of the TTZ, and both the direct Rayleigh wave and its coda have been analysed. On the one hand, the deviation of the wave-propagation paths relative to the great circle observed in the direct wave for the events on the eastern side of the TTZ confirms earlier results, i.e. it gives independent evidence for a thicker crust and up to 10 per cent higher velocities in the first 150 km of the upper mantle beneath the EEP than beneath the TE. Such a contrast also explains observed surface head waves refracted along the TTZ. On the other hand, no energy reflected at the TTZ is detected in the coda for the events on the western side. From synthetic experiments based on a linearized theory, we conclude that, from this absence of reflections, no lower bound can be imposed on the width of the transition zone across the TTZ at different depths. Source mechanisms other than the ones for the events used are needed to observe these reflections at different depths, for both a sharp and a smooth transition.

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Section: Why Refractions?mentioning

confidence: 99%

Constraints on the velocity structure beneath the Tornquist-Teisseyre Zone from beam-forming analysis

Alsina

Snieder

1996

Geophysical Journal International

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“…Body and surface wave studies have indicated a contrast of up to 10% in S wave velocity at the top of the mantle across the TTZ, with higher velocities under the EEP [Snieder, 1988;Zielhuis and Nolet, 1994]. Body wave studies also indicate increased P wave velocity under the EEP [Hurtig et al, 1979;Spakmart et al, 1993].…”

Section: Application To Group Velocity Dispersionmentioning

confidence: 99%

Finding sets of acceptable solutions with a genetic algorithm with application to surface wave group dispersion in Europe

Lomax

Snieder

1994

Geophysical Research Letters

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We discuss the use of a genetic algorithm (GA) to invert data for many acceptable solutions, in contrast to inversion for a single, “optimum” solution. The GA is a directed search method which does not need linearization of the forward problem or a starting model, and it can be applied with a very large model‐space. Consequently, fewer assumptions are required and a greater range of solutions is examined than with many other inversion methods. We apply the GA to fundamental Rayleigh group dispersion estimates for paths across Central Europe and across the East European Platform to determine “average”, layered S velocity models separately for each region. The use of the GA allows an identical model parameterization and broad parameter search range to be used for both regions. The scatter of acceptable solutions shows velocity‐depth trade‐offs around the Moho, indicates the depth resolution of the inversion, and shows the uncertainty in upper mantle, S velocity estimates. The results indicate that a thicker crust and up to 0.3 km/sec (7%) higher S wave velocities in the upper 100 km of the mantle under the older East European Platform than under Central Europe explain most of the differences in the data sets.

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Upper mantle heterogeneity in the northern part of Eurasia

Павленкова

Yegorkin²

1983

Physics of the Earth and Planetary Interiors

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Velocity variations in the upper mantle beneath central Europe and the East European platform

Cited by 20 publications

References 16 publications

Constraints on the velocity structure beneath the Tornquist-Teisseyre Zone from beam-forming analysis

Constraints on the velocity structure beneath the Tornquist-Teisseyre Zone from beam-forming analysis

Finding sets of acceptable solutions with a genetic algorithm with application to surface wave group dispersion in Europe

Upper mantle heterogeneity in the northern part of Eurasia

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