Papers by Vladislav Babuska
—Systematic variations of the seismic radial anisotropy x to depths of 200–250 km in North Americ... more —Systematic variations of the seismic radial anisotropy x to depths of 200–250 km in North America and Eurasia and their surroundings are related to the age of continental provinces, and typical depth dependences of x R are determined. The relative radial anisotropy x R in the mantle lithosphere of Phanerozoic orogenic belts is characterized by 6 SH \6 SV , with its maximum depth of about 70 km, on the average, while beneath old shields and platforms, it exhibits a maximum deviation from ACY400 model (MONTAGNER and ANDERSON, 1989) at depths of about 100 km with 6 SV ]6 SH signature. An interpretation of the observed seismic anisotropy by the preferred orientation of olivine crystals results in a model of the mantle lithosphere characterized by anisotropic structures plunging steeply beneath old shields and platforms, compared to less inclined anisotropies beneath Phanerozoic regions. This observation supports the idea derived from petrological and geochemical observations that a mode of continental lithosphere generation may have changed throughout earth's history.
Geophysical Journal International, 1984
Summary. Relative travel-time residuals of 224 earthquakes and nuclear explosions at distances fr... more Summary. Relative travel-time residuals of 224 earthquakes and nuclear explosions at distances from 20° to 100° were calculated for 100 European seismic stations using the Jeffreys-Bullen tables. The P residuals were corrected for the Earth's ellipticity, altitude of the stations, as well as the thickness of sediments and crust, taking into consideration the velocities and Moho relief determined by DSS measurements. Other effects than those arising from deep-seated structures in the uppermost mantle beneath the stations were minimized by subtracting the average delays calculated for each event at 15 basic stations, uniformly covering the investigated territory. Spatial variations of these normalized residuals, as large as 2 s, were derived from events in different focal regions. An average residual at each station was calculated from 23 selected groups, compiled from 181 events evenly distributed as to their azimuths and distances. The 3-D inversion of the residuals yielded very much the same picture of the relatively high- and low-velocity provinces for the upper layer of the mantle as compared with the map of average residuals.The map of average residuals mainly reflects variations in the thickness of the lithosphere and its thermal state. Regions of low velocities include the Pannonian Basin and Central Carpathians, the Northern Apennines and the Po Plain, as well as the Rhine Graben, the Rhenish Massif and the North German-Polish Platform. High velocities are observed in the south-western margin of the East European Platform and in three well-defined zones situated in the inner part of the Western Alps, in the eastern part of the Austrian Alps and in the Eastern Carpathians. Besides the effects of inhomogeneities, also anisotropic effects are anticipated. From the spatial diagrams of the residuals, which show a similar pattern within large tectonic provinces, systematic orientations of relatively slow and high-velocity directions are recognized. This suggests the existence of large-scale anisotropic structures in the uppermost mantle which are consistent as to their dips and orientations over several hundred kilometres. They provide new structural information about the geodynamic development of deep continental tectonics.
Terra Nova, 1990
Teleseismic P arrivals at seismological stations are inverted into a model of velocity perturbati... more Teleseismic P arrivals at seismological stations are inverted into a model of velocity perturbations down to a depth of about 470 km. Directionally independent average residuals, computed from steeply inciding waves, are transformed into a model of lithospheric thickness. Both models show a good correspondence with the main tectonic features of the Italian Peninsula. Positive velocity perturbations are observed beneath the Alps and in depths over 200 km also beneath the Po Basin. A high-velocity anomaly of the Tyrrhenian subduction is less pronounced, probably due to a directional dependence of P velocities in the mantle. Negative velocity perturbations indicate several low-velocity regions, e.g. beneath the Northern Apennines, the Sicily region and in the upper 100 km beneath the Po Basin. The amplitudes of velocity perturbations beneath the depth of 200 km are smaller on the average than those in the upper two layers. The whole region is characterized by large undulations of the lithosphere base which reaches depths from less than 60 km to more than 150 km. The most prominent lithospheric root beneath the Alps is a product of the collision between the European and the Adriatic plates while the lithospheric thickening beneath the Calabrian coast is likely to be connected with the eastern wing of the Tyrrhenian subduction. The dramatic changes of lithosphere thickness between the northern and the southern Apenninic arcs and northern Calabria as well as the thinnings at the western closure of the Po Basin, indicate important deep-seated boundaries of lithospheric blocks of autonomous geodynamic development.
Studia Geophysica Et Geodaetica, 1984
В сmamье сmрояmся регuонaльные временa nробегa волн Pn, Pg, Sn u Sg nрuхо¶rt;ящuх в Чешскuŭ мaссu... more В сmamье сmрояmся регuонaльные временa nробегa волн Pn, Pg, Sn u Sg nрuхо¶rt;ящuх в Чешскuŭ мaссuв с северо-восmокa. Покaзaно, чmо ¶rt;о рaссmоянuя в 5° оm эnuценmрa регuонaльныего¶rt;огрaфы ¶rt;aюm более короmкuе временa nробегa nо срaвненuю со сmaн¶rt;aрmнымu u скоросmu рaсnросmрaненuя волн, блuзкuе к скоросmям nолученным uз сmaн¶rt;aрmныхго¶rt;огрaфов. Дaеmся соnосmaвленuе локaльных uзмененuŭ скоросmеŭ рaсnросmрaненuя волн с mекmонuкоŭ Чешского мaссuвa.
Geophysical Journal International, 2007
We present the first results of a high-resolution teleseismic traveltime tomography and seismic a... more We present the first results of a high-resolution teleseismic traveltime tomography and seismic anisotropy study of the lithosphere–asthenosphere system beneath the western Bohemian Massif. The initial high-resolution tomography down to a depth of 250 km did not image any columnar low-velocity anomaly which could be interpreted as a mantle plume anticipated beneath the Eger Rift, similar to recent findings of small plumes beneath the French Massif Central and the Eifel in Germany. Alternatively, we interpret the broad low-velocity anomaly beneath the Eger Rift by an upwelling of the lithosphere–asthenosphere transition. We also map lateral variations of seismic anisotropy of the mantle lithosphere from spatial variations of P-wave delay times and the shear wave splitting. Three major domains characterised by different orientations of seismic anisotropy correspond to the major tectonic units—Saxothuringian, Moldanubian and the Teplá-Barrandian—and their fabrics fit to those found in our previous studies of mantle anisotropy on large European scales.
Tectonophysics, 1992
BabuSka, V. and Plomerovi, J., 1992. The lithosphere in central Europe-seismological and petrolog... more BabuSka, V. and Plomerovi, J., 1992. The lithosphere in central Europe-seismological and petrological aspects. In: R. Freeman and St. Mueller (Editors), The European Geotraverse, Part 8. Tectonophysics, 207: 141-163. the dipping anisotropic structures may represent paleosubductions which retain olivine preferred orientations originating from an ancient oceanic lithosphere. The Variscides of central Europe may thus represent a collision zone characterized by two systems of paleosubductions divergent relative to the suture between the Moldanubicum and the Saxothuringicum.
Pure and Applied Geophysics, 1998
—Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North Americ... more —Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North America and Eurasia and their surroundings are related to the age of continental provinces, and typical depth dependences of ξ R are determined. The relative radial anisotropy ξ R in the mantle lithosphere of Phanerozoic orogenic belts is characterized by ν SH > ν SV , with its maximum depth of about 70 km, on the average, while beneath old shields and platforms, it exhibits a maximum deviation from ACY400 model (Montagner and Anderson, 1989) at depths of about 100 km with ν SV ≥ν SH signature. An interpretation of the observed seismic anisotropy by the preferred orientation of olivine crystals results in a model of the mantle lithosphere characterized by anisotropic structures plunging steeply beneath old shields and platforms, compared to less inclined anisotropies beneath Phanerozoic regions. This observation supports the idea derived from petrological and geochemical observations that a mode of continental lithosphere generation may have changed throughout earth's history.
Physics of The Earth and Planetary Interiors, 1993
Seismological observations (SKS-wave polarizations, systematic P-residual variations, azimuthal d... more Seismological observations (SKS-wave polarizations, systematic P-residual variations, azimuthal dependence of P n- and surface-wave velocities or a dispersion of surface waves) are not consistent with isotropic, if laterally heterogeneous, upper-mantle structure. Therefore, an anisotropy should be considered as an a priori aspect of future large-scale studies of mantle structure. Most studies of anisotropy, however, have assumed horizontal or vertical axes of symmetry, but such orientations cannot explain bipolar patterns of spatial variations of P residuals, which we have observed at many seismological stations. On the basis of the petrophysical properties of real upper-mantle rocks we consider anisotropy formed either by hexagonal or by orthorhombic aggregates composed of olivine, orthopyroxene, and clinopyroxene. Rotations of the aggregates about vertical and horizontal axes allow us to find the three-dimensional orientations of symmetry axes that fit combinations of both P and S seismological observations in Central Europe and in western North America. The orientations with plunging symmetry axes (velocity extremes) seem to be consistent across large, spatially uniform tectonic units and change abruptly at important suture zones.
Tectonophysics, 2002
The alignment of olivine crystals is considered as the dominant source of seismic anisotropy in t... more The alignment of olivine crystals is considered as the dominant source of seismic anisotropy in the subcrustal lithosphere and asthenosphere. Different components of large-scale anisotropy can be traced in depth distributions of the radial and azimuthal anisotropy of surface waves. We propose a global model of the lithosphere -asthenosphere boundary (LAB) as a transition between a 'frozen-in' anisotropy in the lithosphere to anisotropy in the sublithospheric mantle related to the present-day flow. Due to different orientations of velocity maxima in the anisotropic subcrustal lithosphere and the asthenosphere, the velocity contrast related to the LAB can increase in particular directions. Because of their long wavelengths and horizontal propagation, surface waves suffer from poor lateral resolution. However, surface waves with various wavelengths allow us to map gross features of the LAB with a good vertical resolution. We estimate depths to the LAB to be between 200 and 250 km for the Precambrian shields and platforms, around 100 km for the Phanerozoic continental regions and 40 -70 km beneath oceans from the world-wide depth distribution of the radial and azimuthal anisotropy of surface waves. D
Pure and Applied Geophysics, 1998
—We report on results of a passive seismic experiment undertaken to study the 3-D velocity struct... more —We report on results of a passive seismic experiment undertaken to study the 3-D velocity structure and anisotropy of the upper mantle around the contact zone of the Saxothuringicum and Moldanubicum in the western margin of the Bohemian Massif in central Europe. Spatial variations of P-wave velocities and lateral variations of the particle motion of split shear waves over the region monitor changes of structure and anisotropy within the deep lithosphere and the asthenosphere. A joint interpretation of P-residual spheres and shear-wave splitting results in an anisotropic model of the lithosphere with high velocities plunging divergently from the contact of both tectonic units. Lateral variations of the mean residuals are related to a southward thickening of the lithosphere beneath the Moldanubicum.
Studia Geophysica Et Geodaetica, 1984
В сmamье сmрояmся регuонaльные временa nробегa волн Pn, Pg, Sn u Sg nрuхо¶rt;ящuх в Чешскuŭ мaссu... more В сmamье сmрояmся регuонaльные временa nробегa волн Pn, Pg, Sn u Sg nрuхо¶rt;ящuх в Чешскuŭ мaссuв с северо-восmокa. Покaзaно, чmо ¶rt;о рaссmоянuя в 5° оm эnuценmрa регuонaльныего¶rt;огрaфы ¶rt;aюm более короmкuе временa nробегa nо срaвненuю со сmaн¶rt;aрmнымu u скоросmu рaсnросmрaненuя волн, блuзкuе к скоросmям nолученным uз сmaн¶rt;aрmныхго¶rt;огрaфов. Дaеmся соnосmaвленuе локaльных uзмененuŭ скоросmеŭ рaсnросmрaненuя волн с mекmонuкоŭ Чешского мaссuвa.
Tectonophysics, 2002
A passive teleseismic experiment (TOR), traversing the northern part of the Trans-European Suture... more A passive teleseismic experiment (TOR), traversing the northern part of the Trans-European Suture Zone (TESZ) in Germany, Denmark and Sweden, recorded data for tomography of the upper mantle with a lateral resolution of few tens of kilometers as well as for a detailed study of seismic anisotropy. A joint inversion of teleseismic P-residual spheres and shear-wave splitting parameters allows us to retrieve the 3D orientation of dipping anisotropic structures in different domains of the sub-crustal lithosphere. We distinguish three major domains of different large-scale fabric divided by first-order sutures cutting the whole lithosphere thickness. The Baltic Shield north of the Sorgenfrei -Tornquist Zone (STZ) is characterised by lithosphere thickness around 175 km and the anisotropy is modelled by olivine aggregate of hexagonal symmetry with the high-velocity (ac) foliation plane striking NW -SE and dipping to NE. Southward of the STZ, beneath the Norwegian -Danish Basin, the lithosphere thins abruptly to about 75 km. In this domain, between the STZ and the so-called Caledonian Deformation Front (CDF), the anisotropic structures strike NE -SW and the high-velocity (ac) foliation dips to NW. To the south of the CDF, beneath northern Germany, we observe a heterogeneous lithosphere with variable thickness and anisotropic structures with high velocity dipping predominantly to SW. Most of the anisotropy observed at TOR stations can be explained by a preferred olivine orientation frozen in the sub-crustal lithosphere. Beneath northern Germany, a part of the shear-wave splitting is probably caused by a present-day flow in the asthenosphere. D
Tectonophysics, 2001
We have modelled the thickness and large-scale fabric of the subcrustal lithosphere from the vari... more We have modelled the thickness and large-scale fabric of the subcrustal lithosphere from the variations of P-wave delay times and the shear-wave splitting observed at seismological observatories and four mobile stations in central Europe. The Saxothuringian (S) lithosphere is characterized by a total thickness of 90±120 km and by a coherent fabric in its mantle part with olivine (a,c) foliation planes dipping to the north±northwest. The Moldanubian (M) lithosphere is generally thicker Ð 120±140 km, on the average, and characterized by (a,c) foliations dipping to the south. The divergently dipping anisotropic structures may represent remnants of successive paleosubductions of the ancient oceanic lithosphere ªfrozenº in the subcrustal lithosphere of both units a long time before their Variscan collision. The deep S/M contact is marked by a lithosphere thinning to about 80±90 km beneath the S/M surface boundary. Within the subcrustal lithosphere, a complex structure of the transition of both units extends to about 150 km toward the south as indicated by the anisotropic characteristics of body waves. q
Geophysical Journal International, 2007
We present the first results of a high-resolution teleseismic traveltime tomography and seismic a... more We present the first results of a high-resolution teleseismic traveltime tomography and seismic anisotropy study of the lithosphere–asthenosphere system beneath the western Bohemian Massif. The initial high-resolution tomography down to a depth of 250 km did not image any columnar low-velocity anomaly which could be interpreted as a mantle plume anticipated beneath the Eger Rift, similar to recent findings of small plumes beneath the French Massif Central and the Eifel in Germany. Alternatively, we interpret the broad low-velocity anomaly beneath the Eger Rift by an upwelling of the lithosphere–asthenosphere transition. We also map lateral variations of seismic anisotropy of the mantle lithosphere from spatial variations of P-wave delay times and the shear wave splitting. Three major domains characterised by different orientations of seismic anisotropy correspond to the major tectonic units—Saxothuringian, Moldanubian and the Teplá-Barrandian—and their fabrics fit to those found in our previous studies of mantle anisotropy on large European scales.
Geophysical Journal International, 1993
Teleseismic P- and PKP-arrival times recorded by a network of 40 seismic stations deployed along ... more Teleseismic P- and PKP-arrival times recorded by a network of 40 seismic stations deployed along a 300 km profile across the Adamawa Plateau at the northern end of the Volcanic Line in central Cameroon provide constraints on lithospheric thickness and anisotropy within the subcrustal lithosphere. These data indicate a thinned lithosphere beneath the Central African Shear Zone, where seismologically defined asthenosphere upwells from a depth of about 190 km to about 120 km in a relatively narrow belt. Thus it has only a low-amplitude effect on the observed gravity anomalies; the Bouguer gravity high over the Garoua Rift is consistent with crustal thinning beneath it. An abrupt change of the lithospheric thickness beneath the Northern Boundary Fault correlates with both the topographic relief and a distinct change of the orientation of relatively high- and low-velocity directions, which we infer to be due to anisotropy within the subcrustal lithosphere. This fault may represent an important accretionary suture zone dividing lithospheric blocks that originated in different tectonic settings and acquired different, frozen-in anisotropy.
Tectonophysics, 1992
BabuSka, V. and Plomerovi, J., 1992. The lithosphere in central Europe-seismological and petrolog... more BabuSka, V. and Plomerovi, J., 1992. The lithosphere in central Europe-seismological and petrological aspects. In: R. Freeman and St. Mueller (Editors), The European Geotraverse, Part 8. Tectonophysics, 207: 141-163. the dipping anisotropic structures may represent paleosubductions which retain olivine preferred orientations originating from an ancient oceanic lithosphere. The Variscides of central Europe may thus represent a collision zone characterized by two systems of paleosubductions divergent relative to the suture between the Moldanubicum and the Saxothuringicum.
Journal of Geodynamics, 2007
Please cite this article as: Babuška, V., Plomerová, J., Fischer, T., Intraplate seismicity in th... more Please cite this article as: Babuška, V., Plomerová, J., Fischer, T., Intraplate seismicity in the western Bohemian Massif (central Europe): A possible correlation with a paleoplate Abstract Locations of the Eger Rift, Cheb Basin, Quaternary volcanoes, crustal earthquake swarms and exhalation centers of CO 2 and 3 He of mantle origin correlate with the tectonic fabric of the mantle lithosphere modeled from seismic anisotropy. We suggest that positions of the seismic and volcanic phenomena, as well as of the Cenozoic sedimentary basins, correlate with a "triple junction" of three mantle lithospheres distinguished by different orientations of their tectonic fabric consistent within each unit. The three mantle domains most probably belong to the originally separated microcontinents -the Saxothuringian, Teplá-Barrandian and Moldanubian -assembled during the Variscan orogeny. Cenozoic extension reactivated the junction and locally thinned the crust and mantle lithosphere. The rigid part of the crust, characterized by the presence of earthquake foci, decoupled near the junction from the mantle probably during the Variscan. The boundaries (transitions) of three mantle domains provided open pathways for Quaternary volcanism and the ascent of 3 He-and CO 2 -rich fluids released from the asthenosphere. The deepest earthquakes, interpreted as an upper limit of the brittleductile transition in the crust, are shallower above the junction of the mantle blocks (at about 12 km) than above the more stable Saxothuringian mantle lithosphere (at about 20 km), probably due to a higher heat flow and presence of fluids.
Pure and Applied Geophysics, 1998
—Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North Americ... more —Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North America and Eurasia and their surroundings are related to the age of continental provinces, and typical depth dependences of ξ R are determined. The relative radial anisotropy ξ R in the mantle lithosphere of Phanerozoic orogenic belts is characterized by ν SH > ν SV , with its maximum depth of about 70 km, on the average, while beneath old shields and platforms, it exhibits a maximum deviation from ACY400 model (Montagner and Anderson, 1989) at depths of about 100 km with ν SV ≥ν SH signature. An interpretation of the observed seismic anisotropy by the preferred orientation of olivine crystals results in a model of the mantle lithosphere characterized by anisotropic structures plunging steeply beneath old shields and platforms, compared to less inclined anisotropies beneath Phanerozoic regions. This observation supports the idea derived from petrological and geochemical observations that a mode of continental lithosphere generation may have changed throughout earth's history.
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Papers by Vladislav Babuska