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  • 1
    Electronic Resource
    Electronic Resource
    A seismic reflection-refraction experiment across the exposed lower crust in Calabria (southern Italy): first results (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 4 (1992), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Exposed crystalline basement of the Serre Mountains in Calabria presents a tilted block of a nearly complete section of the Hercynian continental lower crust (HCLC). In addition to petrological and structural data from surface mapping, and petrophysical data from the laboratory, a seismic reflection-refraction experiment was conducted in May 1990. This consisted of a 40 km long N-S profile crossing the HCLC and of four short transverse profiles, each recorded using 3-component receivers with an 80 m spacing and explosive sources.The reflectivity of the outcropping lower crustal units is lower than theoretically predicted from the observed compositional layering. A low-velocity zone, outcropping in the north, and dipping to the south, marks the contact between the HCLC and the underlying Alpine metamorphic units. Below this zone, the deeper crust appears well-structured by strong and continuous, discrete reflections down to 6.5–8 s t.w.t. (presumably the crust-mantle boundary at 19–24 km depth) with a dominant dip toward the south.Analysis of refracted-wave velocities reveals values systematically lower by up to 30% than laboratory data on rock samples or calculated data from modal analysis. This discrepancy can only partly be explained by the effect of microcracks (10%), the underestimation of the amount of leucosomes (2–5%) and the effect of seismic anisotropy (0–5%). The remaining discrepancy must be attributed to large scale alteration of the rocks due to Apennine tectogenetic events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1992.tb00452.x
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  • 2
    Electronic Resource
    Electronic Resource
    Seismic anisotropy within the uppermost mantle of southern Germany (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: This paper presents an updated interpretation of seismic anisotropy within the uppermost mantle of southern Germany. The dense network of reversed and crossing refraction profiles in this area made it possible to observe almost 900 traveltimes of the Pn phase that could be effectively used in a time-term analysis to determine horizontal velocity distribution immediately below the Moho. For 12 crossing profiles, amplitude ratios of the Pn phase compared to the dominant crustal phase were utilized to resolve azimuthally dependent velocity gradients with depth. A P-wave anisotropy of 3–4 per cent in a horizontal plane immediately below the Moho at a depth of 30 km, increasing to 11 per cent at a depth of 40 km, was determined. For the axis of the highest velocity of about 8.03 km s−1 at a depth of 30 km a direction of N31°F was obtained. The azimuthal dependence of the observed Pn amplitude is explained by an azimuth-dependent sub-Moho velocity gradient decreasing from 0.06 s−1 in the fast direction to 0 s−1 in the slow direction of horizontal P-wave velocity. From the seismic results in this study a petrological model suggesting a change of modal composition and percentage of oriented olivine with depth was derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb06021.x
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  • 3
    Electronic Resource
    Electronic Resource
    A new constraint on the composition of the topmost continental mantle—anomalously different depth increases of P and S velocity (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 103 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Compared to clear crustal P- and S-waves as well as a strong refracted Pn-wave propagating in the topmost mantle (i.e., 10 to 15 km below the Moho), an anomalously weak appearance of the corresponding refracted shear wave Sn is observed on refraction seismic profiles in SW Germany, France, coastal Maine (NE United States) and Fennoscandia. It is possible that the observation of Pn/PMP ratios close to unity combined with small Sn/SMS ratios (i.e., small Sn amplitudes) is typical for the continental uppermost mantle since this was observed for quite different types of continental crust. It is shown that the observed phenomenon is not a source effect. Several possible causes to explain the observations are studied, also with the aid of synthetic seismograms. The effects of temperature, attentuation and anisotropy have been investigated. Their influence cannot explain the observations. The most likely candidate is a depth-increasing VP/VS ratio (an increase in the order of 0.027 over a depth range of 10 km), forcing P- and S-waves to propagate on different paths in the topmost mantle. The observed phenomenon provides new constraints on the change of composition with depth for the crust mantle transition zone with basalt depletion as the most likely explanation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb01787.x
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  • 4
    Electronic Resource
    Electronic Resource
    Massif Central (France): new constraints on the geodynamical evolution from teleseismic tomography (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Massif Central, the most significant geomorphological unit of the Hercynian belt in France, is characterized by graben structures which are part of the European Cenozoic Rift System (ECRIS) and also by distinct volcanic episodes, the most recent dated at 20 Ma to 4000 years BP. In order to study the lithosphere-asthenosphere system beneath this volcanic area, we performed a teleseismic field experiment.During a six-month period, a joint French-German team operated a network of 79 mobile short-period seismic stations in addition to the 14 permanent stations. Inversion of P-wave traveltime residuals of teleseismic events recorded by this dense array yielded a detailed image of the 3-D velocity structure beneath the Massif Central down to 180 km depth. The upper 60 km of the lithosphere displays strong lateral heterogeneities and shows a remarkable correlation between the volcanic provinces and the negative velocity perturbations. The 3-D model reveals two channels of low velocities, interpreted as the remaining thermal signature of magma ascent following large lithospheric fractures inherited from Hercynian time and reactivated during Oligocene times. The teleseismic inversion model yields no indication of a low-velocity zone in the mantle associated with the graben structures proper. The observation of smaller velocity perturbations and a change in the shape of the velocity pattern in the 60–100 km depth range indicates a smooth transition from the lithosphere to the asthenosphere, thus giving an idea of the lithosphere thickness. A broad volume of low velocities having a diameter of about 200 km from 100 km depth to the bottom of the model is present beneath the Massif Central. This body is likely to be the source responsible for the volcanism. It could be interpreted as the top of a plume-type structure which is now in its cooling phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb03509.x
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  • 5
    Electronic Resource
    Electronic Resource
    Wave propagation in a multiple-scattering upper mantle—observations and modelling (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 127 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A striking feature of Russian long-range seismic refraction data from Peaceful Nuclear Explosions is the observation of a high-frequency teleseismic Pn, phase, which travels with a group velocity of 8.0 km s-1 out to distances of several thousands of kilometres. Modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random RMS velocity fluctuations of about ±4 per cent superimposed on a positive velocity gradient. This class of model explains the existence of the teleseismic Pn, its high-frequency content and its coda length. A teleseismic Pn can only be generated if velocity flucluations are strong enough to cause multiple scattering and occur on a subwavelength scale. Cross-correlation properties of P- and S-wave velocity fluctuations exert a substantial influence on the wavefield. A completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb04735.x
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  • 6
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    Data from the 1978-79 Rhenish Massif seismic refraction experiment (2020)
    GFZ Data Services
    Details
    Publication Date: 2020-05-11
    Description: During 1978-79, a seismic refraction experiment was carried out in the Rhenish Massif, West Germany, and adjacent areas, extending through Belgium and Luxembourg into the Paris Basin in France. The experiment was designed to investigate the structure of the crust and uppermost mantle beneath the massif and thus help in a multidisciplinary study, sponsored by the Deutsche Forschungsgemeinschaft, into the causes and mechanisms of uplift of the massif. The Aachen-Baumholder (L1/L2-M1/M2) profile was completed in May and August, 1978. The 600 km long, main profile and the cross profiles, B-K and K-F, were completed in May 1979. During the main experiment in May 1979, 137 recording units of the MARS type from various European countries participated. 20 shots were fired in 1979 and thus a total of 2740 three-component recordings were made.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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