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  • 1
    Electronic Resource
    Electronic Resource
    Seismicity and structural complexity of the Dinkelberg block, southern Rhine Graben (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A detailed analysis of the Dinkelberg seismicity is presented. The seismic activity of the central Dinkelberg block starts at about 10 km and increases with depth to a maximum between 18 and 20 km. Joint hypocentre determinations clearly prove that no hypocentres are located within the lower crust which starts at a depth of about 20 km according to results from recent reflection seismic surveys. The seismic activity is concentrated just above the top of the lower crust. Fault-plane solutions of the Dinkelberg events show that the strike of the nodal planes is parallel to the directions of near-surface tectonic features. A correlation also exists between the main fault directions and the spatial distribution of the hypocentres in the Pratteln earthquake cluster at the southern end of the Dinkelberg block. The occurrence of negative P residuals from local earthquakes for special propagation directions of waves crossing the Dinkelberg block is modelled by a westward-dipping layer. This postulated upper crustal structure together with observations of preferred S-wave polarizations are discussed in regard to recent tectonic models and geological findings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb01805.x
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  • 2
    Electronic Resource
    Electronic Resource
    Investigations of Sn and Pn phases in the area of the upper Rhine Graben and northern Switzerland (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 119 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: 22 regional earthquakes in SW Germany and northern Switzerland, recorded with the Southern Black Forest Digital Seismic Network, are studied for Pn and Sn phases. In contrast to the results of some seismic-refraction studies a large number of these earthquake recordings show clearly correlatable Sn phases. So far there are two remarkable trends concerning the appearance or disappearance of Sn:〈list xml:id="l1" style="custom"〉1earthquakes with large focal depths (z= 20–30 km) preferentially show Sn phases.2Earthquakes from the SW with rays crossing the southern Rhine Graben show no Sn energy, regardless of focal depth.To investigate the amplitude behaviour of the Sn phase, synthetic seismograms for varying focal parameters, as well as for different structural parameters (submoho velocity gradient and attenuation of S waves), are calculated using the reflectivity method. The synthetics show that the Sn amplitude is sensitive, especially to the fault-plane orientation and the submoho velocity gradient. After correction for the radiation pattern, the missing of the Sn phase from earthquakes in the south-western part of the studied area seems to be associated with structural effects in the uppermost mantle. A small submoho S-wave gradient or a high upper mantle attenuation are the most likely explanations.Another very interesting observation relates to the Pn velocities. The azimuthal variation of the velocity, as well as the high maximum Pn velocity (v= 8.6–8.8 km s−1) itself, point to an anisotropic uppermost mantle. The velocity variation of 0.6km s−1 and the directions of minimum and maximum velocities are in accordance with earlier results from seismic-refraction experiments and their petrological interpretation.The derived Sn velocities have a mean value of 4.71 km s−1. Up to now the quality and number of the Sn recordings do not allow us to resolve a possible S-wave anisotropy of the uppermost mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb00131.x
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  • 3
    Electronic Resource
    Electronic Resource
    Moment tensor inversion of small earthquakes in southwestern Germany for the fault plane solution (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 101 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The amplitudes of direct P- and S-waves as well as Pn and other deep crustal body-wave phases from events in southwestern Germany are studied for the effects of the double-couple earthquake radiation pattern. The direct P- and S-wave amplitudes for six earthquakes in the southern Black Forest of West Germany with magnitudes between 2.2 and 0.5 were inverted for the source moment tensor, and the double-couple components were extracted from the solutions and refined by a further inversion. The inversion focal mechanisms using both P- and S-wave amplitudes were quite consistent with those found from a large set of first motion readings, even when very different crustal models were used. For the events at or above magnitude 1.4, inversions using only direct P-wave amplitudes also yielded good focal mechanisms. Furthermore, the vertical component record at a station at Pn distance from the largest of the events was successfully synthesized using local mechanisms representative of those found from the inversions. The phases modelled included Pn, PmP and several free-surface reflections. The effect of the earthquake radiation pattern was also noted in the amplitudes of the Pn arrivals of a set of azimuthally distributed stations for two other earthquakes. This study confirms that direct P and S amplitudes can be inverted for the source focal mechanism and suggests that deeper crustal phases, like Pn, PmP, etc., are also affected by the earthquake radiation pattern.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb00763.x
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