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Backazimuthal Variations of Splitting Parameters of Teleseismic SKS Phases Observed at the Broadband Stations in Germany (1998)

Brechner, S. ; Klinge, K. ; Krüger, F. ; [et al.]

Springer

Pure and applied geophysics 151 (1998), S. 305-331

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ISSN: 1420-9136

Keywords: Key words: Anisotropy, shear-wave splitting, SKS waves.

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract —SKS phases observed at broadband stations in Germany show significant shear-wave splitting. We have analyzed SKS and SKKS phases for shear-wave splitting from 13 stations of the German Regional Seismic Network (GRSN), from 3 three-component stations of the Gräfenberg array (GRF) and from one Austrian station (SQTA). The data reveal strong differences in the splitting parameters (fast direction φ and delay time δt from a single event at various stations as well as variations at the individual stations for events with different backazimuths. The backazimuthal variations of the splitting parameters at some stations can be explained by two-layer anisotropy models with horizontal symmetry axes. The best resolved two-layer model is the GRA1 model (upper layer φ = 40°, δt = 1.15s; lower layer φ = 115°, δt = 1.95s). The upper layer can be attributed to the lithosphere. Because of the magnitude of the delay time of the upper layer, the lower layer must lie within the asthenosphere. At other stations splitting parameters are consistent with an anisotropic one-layer model for the upper mantle. Stations near the Bohemian Massif show fast directions near EW. Throughout NE Germany the directions are oriented NW/SE. The reason for this direction is probably the nearby Tornquist-Teisseyre line. The observed fast axes are subparallel to this prominent Transeuropean suture zone. At stations in southern Germany near the Alps we observed ENE/WSW directions. Below some stations we also found indications of inclined anisotropic layers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s000240050116

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Faulting style and stress field investigations for swarm earthquakes in NE Baveria/Germany - The transition between Vogtland/NW-Bohemia and the KTB-site (2006)

Seht, M. Ibs-von ; Plenefisch, T. ; Schmedes, E.

Springer

In: Journal of Seismology. 2006; 10(2): 197-211. Published 2006 Mar 15. doi: 10.1007/s10950-005-9008-5.

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Publication Date: 2006-03-15

Description: A seismicity and stress field analysis of a region in NE Bavaria reveals a complex picture of seismic dislocation. The magnitudes are generally low, the strongest event recorded had a magnitude of 2.3. In the southern part of the area investigated, earthquakes occur very rarely. During the observation period of approximately four years, only four events, two of them forming a doublet, were recorded. Hypocentral depths in the southern part are considerably great (15 to 17 km) and indicate a mafic lower crust. The seismicity of the Marktredwitz area, located in the western extension of the Eger rift, is dominated by earthquake swarms that are strongly clustered in space and time. The swarms occurred at depths between 10 and 14 km. Precise relative relocations show clear planar arrangements of the hypocentres and enable to identify the orientation of active fault planes. A comparison of the structural and geomorphological settings reveals major similarities in the occurrence of earthquake swarms compared to the situation in the bordering Vogtland/NW-Bohemia swarm area. Focal mechanisms cover a wide range of faulting styles. Normal fault, strike slip and reverse fault mechanisms as well as movements along sub-horizontal planes were found. The focal mechanisms were used to invert for the stress field. The inversion results reveal an ambiguity for the state of stress in the area of investigation and allow two different interpretations: A clockwise rotation of the stress field from North to South as well as a predominance of two slightly different stress regimes are possibilities. © Springer Science+Business Media, Inc. 2006.

Print ISSN: 1383-4649

Electronic ISSN: 1573-157X

Topics: Geosciences , Physics