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151.
Introduction It is found that there are some relationships between the thermal structures of subduction zones and the deep seismicity, while the mechanism relates the thermal structure and the deep seismicity is still unsure (Helffrich, Brodholt, 1991; Furukawa, 1994; Kirby, et al, 1996). From 1980s, geoscientists have constituted a series of numerical simulations on the stress states of subduction slabs. Based on the kinetic computation of Sung and Burns (1976a, b), Goto, et al (1983, 1987… 相似文献
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Shallow seismicity and available source mechanisms in the Andaman–westSunda arc and Andaman sea region suggest distinct variation in stressdistribution pattern both along and across the arc in the overriding plate.Seismotectonic regionalisation indicates that the region could be dividedinto eight broad seismogenic sources of relatively homogeneousdeformation. Crustal deformation rates have been determined for each oneof these sources based on the summation of moment tensors. The analysisshowed that the entire fore arc region is dominated by compressive stresseswith compression in a mean direction of N23°, and the rates ofseismic deformation velocities in this belt decrease northward from 5.2± 0.65 mm/yr near Nias island off Sumatra and 1.12 ±0.13 mm/yr near Great Nicobar islands to as much as 0.4 ±0.04 mm/yr north of 8°N along Andaman–Nicobar islandsregion. The deformation velocities indicate, extension of 0.83 ±0.05 mm/yr along N343° and compression of 0.19 ±0.01 mm/yr along N73° in the Andaman back arc spreadingregion, extension of 0.18 ± 0.01 mm/yr along N125° andcompression of 0.16 ± 0.01 mm/yr along N35° in NicobarDeep and west Andaman fault zone, compression of 0.84 ±0.12 mm/yr N341° and extension of 0.77 ± 0.11 mm/yralong N72° within the transverse tectonic zone in the Andamantrench, N-S compression of 3.19 ± 0.29 mm/yr and an E-Wextension of 1.24 ± 0.11 mm/yr in the Semangko fault zone ofnorth Sumatra. The vertical deformation suggests crustal thinning in theAndaman sea and crustal thickening in the fore arc and Semangko faultzones. The apparent stresses calculated for all major events range between0.1–10 bars and the values increase with increasing seismic moment.However, the apparent stress estimates neither indicate any significantvariation with faulting type nor display any variation across the arc, incontrast to the general observation that the fore arc thrust events showhigher stress levels in the shallow subduction zones. It is inferred that theoblique plate convergence, partial subduction of 90°E Ridge innorth below the Andaman trench and the active back arc spreading are themain contributing factors for the observed stress field within the overridingplate in this region. 相似文献
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Determination of the influence zone for surface wave paths 总被引:6,自引:1,他引:6
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The effect of scattering in surface wave tomography 总被引:6,自引:1,他引:6
Jesper Spetzler Jeannot Trampert Roel Snieder 《Geophysical Journal International》2002,149(3):755-767
159.
Annealing at 400?T?600 °C (40?P?60 MPa and HM buffer-controlled f(O2)) of tourmalines synthesised at the same T and P with NNO buffer induces an oxidation of Fe2+ into Fe3+ in some Y sites only (Mössbauer Spectroscopy data). Annealing in the same conditions of natural tourmalines is consistent with these results. FTIR spectroscopy shows that oxidation of Fe2+ into Fe3+ is charge-balanced by deprotonation of the external OH(3) groups. To cite this article: Y. Fuchs et al., C. R. Geoscience 334 (2002) 245–249. 相似文献
160.