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Five successive geodimeter surveys during a five-year period yield hints as to the manner and rate of crustal extension in the Ethiopian rift valley. The northern geodimeter network traverses an en-echelon offset in the Wonji fault belt at latitude 8°30′N; this belt comprises the youngest volcanism and faulting of the rift floor. The northern network surveys reveal progressive rift extension at mean rates of 3–5 mm/year and strain rates of 6–16 · 10−7/yr, essentially confined within the Wonji fault belt segments. Small longitudinal motions of persistent dextral sense have occurred in the intervening zone between the offset segments. It is too early to say whether these deformations are local, regional or plate-tectonic phenomena, but the present aseismicity of the rift suggests the buildup of regional strain. 相似文献
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Summary. The linearized equation is derived which relates observed long-period seismic waveforms to the aspherical perturbations of a spherically symmetric earth model. This is accomplished by formulating the theory of spectral splitting in the time domain. It is shown to be possible greatly to simplify the resulting equations in a way which makes it apparent that for each modal multiplet the 'scattered' field depends only upon three local functional of earth structure. The effect of regional structural variations may then be quantified in a manner analogous to that assumed in the 'pure path technique', but without making the usual asymptotic approximations. These results are used to investigate the validity of the asymptotic result for the locations of the centroids of spectral peaks in individual recordings, for a regionalized model of the Earth. A technique is suggested for retrieving information about geographical structural variations from low-frequency waveform data. 相似文献
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The results of a kinematical population classification of 497 Hipparcos orbital binaries are discussed. Less than 10% of the
stars from the sample belong to the thick disk. Only seven stars have halo kinematics. There are no direct dynamical mass
determinations for extreme halo stars. Some suggestions, concerning Population II visual binaries for which ground-based astrometric
observations in combination with GAIA data will be useful in the future for the better determination of orbits for long period
Population II binaries, are offered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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