共查询到20条相似文献,搜索用时 15 毫秒
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Free-mode surface-wave computations 总被引:8,自引:0,他引:8
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Göran Ekström 《Geophysical Journal International》2006,165(2):668-671
We describe a method of expressing azimuthally anisotropic surface wave velocities on the Earth using a local and smooth spherical-spline parametrization. Anisotropy in the Earth leads to azimuthally varying Love and Rayleigh wave velocities that can be expressed as (cos 2ζ, sin 2ζ) and (cos 4ζ, sin 4ζ) perturbations to the isotropic velocities, where ζ is the direction of surface-wave propagation. The strength of the perturbations varies laterally, and a current goal of seismic tomography is the detailed global mapping of these variations. Several parametrizations have previously been used to describe azimuthally varying velocities. The representation proposed here uses spherical splines and is designed to describe smooth variations in both the strength and geometry of azimuthal anisotropy. The method builds on a simple geometrical approximation for the local azimuth of propagation expressed at the defining spline knot points. It avoids the singularities at the poles that result when azimuthal variations are parametrized using traditional scalar spherical harmonics. Compared with a generalized spherical-harmonic expansion of the tensor fields that represent 2ζ and 4ζ azimuthal variations smoothly on a sphere, the new method offers the advantages of local geographical support and simplicity of implementation. 相似文献
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A first detailed look at the Greenland lithosphere and upper mantle, using Rayleigh wave tomography 总被引:2,自引:1,他引:2
Fiona A. Darbyshire Tine B. Larsen Klaus Mosegaard Trine Dahl-Jensen Ólafur Gudmundsson Torben Bach Søren Gregersen Helle A. Pedersen Winfried Hanka 《Geophysical Journal International》2004,158(1):267-286
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A Maslov-propagator seismogram for weakly anisotropic media 总被引:1,自引:0,他引:1
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A higher order approximation to the wave propagation constants for a cracked solid 总被引:18,自引:0,他引:18
J. A. Hudson 《Geophysical Journal International》1986,87(1):265-274
Summary . Expressions are available in the literature for the propagation constants of a 'mean' wave travelling in a material with a random distribution of cracks. These are approximations for small crack density and crack dimensions small compared with a wavelength. The formulae provided to second order in crack density by the method of smoothing are here extended to the case where the cracks consist of two or more sets, aligned in different directions. 相似文献