Spherically symmetric attenuation within the Earth from normal mode data
Spherically symmetric attenuation within the Earth from normal mode data
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DOI：
10.1111/j.1365-246x.1991.tb05700.x
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发表时间：
2007-04
影响因子：
2.8
通讯作者：
R. Widmer;G. Masters;F. Gilbert
中科院分区：
文献类型：
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作者：
R. Widmer;G. Masters;F. Gilbert
对大地震后自由振荡衰减的总结观测被用来确定地球内部的球对称耗散结构。我们用与频率无关的Q模型模拟了0.3-10 MHz范围内地震能量的本征衰减。我们数据的分辨率表明，Q的简单模型可以解释我们的观测，而我们没有足够的信息来约束详细的吸收带模型。平均剪切Q对地幔的约束相对较好，为250f2%。内核的切变Q主要受新观测到的PKIKP等效模的限制，为110f25%。这比以前的一些模型要低，以前的一些模型使用了可能错误的核心模式观测，尽管新模型预测的衰减仍然太小，无法与PKP的BC和DF分支在大约1赫兹的频率下的强微分衰减的观测相匹配。模式数据集和体波数据集之间的一致性可能不会被期望，因为现在看来PKIKP数据检测到的吸收带与模式数据检测到的吸收带不同。尽管在某些地方需要体积衰减来解释径向模式的衰减，但地球上的体衰减的分布仍然是不受约束的。成功的模型往往会将大量的Q放在上地幔中。
SUMMARY Observations of the attenuation of free oscillations after large earthquakes are used to determine the spherically symmetric dissipative structure within the Earth. We model intrinsic attenuation of seismic energy between 0.3 and 10mHz with a frequency-independent Q model. The resolving power of our data indicates that simple models of Q can explain our observations and that we do not have enough information to constrain detailed absorption band models. The average shear Q is relatively well constrained for the mantle and is 250 f 2 per cent. The shear Q in the inner core is mostly constrained by new observations of PKIKP equivalent modes and is 110 f 25 per cent. This is lower than in some previous models, which have used possibly erroneous observations of core modes, though the new models still predict too little attenuation to match the observations of strong differential attenuation of the BC and DF branches of PKP at frequencies of about 1 Hz. Agreement between the mode and body-wave data sets should probably not be expected since it now seems likely that the PKIKP data sense an absorption band which is distinct from that sensed by the mode data. The distribution of bulk attenuation in the Earth remains ill-constrained though bulk attenuation is required somewhere to explain the attenuation of the radial modes. Successful models tend to put significant bulk Q in the upper mantle.