Isostatic compensation on a continental scale: local versus regional mechanisms
Isostatic compensation on a continental scale: local versus regional mechanisms
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DOI：
10.1111/j.1365-246x.1977.tb06927.x
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发表时间：
1977-11
影响因子：
2.8
通讯作者：
R. Banks;R. Parker;S. Huestis
中科院分区：
文献类型：
--
作者：
R. Banks;R. Parker;S. Huestis
摘要利用线性和二次规划技术，可以证明，由刘易斯和多尔曼（1970）计算的美国大陆的均衡响应函数，与任何只涉及地形荷载下的负密度对比的局部补偿模型是不相容的。我们解释需要积极的密度，表明补偿是区域性的，而不是本地的。我们所研究的区域补偿模型将地球的外壳视为漂浮在液体表面上的薄弹性板。这样一个模型的响应可以被反转，以产生在板的绝对密度梯度，提供板的抗弯刚度和地幔和地形之间的密度对比被指定。如果只允许正密度梯度，这样的区域模型适合美国的响应数据提供的板的抗弯刚度位于1021和1022 N m之间。模型的拟合对地幔/载荷密度对比不敏感，但如果模型假设正确，则可以建立密度结构的某些界限。特别是，在深度大于34 km的板块内，最大密度增加不得超过470 kg m−3;这可以被视为莫霍洛维奇不连续面处密度对比的上限。抗弯刚度的允许值对应于5-10 km范围内的板厚，但其他地球物理数据表明深度大于20 km时的变形。我们的结论是，板不可能是完全弹性的，它的有效弹性模量必须比地震测定值小得多。用弹性板模型和地震确定的弹性参数来估计地形荷载在地球上产生的应力差，将是四倍或更多。
Summary. Using the techniques of linear and quadratic programming, it can be shown that the isostatic response function for the continental United States, computed by Lewis & Dorman (1970), is incompatible with any local compensation model that involves only negative density contrasts beneath topographic loads. We interpret the need for positive densities as indicating that compensation is regional rather than local. The regional compensation model that we investigate treats the outer shell of the Earth as a thin elastic plate, floating on the surface of a liquid. The response of such a model can be inverted to yield the absolute density gradient in the plate, provided the flexural rigidity of the plate and the density contrast between mantle and topography are specified. If only positive density gradients are allowed, such a regional model fits the United States response data provided the flexural rigidity of the plate lies between 1021 and 1022 N m. The fit of the model is insensitive to the mantle/ load density contrast, but certain bounds on the density structure can be established if the model is assumed correct. In particular, the maximum density increase within the plate at depths greater than 34 kin must not exceed 470 kg m−3; this can be regarded as an upper bound on the density contrast at the Mohorovicic discontinuity. The permitted values of the flexural rigidity correspond to plate thicknesses in the range 5–10 km, yet deformations at depths greater than 20 km are indicated by other geophysical data. We conclude that the plate cannot be perfectly elastic; its effective elastic moduli must be much smaller than the seismically determined values. Estimates of the stress-differences produced in the earth by topographic loads, that use the elastic plate model, together with seismically determined elastic parameters, will be too large by a factor of four or more.