ELASTICITY AND CONSTITUTION OF THE EARTH INTERIOR
ELASTICITY AND CONSTITUTION OF THE EARTH INTERIOR
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DOI：
10.1029/jz057i002p00227
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发表时间：
1952-01-01
影响因子：
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通讯作者：
BIRCH, F
中科院分区：
文献类型：
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作者：
BIRCH, F
参考均匀介质中预期的变化来检查观察到的地壳以下地震速度随深度的变化。推导了具有任意温度梯度的均匀引力层中的量变化的一般方程。然后根据固体的实验和理论关系讨论该方程的参数。主要参数是等温不可压缩性随压力的变化率，可以从布里奇曼的测量中找到大压缩情况。比较观测到的和预期的整个地球内部的变化率得出关于均匀性的结论，并在更大的不确定性下得出温度的估计。正如古腾堡所建议的，深度约 100 公里的阴影区可以通过超基性岩石均质层中约 6°/km 的温度梯度来解释。在大约 900 至 2,900 公里的深度之间，地幔看起来基本上是均匀的，并且温度相对均匀，约为数千度。在大约 200 到 900 公里之间，速度上升率对于均匀层来说太大，并且表明成分或相或两者的逐渐变化。需要新的相来解释地幔更深部分（900公里以下）的高弹性，并且建议从大约200至300公里开始，铁镁硅酸盐（可能是密排氧化物）逐渐向高压改性转变，转变在大约800至900公里时完成。地幔上部、过渡层内部及其之上但地壳以下也可能存在氧化铝、石灰和碱的浓度，存在于石榴石和硬玉等高弹性矿物中。过渡层似乎掌握着许多重大地球物理问题的关键。还审查了地核和内核的速度。内核最简单地解释为结晶铁，外部为液态铁，可能与一小部分较轻的元素形成合金。铁在高压下的密度和可压缩性是借助碱金属的实验压缩来估计的；发现中心密度约为 15。讨论了最近关于地壳的其他几个提议。
The observed variation of the seismic velocities with depth, below the crust, is examinedwith reference to the variation to be expected in a homogeneous medium. A general equation is derived for the variation of the quantity,, in a homogeneous gravitating layer with an arbitrary gradient of temperature. The parameters of this equation are then discussed in terms of the experimental and theoretical relations for solids. The principal parameter is, the rate of change of isothermal incompressibility with pressure, which can be found for large compressions from Bridgman's measurements. Comparison of observed and expected rates of variation of ϕ throughout the Earth's interior leads to conclusions regarding homogeneity and, with a larger uncertainty, to estimates of temperature.A shadow zone at a depth of about 100 km, as suggested by Gutenberg, may be accounted for by a gradient of temperature of about 6°/km in a homogeneous layer of ultrabasic rock. Between depths of about 900 and 2,900 km, the mantle appears to be substantially uniform, and at a relatively uniform temperature of the order of several thousand degrees. Between about 200 and 900 km, the rate of rise of velocity is too great for a homogeneous layer, and indicates a gradual change of composition, or of phase, or both. New phases are required to account for the high elasticity of the deeper part of the mantle (below 900 km), and it is suggested that, beginning at about 200 to 300 km, there is a gradual shift toward high‐pressure modifications of the ferro‐magnesian silicates, probably close‐packed oxides, with the transition complete at about 800 to 900 km. There may also be a concentration of alumina, lime, and alkalis toward the upper part of the mantle, in and above the transitional layer but below the crust, existing in minerals of high elasticity such as garnets and jadeites. The transitional layer appears to hold the key to a number of major geophysical problems.The velocities in the core and inner core are also reviewed. The inner core is most simply interpreted as crystalline iron, the outer part as liquid iron, perhaps alloyed with a small fraction of lighter elements. The density and compressibility of iron at high pressures are estimated with the aid of the experimental compressions of the alkali metals; the central density is found to be about 15. Several other recent proposals regarding the crust are discussed.