Structure of the Moon
Structure of the Moon
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DOI：
10.1029/rg012i004p00539
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发表时间：
1974-11
影响因子：
25.2
通讯作者：
M. Toksöz;A. Dainty;Sean C. Solomon;Kenneth R. Anderson
中科院分区：
文献类型：
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作者：
M. Toksöz;A. Dainty;Sean C. Solomon;Kenneth R. Anderson
分析了阿波罗无源地震台网四个台站的地震资料，得到了月球的速度结构。在月球地震图中观察到的地震能量的长时间反射串可以用近地表区域的散射来解释。地震记录的最早部分对应于体波相位，可以用常规方法解释。在月震图上没有清晰可辨认的分散表面波列。这种缺失可以解释为近地表不均匀性对表面波的散射。对已知撞击时间和位置的人工撞击产生的体波相位进行分析，得到地壳剖面。在认识海区域，地壳厚约60公里，呈层状。在20公里厚的上层，速度梯度很高，微裂纹可能起着重要作用。40公里厚的下层具有几乎恒定的6.8公里/秒的速度。在地壳下面可能存在一个薄的高速层。利用自然撞击和深月震，尝试确定月球地幔中的地震速度。可以提出的地幔最简单的模型是由一个“岩石圈”覆盖在一个“软流圈”上。剪切波在“软流圈”中衰减，这一区域可能部分熔融。没有地震数据与这个模型相矛盾。岩石圈纵波速度的最佳值为8.0 → 8.3 km/s，但这可能是几个不同地区的平均值。月球的密度模型是使用最新的惯性矩（C/MR² = 0.395±0.005）、平均密度以及可能的月球模型的密度对温度和压力的依赖性来计算的。在标准（表面温度，零压力）条件下，月球地幔的平均密度为3.4-3.5 g/cm³。这些值与平均压缩波速度是一致的橄榄石辉石（富橄榄石）月球地幔，但不排除其他成分。在密度模型的基础上，可以对富铁的月核的最大允许半径进行一些限制。如果月球地幔在化学和矿物学上都是均匀的，那么这样一个核心的最大半径对于FeS成分来说大约是700 km，对于纯铁成分来说大约是450 km。目前还没有地球物理数据表明月球是否有富含铁的核心。
Seismic data from the four stations of the Apollo passive seismic network have been analyzed to obtain the velocity structure of the moon. The long reverberating train of seismic energy observed in lunar seismograms may be explained by scattering in a near-surface zone. The earliest parts of the seismogram correspond to body wave phases and may be interpreted by conventional methods. There are no clearly identifiable dispersed surface wave trains present on lunar seismograms. This absence can be explained by scattering of surface waves by near-surface heterogeneities. Analysis of body wave phases from artificial impacts of known impact time and position yields a crustal section. In the Mare Cognitum region the crust is about 60 km thick and is layered. In the 20-km-thick upper layer, velocity gradients are high and microcracks may play an important role. The 40-km-thick lower layer has a nearly constant 6.8-km/s velocity. There may be a thin high-velocity layer present beneath the crust. The determination of seismic velocities in the lunar mantle is attempted by using natural impacts and deep moonquakes. The simplest model that can be proposed for the mantle consists of a ‘lithosphere’ overlying an ‘asthenosphere.’ Shear waves are attenuated in the ‘asthenosphere,’ and this zone may be partially molten. No seismic data contradict this model. The best value for the compressional wave velocity of the lithosphere is 8.0 → 8.3 km/s, but this may be an average over several differing regions. Density models are calculated for the moon by using the latest value for the moment of inertia (C/MR² = 0.395±0.005), mean density, and temperature and pressure dependence of density for likely lunar models. The mean density in the lunar mantle, corrected to standard (surface temperature, zero pressure) conditions, is 3.4–3.5 g/cm³. These values together with the mean compressional wave velocities are consistent with an olivine-pyroxene (olivine-rich) lunar mantle but do not exclude other compositions. On the basis of the density models, some limitations can be placed on the maximum allowable radius of an iron-rich lunar core. If the lunar mantle is chemically and mineralogically homogeneous, the maximum radius of such a core is about 700 km for an FeS composition and about 450 km for pure Fe composition. There are no geophysical data that indicate whether the moon does or does not have an iron-rich core.