论文部分内容阅读
本文收集了苏联境内数千公里三分向地震台测得的深地震测深剖面。结果表明,通常在井中或在水池中放炮不仅产生P波,而且也产生S波。产生这些波的最有利条件是在震源附近存在尖锐的地震界面,例如基底界面。一般说来,S波场中包括在P波场中见到的所有类型的反射波和折射波。其差别在于剪切波的频率较低,强度稍高,振幅变化较大。记录到S波时,可根据速度比V_P/V_S=γ随深度及横向变化关系获得重要信息,揭示出影响速度关系的三个主要因素:地下深处岩石的破裂程度、岩石的成份及温度。裂缝随深度的增加(震源距增大)而减少使γ值全面下降。由于地壳顶部岩石成份的改变(乌拉尔斯),由基性岩组成的地块中γ值增加。波罗的海和乌克兰地盾的γ值变化不大。在西伯利亚地台,γ值先是随深度的增加而增加从1.71增至1.76,可能是扩容效应;而后γ值下降,在下地壳和上地幔γ值小于1.7。在西伯利亚西部,γ值随深度而增加,在下地壳达1.79,在地幔中稍有下降,但仍高于1.7。这可能在西伯利亚西部下地壳为高温区。在许多地区观测到了由于速度各向异性产生的不同偏振剪切波的分裂。在乌拉尔斯地台的首波(折射波)中和在西伯利亚地台的莫霍界面反射波中发现了这种现象。在这两种情况下,各向异性与地壳有关。在乌克兰和波罗的海地盾,没有记录到SH和SV波的速度差异。
This paper collects the deep seismic sounding profiles measured by the three-point seismographs in the Soviet Union thousands of kilometers away. The results show that it is usually the case that not only the P-wave but also the S-wave is generated in the well or in the tank. The most favorable conditions for generating these waves are the presence of sharp seismic interfaces near the source, such as the basement interface. In general, the S wavefield includes all types of reflected and refracted waves seen in the P wavefield. The difference is that the frequency of shear waves is lower, the intensity is higher, and the amplitude changes more. When S wave is recorded, important information can be obtained according to the relationship between velocity and velocity V_P / V_S = γ with depth and lateral variation. Three main factors that affect velocity are revealed: the degree of rock rupture, the composition and temperature of rock in underground depth. The decrease of fissures with the increase of depth (the increase of focal distance) reduces the value of γ completely. Due to changes in rock composition at the top of the crust (Urals), the value of γ increases in the mass of mafic rocks. The values of γ in the Baltic and Ukrainian shields did not change much. On the Siberian platform, the γ value firstly increases from 1.71 to 1.76 with increasing depth, which may be the dilatancy effect; then, the γ value decreases and the γ value in the lower crust and the upper mantle is less than 1.7. In western Siberia, the value of γ increases with depth, reaching 1.79 in the lower crust and slightly lower in the mantle, but still higher than 1.7. It is possible that the crust is high in the western part of Siberia. The splitting of different polarized shear waves due to velocity anisotropy was observed in many areas. This phenomenon was found in the first wave of the Uralz platform (refracted waves) and in the Moho interface reflected waves on the Siberian platform. In both cases, the anisotropy is related to the crust. In Ukraine and the Baltic Shield, no difference in velocity between SH and SV waves was recorded.