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1957年我们研究了1556年陕西关中8级大震前约8小时在震中区两县出现的“地旋”和“地旋运”现象,认为这是一种前震现象。1971年作者和秦保燕再次研究了上述地旋和地旋运的现象,认为它与一般前震的波动不同,可能是一种较缓慢的地面旋转运动,並指出这种现象可能是大震前震源断层面上较大部份弱化並产生预运动所致。本文进一步指出产生地旋和地旋运的原因是由于未来大震震源断层面上不同子源发出的波到达震中区地面后具有不同的振动方向但又相遇在一起互相迭加的结果。要造成这种迭加结果大致有以下三种情况:一个是大震前震源断面上同一部位有异向的缓慢错动(相夹角不大于90度);另一个是两个或两个以上的缓慢错动虽是同一方向但它们相距较远(都位于未来大震的震源断层面上);第三个是只有一个错动但错动面积很大,该面积上不同边界处的错动部份相距较远。以上三种情况发生的波在地表的合成皆会形成明显的旋转运动,其中第三种情况包含第二种情况,它是我们1971年提出的产生地旋和地旋运现象需要较大断层面积上发生预运动的原因。当然也不排除震源地方有单旋和双旋运动在地表产生地旋和地旋运的可能。以上讨论的是临震前的地旋前兆,我们建议设计专门的仪器记录这种缓慢的地面旋转运动。在中长期地震预报方面尚有地块旋转运动的可能。对此我们在1987年曾讨论过。即某些大震是走滑兼块体的旋转。这种现象可由大震在地表造成的错动后果分析出来。即全段是走滑但两个端部地段分别兼有正断层式和逆断层式倾滑成份。1920年海原8.5级大震就是这样的。从力学道理上来说,这是在大区域水平挤压情况下沿断层不同地方其地壳下方有不同的垂直力作用的结果。这种不同的垂直力作用可造成断层盘体的旋转。根据布里季曼(Bridgman)效应,旋转是有利于粘滑错动的,因之它在走滑上的迭加可能对大震的发生具有重要意义。作者建议在野外应寻找与旋转有关的形变指标和新构造运动指标,以利于判定潜在的大震危险区。此可称为剪旋模式。
In 1957, we studied the phenomenon of “spin” and “spin”, which occurred in two counties in the epicenter area about 8 hours before the M8.8 earthquake in Shaanxi Province in 1556, and considered it a foreshock phenomenon. In 1971, the author and Qin Baoyan once again studied the above-mentioned phenomenon of geocentrism and geosynclination, which is considered to be a slower ground rotation movement, which is different from that of a general foreshock. It is pointed out that this phenomenon may be caused by a focal source break The larger part of the level of weakening and pre-movement caused. This paper further points out that the origin of the geostrophic rotation is that the waves from different sub-sources on the source fault plane of the future earthquakes have different vibration directions after reaching the epicenter area, but they meet each other and overlap with each other. To result in such superimposed results generally have the following three cases: one is the source before the earthquake on the same part of the same part of the slow misalignment (phase angle of not more than 90 degrees); the other is two or more Are slowly moving in the same direction but they are far apart (both located on the focal fault plane of future earthquakes); the third is that there is only one misaligned but large displacement area, and the misalignment at different boundaries in the area Part of the distance. The above three cases of waves in the synthesis of the surface will form a significant rotational movement, of which the third case contains the second case, it is our proposed 1971 spin and ground rotation phenomenon requires a larger fault area The reason why pre-exercise occurs. Of course, we do not rule out the possibility of a single-and double-swirling motions occurring in the earth’s surface at the place of rotation and rotation. Discussed above are pre-earthquake precursors, and we recommend designing specialized instruments to record such slow ground motion. In the long-term earthquake prediction there is the possibility of rotating block. We discussed this in 1987. That is, some of the major shocks are slippery and block rotation. This phenomenon can be analyzed by the dislocation of the earthquakes caused by the earthquake. That is, the whole section is a slippery but the two end sections have both normal faulting and reverse faulting. 1920 Haiyuan 8.5 earthquake is like this. From a mechanistic point of view, this is the result of different vertical forces acting beneath the crust along different parts of the fault under horizontal crushing in large areas. This different vertical force can cause the rotation of the fault disk. According to the Bridgman effect, rotation is beneficial to slip-slip, so its superimposition on strike-slip may be of great importance to the occurrence of a large earthquake. The author suggests that in the field, rotation-related deformation indexes and neotectonic movement indexes should be searched to facilitate the determination of potential earthquake-prone areas. This can be called shear mode.