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本文从测震学方法讨论了大震前可能的前兆性地旋问题。得到以下初步结果 1.大地震前人们感到的地旋运,有可能是大震前预位移区内不同位置的小震源准同时发波时存在一定相差的P,SV,与SH波在震中区某点叠加形成旋转运动所致。这种旋转运动在震中区比较明显,由此现象可进行大震位置的预报。 2.未来大震震源断层面上小震源准同时发波表明震源断层面已处于发震的临界状态,因之,如观测到地旋运现象,其大震的发生时间已十分临近,地震震级较大。 3.震源断层面本身的单旋或双旋运动对于减少断层面及其底部的约束是有利的。这可能加速大地震的发生。因此由震源单旋或双旋激发的旋转波到达地表预示着大地震的到来。 如上所述,大震前震中区及其附近出现的地面旋转现象可以作为短临预报指标。
In this paper, we discuss the possible precursory rotation problems before large earthquakes from seismometry. The following preliminary results are obtained: 1. Before earthquakes, people may feel that the earth rotation, which may be caused by the difference of P, SV and SH waves in the small earthquakes with different locations within the pre-displacement area before the earthquake, A point superimposed on the formation of rotary motion. This rotational movement is more obvious in the epicenter area, which can be used to predict the location of large earthquakes. 2. Simultaneous small-source quasi-simultaneous wave propagation on the source fault plane of the future earthquake indicates that the focal fault plane has been in a critical state of earthquake occurrence. Therefore, if the phenomenon of local rotation is observed, the occurrence time of the large earthquake is very near, and the magnitude of the earthquake Larger. 3. The single-phase or double-phase motion of the focal plane itself is advantageous for reducing the constraint of the fault plane and its bottom. This may speed up the earthquake. Therefore, the arrival of the earthquakes by rotating waves excited by the single or double rotation of the source signals the earthquakes. As mentioned above, the ground rotation occurring in and around the epicenter area before a large earthquake can be used as a short-term forecast indicator.