龙陵地区大地震前后平均应力轴取向的时间变化

本文根据区域台网的观测资料,研究了云南省龙陵地区1971年至1980年的小震平均节面解的变化特点。结果表明:1.1971年2月至1975年11月,平均节面解的P轴方位同北东-南西向的区域应力场一致;2.大震前半年和大震后两天的P轴方位变为340°和176°,同主震的P轴相一致;3.强余震前的小震平均节面解同强余震的节面解相似;4.1977年至1980年3月,P波初动符号的矛盾比上升到30％以上,在此期间本区未发生5级以上的地震。最后讨论了本文所得的结果及其前兆意义。

THE TEMPORAL VARIATION OF THE ORIENTATION OF THE MEAN STRESS AXIS BOTH BEFORE AND AFTER THE STRONG LONGLING EARTHQUAKE

The temporal variation of the mean nodal plane solution of small earthquakes occurred in Longling region, Yunnan Province from 1971 to 1980 is studied in this paper based on the data obtained by the regional seismic networks. The results are as follows: 1) The P-axis azimuth of the mean nodal plane solution is similar to the regional stress field from Feb. 1971 to Nov. 1975; 2) About 6 months prior to the main shock up to two days after the shock, the P-axis azimuth changed to 340° and 176°, this was just the same with the P-axis of the main shock; 3) The mean nodal plane solution of small earthquakes before the strong aftershock is similar to that of the aftershock; 4) From 1977 to March, 1980, the contradictory ratio rose to more than 30%. No earthquake of magnitude 5 or above occurred in that region during this period. Finally, the precursory significance of the result obtained in this paper is also discussed.