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地震前兆是指地震前出现的与该地震孕育和发生相关联的现象。地震是地壳运动中岩石应力应变不断积累、增加,当其超过岩石破裂强度时所发生的岩体突然破裂。所以,地震的孕育总是伴随有一个应力应变长时期积累的过程,当这个过程中应力强度增长到接近岩石破裂强度时,岩石中出现小的破裂,且其数量和长度随应力的增长而增大,并因此而导致岩石体积变形,于是在地表就能观测到地壳形变。例如,1966年邢台地震前,震区内某水准点的高程变化有明显的震前异常,从1964年底开始,一反其历年来长趋势下降的常态,而以每年100毫米的速度急剧上升,至震前又转为
Earthquake precursors are phenomena that precede earthquakes that are associated with the occurrence and occurrence of the earthquake. Earthquake is the crustal movement of rock stress and strain continue to accumulate, increase, when it exceeds the rock burst strength occurred when the rock burst suddenly. Therefore, the inoculation of an earthquake is always accompanied by a process of accumulation during a long period of stress and strain. When the stress intensity in this process increases to a value close to the rupture strength of the rock, small rupture occurs in the rock and the amount and length of the earthquake increase with increasing stress Large, and as a result rock volume deformation, so the earth’s crust can be observed deformation. For example, before the Xingtai earthquake in 1966, there was a clear pre-earthquake anomaly in elevation at a certain level in the earthquake zone. Since the end of 1964, contrary to the long-standing tendency of its decline over the years, it has risen sharply at a rate of 100 millimeters per year, Reverted to before the earthquake