大华北M≥4(3/4)地震阶段性相对同步活动特征及其意义

大华北M≥4(3/4)地震的纵向活动,除了活动期和活动幕以外,其间还存在一个特征活动时段--活动阶段。一个活动期由三个活动阶段组成:预释放（预破裂）、准释放（准破裂）和大释放（大破裂）阶段。一个活动阶段包括三个以上活动幕。对整个大华北来说,三者均有普遍意义;对大华北内分区分带来说,活动期和活动阶段较有普遍意义,活动幕不具普遍意义。我们称活动阶段的普遍意义为阶段性相对同步活动特征,即对每一活动阶段,各分区分带在此阶段内都将先后发生相应的破坏性地震活动,它对判断大华北地震活动趋势和主要危险区具有重要意义。

THE SIGNIFICANCE AND THE CHARACTER OF THE SYNCHRONOUS STEPS OF M≥4（3/4）EARTHQUAKES IN NORTH CHINA

According to the study of the vertical activity of M ≥ 4（3/4） earthquakes since 300 years. A. D. in north China, "this paper proposes that in an active period there are three active phases: initial release （or fracture） phase, secondary release （or fracture） phase and large release （or fracture） phase. Different phase possesses differne active characters. There results experiment in rock mechanics indicate that these phases do exist when rocks are forced to break. Earthqukes in north China show that these phases occur synchronously. This character of phasicity may be of considerable importance in judging the main dangerous areas and the dangerous trend in a seismological active region.