溧阳-介休-五原北西地震带强震的破裂特征
ON CERTAIN FEATURES OF RUPTURE OF THE NORTHWESTERLY LIYANG-JIEXIU-WUYUAN STRONG EARTHQUAKE BELT
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摘要: 溧阳——介休——五原北西向地震条带,是唐山地震后华北地区地震活动最为活跃的地带。通过研究发生在这条带上强震的震源机制,破裂过程,震源参数及迁移特点,发现这条带上的较强地震具有以下特点: 1.ML5.0级地震的破裂面走向均为北西向,与条带的总体走向基本一致。反映这些地震具有沿破裂面方向迁移的特点。 2.强震是从中间向北西及南东两个条带的延伸方向交替扩展迁移的,并且强度有逐个增大的趋势。而1980年3月9日在条带上平遥地区发生ML=5.7级地震后,再不具备上述迁移,震级增大的特点。 3.截止现在,均以中强震释放能量。其中多数的主压应力P轴与华北地区统一的主压应力方位基本一致,但仍有几个强震与华北地区总体走向明显不同,说明局部条件的影响在这个带上有时可以起主导作用。Abstract: The Liyang-Jiexu-Wuyuan strong earthquake belt became the most active seismic belt in north China after the 1976 Tangshan great earthquake. By studying the source mechanism, rupture process, source parameters and migration of strong earthquakes occurring on this belt, a few special features can be noticed:(1) Direction of the rupture surfaces of all earthquakes ML5.0 strikes northwest, same as the general strike direction of the belt, showing migration of earthquakes along the direction of rupture.(2) Strong earthquakes migrate usually from the center part of the belt towards both directions of the belt in its northwestern and southeastern elongations. Their magnitudes tend to increase, however, after the Pingyao earthquake of magnitude 5.7 on March 9, 1980, such feature of migration and increase of magnitude no longer appear.(3) Until present, all earthquakes have released their energy by moderate and strong earthquakes. The P axes of tE'e principal compressive stress basically coincide with the direction of the general compressive stress. But a few of them do not, showing local conditions may affect the direction.