1979年加州凯奥蒂湖地震序列震源机制分析:美国加州地震比中国大陆地震破裂过程简单的证据

本文详细分析了1979年美国加利福尼亚凯奥蒂湖地震序列在时间和空间之中发展的非常有序的过程.对凯奥蒂湖地震序列,在三种情况下分别做出34次地震的断层面解.分析了美国地质调查局观测报告中地震初动的可信性.论证了伯克利加利福尼亚大学的地壳模型与美国地质调查局的地壳模型对于求断层面解的等效性.与唐山地震序列相比,凯奥蒂湖地震序列表现出4个主要特点:1.震中分布呈规则的狭长条带,与断层的关系密切;2.断层面解中出现的矛盾初动少;3.断层面解之间的一致性好;4.断层面解随时间没有明显的变化.这些都表明,凯奥蒂湖地震序列比唐山地震序列特征简单,前者基本上是沿卡拉维拉斯断层发生的面破裂,而后者却是在一定震源区中发生的体破裂.唐山地震序列的特征在中国大陆是有代表性的.若凯奥蒂湖地震序列的这些特点,在加州也具有代表性,则这两个地震序列的差别,可以作为美国加州地震比中国大陆地震发生环境和发生过程都简单的一个证据.

ANALYSIS OF SOURCE MECHANISMS OF THE 1979 COYOTE LAKE EARTHQUAKE SEQUENCE: EVIDENCE FOR THAT THE RUPTURE PROCESS OF EARTHQUAKES IN CALIFORNIA IS SIMPLER THAN THAT IN CHINESE MAINLAND

A rather orderly development in time and space of the 1979 Coyote Lake, California, earthquake sequence was analyzed in detail. Fault plane solutions （FPS） of 34 earthquakes in the sequence were obtained respectively for three cases. Reliability of first motions in observation report of U. S. Geological Survey （USGS） used in this work was analyzed. Equivalency to extract FPS of the crustal velocity model of Seismographic Station of University of California, Berkeley, and that of USGS was demonstrated. Compared with the 1976 Tangshan earthquake sequence, the Coyote Lake sequence shows four main features:1.The epicenters display a regular narrow belt which is closely related to fault;2.Contradictory first motions appeared in FPS are less;3.There is a good consistency between FPS;4.There is no obvious variation of FPS with time.All these indicate that the features of Coyote Lake sequence are simpler than those of Tangshan sequence. It seems that the Coyote Lake sequence is a planar fracture process occurred along Calaveras fault and the Tangshan sequence is a cubic rupture process occurred in a certain volume. The features of Tangshan earthquake sequence are representative in Chinese Mainland. If the features of Coyote Lake sequence are representative in California, then these differences between the two sequences can be regarded as an evidence for that the occurrence environment and process of earthquakes in California are all simpler than those in Chinese Mainland.