由瑞雷波方向性函数研究1974年5月11日云南省昭通地震的震源过程
A STUDY OF THE FOCAL PROCESS OF THE ZHAO TONG EARTHQUAKE (M=7.l), YUNNAN PROVINCE OF MAY 11, 1974 FROM THE DIRECTIVITY FUNCTION OF RAYLEIGH WAVES
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摘要: 根据国内外100多个地震台的 P 波初动符号资料, 确定了1974年5月11日昭通地震的断层面解.用面波方向性函数和广义的面波方向性函数, 确定走向为 N45°E 的节面是这次地震的断层面, 破裂传播方向是北东向, 破裂速度为1.3公里/秒, 破裂长度为53公里.根据谱密度估算这次地震的地震矩为6.5×1025 达因-厘米.从上述结果, 结合昭通地区的地震活动和区域构造特点, 认为昭通地震是在东西向构造应力场的作用下, 北东向的巧家—莲峰大断裂朝着北东方向继续破裂的结果, 它把中断了的巧家—莲峰大断裂和华鎣山—宜宾大断裂贯通起来.基于上述发震模式, 我们认为, 在同一构造应力场的作用下, 与北东构造共轭的北西向的彝良—水城断裂及峨眉—盐津构造带的地震危险性应予以注意.Abstract: Based on the data of the first P-motion recorded at more than 100 seismographic stations located in China and other parts of the world, the fault plane solution of the Zhao-Tong earthquake of May 11, 1974, Yunnan Province was determined. Using the directivity function and its generalized form of surface waves, the nodal plane striking N45°E has been preferred as the fault plane of this earthquake. The direction of propagation of the fracture is northeast with a velocity of 1.3 km/sec and the total length of the fracture 53 km. The estimation of the seismic moment of this earthquake by spectra density analysis gives a value of 6.5×1025 dyne-cm. From the result thus obtained and in the light of the seismicity and tectonic features of the Zhao-Tong region, it is believed that this earthquake was caused by the action of eastwest tectonic stress field, under which the northeast striking Qiaojia-Lianfeng major fault continued to be fractured toward the northeast, so as to link-up with the Huaying-Yibin major fault by breaking through the gap between them.From the above viewpoint for the model of focal process, we suppose that under the action of the same regional tectonic stress field, the conjugating geological figures, namely, the northwest striking Yiliang-Shuicheng fault and the Emei-Yanjin tectonic structural belt might be seismically dangerous.
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