1974年云南省昭通地震破裂机制

1974年5月11日,在云南省昭通地区发生了7.1级地震。震中区位于金沙江下游南岸的山地中。 本文中,作者分析了震区大地测量资料,根据破裂与应变的关系,确立这次地震震源破裂属于逆冲型。依据烈度衰减和余震分布特征建立了矩形滑动断层模式参数,并应用曼辛哈（Mansinha）和斯迈利（smylie）给出的倾斜、有限滑动断层位移场的精确解析表达式,求得平均倾向滑距。结果是:断层走向N6°W,倾向N84°E,倾角60°,断面长20公里,宽30公里;断面顶部距地表深度2.5公里;平均倾向滑距2.8米,地震矩5.4×10²⁶达因·厘米;应力降51巴;释放的应变能下限1.2×10²³尔格。 作者还扼要地讨论了P波节面解和这次地震发生的构造条件,并解释了一些宏观地震现象。

THE RUPTURE MECHANISM OF THE ZHAOTONG EARTHQUAKE OF 1974 IN YUNNAN PROVINCE

On May 11, 1974, an earthquake of magnitude 7.1 occurred in the Zhaotong County, Yunnan Province. The epicenter is located in the mountainous region on the southern bank of lower Jinsha RiverIn this paper, by analyzing the geodetic data in and around the epicentral region, a thrust fault pattern of focal rupture has been established from the rela-tionship between rupture and strain. Based on intensity attenuation and after-shock distribution, we obtain the parameters of a rectangular slip fault model, and by applying the analytical expressions for the displacement field of a finit-slip inclined fault given by Mansiha and Smylie, the average dip-slip dislocation is calculated. The results are as follows: fault strike, N6°W; dip direction N84°B; dip angle, 60°; length of fault plane 20 kms, width 30 kms; depth of the top of the fault, 2.5 kms below the surface; average dislocation of dip-slip, 2.8 m; seismic moment, 5.4 × 10²⁶ dyne · cm; stress drop, 51 bars; lower limit of the strain energy released, 1.2 × 10²³ ergs.The authors also briefly discuss the nodal plane solution based on P waves and the tectonic conditions relating to the occurrence of the earthquake. Finally some macroseismic phenomena are explained.