Abstract: The results of field investigations demonstrate that the 1927 Gulang M 8 earthquake caused six segments of ground ruptures which have different scales, strikes, mechanisms and grades. They composed a complex seismic fracture zone with plane shape distribtuion which is different from ruptures caused by strike slip faulting in western China. Among them four segements of rupture have the coincident locations with the epicentral and aftershock area and are distributed along the north rim of the Dongqingding mountain and the eastern section of the Huangcheng Shuangta fault and the north section of the Wuwei Tianzhu fault, forming the main rupture zone of the earthquake. The other two segments, as the secondary rupture zones are located in the middle section of the Huangcheng Shuangta fault and the Xishanpu Dishuiya fault, respectively. The four segments of the main rupture are the resluts from the uniform tectonic stress field and have consistent deformation mechanism. The Dongqingding extensional rupture zone was developed on the hanging wall of the Xiafangzhai Yanjiaxinzhuang reverse fault as a secondary fracture, while the main rupture was caused by the reverse faulting on the piedmont fluvial terrace.

Key words: Seismic rupture, Active fault, Tectonic stress field, Gangsu

摘要： 野外考察结果表明,1927年古浪8级大地震造成了6段不同规模、不同方向、不同力学成因、不同等级的地表破裂,构成了呈面状分布的复杂地震破裂带,与我国西部地区由走滑断层运动形成的破裂带相比具有较大差异。其中的4段破裂与极震区及余震分布的位置相重合,主体散布在冬青顶北麓一带,沿皇城-双塔活动断裂的东段和武威-天祝活动断裂北段分布,是1927年古浪地震的主破裂带。其余两段分别分布在Ⅸ度区内的皇城-双塔断裂中段和西山堡-滴水崖断裂带上,是高烈度区内的次级破裂。4段主破裂是在统一构造应力场作用下形成的产物,具有统一变形机制。其中冬青顶张性破裂带是发育在山前下方寨-严家新庄逆断层上盘的次级张性破裂,而主破裂是由逆断层运动在寺儿沟滩等处的山前洪积台地上产生的。

关键词: 地震破裂, 活动断裂, 构造应力场, 甘肃