滇西北程海断裂带主要古地震滑坡及其分布特征的构造解释

位于红河断裂带西北端,滇西北断陷带东侧的程海断裂带第四纪活动显著,沿断裂盆山地貌与高山峡谷地貌发育,地质灾害频发。综合利用目视解译与野外调查,对程海断裂带沿线滑坡调查发现,沿程海断裂带共发育各类滑坡940余个,含巨型滑坡61个、大型滑坡125个、中型滑坡316个、小型滑坡438个。这其中有32个巨型滑坡、61个大型滑坡分布在程海断裂带下盘,距断裂约5 km范围内的断层崖和断层三角面上。它们往往具有规模大、滑动距离远、有高速远程碎屑流为主要特征的动力学特性,属于程海断裂带上地震活动触发的古地震滑坡。对区内主要古地震滑坡的调查发现,大型特别是巨型古地震滑坡,主要集中分布在金官和程海盆地东侧,期纳盆地南部金沙江与程海断裂带交汇处,以及弥渡盆地西部。并且在垂向活动速率最大的程海断裂带北端最为发育,明显受程海断裂带不同段落活动的控制。结合程海断裂带晚新生代活动及青藏高原东南缘地壳变形特征的分析显示,程海断裂带端部更为强烈的活动性、更为频发的地震以及更多的古地震滑坡,是在川滇内弧带顺时针旋转及南汀河断裂、畹町断裂与理塘断裂的走滑拉分共同作用下,滇西北地区发生顺时针旋转变形作用的结果。

Tectonic interpretation of the main paleoseismic landslides and their distribution characteristics in the Chenghai fault zone,Northwest Yunnan

The Chenghai fault zone, located at the northwest end of the Red River fault zone and the east side of the Northwest Yunnan fault depression zone, has significant Quaternary activity. Geological disasters occur frequently along the fault where basin range and high valley landforms are apparant. Based on visual interpretation and field investigations, a total of 940 landslides were found along the Chenghai fault zone, which included 61 giant landslides, 125 large landslides, 316 medium-sized landslides, and 438 small-sized landslides. Among them, 32 giant and 61 large landslides are located on the fault scarps and fault triangles within about 5 km from the footwall of the Chenghai fault zone. These large scale landslides often have long sliding distance, high speed and long-distance debris flow as the main characteristics, and belong to the paleoseismic landslides triggered by earthquakes in the Chenghai fault zone. According to the investigation of the main paleoseismic landslides in this area, these landslides are mainly distributed in the areas east of the Jinguan and Chenghai Basins, south of the Qina Basin at the intersection of the Jinsha River and the Chenghai fault zone, and across the western Midu Basin. They are obviously controlled by the activities of different sections of the Chenghai fault zone. The giant and large paleoseismic landslides are mostly developed at the north end of the Chenghai fault zone where it has the highest vertical activity. According to the analyses of the late Cenozoic activity of the Chenghai fault zone and crustal deformation characteristics of the southeastern margin of the Tibetan Plateau, it is the clockwise rotation of the Northwest Yunnan fault depression zone that led to more intense fault activity and more frequent earthquakes. As a result, more paleoseismic landslides occurred at the end of the Chenghai fault zone. The power of the clockwise rotation of the Northwest Yunnan fault depression zone comes from the clockwise rotation of the Sichuan Yunnan inner arc zone and the strike-slip pull-apart of the Nantinghe, Wanding, and Litang faults.