Abstract: Wanding Fault lies along the border of west Yunnan,China and Myanmar,striking near EW on the west and NE on the east of Bengdong,dipping to N and NW,with a length of 170km. Recent studies show that there are neotectonic landforms along the fault,represented as clear fault facets,straight fault troughs,fault scarps,linear ridges,multi-level waterfalls,and etc. The fault has played an obvious control role in the development of Quaternary basins,such as Wanding,Manhai,Menglianba,Jiucheng and Wandian Basins etc. ,which show a beaded distribution along the fault. The Quaternary faults near the Longzhen bridge and the displacement of the alluvial fans at Gaijiazhai reveal that the Wanding Fault has offset the late Pleistocene deposits with TL age of(17.60±1.49)ka BP to(38.24±3.25)ka BP,indicating that the fault was obviously active in late Quaternary. The Nujiang River extends along the fault in the Bengdong area,the main river course was offset left-laterally about 9.5km,forming a hairpin-like bend. The Gongyanghe River,Zhongshanhe River,Wanmahe River,Manxinhe River,Mengguhe River,Wandinghe River and their tributaries all run along the Wanding Fault,and there are clear evidences that these river segments are partially or entirely dominated by the fault,suggesting that these segments were formed by tracking erosion along the fault fracture zone after the faults latest activity. Synchronous left-lateral displacement of drainage systems was observed at many parts along the Wanding Fault,such as between Pingziting to Gongyanghe,where 11 streams were synchronously displaced left-laterally,and more than 10 streams between Zhongshan to Wanmahe displaced. The displacements can be divided into 5 levels,i.e.40～50m,90～100m,200～250m,300～400m and 600～1100m. Comb-form rivers are developed along the fault. The synchronous left-lateral displacement of drainage systems and the displacement of terraces and alluvial fans suggest that the Wanding Fault was dominated by horizontal left-lateral slip in late Quaternary,with an average rate of 1.7～2.2mm/yr. Several moderate earthquakes occurred along the fault,which are assumed to be the aftershocks of the May 29,1976 Longling M_S7.3 and M_S7.4 earthquakes,e.g.the January 26,1946 Myanmar M_S6.0 earthquake,and the June 1,1976 Anding M_S6.0 earthquake,and the July 4,1976 M_S6.0 earthquake at east of Mengbang,Yunnan,etc. These aftershocks are not distributed in a band-like pattern along the Longling-Ruiling Fault-the seismogenic fault,but concentrated in an area of 55km in length and 32km in width between the Longling-Ruili Fault and the Wanding Fault. So,it is inferred that the extensive distribution of the aftershocks is the result of the successive activities of the Longling-Ruili Fault and Wanding Fault.

Key words: Wanding Fault, late-Quaternary, left-lateral strike-slip, drainage systems displacement, moderate earthquake

摘要： 畹町断裂位于滇西中缅交界地带,蚌冬以西走向近EW,以东走向NE,倾向N和NW,全长170km。最新考察发现,沿断裂新活动的断层地貌明显,表现为清晰的断层三角面、平直的断层槽地、断层陡崖、线性山脊、多级跌水等。断裂对第四纪盆地有着明显的控制作用,畹町、曼海等盆地呈串珠状沿断裂展布。龙镇大桥等地第四纪断层及高家寨洪积扇位错等揭示出畹町断裂切错了晚更新世堆积层,被错堆积层热释光年龄为(17.60±1.49)ka～(38.24±3.25)ka BP,表明断裂在晚第四纪有过明显活动。蚌冬一带怒江沿断裂展布,主河道被左旋位错了约9.5km并形成 "发卡"型拐弯; 公养河等6条河流及其支流均沿断裂发育,局部或整体河段受断裂控制明显,说明这些河段是在断裂新活动后沿断裂破碎带追踪侵蚀形成的。沿断裂多处可见水系同步左旋位错现象,如平子亭-公养河间有11条小溪同步左旋位错,中山-万马河一线有10余条水系表现出同步左旋位错。位错量可分为40～50m、90～100m、200～250m、300～400m和600～1 100m 5个量级; 梳状水系发育。水系左旋位错、阶地及洪积扇等位错现象表明,断裂在晚第四纪以水平左旋走滑为主,滑动速率为1.7～2.2mm/a. 。沿断裂曾发生多次中强地震,被认为是 1976年龙陵7.3、7.4级地震的余震,但它们不是沿发震断层——龙陵-瑞丽断裂呈带状分布,而是集中于龙陵-瑞丽断裂与畹町断裂间南北长55km、东西宽32km的广阔区域。因此,推断这些余震的发生是龙陵-瑞丽断裂与畹町断裂相继活动所致。

关键词: 畹町断裂, 晚第四纪, 左旋走滑, 水系位错, 中强地震