Abstract: As the most important fault of Late Pleistocene in the Lhasa area,the Nalinlaka Fault is a left-lateral thrust fault,striking NWW,dipping SSW with a high dip angle,and extending over 33km.According to the studies on the latest strata on the Nalinlaka Fault zone,this fault zone has been obviously active since Late Pleistocene and the movement left behind some geomorphologic phenomena on the earth's surface,especially at the sites of the gully west of Cijiaolin and around Xiecun village.For example,some rivers,ridges and terraces are dislocated,forming beheaded gullies,fault escarps and so on.The horizontal displacements since Late Pleistocene at the above two places are 54～87m and 20～67m,respectively.Based on the studies on the 4 trenches along the fault using progressive constraining method,we conclude that there might have occurred 5 paleoearthquake events along the Nalinlaka Fault since 70ka BP,the ages of each paleoearthquake are 8.53,54.40,<41.23,21.96,and 9.86 ka BP,and the average recurrence interval is 14.67ka.Because of the limits of trenches and earthquake events exposed by each trench,no single trench revealed completely all the 5 events.So,there may be some errors in determining the upper and lower limits of some events in this article.

Key words: active fault, paleoearthquake, Lhasa

摘要： 拉萨地区最主要的一条晚更新世活断层为那林拉卡断裂带,是走向NWW、倾向SSW、高陡倾角的左旋逆走滑断层,全长33km。通过对该断裂带的研究,发现其从晚更新世以来有明显的活动,并在地表保留了断错地貌现象。其中,在次角林西沟及谢村最为明显,断层错断河流、山脊、阶地等地质体,形成断头沟、断层陡坎等断错地貌,并且两处晚更新世以来的水平位错分别为54～87m和20～67m。通过对断裂带上4个探槽的研究,发现距今约7万年以来,沿那林拉卡断裂带可能发生了5次古地震事件,各次事件的大致发生年龄为距今68.53,54.40,<41.23,21.96,9.86ka,事件平均复发间隔为14.67ka。由于探槽有限,并且各探槽揭露出的地震事件有限,没有一个探槽能完全揭露5次事件,因此文中对一些事件上下限年龄的确定存在一定的不确定性。

关键词: 活断层, 古地震, 拉萨