关键词: 喀喇昆仑断裂, 晚第四纪, 断错地貌, 最近强震活动时代

Abstract: Karakorum Fault is a large boundary fault in the Western Tibetan Plateau, which regulates the collision deformation between the Indian plate and the Eurasian plate and plays an important role in the tectonic evolution of the Western Tibetan Plateau. The fault trace in Ngari Prefecture is clear and the faulted landforms are obvious, which show the strong activity characteristics in late Quaternary. At present, the fault activity parameters such as recent strong earthquake active age and recurrence interval are not clear, which greatly limit the accuracy of seismic risk assessment. In this work, we investigated the fault geometry and faulted landforms in Ngari Prefecture, and collected OSL samples of the faulted landforms and sag ponds in Zhaxigang, Menshi and Baga towns. Study shows that the fault can be divided into three sections by Zhaxigang town and Suoduo village, and the structure and property of each section are significantly different. In west Zhaxigang town section, fault moves in the form of almost pure dextral strike slip and the fault trace is almost straight linear. In Zhaxigang town to Suoduo village section, the normal fault movement is remarkable, and the main fault constitutes the boundary fault between Ayilari Mountain and Gar Basin, there are also secondary faults in the basin near the mount with the same or opposite dip as the main fault. The east Suoduo village section is dominated by several dextral strike slip faults, which are nearly parallel in space. According to the OSL dating of sag ponds and faulted landforms, the recent strong earthquake active ages of faults in the west of Zhaxigang town, east of Menshi town and the south of Angwang village is close to 2.34 ka BP, 3.01 ka BP, and 2.54 ka BP respectively. If the faults of above three places are active at the same time, the fault recent strong earthquake active age is close to 2.63 ka BP. The Karakorum Fault in Ngari Prefecture has obvious segmented boundary, and each segment and its internal branch faults are more likely to be active alone. Time since the last strong earthquake activity of Karakorum Fault may be very close to the interval of earthquake recurrence, if the fault is characterized by quasi periodic in-situ recurrence, the fault energy accumulation may has reached a very high degree. The risk of recurrence of strong earthquake events may be very high, more attention should be paid and more detailed research about paleo-earthquake events and recurrence intervals should be carried out as quickly as possible.

Key words: Karakorum Fault, late Quaternary, faulted landform, recent strong earthquake active age