Abstract: Kalpin thrust tectonic system is an important part of foreland thrust tectonic of the south Tianshan. This paper tries to discuss paleoearthuakes along the east section of the range front fault of Kalpintag during late Quaternary by doing field investigation along the fault, measuring geomorphic deformation and excavating trenches in some important sites where young alluvial fans were displaced obviously. There are 6 rows of fold-thrust faults from Puchang fault to Shanchakou and 4 rows from Shanchakou to Kalpin. Furthermore, the offset alluvial fans of Holocene have been found along two sections of the fault. One is Sanjianfang-Wudaoban section to the west of Sanchakou, another is Dakouzidaoban section to the east of Sanchakou. Both sections are located near arcuate top of thrust-sheet. We can find more than two periods of Holocene fans were displaced by thrust fault except the modern fan in both sections, and only Pleistocene fans were offset in other parts along the fault. It suggests that there are two segments to the east of Puchang fault along the range front fault of Kalpintag. 3 trenches are excavated along the Sanjianfang-Wudaoban segment and 4 events are discovered. Ages of the events are obtained by controlling deposit dating of TL samples. Referenced ages of events are 22, 14, 6.5 and 4.4ka BP and recurrence intervals are 8, 7 and 2ka, respectively. The vertical displacement of events is 1～1.2m and shortening slip 1.3～1.4m for events of long return-time, and they are 0.2～0.3m and 0.6～0.7m for events of short return-time, respectively. And one trench is excavated and 2 events since the end of late Pleistocene are exposed along Dashankoudaoban segment. Ages of the two events in this segment are a bit older than 13 and younger than 6ka BP, respectively. The recurrence interval is about 7ka. The coseismic displacement of each event is about 0.5m and the shortening slip 1.3m, respectively. It is necessary to tell that there is an uncertainty for the event age given in this paper because it is difficult to get good samples for dating. However, we can learn more on the large earthquake activity during late Quaternary along the range front fault of Kalpintag from these events.

Key words: Kalpintag, range front fault, late Quaternary, paleoearthquakes

摘要： 柯坪推覆构造系是西南天山前陆推覆构造的重要组成部分。文中试图通过对柯坪推覆构造区的影像解译和野外观察、断错地貌的实测和探槽开挖,探讨柯坪塔格山前断裂东段晚第四纪以来的古地震活动。在三岔口以西的五道班-三间房一带和三岔口以东的大山口道班一带,除现代洪积扇外,明显可见2期保存较完整的洪积扇被断错。五道班-三间房地段的3个探槽揭露出了晚更新世末期以来该破裂段发生的4次事件,其参考年代为:距今22、14、6.5和4.4ka;重复间隔时间约为:8、7和2ka左右。间隔时间长的事件垂直位移量约1～1.2m,缩短量约1.3～1.4m;间隔时间短的事件,垂直位移量0.20～0.30m,缩短量0.6～0.7m。大山口道班段探槽揭露出了晚更新世末期以来的2次事件,分别发生在稍早于距今13ka和稍晚于距今6ka。重复间隔时间约7ka。同震垂直位移量约50cm,缩短量130cm左右。

关键词: 柯坪塔格, 山前逆断层, 晚第四纪, 古地震