关键词: 古地震, 柯坪塔格断裂, 西南天山

Abstract: The Kalpintag Fault locates at the most forefront of Kalpintag nappe tectonics, and can be separated into eastern and western segments by Piqiang Fault. Six large trenches are excavated along the western segment and four paleoearthquakes can be distinguished in the three trenches of them. The first paleoevent occurred about 12ka BP, the second event occurred about 8.6ka BP, the third event occurred about 5ka BP,and the last event occurred after (1.73±0.15) ka BP, which probably is the Xike'er M6.8 earthquake in 1961 AD. The four paleoevents are characterized by 3～4ka quasi-periodic recurrence interval. The Kalpintag nappe structure are composed of 5～6 rows of fold-reverse fault zones. The faults with the latest activity are located at the forefront of the fold-reverse fault zones with 10km spacing between each fault. The north-dipping and listric style fault surfaces merged into the detachment surface in the deep along the bottom of Cambrian at 6～10km depth. The field investigation discovered that earthquake ruptures and paleoearthquake traces can be found not only along Kalpintag Fault but also along other faults, but the rupture length and seismic slip are smaller than that formed by an M≥7 earthquake. Although five paleoearthquakes since 14ka BP are obtained along western segment of Kalpintag Fault, some events are probably missed because of less trenches and dating samples. Many problems such as magnitude of these events, seismogenic fault and their rupture zones formed by one or several events await study in the future.

Key words: paleoearthquake, Kalpintag Fault, southwest Tianshan