Active Characteristics and Paleoearthquakes in the West Kalpin Nappe Since the Holocene, SW Tianshan Mountain

doi:10.11867/j.issn.1001-8166.2016.04.0377.

Advances in Earth Science ›› 2016, Vol. 31 ›› Issue (4): 377-390. doi: 10.11867/j.issn.1001-8166.2016.04.0377.

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Active Characteristics and Paleoearthquakes in the West Kalpin Nappe Since the Holocene, SW Tianshan Mountain

An Li ¹( ), Yongkang Ran ², Huaguo Liu ³, Liangxin Xu ⁴

1.Key Laboratory of Crustal Dynamics, Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China
2.Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029,China
3.China Earthquake Disaster Prevention Center, Beijing 100029, China
4.Earthquake Administration of Shaanxi Province, Xi'an 710068, China

Received:2016-02-18 Revised:2016-03-17 Online:2016-04-20 Published:2016-04-10
About author:
First author:Li An (1983- ), male, Changsha City, Hu’nan Province, Research assistant.Research areas include the active tectonic and paleoseismology.E-mail:antares_lee@163.com
Supported by:
Project supported by the Young Scientists Fund of the National Natural Science Foundation of China “The topography of alluvial fans and their geomorphic response of the structure activity of the thrust fault-fold belt” (No.41402185);The Institute of Crustal Dynamics, China Earthquake Administration Research Fund “the Geomorphic response of the structure activity of the Yumen fault belt since the late Quaternary in the north Qilian Mountains ” (No.ZDJ2014-12)

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An Li, Yongkang Ran, Huaguo Liu, Liangxin Xu. Active Characteristics and Paleoearthquakes in the West Kalpin Nappe Since the Holocene, SW Tianshan Mountain[J]. Advances in Earth Science, 2016, 31(4): 377-390.

the Kalpin nappe is an important multiple thrust system. It is important to study the Cenozoic tectonic of the Tianshan Mountain. Holocene active characteristics and paleoearthquake of the Kalpin nappe can be used to evaluate the neotectonic of this area. In this paper, we accurately measured the fault scarp in the front of three thrust-fold faults and analyzed paleoearthquake events in the trenches of the Kalpin nappe. Using the ¹⁰Be exposure age, we obtained those geomorphic surface ages and paleoearthquake times. The result showed that the slip rates of the west Kalpintag fault, aozitag fault and the tuoketag fault were 1.45(+1.68/-0.44) mm/a, 0.81(+0.35/-0.19) mm/a and (0.3±0.05) mm/a, respectively since the Holocene. The slip rate indicated that the increased activity transferred from back-row fault to front-row fault and accorded with the piggy-back propagation model in the Tianshan Mountain. Displacements and recurrence intervals of paleoearthquakes was similar to the slip rate characteristics. It also showed paleoearthquakes in the front row fault were stronger than paleoearthquakes of the back row fault. The strong paleoearthquake which caused the highest surface rupture happened in the Kalpintag fault. The interval of paleoearthquakes was about 4 ka and the displacement of every paleoearthquake was about 3 m in the west Kalpintag fault; the interval of paleoearthquakes was about 2 ka and the displacement of every paleoearthquake was about 1m in the aozitag fault; the tuoketag fault ruptured only one paleoearthquake since 7 ka. The Piqiang tear fault was the tectonic result of different shortening rate between the west Kalpin system and the east Kalpin system. The shortening rate of west Kalpin system was obviously stronger than the east Kalpin system. The huge separation distance was near 20 km between the east and the west back-row fault. Because the slip rate of system transferred to the front-row fault in the piggy-back propagation model, the separation distance (~4 km) between the east and the west front-row fault was increasing.

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