SEISMOLOGY AND GEOLOGY ›› 2011, Vol. 33 ›› Issue (4): 739-751.DOI: 10.3969/j.issn.0253-4967.2011.04.001

• Paleoearthquak • Previous Articles     Next Articles

PALEOEARTHQUAKE EVENTS AND FORMATION OF RIVER TERRACES IN ACTIVE ANTICLINE REGION, NORTHERN PIEDMONT OF TIANSHAN MOUNTAINS,CHINA

YANG Xiao-ping, LI An, HUANG Wei-liang, ZHANG Ling   

  1. National Center for Active Fault Studies, Institute of Geology, China Earthquake Administration, Beijing 100029, China
  • Received:2011-10-28 Revised:2011-11-19 Online:2011-12-30 Published:2012-01-12

天山北麓活动背斜区河流阶地与古地震事件

杨晓平, 李安, 黄伟亮, 张玲   

  1. 中国地震局地质研究所, 国家地震活动断层研究中心, 北京 100029
  • 作者简介:杨晓平,男,1963年生,1995年在中国地震局地质研究所获得理学博士学位,研究员,主要从事新生代构造、活动构造和工程地震等方面的研究,电话: 010-62009144,E-mail: yangxiaopingdzs@sina.com。
  • 基金资助:

    地震行业科研专项(200808013)和国家自然科学基金(40572126)共同资助

Abstract:

Using the aerial remote sensing photos and Google earth satellite images,we find seven terraces at the both sides along the Kuytun River in Dushanzi active anticline area,northern piedmont of Tianshan.Based on the field investigation,we find that all these terraces are pedestal terraces.The rock of pedestal is Pliocene mud rock,and on the top of each terrace pedestal are the stratums of sandy gravel or sandy clay with 2.5~15m in thickness.We collected samples from deposits of all terraces for OSL(optically stimulated luminescence)geological dating using the SMAR(single-multiple-aliquot-regeneration)method on fine grains.We also performed dating using the 14 C method to the samples from the deposit of terrace T1 of the Kuytun River.The results show that the ages of all these deposits are the later phase of the Late Pleistocene.The accumulation time of the upper stratum for T1,T2,T3,T5,T6and T7 terraces is about 1.7ka,14.98ka,20.7~27.3ka,29.3~39.2ka,47~56ka and 103~118ka,respectively.Combining with late Quaternary climate change,we believe that the formation age for T1~T7 terraces of Kuytun River are 1.7ka,14ka,20ka,25ka,30ka,50ka and 100ka BP.Paleoearthquake data reveal that eight paleoearthquake events occurred on the Dushanzi-Anjihai reverse fault since about 25ka BP,respectively at 2ka,3.4ka,4.3ka,5.8ka,7.5ka,12.8ka,18ka and 24ka BP.Comparing the ages of paleoearthquakes and terraces,we find that the ages of the latest,the sixth,the seventh and the eighth paleoearthquake are roughly corresponding to the formation times of T1,T2,T3and T4 terraces,respectively.The other four paleoearthquake events occurred during the period after the formation of T2and before the formation of T1.In this time,no terraces developed along the Kuytun River,but the Kuytun River incised rapidly for 40m.We believe that the paleoearthquake events resulted in the fast uplift of Dushanzi active anticline on the hanging wall of Dushanzi-Anjihai Fault and the increase of riverbed slope and river incision ability,which led to the formation of river terraces or deep canyons.The terrace sequence in active anticline region may reflect the paleoearthquake sequence associated with fault or blind fault.

Key words: river terrace, paleoearthquake, coseismic uplift, active fault, Tianshan

摘要:

利用航空遥感照片和Google earth卫星影像,对天山北麓独山子活动背斜区奎屯河两侧的河流地貌进行解释,结合野外调查发现,奎屯河流经独山子背斜段发育7级基座阶地,阶地基座为上新统独山子组泥岩,其上部为2.5~15m厚的砂砾石层和砂质黏土。在开挖或剥离的各级阶地堆积物剖面中采集细粒堆积物样品,实验室中采用细粒石英光释光测年的简单多片再生法对每件样品进行测试,得到独山子背斜区T1、T2、T3、T5、T6和T7阶地堆积上部的堆积时代分别为距今1.7、14.98、20.7~27.3、29.3~39.2、47~56和103~118ka。结合晚第四纪的气候变化,认为奎屯河T1~T7阶地的下切形成时代分别为距今约1.7、14、20、25、30、50和100ka。独山子-安集海断裂带上的古地震资料表明,距今约25ka以来发生了8次古地震事件,发生时间分别为距今2、3.4、4.3、5.8、7.5、12.8、18和24ka。对比古地震发生的时代和阶地形成的时代发现,最新1次、第6次、第7次、第8次古地震事件发生时代分别与T1、T2、T3和T4阶地形成时代大致相同。T2阶地形成之后到T1阶地形成之前还发生了4次古地震事件,这期间沿奎屯河没有发育河流阶地,但奎屯河快速下切约40m。我们认为独山子-安集海断裂带上古地震的发生使得其断层上盘的独山子背斜快速隆起,以及奎屯河河床坡度增大,从而使水流的下切能力增强,引起河流快速下切而形成河流阶地或深切峡谷,活动背斜段的阶地序列可能反映与其相关断裂上的古地震序列。

关键词: 河流阶地, 古地震, 同震隆升, 活动褶皱, 天山

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