SEISMOLOGY AND GEOLOGY ›› 2015, Vol. 37 ›› Issue (3): 851-868.DOI: 10.3969/j.issn.0253-4967.2015.03.015

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THE U SERIES DATING AND ITS SIGNIFICANCE FOR CALCAREOUS COATS OF EARTHQUAKE-GENERATED REGIONAL ROCKFALL ALONG YUSHU FAULT ZONE, IN EASTERN QINGHAI-XIZANG PLATEAU

TIAN Ting-ting1,2, WU Zhong-hai2, MA Zhi-bang3, ZHOU Chun-jing2, ZHANG Ke-qi2, JIANG Yao1,2, ZHANG Xu-jiao1   

  1. 1 College of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;
    2 Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;
    3 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
  • Received:2014-06-13 Revised:2015-01-22 Online:2015-09-20 Published:2015-10-20

玉树活动断裂带古地震落石的钙膜U系年代学测试分析及其意义探讨

田婷婷1,2, 吴中海2, 马志邦3, 周春景2, 张克旗2, 蒋瑶1,2, 张绪教1   

  1. 1 中国地质大学(北京), 地球科学与资源学院, 北京 100083;
    2 中国地质科学院地质力学研究所, 北京 100081;
    3 中国科学院地质与地球物理研究所, 北京 100029
  • 通讯作者: 吴中海,研究员,E-mail:wzhh4488@sina.com
  • 作者简介:田婷婷,女,1986年生,中国地质大学(北京)地理学专业在读硕士研究生,现主要从事第四纪年代学与活动构造研究,电话:010-88815090,E-mail:wstingt815@126.com.
  • 基金资助:

    中国地质调查局项目(1212011120163,12120114002101)、国家自然科学基金(41171009)和中国地质科学院地质力学研究所基本科研业务专项(DZLXJK201410)共同资助.

Abstract:

In 2010, the MS7.1 earthquake in Yushu, Qinghai Provence caused an obvious phenomenon of earthquake-generated rockfall in many places along the seismogenic fault zone. In the course of surface investigation, it was found that in several typical development areas of latest earthquake-generated rockfall, there are entirely multi-period in-situ recurrent earthquake-generated rockfalls with most typical characteristics. It is so common with thin calcareous coats on the surface of earthquake-generated rock fall. On the basis of systematic sampling for the calcareous coats, which are on the surface of earthquake-generated rock fall in several typical distribution areas near the Yushu active fault belt, the author made an attempt on U-series dating analysis for calcareous coats of the earthquake-generated rock fall, by applying dilute acid leaching method. The ages are mainly distributed in the range of about 69 980a BP, 36 300a BP, 14 900~12 700a BP, 6 030a BP, 4 720a BP, 3 560~3 530a BP, 2 010~1 090a BP, about 760a BP and 230 a BP. This result tallies basically with the multi-period characteristic of earthquake-generated rock fall by surface observation, and primarily with the seismic events reflected from paleo-earthquake trench and paleo-earthquake landslide. It is preliminary confirmed that the development of rock fall near the Yushu Fault zone is of obvious multi-period, and the multi-period rock fall is in close genetic relationship with paleo-earthquake activities. In addition, combined with results of field investigation and the data of paleo-seismic research, it can be judged that the phenomenon of several extensive earthquake-generated rock falls is mainly a reflection of larger intensity of paleo-earthquake events since the late of Q3p period, of which the paleo-earthquake events occurring in about 3 560~3 530a BP and 14 900~12 700a BP may be the biggest. The exploratory research on U series dating method for calcareous coats in Yushu earthquake-generated rock fall may provide a new way for the future study of paleo-earthquake activity in active tectonic region.

Key words: Yushu Fault zone, paleo-earthquake generated rockfall, U series, paleo-earthquake, calcareous coats dating

摘要:

在2010年青海玉树7.1级大地震中, 沿发震断裂带多处出现了明显的地震落石现象.地表调查发现, 典型的最新地震落石发育区均存在非常典型的具原地复发特征的多期古地震落石现象, 且落石表面常见薄层(厚度≤2mm)钙膜发育.在对几处典型古地震落石钙膜进行系统采样的基础上, 应用稀酸淋滤法, 开展了地震落石钙膜的U系年代测定分析工作.测年结果指示, 其年龄主要分布在69 980a、36 300a、14 900~12 700a、6 030a、4 720a、3 560~3 530a、2 010~1 090a、760a和230a左右.这一结果与地表观测到的地震落石多期性特征基本吻合, 也与古地震探槽和古地震滑坡所揭示的古地震事件年龄大致吻合, 这进一步证实了玉树活动断裂带附近的地震落石发育具有明显的多期性特征, 并且多期落石很可能与该区的古地震活动之间存在密切的成因联系.进一步结合野外调查结果及已有的古地震研究资料推断, 该区几处较大规模的古地震落石现象应该主要是Q3p晚期以来较大强度古地震事件的反映, 其中发生在3 560~3 530a BP和14 900~12 700a BP左右的2期古地震事件的强度可能最大.上述探索性研究工作表明, 地震落石的钙膜测年有可能成为研究活动构造区古地震活动的新途径.

关键词: 玉树断裂带, 古地震落石, 铀系, 古地震, 钙膜测年

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