SEISMOLOGY AND GEOLOGY ›› 2018, Vol. 40 ›› Issue (5): 1149-1169.DOI: 10.3969/j.issn.0253-4967.2018.05.014

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ZHANG Jin-yu1, ZENG Jing1, WANG Heng1, SHI Xu-hua2, YAO Wen-qian1, XU Jing1, XU Xin-yue1   

  1. 1 State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
    2 Earth Observatory of Singapore, Nanyang Technological University 639798, Singapore
  • Received:2018-01-08 Revised:2018-05-27 Online:2018-10-20 Published:2018-11-29


张金玉1, 刘静1, 王恒1, 石许华2, 姚文倩1, 徐晶1, 徐心悦1   

  1. 1 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029;
    2 南洋理工大学新加坡地球观测中心, 新加坡 639798
  • 作者简介:张金玉,女,1986年生,2014年于中国地质大学(北京)获构造地质学博士学位,助理研究员,现主要研究方向为活动构造与河流地貌,电话:010-62009085,。
  • 基金资助:

Abstract: The bedrock scarps are believed to have recorded the continuous information on displacement accumulation and sequence of large earthquakes. The occurrence timing of large earthquakes is believed to be correlated positively with the exposure duration of bedrock fault surfaces. Accordingly, cosmogenic nuclides concentration determined for the bedrock footwall can offer their times, ages, and slip over long time. In general, multiple sites of fault scarps along one or even more faults are selected to carry out cosmogenic nuclide dating in an attempt to derive the temporal and spatial pattern of fault activity. This may contribute to explore whether earthquake occurrence exhibits any regularity and predict the timing and magnitude of strong earthquakes in the near future. Cosmogenic nuclide 36 Cl dating is widely applied to fault scarp of limestone, and the height of fault scarp can reach as high as 15~20m. It is strongly suggested to make sure the bedrock scarp is exhumed by large earthquake events instead of geomorphic processes, based on field observation, and data acquired by terrestrial LiDAR and ground penetration radar (GPR). In addition, it is better for the fault surface to be straight and fresh with striations indicating recent fault movement. A series of bedrock samples are collected from the footwall in parallel to the direction of fault movement both above and below the colluvium, and each of them is~15cm long,~10cm wide, and~3cm thick. The concentrations of both cosmogenic nuclide 36 Cl and REE-Y determined from these samples vary with the heights in parallel to fault scarps. Accordingly, we identify the times of past large earthquakes, model the profile of 36 Cl concentration to seek the most realistic one, and determine the ages and slip of each earthquake event with the errors. In general, the errors for the numbers, ages, and slips of past earthquake events are ±1-2, no more than ±0.5-1.0ka, and ±0.25m, respectively.

Key words: normal faulting, bedrock fault scarp, cosmogenic nuclides, long-period earthquake record, fault slip rates

摘要: 正断层基岩断面可以连续地记录大地震位移累积的过程以及地震事件序列。该地震序列发生的时间与地震位移导致的基岩断面的暴露时间呈正相关。因此,通过测定断面基岩表层的宇宙成因核素浓度,可获得过去大地震发生的次数、时间和滑动量。目前研究工作中广泛选用灰岩的宇宙成因核素36Cl测年方法,最佳采样基岩断面的高度距地表15~20m。选择采样剖面时,需确保基岩表面记录的是构造事件而并非地貌剥蚀过程,断面平直新鲜。基本采样策略是,在崩积楔之上和之下平行断层滑动方向连续采集一系列基岩样品,单件样品的长×宽×厚约15cm×10cm×3cm。基于样品的宇宙成因核素36Cl和稀土元素-钇(REE-Y)浓度随着样品距地表高度的变化情况,识别出强震次数及其发生时间范围,然后运用数值模型模拟36Cl剖面来获得最可能的强震事件发生时间和滑动量以及相应的误差。

关键词: 正断层, 基岩断面, 宇宙成因核素, 长周期地震记录, 断层滑动速率

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