地震地质 ›› 2015, Vol. 37 ›› Issue (2): 400-412.DOI: 10.3969/j.issn.0253-4967.2015.02.005

• 研究论文 • 上一篇    下一篇

利用基岩断层面形貌定量特征识别古地震——以霍山山前断裂为例

何宏林1, 魏占玉1, 毕丽思2, 徐岳仁3   

  1. 1. 中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029;
    2. 广东省地震局, 地震监测与减灾技术重点实验室, 广州 510070;
    3. 中国地震局地震预测研究所, 北京 100717
  • 收稿日期:2014-10-29 修回日期:2015-03-26 出版日期:2015-06-20 发布日期:2015-08-19
  • 作者简介:何宏林,男,1964年生,2000年于东京大学获理学博士学位,研究员,博士生导师,主要从事活动构造与古地震、新构造与数值构造地貌、GIS应用与工程地震研究,电话:010-62009215,E-mail:honglin@ies.ac.cn。
  • 基金资助:

    国家自然科学基金(41372210, 40872128)、中国地震局地质研究所基本科研业务专项(IGCEA1416, IGCEA1113)和中国地震局地震行业科研专项(200908001)共同资助。

IDENTIFY PALEO-EARTHQUAKES USING QUANTITATIVE MORPHOLOGY OF BEDROCK FAULT SURFACE——A CASE STUDY ON THE HUOSHAN PIEDMONT FAULT

HE Hong-lin1, WEI Zhan-yu1, BI Li-si2, XU Yue-ren3   

  1. 1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
    2. Key Laboratory of Earthquake Monitoring and Disaster Mitigation Technology, China Earthquake Administration, Earthquake Administration of Guangdong Province, Guangzhou 510070, China;
    3. Institute of Earthquake Science, China Earthquake Administration, Beijing 100717, China
  • Received:2014-10-29 Revised:2015-03-26 Online:2015-06-20 Published:2015-08-19

摘要:

基岩断层面形貌特征的定量分析方法是研究断层活动历史和识别古地震的有效手段, 是对探槽技术的有力补充, 可以弥补在基岩区开展古地震研究技术手段的严重不足。文中以山西霍山山前断裂上的断层面(崖)为例, 采用各向同性变差函数法计算了断层面形貌的2D分维值, 并通过沿断层走向逐条平均的方式获得了2D分维值在断层倾向上的分布特征, 结果显示断层面形貌在倾向上具有显著的分带性特征, 由此获得的每个分带的特征分维值随断层面高度的增加呈阶跃式增加。这种断层面形貌在倾向上的显著分带性特征、特征分维值的阶跃式增加反映了断层面的出露方式不是渐进式, 而是不连续的间歇式; 这种间歇式分带性出露方式与断层的周期性地震活动相关, 每个分带的特征值与每个分带的出露时间相关, 即与地震发生时间相关。因此: 1)可以通过每一个断层面分带的特征分维值估计该分带出露的时间; 2)断层面分带的宽度可以用来估计每次破裂地震的同震位移量。霍山山前断裂带上3个基岩断层面形貌分带揭示出3次地震事件; 3个2D特征分维值不仅显示3个分带自上而下由老变新的阶跃特征, 而且3个阶跃之间大致相等的特征分维值差显示了3次地震发生间隔是大致相等的; 断层面分带的宽度反映出破裂地震的倾向同震位移量大约为3.5m。此外, 在阶跃式分带之间还存在宽0.5~1m的较窄分带, 这些窄分带的特征分维值是随断层面高度增加而逐渐增大的, 显示在间震期基岩断层面被逐渐剥露的特征。

关键词: 基岩断层面形貌, 古地震, 各向同性变差函数法, 霍山山前断裂

Abstract:

The quantitative analysis of morphologic characteristics of bedrock fault surface is a useful approach to study faulting history and identify paleo-earthquake. It is an effective complement to trenching technique, especially to identify paleo-earthquakes in a bedrock area where the trenching technique cannot be applied. In this paper, we calculate the 2D fractal dimension of three bedrock fault surfaces on Huoshan piedmont fault in Shanxi graben, China using the isotropic empirical variogram. Taking average fractal dimensions of every horizontal tape and plotting them along the vertical axis, we find the fractal dimension presents pronounced segmentation in vertical direction. This step change of the average fractal dimensions demonstrates obvious segmentation of the fault surface morphology. Then, the segmentation of fault surface morphology, showing different exposure duration of each segment, is caused by periodic faulting earthquake, but not continuous erosion. Therefore, taking best normal fitting of average fractal dimensions of each segment as a characteristic value to describe the surface morphology of the fault surface segment, the characteristic value can be used to estimate the exposure duration of the fault surface segment and then the occurrence time of the faulting earthquake that made the segment exposed. The width of each fault surface segment can also be regarded as an approximate vertical coseismic displacement. Based on the segmentation of quantitative morphology of the three fault surfaces on the Huoshan piedmont fault, we identify three faulting earthquake events. Combined with trenching results reported by previous researches, we attempt to fit an empirical relationship between the exposure time and the morphological characteristic value on the fault. The co-seismic vertical displacement of a characteristic earthquake on the Huoshan piedmont fault is estimated to be 3.5m(3~4m), the average width of all middle fault surface segments. Moreover, the small gap of average 0.5~1m width between two adjacent segments, where fractal value increases gradually with the increased fault surface height, is inferred to be caused by erosion between two faulting earthquakes.

Key words: morphology of bedrock fault surface, paleo-earthquake, isotropic empirical variogram, Huoshan piedmont fault

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