中国大陆古地震研究的关键技术与案例解析(5)——断层隐形、尖灭与年轻事件识别

doi:10.3969/j.issn.0253-4967.2015.02.001

摘要/Abstract

摘要：

断层隐形或尖灭现象在年轻事件影响的地层中较为突出, 可能造成年轻事件识别的误判, 增大地震危险性评价的不确定性。文中在前人相关研究成果的基础上, 结合中国的研究实例, 讨论断层隐形与年轻事件识别的问题。断裂在砂层、土壤、粉砂层、黄土、黏土质砂中的隐形比较普遍。在走滑、逆断层和正断层3种构造类型中走滑断层出现隐形的比例最高。汶川地震破裂带及其他一些探槽研究的案例显示, 易 "隐形"地层中年轻事件的识别需要从探槽开挖地点选择、探槽开挖方式、探槽信息的综合分析等相关技术入手。选择多韵律地层开挖探槽是避免断层隐形影响事件识别的关键; 组合或3维探槽有利于减小断层局部隐形的影响; 上下层位推延、粒度、色度以及土壤发育程度等综合分析是识别隐形断层的基本手段; 显微构造、粒度和磁化率分析等是隐形断层识别的重要发展方向之一。

关键词: 断层隐形, 研究案例, 年轻事件, 识别技术

Abstract:

Nonvisibility(dieout)of fault strands occurs primarily in stratigraphic units associated with young paleoseismic events, which may cause misidentification of the young events and bring more uncertainties for seismic risk assessment. Based on previous related studies, this paper integrates case studies in mainland China to discuss the nonvisibility of fault strands and identification of young paleoseismic events. Nonvisibility of fault strands is prevailing in sandy, soil, silty, loess, and clay-sandy units, and is more possibly associated with strike-slip faults comparing with normal and reverse faults. Case studies on several trenches across surface ruptures produced by the Wenchuan earthquake and others located at different regions suggest that trench siting, excavation, and comprehensive analysis are key technical points to identify young paleoseismic events in the stratigraphic units where nonvisibility of fault strands is prone to occur. Stratigraphic units with more sequences have been suggested to be good sites for trenching to avoid misidentification produced by nonvisibility of fault strands. Multiple trenching is facilitated to lower the influence of local nonvisibility. Assumed extending of upper and lower units, grain sizes, color, and soil horizon are the basic methods to identify nonvisibility. Analysis of microstructures, grain sizes and magnetic susceptibility is one of the future studies related to identification of nonvisibility of fault strands.

Key words: nonvisibility of fault strands, case study, young paleoseismic events, identification technique

中图分类号:

P315.2

冉勇康, 王虎, 李彦宝. 中国大陆古地震研究的关键技术与案例解析(5)——断层隐形、尖灭与年轻事件识别[J]. 地震地质, 2015, 37(2): 343-356.

RAN Yong-kang, WANG Hu, Li Yan-bao. KEY TECHNIQUES AND SEVERAL CASES ANALYSIS IN PALEO- SEISMIC STUDIES IN MAINLAND CHINA(5): NONVISIBILITY, DIEOUT OF FAULT STRANDS AND IDENTIFICATION OF YOUNG PALEOSEISMIC EVENTS[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(2): 343-356.

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