第四纪松散沉积物中活断层滑动面的显微构造研究方法

Study on Active Faults in Quaternary Unconsolidated Sediments by Microstructural Method

第四纪松散沉积物中的活断层滑动面是重要的古地震遗迹 ,也是鉴定古地震事件和确定古地震时代的重要标志。以往 ,对第四纪松散沉积物中活断层滑动面主要借助宏观观察进行研究 ,但遇到了一些难以解决的问题 ,如隐性断层问题。作者利用显微构造分析 ,找到了研究这些问题的途径 ,其方法是对第四纪松散沉积物进行定向原状样品采集 ,通过室内样品固结、显微薄片制作和显微构造现象观察等 ,从显微域里研究各种变形现象。用此方法 ,可以在没有宏观资料支持的情况下确定断层的运动性质 ;发现并描述第四纪松散沉积物中的隐性断层 ,研究断层的尖灭机制 ;还可以对工程建设场地发现的不同松散沉积物相接触的现象进行活断层鉴别。

Active faults in Quaternary unconsolidated sediments are important indicators to determine paleoearthquake events. They can be studied by macroscopic geological survey, but some problems have been encountered, such as invisible active faults. The writers found an approach to solve these problems by microstructural observation. Firstly, original-state directional samples of Quaternary unconsolidated sediments in active fault zone are collected. Secondly, the samples are consolidated in laboratory. Thirdly, microstructural slides are ground in three-dimension coordinate system. Lastly, microstructures are observed in microscopic field. By this method, the movement properties of active faults can be determined in lack of the support of macroscopic data. The invisible faults in Quaternary unconsolidated sediments can be found and described. The mechanisms of die-out faults can be also studied. Moreover, the boundaries of different unconsolidated sediments in engineering sites can be easily confirmed whether they are active faults or not.