活动褶皱研究及其识别

通过对发生在活动构造挤压区内的Coalinga、El.Asnam、Spitak等地震实例及新疆活动褶皱的分析研究,提出了活动褶皱的分类、活动褶皱研究的意义、内容、方法及其识别。指出同活动断层相似,活褶皱也有粘滑和蠕滑两种形成机制。年轻而快速增长的活褶皱不仅可能是发生地震的地点,其本身也有可能是连续地震的产物。我们称这些具有粘滑机制的活褶皱为地震褶皱;活动褶皱发育的挤压性构造区具有发生中强地震的潜在危险。地震褶皱则是地震震源的一种“指示构造”。同时作为古地震标志,地震褶皱及其派生的近地表活动弯滑断层和弯矩断层等次生断层,其同震生长和滑动可以提供下伏发震断层的复发间隔及其活动历史;由于逆断型地震其发震道断层的滑动不仅在平面分布上具有不均匀性,而且在剖面分布上也存在不均匀性,其量从震源深处向地表有渐小趋势。故主要根据对第四纪地表变形的分析来进行地震危险性评价的方法。在活动构造挤压区有很大的局限性。而平衡剖面法乃是识别和定量研究活动逆断层,特别是隐伏断层的最好方法。

THE STUDY AND RECOGNITION OF ACTIVE FOLD

Through analysing and studing the earthquake examples occurred in Coalinga, El. Asnam.Spitak etc. and the active folds of Xinjiang in areas compression, the conception of active folds, the significance, content, method and recognition of active fold study were put forward. The result shows (1) Similar to active fault, active folds also have two kinds of mechanism- strick slip arid creepslip. The yorng and faot-groaing active folds-are not only the seismogenic places, but also the result of earthquake action, mechanism as earthquake folds. (2)There is potential risk of medium and strong earthquakes in compressional structure area where active foids is developing. Earthquake fold is a kind of "indicator structure"of earthquake focus, meanwhile, itis a msrk of pslaeo esrthquakes. Earthquake folds and its derivative sab-farlts,srch as flexural-slip and bending-moment fault acting near suface and itscoseismic growth and slip can provide recurrence interval and history for underlying seismogenic faults. (3)The slip of seismogenic thrust fault is uneven not only in horizontal but also in vertical plane. The slip has diminishing tendency from depth to surface. So,it has great limitation to use the e-valuation method, which was used for evaluating earthquake hazard mainly thuough analyzing Quaternary ground surface,in compressional area of active structure. It was considered that method of equilibrium profile is the best method to recognize and quantitatively study active thrust fault and underlying fault.