汶川地震断裂带显微结构、矿物学和地球化学特征及其变形机制

The reality of earthquake rupture is fault mechanics, which is related to the absolute strength of the fault slip zone, reflected in the microstructures of fault gouge in the cyclic, transient deformation and fault healing phases during seismic cycle. This application fouces on the two faults ruptured during the Wenchuan earthquake, the Yingxiu-Beichuan and Guanxian-Anxian faults, and plans to sample the fault rocks from outcrops and deep drilling (WFSD) cores, using optical microscope, SEM combined with advanced FIB preparation technique, TEM, Synchrotron, Itrax XRF Core Scanner, to analyse the microstructural, mineralogical, geochemical characteristics and physical properties of the fault rocks. Emphasized on the study of the micro-ultrastructural, substance components, clay mineral fabric, physical-chemical properties and fluid behavior in fault slip zone, we’d like to figure out the different deformation mechanims (stick-slip and/or creep), microstructural features and marking materials between outcrops and deep depths in the two fault zones, which help to reveal the physical and chemical conditions that control the fault deformation at shallow crust (0-5 km depth). Based on the above analyses, we will discuss the Wenchuan earthquake fault mechanisms. The results of this study are expected to contribute to understanding the active fault deformation process, and provide reliable basis for seismic risk assessment, major project site selection and seismic design.

断裂力学是影响地震破裂的实质，其关键问题与断层主滑动带的强度有关，体现在地震周期过程中滑动带周期变形、瞬时变形和断裂愈合期断层泥的显微结构中。本申请以汶川地震中破裂的两条不同变形行为的断裂：映秀－北川和灌县－安县断裂为研究对象，采集断裂带地表和深部（汶川科钻岩心）断裂岩样品。应用SEM、FIB、TEM、同步辐射、XRF扫描等多种实验测试方法，对所采集样品进行微构造、矿物学、地球化学和物性等方面的对比研究。重点对断裂滑动带显微-超微结构、物质成分、粘土矿物组构、物理－化学性质及流体行为等方面进行详细研究，识别两条断裂相似和不同之处，确定不同断裂在地表和地下深部的变形机制（粘滑/蠕滑）、特征显微结构和标志物质，揭示地壳浅部（0-5km深度）控制断层变形的物理和化学条件，探讨汶川地震破裂机制。这不仅对活动断裂的变形过程和地震危险性评价具有重要意义，而且可为重大工程选址和抗震设计提供可靠依据。

本项目以汶川地震中破裂的两条不同变形行为的断裂：映秀－北川和灌县－安县断裂为研究对象，采集断裂带地表和深部（汶川科钻岩心）断裂岩样品。应用SEM、FIB、TEM、同步辐射、XRF扫描等多种实验测试方法，对所采集样品进行微构造、矿物学、地球化学和物性等方面的对比研究。通过对断裂滑动带显微-超微结构、物质成分、粘土矿物组构、物理－化学性质及流体行为等方面进行详细研究，本项目取得了一系列重要的新认识，相关成果在国内外重要期刊上发表，标注本项目资助的学术论文共14篇，其中包括2篇Tectonics、1篇Geology、1篇Quaternary International、1篇英文版地质学报、2篇岩石学报、3篇地球物理学报和4篇地球学报。这些研究成果帮助我们理解认识汶川地震、对龙门山地区区域地震危险性评价以及重大工程选址和抗震设计提供理论基础和可靠依据。主要成果介绍如下：（1）映秀-北川断裂带为一条典型的铲式逆冲断层，断裂带宽约155-290 m，发育有假玄武玻璃、碎裂岩、断层泥和角砾岩等多种断裂相关的岩石，为一条经常发生大地震的断裂。（2）灌县-安县断裂带宽度为40-50米，断裂岩主要为断层泥和断层角砾岩，压溶构造发育，是一条具有长期蠕滑性质的断裂。（3）多重逆冲岩片组成的叠瓦状构造为龙门山断裂的主要构造格架。

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