地震断裂带物理化学行为的磁学响应研究

The analysis of physical and chemical properties and their formation mechanism of fault materials within a seismic fault zone, which are called microscopic studies, can help us understand the faulting dynamics during a large earthquake, such as fault friction, energy dissipation, and coseismic fault fluid flow. It also has been being a new breakthrough point of seismology and tectonophysics. In the present proposal, magnetic fabric and rock magnetic studies will be conducted on fault rocks from the Wenchuan earthquake fault ruptures and the core samples within the fault zones from the Wenchuan Earhquake Fault Scientific Drilling Project. The relationship between magnetic properties, mineralogical and geochemical compositions, and textural features will be fully explored. All these works are aiming at: (1) revealing the characteristics of tectonic activities in Wenchuan earthquake fault zones via the magnetic fabric studies, (2) exploring the magnetic responses of the frictional heating and coseismic fluid flow within the seismic slip zone, and (3) deducing the seismic physicochemical behaviors related information carried by the abnormal magnetic properties of fault materials. All these results are expected to give important magnetic constraints for understanding seismogenic mechanism, rupture process, slip mechanism and energy release of the 2008 Wenchuan earthquake.

以地震断裂带物质的物理、化学性质及其形成机制为主要内容的地震微观研究，是认识与理解地震过程中的断层摩擦、温度变化与同震流体活动等地震物理化学行为的重要手段，已成为地震学与构造物理学研究新的突破点。本项目以汶川地震断裂带典型露头的断层岩和汶川地震断裂带科学钻探钻孔中的断裂带岩芯样品为研究对象，以断层物质的磁组构与岩石磁学特征为基础，以断层带物质的系统磁学特征与矿物组成、化学成分及显微结构之间的相互关系为桥梁，结合区域地质构造背景，分析断层物质磁组构特征所揭示的汶川地震断裂带的构造活动特性；探讨地震断层破裂滑动过程中，断层摩擦行为导致的断层区域温度变化与同震流体活动的磁学响应特性，解译断层物质磁性特征所蕴含的与断层物理化学行为相关的地质与地球物理信息。研究结果将为深入认识与理解汶川地震的孕震机理、断层破裂与滑动机制及能量释放等提供磁学依据。

地震断裂带物质的岩石磁学特征蕴涵了有关地震过程中断层摩擦、温度变化与同震流体活动等地震物理化学行为的丰富信息。本项目以汶川地震断裂带典型露头断层岩和综合大洋钻探计划343航次C0019站位岩芯样品为研究对象，通过系统的磁组构与岩石磁学研究，取得了以下代表性成果：（1）发现日本海沟北美板块与太平洋板块浅部滑脱带长期处于应变“解耦”状态，为诠释日本3.11地震的巨大滑移机制提供了新证据。（2）揭示了北美板块与太平洋板块浅部滑脱带中存在300-500℃的地震摩擦生热记录，发展了地震断层带的岩石磁学“地温计”；（3）揭示了地震循环过程中断层流体活动对磁性矿物的改造与控制，建立了断层演化过程中流体活动与断层岩磁性变化相互关系的概念模型。上述研究结果将为深入认识与理解汶川地震和日本3.11地震的孕震机理、断层破裂与滑动机制及能量释放等提供磁学依据。同时，基于上述工作，初步建立了地震断层带的岩石磁学“应力计”、“温度计”和“流体计”思路。项目进行期间，以项目组成员第一作者共发表国际SCI论文3篇论文。