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岩石磁学能揭示岩石的磁性矿物组合,通过断裂岩不同的磁性矿物组合可揭示地震过程中磁性矿物变化、地震摩擦温度及地震滑移机制等基础地震地质问题。2008年Mw 7.9级汶川地震使两条断裂带同时发生地表破裂,包括映秀-北川和灌县-安县断裂地表破裂带,破裂带上地震断裂岩为岩石磁学提供了大量的研究对象。本研究主要以汶川地震地表破裂带上两个探槽内断裂岩为对象,包括映秀-北川地表破裂带上的八角庙探槽和灌县-安县地表破裂带上的九龙探槽,结合目前已发表的地表及WFSD-1孔的研究成果,从岩石磁学角度探讨汶川地震断裂带经历的地震滑移机制:1综合映秀-北川地震断裂带上八角庙探槽和其它位置的断裂岩岩石磁学研究,结果显示该地震断裂带附近断层泥的高磁化率源于新生的亚铁磁性矿物,如磁铁矿和磁赤铁矿等,故映秀-北川地震断裂曾经历高温快速热增压地震滑移机制;2灌县-安县地震断裂带上九龙探槽内断层泥略低的平均磁化率源于其铁的硫化物含量比断层角砾及侏罗纪砂岩多,铁的硫化物可能源于地震过程或断裂岩抬升到地表后的地表作用,如果断层泥中铁的硫化物多含量源于地震过程,则灌县-安县地震断裂带曾经历低温慢速机械润滑地震滑移机制;3两条断裂经历的不同地震滑移机制可能受控于断裂深部结构,如断层产状,映秀-北川地震断裂带的陡倾角易产生高温快速地震滑移,而灌县-安县地震断裂带的缓倾角更易产生低温慢速地震滑移。
Rock magnetism can reveal the magnetic mineral assemblage of rocks. The different magnetic mineral assemblages of the fractured rocks can reveal the basic seismic geological problems such as the change of magnetic minerals during earthquake, the earthquake friction temperature and the earthquake slipping mechanism. The 2008 Mw 7.9 magnitude Wenchuan earthquake caused simultaneous surface rupture of two fault zones, including the Yingxiu-Beichuan and Guanxian-Anxian fault surface rupture zones, and the seismic fracture rocks on the rupture zone provided a great deal of research objects for rock magnetism. This study is mainly aimed at the fault rocks in the two trenches on the surface rupture zone of the Wenchuan earthquake, including the Bajiaomiao trough on the Yingxiu-Beichuan surface rupture zone and the Kowloon trough on the Guxian-An County surface rupture zone, Published the surface and WFSD-1 hole research results from the point of view of rock magnetism earthquake Wenchuan earthquake fault mechanism experienced by the earthquake: 1 integrated Yingxiu - Beichuan earthquake fault zone octagonal temple and other locations of fracture rock rock magnetic The results show that the high magnetic susceptibility of fault mud near the earthquake fault zone originates from new-born ferrimagnetic minerals such as magnetite and maghemite. Therefore, the Yingxiu-Beichuan earthquake fault once experienced the rapid thermal booster earthquake Slipping mechanism; 2) the average magnetic susceptibility of fault gouges in the Jiulong trough on the Guanxian-Anxian seismic fault zone is slightly lower than that of the iron-bearing sulfides of more than that of fault breccias and Jurassic sandstones. In the event of an earthquake or the surface effect of a fracture rock rising to the surface, the Guxian-Anxian seismic fault zone has experienced the mechanism of low-temperature and slow mechanical lubrication of earthquake-induced slip if the amount of sulfide in the fault mud stems from the seismic process; 3 The different seismic slip mechanisms experienced by the faults may be controlled by the deep faults in the fault structure, such as the fault shape. The steep dip of the Yingxiu-Beichuan seismic fault zone tends to produce high-temperature and rapid seismic slip, whereas the gentle dip of the Guanxian-Anxian seismic fault zone More prone to low temperature and slow earthquake slippage.