摘要
大量的野外观察和实验研究表明,高应变速率的变形作用会在岩石中留下特殊的构造特征。地震作为一种断层快速破裂变形行为,在其作用过程中会使震源及邻近岩石变形从而产生一些特征构造及矿物相组合。剥露地表的断裂带为研究地震相关变形及过程提供了很好的物质材料。识别其中的地震滑动标志,对于确定古地震事件及其发生的机制具有重要意义。Cowan(1999)将断层快速滑动摩擦使得断层面岩石熔融产生的假玄武玻璃作为断层中记录地震滑动的唯一可靠的标识。近年来断裂岩研究取得的一系列重大进展揭示,断层发生地震滑动造成的多种构造产物均可记录其滑动的信息,如碳酸岩和含水硅酸岩的脱挥发分作用、微量元素迁移特征、有机质成熟度、断层镜面构造、液化粒状流、碎屑-皮层集合体、同震晶体塑性变形以及非晶质物质等。此外,与地震破裂传播有关的、在极端瞬态应力条件下形成的,如注入脉、碎粉化作用等特征也可以作为地震发生的岩石记录。因此假玄武玻璃不再是地震破裂的唯一指示物。断层滑动速率在10–4～101 m/s范围内几乎都是动态的,也就是说在实验中10–4 m/s的滑动速率可能指示着地震滑动。本文总结地震滑动和破裂的岩石记录,对认识地震发生机制和完善地震断裂理论具有极其重要的意义。
A large number of field observations and experimental studies have demonstrated that the high strain rate deformation can cause special structures in the rocks. Some characteristic structures and mineral facies combination can be formed in the seismogenic zone and its adjacent rocks during an earthquake rupture process. Exhumed fault zones offer insights into deformation processes associated with earthquakes. Identifying the seismic slip signatures is of great importance for determining the paleoearthquakes and their faulting mechanisms. Cowan(1999) defined the pseudotachylyte, which is produced by the frictional melt during seismic slip, as the only reliable indicator of past earthquakes found in ancient faults. In recent years, significant progress in fault rock studies has revealed a range of reaction products which can be considered as seismic slip signatures, such as frictional devolatilization of carbonates and hydrous silicates, trance element mobility, maturation of organic material, fault mirrors, fluidized granular flow, clast-cortex aggregates, coseismic crystal plastic deformation and amorphous material. In addition, features formed under extreme transient stress conditions associated with propagating tip of an earthquake rupture, such as injection veins and pulverization can also be preserved in rocks as seismic records. Therefore, pseudotachylyte is no longer the only indicator of fossilized earthquake ruptures. Fault slip at rates in range 10–4–101 m/s is almost certainly dynamic, which means that features produced at rates as slow as 10–4 m/s in experiments may be tracers of seismic slip. The authors have summarized the rock records of seismic slip, which provide important information for learning the seismic fault mechanisms and complementing the earthquake theory.