Understanding the physical processes of frictional slip of subduction zone earthquakes from the characteristics of fault rocks.

通过对穿过1999年台湾集集地震的地震断层--雪龙铺断层的南部和北部钻孔的岩心样品的分析，我们了解到以下几点。在南部井深176米处，我们发现了约2米厚的破碎假硅质岩层。再循环的假玄武岩颗粒很常见，表明地震滑动在该剪切带中反复发生。粉碎的假黄晶的很小一部分颗粒记录了高温(高达1730℃)的特征，但大部分颗粒表现出极低熔化度的结构。在北部井深223-227m和283-320m处，我们发现了石龙堡断裂的几条剪切带。这些剪切带的断层核由1-3厘米厚的软粘土层组成，通常伴生有一层约1m厚的马赛克结构的断层角砾岩。来自断层核部的粘土矿脉经常侵入断层角砾岩。这种粘土注入结构表明…瞬时孔压和异常高孔压的产生越多。1999年楚楚地震期间，石龙铺断裂南段和北段表现出截然不同的特征：中等滑动伴随着高频波的辐射，而极大而光滑的滑动缺乏高频波的辐射。这些截然不同的滑动行为似乎与断层岩相吻合。也就是说，南方熔融程度极低的高粘度熔体抑制了地震滑动，而断层粘土层的弹流动力润滑(Brodsky和Kanamori，2001)则促进了地震滑动。粉碎开始于粒度频率的分维2.5，分维随着粉碎的加深而增大。当分维为2.5时，颗粒材料的堆积密度最大。因此，粉碎本身就是一种滑移弱化机制。我们开发了一种新的方法来区分是否经历了流态化。Brune等人的正常界面振动。(1993)是流态化最合理的原因，我们提出了两个支持这一机制的现场证据。粉末科学的知识告诉我们，当断层泥流态化时，断层面几乎是无摩擦的。较少

Followings were known from the analysis of the core samples from the southern and northern boreholes penetrating the Shelungpu fault, the seismic fault of the 1999 Chi-Chi earthquake in Taiwan.1. At the depth of 176m of the southern borehole, we found the crushed pseudotachylyte layer about 2m thick. Recycled pseudotachylyte grains are common, indicating that seismic slips have repeated in this shear zone. Very small part of grains of crushed pseudotachylyte record high temperature (up to 1730℃) signatures, but major part of grains shows the texture of very low degree of melting.2. At the depth of 223-227m and 283-320m of the northern borehole, we found the several shear zones of the Shelungpu fault. The fault core of these shear zones is composed of soft clay layer of 1-3cm thickness, and it is commonly associated with a layer of about 1m thick fault breccia with mosaic texture. Clay veins from the fault core frequently intrude the fault breccia. This clay injection structure suggests … More the generation of instantaneous and abnormally high pore pressure.3. The southern and northern parts of the Shelungpu fault behaved very differently during the 1999 Chu-Chu earthquake; moderate slip associating the radiation of high frequency wave, while very large and smooth slip lacking the radiation of high frequency wave. These contrasting slip behaviors appear to be consistent with the fault rocks. Namely, the highly viscous melt of very low degree of melting in the south would have restrained the seismic slip, while the slip would have been promoted by the elastohydrodynamic lubrication (Brodsky and Kanamori, 2001) of fault clay layer.We studied the comminution and fluidization of fault gouges through analyzing fault gouges.1. Comminution starts at the fractal dimension 2.5 of grain size frequency, and the fractal dimension increases as further comminution. Fractal granular materials can be packed most densely when the fractal dimension is 2.5. Therefore, comminution itself is a slip-weakening mechanism.2. We developed a new method how to distinguish the gouges whether they have experienced fluidization or not.3. Normal interface vibration by Brune et al. (1993) is a most plausible cause of fluidization, and we presented two field evidences that support this mechanism.4. The knowledge of powder science teaches us that fault plane becomes nearly frictionless when gouge is fluidized. Less