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

通过对1999年台湾池池地震的地震断裂带——佘轮堡断裂带南侧和北侧钻孔岩心样本的分析，我们知道了以下几点：1。在南侧钻孔176m深度处，我们发现了约2m厚的破碎伪木质素层。再循环的伪水杨酸颗粒是常见的，这表明地震滑动在该剪切带反复发生。粉碎后的伪木酸酯颗粒中，有小部分具有高温特征（最高可达1730℃），但大部分颗粒具有极低熔融度的织构。在北钻孔223 ~ 227m和283 ~ 320m深度处，发现了若干个蛇轮堡断裂剪切带。这些剪切带的断层核由1 ~ 3cm厚的软粘土层组成，通常伴生一层约1m厚的断层角砾岩，具有马赛克纹理。断层核中的粘土脉频繁侵入断层角砾岩。这种注粘土构造说明了瞬时、异常高孔隙压力的产生。1999年楚楚地震时，舍伦堡断裂带南段和北段的表现非常不同；中等滑移与高频波的辐射有关，而非常大的平滑滑移则缺乏高频波的辐射。这些对比的滑动行为似乎与断层岩一致。也就是说，南部极低熔融程度的高粘性熔体会抑制地震滑动，而断层粘土层的弹性流体动力润滑（Brodsky and Kanamori, 2001）会促进地震滑动。通过对断层泥的分析，研究了断层泥的粉碎和流态化。粉碎从粒度频率的分形维数2.5开始，随着粉碎的深入，分形维数逐渐增大。当分形维数为2.5时，分形颗粒物料的堆积密度最大。因此，粉碎本身就是一种弱化滑移的机制。我们开发了一种新的方法来区分沟槽是否经历了流态化。Brune et al.（1993）的法向界面振动是流化的一个最合理的原因，我们提出了两个现场证据来支持这一机制。粉末科学的知识告诉我们，当断层泥流化时，断层面几乎没有摩擦。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