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

从断层岩特征认识俯冲带地震摩擦滑移物理过程

基本信息

批准号：
12440132
负责人：
OTSUKI Kenshiro
金额：
$ 9.79万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

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

通过对贯穿1999年台湾集集地震断层蛇龙埔断层的南北钻孔岩心样本的分析得知： 1．在南钻孔深度176m处发现压碎物。约2m厚的假速晶粒层中常见，表明该剪切带内曾发生过极小部分的地震滑移。假速成岩记录了高温(高达1730℃)特征，但大部分颗粒呈现出极低熔融程度的结构。2．在北钻孔223-227m和283-320m深度，我们发现了几次剪切。这些剪切带的断层核心由厚度为1～3cm的软粘土层组成，通常伴有1m左右的地层。断层核心的粘土脉经常侵入断层角砾岩，这种粘土注入结构表明瞬时异常高的孔隙压力的产生。 3． 1999年楚楚地震期间，中度滑移与高频波辐射有关，而非常大且光滑的滑移缺乏高频波辐射，这些对比滑移行为似乎与此一致。也就是说，南部熔化程度极低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会促进滑动（Brodsky and Kanamori，2001）。通过对断层泥的分析，研究了断层泥的粉碎和流化现象。 1．随着进一步粉碎，分形维数增加，当分形维数为2.5时，分形颗粒材料堆积最密，因此粉碎本身就是一种滑移弱化机制。2． 3. Brune 等人（1993）的正常界面振动是流化的最可能的原因，并且我们提出了支持该机制的两个现场证据。粉末科学知识告诉我们，当凿岩流化较少时，断层面几乎变得无摩擦。