Grain size distribution and fracture energy of Chelungpu-fault gouge

• Main Authors: Chein-Hung Chen, 陳建宏
• Other Authors: Kuo-Fong Ma
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/92201804006383845793

碩士 === 國立中央大學 === 地球物理研究所 === 98 === The Taiwan Chelungpu Drilling Project (TCDP) drilled several holes penetrating the Chelungpu fault, and identified a 12-cm slip layer near the depth of 1136 m of Hole-C. This primary slip zone (PSZ) had been recognized as the major slip zone of Chi-chi earthquake on September 21st 1999, with several layers related to historical events along the Chelungpu fault. We examined the fault gouge related to the PSZ to give further exploration on the fracture energy, which is related to the surface area of the broken particles, to understand the possible partition of the energy for the most recent event and historical events. Previous studies in observation of the particle, related to the Chi-Chi earthquake, show that the grains smaller than 100 nm, having the spherical shape, and did not follow the power law. We further made the similar studies for the layers in the PSZ and made the comparison of the observations of these layers. We cut the PSZ into 10 samples with the dimension of 2cm * 2cm. By observation, we defined 16 different layers, which might be related to different historical events, in the PSZ. In the observation of scanning electron microscope (SEM), we obtain the relationship between particle diameter D and particle density N(D), and make a power-law of grain size distribution for each layer. In the weak layers, which might be associated with the most recent Chi-Chi event, we found the fractural dimension of about 2.2 and 2.3. Other layers have the fractural dimension of near 2.0, and with no observation of spherical grain of less than 100nm. It suggests the existence of the spherical grains might be resulted from dynamic processing during faulting, and would be disappeared after healing. According to the grain size distribution, we calculated the fracture energy from total surface area of the grains by EG=SλGC (S is surface area (m2), λ is grain roughness, GC is specific energy (Jm-2)). In the weak layer, the surface fracture energy is about 2.93-4.38MJm-2, other layers have relatively lower values of about 0.88MJm-2. Further studies on the comparison of the surface fracture energy, and chemical composition will be made to understand the dynamic process of fauling.