[S-MP24] 変形岩・変成岩とテクトニクス

[SMP24-12] Creep behavior of the Chegualin Fault in southwestern Taiwan

*Yen-Hua Chen¹、Pin-Hao Chen¹、Yun-Syuan Yan¹、 Ming-Chih Hsieh¹、Yan-Wei Huang¹ (1.Dept. of Earth Sciences, National Cheng Kung University)

キーワード：Creep, Chegualin fault, Clay minerals, Microstructure, water, Deformation & weakening mechanism

The Chegualin and Chishan Faults in the mudstone area of southwestern Taiwan are both active faults. GPS monitoring shows extremely high horizontal and vertical displacement rates between these two faults every year, which is causing serious damage to the National Highway No. 3 section and jeopardizing driver safety. This study specifically analyzed the characteristics of the geo-materials of the Chegualin fault zone and explored the effects of mineral composition, microstructure, and water content on the fault behavior in the fault zone. The experimental results showed that the deformation and weakening mechanism of the Chegualin Fault rock mass are related to ¹mechanical deformation (cracking and frictional sliding, dislocation creep, and mechanical twining), ²mineral composition (pyrite, carbonate and clay minerals), ³water (meteoric water, formation water and water from clay minerals), and ⁴fluid–rock reaction (chemical reactions). The fault sliding caused the rock mass to become broken and finer-grained, which increases the specific surface area of the rock and adsorption of water, thereby reducing the mechanical strength of the rock mass. The observation of optical microscope (OM) and scanning electron microscope (SEM) revealed that the fault rock mass developed microstructure and strained carbonate and mica minerals occurred, which suggested the stress effect. The high clay minerals content in the fault core zone affected the water content, friction coefficient, and rate of healing of the fault, making it easier for fault slip to occur. Therefore, water is an important factor affecting the deformation and creep of the fault rock mass. Because the fault creep will continue, monitoring rainfall, variations of groundwater level, mineral phases, and microstructure development is recommended. These can be used as monitoring indicators for disaster prevention and early warning for this area.