ScholarWorks@경상국립대학교

초록

The materials and microstructures of active faults provide essential information to better understand the slip properties of past faults through geological hazard assessments and paleoseismology studies. This study aimed to elucidate the slip properties of the Quaternary fault during Quaternary slip. This was done through analyses of the internal structure, fault materials, and microstructure of the Quaternary fault zone observed in the trench section of the Pohang area. An E-W trending trench section excavated perpendicular to the NNE-SSW trending Yangsan fault line, which divides Hayang Supergroup and Bulkuksa Granite, reveals that a >6 m thick mature fault core zone composed of foliated gouges and breccia thrusts poorly lithified Quaternary sand and gravel deposits. Its shape boundary strikes N15 degrees E and dips 42 degrees SE. The Quaternary fault zone is defined by clay-rich gouges, mainly composed of poorly crystallized smectite and palygorskite, and deformed Quaternary sediments. The microstructure of the Quaternary fault zone shows a <1 cm thick principal slip zone (PSZ) and <400 mu m thick micro-PSZ with sharp boundaries and strong foliations between paleo fault rocks and deformed Quaternary sediments. In addition, the microstructure of deformed Quaternary sand exhibits interconnected and partially fractured structures between the grains. These microstructural and mineralogical characteristics of the Quaternary fault suggest that the coseismic Quaternary faulting, which caused surface rupture along the Yangsan fault, was activated, resulting in rapid slips between the pre-existing fault core zone and unconsolidated sediments near the surface. Quaternary fault material and microstructural studies expect to contribute to anticipating the slip properties of the fault after reactivation and to determine a more accurate timing of faulting.

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