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<p>The Korean Peninsula is more than 400 km away from passive plate margins and considered a stable continent region. However, it has suffered from damaging earthquakes in the last 20 years. There are two major North–North East tectonic faults in the region: the Chugaryong fault running from Wonsan through Seoul to the west coast and the Yangsan fault in the southeastern part of the peninsula. The Yangsan fault extends for over 170 km and has been active since the late Cretaceous period. The fault has experienced many earthquakes in the last 2000 years, most recently  Mw 5.5 earthquake in its vicinity without any surface rupture. The fault has been studied by various disciplines, such as structural geology to determine the characteristics of the fault, geophysical exploration to determine the extension of the fault, and mineralogy to analyze fault gouges.[A1]  However, the last fault movement remains unknown. Trench studies on the Yangsan Fault undertaken in the central south of the Yangsan Fault to obtain its last movement revealed that the fault had been reactivated at least twice during the Holocene period, at approximately 2 ka and 4 ka. Before the Holocene, another fault movement occurred at approximately 50 ka, with a strike-slip motion creating a meter-wide fault damage zone. LIDAR and aerial photographs demonstrated that a higher terrace younger than 320 ka had moved by 1.5 km with a left-lateral-strike-slip motion. We now surmise that the Yangsan Fault has been continuously reactivated for more than 60 million years, and could potentially generate severe geohazards in the near future. Furthermore, even if the fault is inside an intraplate, we propose that it has continuously been reactivated from the Late Cretaceous to the present by plate tectonics.</p>

<p>Bleached rocks are commonly formed from CO<sub>2</sub>-saturated water leakage to the surface. It could provide opportunities to understand the mechanisms and controlling factors associated with injected and sequestrated CO<sub>2</sub> leakages as well as fluid flow in the subsurface. In this study, we investigated the various bleaching patterns and their related structures in order to understand the characteristics of fluid-flow migration around the major structures. Also, we examined the effects of lithology and structural characteristics on fluid flow in detail along and around the major structures. For this purpose, we analyzed bleaching characteristics of multiple layered sedimentary rocks around two major faults (Moab and Salt Wash Faults) and fold axes (Green river anticline system) based on field observations and quantitative measurements (scanline survey and permeability) in the exhumed reservoir-cap rock systems in SE Utah, USA. The results showed that strongly bleached layers of sedimentary rock have a higher density of deformation bands compared to unbleached layers. This is consistent with the general property of deformation bands that frequently develop in layers with higher porosity and permeability. Although almost all fault zones act as conduits for fluid flow, some fault zones filled with clay-rich gouges could impede fluid flow. In addition, the internal sealing characteristics of the layer boundaries such as bedding planes could be important factors as they can act either as a pathway or a barrier for lateral fluid flow depending on the existence of filling materials such as calcite or kerogen. Our research may be useful for assessing CO<sub>2</sub> leakage in oil reservoirs or CO<sub>2</sub> sequestration sites located in a reservoir-cap rock system of sedimentary basins.</p>