• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2017.10a
• /
• pp.147-148
• /
• 2017

• Journal of the Earthquake Engineering Society of Korea
• /
• v.2 no.4
• /
• pp.41-52
• /
• 1998

The Dongnae Fault in the southeastern part of the Korean Peninsular is not a single fault but a complex fault zone composed of numerous minor faults. In order to deduce the paleostress tensor evolving the Dongnae Fault, we measured 329 faults in outcrops around the fault zone and analyzed the geometries of them. Most of them are steeply dipping(>65˚) and fall into three groups striking N10E, N30E and N70E. More than one half of them show the rakes less than 30˚ Paleostress tensor analysis using the collected fault data has been conducted with the Angelier's direct inversion method and the Choi's method. As result, four different principal paleostress axes each of which subtends an independent tectonic event are found. They are; (1) NNE-SSW compression and ESE-WNW extension (Event I), (2) NNE-SSW extension (Event II), (3) ESE-WNW extension (Event III) and (4) ENE-WSW compression and NNW-SSE extension (Event IV) in chronology. Therefore, the tectonic movement around the Dongnae Fault was firstly governed by strike-slip faulting related to Event I. Afterward, normal faults were formed by Event II and Event III. Finally, the dextral strike-slip faults along the major trace of the Dongnae Fault were formed in NNE direction related to Event IV.

• The Journal of Engineering Geology
• /
• v.26 no.1
• /
• pp.33-49
• /
• 2016

The study area, located in Sinam-ri, Ulsan, in the southeastern part of the Korean Peninsula, is mainly composed of hornblende granite (ca. 65 Ma). Fracturing and reactivation of a fault striking ENE-WSW was strongly controlled by the intrusion of a mafic dyke (ca. 44 Ma), which behaves as a discontinuity in the mechanically homogeneous pluton, increasing the instability of the basement in this area. A geometric and kinematic study undertaken to interpret the faults and fractures was performed in a trench excavated almost perpendicular to the orientation of the dyke. The analysis of structural elements, such as dykes, veins, and faults, is used to infer the deformation history and to determine the paleostress orientations at the time of formation of the structures. The deformation history established based on this analysis is as follows: (1) NNE-SSW, E-W, ENE-WSW, and NE-SW trending fractures had already developed in the pluton before dyke intrusion; (2) felsic dykes intruded under conditions of σ_Hmax oriented N-S and σ_Hmin oriented E-W; (3) mafic dykes intruded under conditions of σ_Hmax oriented E-W and σ_Hmin oriented N-S; (4) dextral reactivation of the main fault associated with the development of hydrothermal quartz veins under conditions of σ_Hmax oriented E-W and σ_Hmin oriented N-S; (5) sinistral reactivation of the main fault and high-angle normal faults under conditions of σ_Hmax oriented NE-SW and σ_Hmin oriented NW-SE; and (6) dextral reactivation of the main fault and NE-SW low-angle reverse faults under conditions of σ_Hmax oriented NW-SE and σ_Hmin oriented NE-SW. These results are consistent with the tectonic history of the Pohang-Ulsan block in the southeastern part of the Korean Peninsula, and indicates the tectonic deformation of the southern area of the Ulsan fault bounded by Yangsan fault was analogous to that of the Pohang-Ulsan area from the Cenozoic. This work greatly aids the selection of sites for critical facilities to prevent potential earthquake hazards in this area.

• Journal of the Korean earth science society
• /
• v.21 no.3
• /
• pp.230-249
• /
• 2000

Southeastern Korean Peninsula has undergone the polyphase deformations according to the changes of regional tectonic settings during the Cenozoic. Through analyses of more than 600 fault-slip data gathered in the study area, five tectonic events are revealed as the followings: (I) NW-SE transtension, (II) NW-SE transpression, (III) NE-SW pure or radial extension, (IV) NNE-SSW transpression, (V) NE or ENE-WSW transpression. Event I was induced by the pull-apart type extension of the East Sea during 24-16 Ma, which resulted in the NW-SE extension of the Tertiary Basins in SE Korea. Event II was resulted from the collision of SW Japan and Izu-Bonnin Arc (or Kuroshio Paleoland) on the Philippine Sea Plate at ${\sim}$ 15 Ma, which stopped the extension of the Tertiary Basins and originated the uplift of fault blocks in and around SE Korean Peninsula. It was continued until ${\sim}$ 10 Ma. Event III is interpreted as the post-tectonic event after the block-uplifts due to the event II, which indicates a temporal lull in activity of the Philippine Sea Plate since 10 Ma. Event IV was originated from the resumption in activity of the Philippine Sea Plate which was restarted to move toward north at ${\sim}$ 6 Ma. The event made the EW compressional structures behind SW Japan as well as in the Korea Straits, and thus the block-uplifts in SE Korea was resumed again. Lastly, event V was resulted from the gradual decrease in influence of the Philippine Sea Plate and the cooperative compression due to the subduction of the Pacific Sea Plate and the collision of the Indian Plate since 5-3.5 Ma, which generated the NS compressional structures in the offshore along the eastern coast of the Korean Peninsula and thrust up the fault-blocks toward west. This event is continuing so far, and thus is making the active faultings resulting in the present earthquakes of the Korean Peninsula.

• Korean Journal of Mineralogy and Petrology
• /
• v.36 no.1
• /
• pp.55-72
• /
• 2023

This study aims to identify the fault zone architecture and geometric and kinematic characteristics of the Yeongdeok Fault, based on the geometry and kinematic data of various structural elements obtained by detailed field survey and anisotropy of magnetic susceptibility (AMS) of the fault rocks. The Yeongdeok Fault extends from Opo-ri, Ganggu-myeon, Yeongdeok-gun to Gilgok-ri, Maehwa-myeon and Bangyul-ri, Giseong-myeon, Uljin-gun, and cuts various rock types from the Paleo-proterozoic to the Mesozoic with a range of 4.6-5.0 km (4.77 km in average) of right-lateral offset or forms the rock boundaries. The fault is divided into four segments based on its geometric features and shows N-S to NNW strikes and dips of an angle of ≥ 54° to the east at most outcrops, even though the outcrops showing the westward dipping (a range of 54°-82°) of fault surface increase as it goes north. The Yeongdeok Fault shows the difference in the fault zone architecture and in the fault core width ranging from 0.3 to 15 m depending on the bedrock type, which is interpreted as due to differences in the physical properties of bedrock such as ductility, mineral composition, particle size, and anisotropy. Combining the results of paleostress reconstruction and AMS in this and previous studies, the Yeongdeok Fault experienced (1) sinistral strike-slip under NW-SE maximum horizontal principle stress (σ_Hmax) and NE-SW minimum horizontal principle stress (σ_Hmin) in the late Cretaceous to early Cenozoic, and then (2) dextral strike-slip under NE-SW maximum horizontal principle stress (σ_Hmax) and NW-SE minimum horizontal principle stress (σ_Hmin) in the Paleogene. It is interpreted that the deformation caused by the Paleogene dextral strike-slip movement was the most dominant, and the crustal deformation was insignificant thereafter.