A study on the characteristics of fault activity in the southern part of the Ulsan fault using paleoseismic method

Gwon, Ohsang; Park, Kiwoong; Naik, Sambit Prasanajit; Hyeoncho, Shin; Kim, Young‐Seog

doi:10.14770/jgsk.2021.57.2.109

Cited by 7 publications

(3 citation statements)

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“…Along the eastern margin of the valley (i.e., the western front of the mountain range), a number of fault outcrops have been identified, some of which show that the fault cuts young unconsolidated sediments (Figure 1C; Table 1). In outcrops, trench walls, and drilling surveys, the faults show typical reverse-slip features, such as east-side-up apparent offset, drag pattern, and flat-ramp geometry (e.g., Ryoo et al, 2001Ryoo et al, , 2002Ryoo et al, , 2004Choi et al, 2002Choi et al, , 2003Park et al, 2020;Kim et al, 2021c;Gwon et al, 2021;Naik et al, 2022;Park et al, 2022). The fault strands are featured by slightly curved multiple strands (generally NNW-SSE to N-S), which anastomose and link up with each other.…”

Section: Fault Characteristics Along the Mountain Rangementioning

confidence: 99%

“…Fault strands on the two sides of the Ulsan Fault Zone show variation in their predominant geometry, that is, their dip angle and kinematics. Faults along the eastern margin of the valley generally exhibit moderate-to low-angle dips (20 °-65 °) and mainly reverseslip sense (Table 1; e.g., Kim et al, 2020b;Kim et al, 2021c;Gwon et al, 2021;Naik et al, 2022). Here, we discuss why the eastern edge of the Ulsan Fault Zone shows different features from the western edge and the potential relationship of the fault zone with the YTL.…”

Section: Definition and Characteristics Of The Ulsan Fault Zonementioning

confidence: 99%

“…Muryongsan (450 m), from north to south. Paleoseismic and structural investigations along the western front of the mountain range, which is composed mostly of alluvial fans, show records of reverse faulting during the late Quaternary, characterized by several NNW-SSE-to N-S-striking fault strands and top-to-the-west kinematics (Figure 1C; e.g., Song and Kyung, 1996;Okada et al, 1998;Chang, 2001;Ryoo et al, 2002;Ryoo, 2009;Choi et al, 2014Choi et al, , 2015Kim et al, 2021c;Gwon et al, 2021;Naik et al, 2022;Park et al, 2022). The geomorphic feature of the western valley has been interpreted as an incised fault valley (Figure 1C;Kim, 1973;Kim et al, 1976;Kang, 1979a and b), although no clear field evidence has been presented for faults within the valley itself.…”

Section: Introductionmentioning

confidence: 99%

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Structural architecture and late Cenozoic tectonic evolution of the Ulsan Fault Zone, SE Korea: New insights from integration of geological and geophysical data

et al. 2023

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Integration of geological and geophysical data is essential to elucidate the configuration and geometry of surface and subsurface structures, as well as their long-term evolution. The NNW–SSE-striking incised valley and parallel mountain range in the southeastern margin of the Korean Peninsula, extending 50 km from Gyeongju to Ulsan cities, are together regarded as one of the most prominent geographical features in South Korea. This paper presents an investigation into the structural architecture and deformation history of the valley and mountain range during the late Cenozoic based on combined data from field observations and gravity and electrical resistivity surveys. Our results based on integrated and reconciled geological, structural, and geophysical data are as follows. First, the incised fault valley can be divided into 1) the northern part, which comprises several distributed buried or exposed fault strands; and 2) the southern part, which comprises a concentrated deformation zone along the eastern margin of the valley. Different deformation features between the two parts are controlled by the lithology of host rocks and by the location and geometry of the neighboring major structures, that is, the Yeonil Tectonic Line (YTL) and the Yangsan Fault. Second, we defined the Ulsan Fault Zone as a NNW–SSE-to N–S-striking fault within the incised valley and along the eastern margin of the valley. In particular, the constituent strands located along the eastern margin of the valley have acted mainly as an imbricate thrust zone, characterized by an east-side-up geometry with moderate to low dip angles and reverse-dominant kinematics in the shallow subsurface during the Quaternary. Third, reactivated strands within the Ulsan Fault Zone during the Quaternary are interpreted as shortcut faults developed in the footwall of Miocene subvertical structures, predominantly the YTL. In addition, movements on the Ulsan Fault Zone and the YTL during the Miocene to Quaternary were arrested by the NNE–SSW-striking Yangsan Fault, which was a prominent and mature pre-existing structure. Our results highlight the spatiotemporal structural variation in SE Korea and emphasize the strong control of the configuration and geometry of pre-existing structures on the distribution and characteristics (i.e., geometry and kinematics) of the subsequent deformation under changing tectonic environments through the late Cenozoic.

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Section: Fault Characteristics Along the Mountain Rangementioning

confidence: 99%

Section: Definition and Characteristics Of The Ulsan Fault Zonementioning

confidence: 99%