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(a) Schematic illustration (a) and (b, c) photographs showing the internal structure of the Yangsan Fault core and the eastern damage zone at the Taegi site.
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The NNE-SSW-striking Yangsan Fault, which can be traced through Busan, Yangsan, Gyeongju, Pohang, and Yeongdeok, is a mature fault with a multi-stage deformation history that has been active since at least the Late Cretaceous. The fault is also associated with Quaternary deformation features at the surface. In the last several decades, academic and...
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The generally NW‐SE‐trending thrusts developed north of the Kunlun Range are the most prominent morphological feature in the western Qaidam Basin, NE Tibet. These folds have played a key role in the Miocene‐Quaternary uplift of the region. However, little is known about the long‐term rupture behavior of this active thrust zon...
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... Since the Late Cretaceous, the fault has undergone multiple deformations, with each stage corresponding to different paleo-stress regimes. The Yangsan Fault exhibited a dextral strike-slip movement with a minor reverse component during the Quaternary, and certain segments remain active under a current stress regime in the E-W or ENE-WSW compression [47,48]. This study focuses on the Byeokgye section, the longest Quaternary surface rupture on the northern Yangsan Fault ( Figure 1d) [13,14]. ...
The spatial variability of input parameters plays a crucial role in the interpretation of geomorphic indices, with digital elevation models (DEMs) being the primary data source. However, the influence of DEM resolution on these indices has rarely been investigated. This study investigated the influence of DEM resolution on the assessment of tectonic activity using the normalized stream length–gradient (SLk) index, which reflects variations along river profiles. The SLk index is sensitive to changes in river gradients that may result from active faulting or differential uplift, making it a valuable tool for identifying zones of active tectonic deformation. Therefore, understanding the impact of DEM resolution on SLk analysis is critical for accurately detecting and interpreting subtle tectonic signals, particularly in intraplate regions where deformation is slow and geomorphic expressions are faint and discontinuous. By comparing high-resolution LiDAR-derived DEMs (L-DEMs) and low-resolution topographic map-derived DEMs (T-DEMs), we analyzed the SLk index distributions along the Yangsan Fault, Korean Peninsula, an intraplate setting with Quaternary activity. According to the results, SLk anomalies derived from L-DEMs had a continuous distribution along the fault, closely aligning with known surface ruptures and indicating active tectonic deformation. In contrast, SLk anomalies derived from T-DEMs were sporadic and less continuous, especially in low-relief landscapes such as alluvial fans and floodplains, highlighting the limitations of T-DEMs in detecting fault-related features. High-resolution DEMs were better able to capture finer-scale geomorphic features, such as fault scarps, deflected streams, and lineaments associated with active tectonics, providing a more comprehensive view of fault-related deformation. This discrepancy highlights the importance of resolution choice in tectonic assessments, as low-resolution DEMs may underestimate the tectonic activities of intraplate faults by missing subtle topographic variations. While the choice of DEM resolution may depend on study area, scope, and data availability, high-resolution DEMs are critical for identifying tectonic activity in intraplate regions where geomorphic features of faulting due to slow deformation are subtle and dispersed.
... Paleoseismic studies on the Korean Peninsula since the 1990s have revealed that most Quaternary surface ruptures were propagated along major structures in the southeastern part of the peninsula, such as the Yangsan Fault, Ulsan Fault, and Yeonil Tectonic Line (Fig. 1b and c;Kee et al., 2009;Kim et al., 2011Kim et al., , 2016Choi et al., 2012). Since the 2016 Gyeongju earthquake, the Yangsan Fault has drawn increasing attention in various fields, including tectonic geomorphology Park and Lee, 2018;Kim and Oh, 2019;Kim et al., 2020c;Kim and Seong, 2021;Hong et al., 2021), fault structure at the outcrop scale and microscale (Woo et al., 2015;Choi et al., 2017;Cheon et al., 2017Cheon et al., , 2019Cheon et al., , 2020aKim et al., 2017aKim et al., , b, 2020aKim et al., , 2021Kim et al., , 2022 DeMets et al., 1990DeMets et al., , 1994Seno et al., 1993Seno et al., , 1996Heki et al., 1999;Bird, 2003;O'Neill et al., 2005;Schellart and Rawlinson, 2010;Kim et al., 2016). The black arrow indicates the moving direction of each plate. ...
... S. Ha et al.: Quaternary surface ruptures of the inherited mature Yangsan Fault Gwon et al., 2020), paleoseismology Choi et al., 2019;Cheon et al., 2020b;Ko et al., 2022;, and fault chronography (Yang and Lee, 2012;Song et al., 2016Song et al., , 2019Sim et al., 2017;Kim andLee, 2020, 2023). Notably, there are many records of Quaternary surface rupturing with dextral kinematics, which were reactivated along the pre-existing mature (long-lived) Yangsan Fault zone (Cheon et al., 2020a). This fault extends > 200 km on land and is several hundred meters wide, with a prevailing horizontal displacement of > 20 km Cheon et al., 2017Cheon et al., , 2019Cheon et al., , 2020a. ...
... Notably, there are many records of Quaternary surface rupturing with dextral kinematics, which were reactivated along the pre-existing mature (long-lived) Yangsan Fault zone (Cheon et al., 2020a). This fault extends > 200 km on land and is several hundred meters wide, with a prevailing horizontal displacement of > 20 km Cheon et al., 2017Cheon et al., , 2019Cheon et al., , 2020a. It underwent multiple stages of deformation with various kinematic senses during the Cretaceous to Cenozoic (Fig. 1b;Chang et al., 1990;Kim, 1992;Chang and Chang, 1998;Chang, 2002;Hwang et al., 2004Hwang et al., , 2007aChoi et al., 2009;. ...
Earthquake prediction in intraplate regions, such as the Korean Peninsula, is challenging due to the complexity of fault distributions. This study employed diverse methods and data sources to investigate Quaternary surface rupturing along the Yangsan Fault, aiming to understand its long-term earthquake behavior. Paleoseismic data from the Byeokgye section (7.6 km) of the Yangsan Fault are analyzed to provide insights into earthquake parameters (i.e., timing, displacement, and recurrence intervals) as well as structural patterns. Observations from five trench sites indicate at least six faulting events during the Quaternary, with the most recent surface rupturing occurring approximately 3000 years ago. These events resulted in a cumulative horizontal displacement of 76 m and a maximum estimated magnitude of Mw 6.7–7.1. The average slip rate of 0.13 ± 0.1 mm yr⁻¹ suggests a quasi-periodic model with possible recurrence intervals exceeding 13 000 years. Structural patterns indicate the reactivation of a pre-existing fault core with top-to-the-west geometry, causing a dextral slip with a minor reverse component. This study underscores the several surface ruptures with large earthquakes along the inherited mature Yangsan Fault, since at least the Early Pleistocene, offering critical insights for seismic hazard and a broader understanding of intraplate earthquake dynamics, enhancing earthquake prediction efforts.
... Lee and Jin, 1991;Hwang et al., 2004Hwang et al., , 2007aCheon et al., 2019Cheon et al., , 2020Lim et al., 2021;Ko et al., 2022;Gil et al., 2023).백악기 후기 좌수향 운동 이래로 양산단층은 조구조적 환경 및 응력장 변화에 따라 미끌림감각의 변화를 수반 한 다중 변형을 경험한 것으로 알려져 있다(e.g., Chang, 2002;Chang and Chang, 1998;Cheon et al., 2017Cheon et al., , 2019Cheon et al., , 2020aCho et al., 2016;Choi et al., 2009Choi et al., , 2017Gu et al. 2021Gu et al. , 2023Gwon et al., 2020;Hwang et al. 2004Hwang et al. , 2007aHwang et al. , 2007bKyung et al., 1999a, b;Ryoo and Cheon, 2019;Song et al., 2020;Yoon and Chough, 1995). ...
... WSW oriented compressional stress fields (Kim et al., 2011;Choi et al., 2012;Jin et al., 2013;Yang and Lee, 2014;Lee et al., 2015;Kim et al., 2016;Choi et al., 2019;Cheon et al., 2020a). ...
... 8), which agrees with the current stress field on the Korean Peninsula . The slickenlines in the pre-existing fault core indicated NE-SW compression, which was consistent with the stress field that causes dextral strike-slip deformation, which is one of the major movements of the Yangsan Fault (Cheon et al., , 2020a. The reconstructed paleo-stress indicated that the dextral strike-slip with a small reverse component identified in the main fault surface occurred in an ENE-WSW compressional stress regime. ...
... However, the Quaternary fault sites south of Mihori show different deformation patterns from those to the north. In the Inbo trench (IB), which is closest to the IBN trench, fault planes developed between unconsolidated sediments (Cheon et al., 2020a), these features are also present in other fault sites of the southern Yangsan Fault (Choi et al., 2012). The deformation pattern of the Quaternary faulting of the northern Yangsan Fault is top to the west, with the main fault core and unconsolidated sedimentary layers abutting the main fault surface, while the Quaternary faulting of the southern Yangsan Fault is characterized by the development of the main fault surface between unconsolidated sedimentary layers. ...
Earthquake prediction in intraplate regions, such as South Korea, is challenging due to the complexity of fault zones. This study employed diverse methods and data sources to detect Quaternary surface rupturing along the Yangsan Fault to improve seismic hazard assessment. Paleoseismic data were analyzed to reveal insights into seismic activity, displacement, and structural patterns. Observations from five trench sites indicate at least three faulting events during the Quaternary, with the most recent surface rupturing occurring approximately 3,000 years ago. These events resulted in a cumulative displacement of 3.1–94.0 m and maximum estimated magnitude of 6.7–7.2. The average slip rate of 0.14 mm/yr suggests a quasi-periodic model with possible recurrence intervals exceeding 10,000 years. The structural patterns imply the reactivation of a pre-existing fault core with top-to-the west geometry, causing a dextral strike-slip with a minor reverse component. This study underscores the continuous faulting along the inherited mature fault, the Yangsan Fault, since at least the Early Pleistocene, contributing valuable insights for seismic hazard assessment in the region and offering a broader understanding of intraplate earthquake dynamics for earthquake prediction.
... The Yangsan Fault is one of the largest faults on the Korean Peninsula (Fig. 1). The fault strikes NNE-SSW with a length of > 200 km on land, dips mainly toward the ESE at a high angle (> 75°), and contains a fault zone comprising multiple fault cores measuring several decameters in width (e.g., Chang et al., 1990;Chang and Chang, 1998;Choi et al., 2009;Cheon et al., 2017Cheon et al., , 2019Cheon et al., , 2020aRyoo and Cheon, 2019;Kim et al., 2022a;Ko et al., 2022). The fault cuts Mesozoic and Cenozoic igneous and sedimentary rocks, and has been identified as a dextral fault with 20-35 km of horizontal offset (Fig. 1b, c) (e.g., Chang et al., 1990;Hwang et al., 2004Hwang et al., , 2007 Kim et al., 2022a). ...
The Yangsan Fault, a long-lived intracontinental fault in SE Korea, exhibits various slip behaviors, including coseismic slip and aseismic creep. However, there is insufficient knowledge of deformation microstructures to reveal the deformation mechanisms operating within the fault. In this study, we present an analysis of the mechanical behaviors displayed by the Byeokgye section of the Yangsan Fault over seismic cycles. Our results are based on detailed microscopic observations of drillcore samples recovered from the Byeokgye section, using an electron backscattered diffraction (EBSD) technique. In injected calcite veins located close to the principal slip zone (PSZ) of < 2 cm in width, plastic deformation (including dynamic recrystallization by subgrain rotation and deformation twins) is concentrated in the blocky calcite grains. In a narrow microbrecciated slip zone (< 1 cm wide) within the granitic damage zone, we observed mechanical Dauphiné twins associated with fractures and microfaults in quartz, as well as intergranular pressure solution (IPS) in the quartz fragments. Given that dynamic recrystallization and IPS are indicative of mechanical behavior of aseismic creep, it is possible that aseismic creep occurs upon the fault during interseismic periods. Conversely, the presence of mechanical Dauphiné twins, coupled with the nature of the PSZ, gouge injections, and the blocky structure of calcite veins, suggests the exposure of the fault section to local seismic stresses during coseismic slip. In conclusion, various deformation processes have operated upon the Yangsan Fault at the studied section throughout multiple seismic cycles. Furthermore, our study demonstrates that EBSD analysis is an effective technique for elucidating the mechanical behavior of fault zones.
... There are notable faults in the southeastern part of the Korean Peninsula, including the Yangsan Fault, Ulsan Fault, Yeonil Tectonic Line, and others. Researchers have extensively utilized various methods, such as imaging, topographic analysis, geological field observations, geophysical exploration techniques, and trench surveys, to investigate structural architectures and paleoseismological features (or Quaternary activities) of these faults (e.g., Okada et al., 1994;Choi et al., 2019;Cheon et al., 2020aCheon et al., , 2020bSong et al., 2020;Gu et al., 2021;Ha et al., 2022;Naik et al., 2022). ...
... The nearly straight incised valley has developed along the southern segment of the Yangsan Fault, where the Miho site is located (Fig. 2). Extending in an NNE-SSW direction and with a total length of approximately 200 km, the Yangsan Fault is one of the longest faults in southeastern Korea (Fig. 2b, c) (e.g., Chang and Chang, 1998;Cheon et al., 2019Cheon et al., , 2020aKim et al., 2023). Based on previous research findings, the Yangsan Fault has been regarded as a dextral fault, despite undergoing multiple stages of deformation with different kinematics during its long-term evolution history since the Late Cretaceous (e.g., Cheon et al., 2019;. ...
The main goal of active fault investigation is obtaining evidence of the Quaternary fault activity through trenching. To accomplish this, electrical resistivity surveys are widely utilized to accurately detect faults buried beneath alluvium. In this study, 2D and 3D electrical resistivity surveys were conducted at the Miho site of the southern Yangsan Fault, the Quaternary active fault area already well-studied via trench investigations. The efficacy of electrical resistivity surveys for fault detection was examined by comparing the resistivity distributions against data in the trench logs. At the Miho site, three lines were installed for the 2D electrical resistivity survey and 22 lines were set within a 27 × 27 m square area for the 3D electrical resistivity survey. The length of each survey line was 27 m with an electrode spacing of 1 m. A dipole-dipole array was used to measure the potential difference between each measurement electrode using the same transmitted current and voltage. To derive the 2D and 3D resistivity distributions from the data acquired in the field, the inversion programs DC_2DPRO and DC_3DPRO were employed. Comparison of the 2D resistivity distribution with trench log data shows that the zone of dacitic welded tuff west of the Quaternary fault plane has relatively high resistivity, while the zone of foliate gouge and breccia derived from sedimentary rocks east of the Quaternary fault plane has a low resistivity of less than 40 Ω·m. From these results, it is evident that the method is effective, particularly when different rock types are distributed on either side of the fault boundary or when highly conductive materials, such as clay-rich fault gouges, are present within the fault zone. The resistivity distribution in the 3D survey area can be depicted using both block diagrams and depth-specific slices, facilitating a spatial understanding of the continuity of fault (or fracture) zones. Consequently, this study demonstrates that 3D surveys offer numerous advantages over 2D surveys by accurately capturing planar structures and enabling spatial interpretation based on 3D resistivity distribution.
... 이러한 측면에서 양산단층이 경험한 고응력장의 변화와 이에 따른 운동학적 역사에 관한 연구결과들이 제시되어왔다 (Chae and Chang, 1994;Chang and Chang, 1998;Choi et al., 2009;Kang and Ryoo, 2009;Cheon et al., 2017Cheon et al., , 2019Kim et al., 2022). 그러나 Lee and Jin, 1991;Hwang et al., 2004Hwang et al., , 2007Cheon et al., 2019Cheon et al., , 2020Lim et al., 2021;Ko et al., 2022;Gil et al., 2023). 연구 지역인 포항시 북구 송라면에 위치한 보경사 사찰 인 근에는 북서-남동 내지 북북서-남남동 방향으로 흐 르는 소하천을 따라 양산단층의 내부구조가 관찰되 는 노두들이 나타난다(그림 1b). ...
... The YF is one of the longest faults in SE Korea and strikes NNE-SSW with a length of ~200 km on land ( Fig. 2a; e.g., Chang and Chang, 1998;Cheon et al., 2019Cheon et al., , 2020b. On the basis of offsets of Cretaceous sedimentary rocks and (~50 Ma) Paleogene A-type granite, the YF has been identified as a dextral strike-slip fault with a cumulative horizontal displacement of 20-35 km (Fig. 2a;Chang et al., 1990;Hwang et al., 2007aHwang et al., , 2007b. ...
... The Yangsan Fault, one of the major tectonic lines on the Korean Peninsula, is the largest fault among the NNE-striking fault systems. On land, it extends~200 km with a fault zone width of several hundred meters, and a dextral offset exceeding 20 km [69][70][71][72][73]. During the Cretaceous-Cenozoic Era, the Yangsan Fault experienced multiple deformations with various kinematics, and the displacement of the most dominant dextral strike-slip among the multiple deformations was found to be~20-35 km (Figure 2b) [70,71,[74][75][76][77]. ...
Korea has been recognized as an earthquake-safe zone, but over recent decades, several
earthquakes, at a medium scale or higher, have occurred in succession in and around the major fault zones, hence there is a need for studying active faults to mitigate earthquake risks. In Korea, research on active faults has been challenging owing to urbanization, high precipitation, and erosion rates, and relatively low earthquake activity compared to the countries on plate boundaries. To overcome these difficulties, the use of aerial light detection and ranging (LiDAR) techniques providing high-resolution images and digital elevation models (DEM) that filter vegetation cover has been introduced. Multiple active fault outcrops have been reported along the Yangsan Fault, which is in the southeastern
area of the Korean Peninsula. This study aimed to detect active faults by performing a detailed topographic analysis of aerial LiDAR images in the central segment of the Yangsan Fault. The aerial LiDAR image covered an area of 4.5 km by 15 km and had an average ground point density of 3.5 points per m2, which produced high-resolution images and DEMs at greater than 20 cm. Using LiDAR images and DEMs, we identified a 2–4 m high fault scarp and 50–150 m deflected streams with dextral offset. Based on the image analysis, we further conducted a trench field investigation and successfully located the active fault that cut the Quaternary deposits. The N–S to NNE-striking fault surfaces cut unconsolidated deposits comprising nine units, and the observed slickenlines indicated dextral reverse strike-slip. The optically stimulated luminescence (OSL) age dating results of the unconsolidated deposits indicate that the last earthquake occurred 3200 years ago, which is one of the most recent along the Yangsan Fault.
... al., 2011;Kim, M.-C. et al., 2016;Cheon et al., 2020a), 이들의 활동시기는 단층비지 및 단층에 의 해 변위된 퇴적물을 대상으로 한 여러 연대측정법 (e.g., ESR, OSL, 14 C)을 통해 제한되었다 (Ree et al., 2003;Lee et al., 2015; (Lin, 2011;Rowe and Griffith, 2015)과 같은 구조가 제4기 단층에서 기대 되는 지진성미끌림 지시자이다(e.g., Han et al., 2020).한편, 국내에서는 아직까지 많이 연구된 바는 없 으나 (Park et al., 2020), 분쇄암(pulverized rock; Brune, 2001;Dor et al., 2006) (Brune, 2001;Dor et al., 2006). ...
