Yangsan Fault Research Articles

Dating drainage reversal using mineral provenance along the Yangsan Fault, South Korea.

Tectonics is broadly accepted as one of the main factors controlling long-term landscape evolution. The impact of tectonics on short timescales is most often observed through earthquake rupturings that produce localized, metric-scale deformations. Although these deformations significantly affect the landscape, it remains challenging to precisely correlate major landscape changes with these localized earthquake deformations. Therefore, linking instantaneous deformation to long-term morphological changes often involves a thought experiment with potentially limited temporal resolution. At a paleoseismological site along the slow-moving strike-slip Yangsan Fault in South Korea, we employed optically stimulated luminescence (OSL) dating and detrital zircon analysis on all exposed unconsolidated layers in trench walls. The results reveal a significant provenance shift in the sediments accumulating in the trench, indicating a major reorganization of the drainage network. Based on our OSL and detrital zircon data, we estimate that this change occurred around 70ka. We propose that this drastic drainage reorganization was caused by a combination of very slow, yet continuous, earthquake activity and a temporary reduction in river erosion during the onset of the cold, dry spell characteristic of the MIS4 stage across the Korean Peninsula.

Segmentation geometry of strike-slip fault systems in slow-deforming regions: a proposed method and case study of the Yangsan Fault, South Korea

Segmentation geometry of strike-slip fault systems in slow-deforming regions: a proposed method and case study of the Yangsan Fault, South Korea

Evidence for large Holocene earthquakes along the Yangsan fault in the SE Korean Peninsula revealed in three-dimensional paleoseismic trenches

Evidence for large Holocene earthquakes along the Yangsan fault in the SE Korean Peninsula revealed in three-dimensional paleoseismic trenches

Determination of the long-term slip rate of a fault in a slowly deforming region based on a reconstruction of the landform and provenance

Determining slip rates is essential for assessing earthquake hazards and understanding their recurrence intervals. However, in regions characterized by slow deformation, the long intervals between seismic events present challenges in understanding the long-term seismic behavior. This study focused on the Yangsan Fault (YF) on the Korean Peninsula, which is a major active fault in a slowly deforming area. We identified paleo-surface ruptures and validated stratigraphic evidence of paleo-earthquakes by geomorphological analyses and trench surveys along the YF. Landform restoration analyses indicate a lateral offset of ~320 m, which is supported by downstream changes in gravel composition in channels that cross the YF. Our investigation into the notable changes in gravel composition within channels forming in the alluvial fan revealed sediments with compositions unlikely to originate from the current topography. Observations of the sediment composition in channels within the alluvial fan, flowing from east to west, suggest a dextral slip sense focused around the YF. The minimum slip rate for the lateral offset was calculated to be 0.38–0.57 mm/yr using a burial age of ca. 698 ka for a gravel deposit exposed in a trench wall. The results show the importance of using diverse approaches to mitigate methodological uncertainties in measuring fault displacements and ages, particularly when determining the long-term slip rate in intraplate settings.

Deformation microstructures of fault rocks from the northern Yangsan Fault, SE Korea: implications for coseismic and aseismic behavior

Deformation microstructures of fault rocks from the northern Yangsan Fault, SE Korea: implications for coseismic and aseismic behavior

Application of electrical resistivity surveys to detect buried active fault: a case study of the southern Yangsan Fault, Korea

Application of electrical resistivity surveys to detect buried active fault: a case study of the southern Yangsan Fault, Korea

The effect of weathering on cohesion in granitic fault rocks: A case study from the Yeongdeok Fault, South Korea

Weathering can alter fault-rock cohesion, which is an important criterion in the classification of fault rocks, and can also alter fault-rock mechanical and hydraulic properties. To investigate the effects of weathering on fault rocks, we studied relatively fresh and weathered fault rocks collected from a drill core and outcrop, respectively, of a granitic fault zone (the Yeongdeok Fault, a northern branch of the Yangsan Fault) on the southeastern Korean Peninsula. At the studied outcrop, the Yeongdeok Fault has juxtaposed Triassic granite against Cretaceous sedimentary rocks. Granitic fault rocks in the outcrop are incohesive, whereas the drill core includes both cohesive and incohesive granitic fault rocks. A detailed correlation of the fault rocks from the drill core with those from the outcrop reveals that some incohesive fault rocks from the outcrop are weathered cataclasite. Cataclasites from the drill core are composed of feldspar, plagioclase, and quartz fragments embedded in a matrix of quartz, plagioclase, muscovite, and chlorite. Locally, foliation defined by the preferred orientation of muscovite is developed. The weathered cataclasite comprises quartz, plagioclase, and feldspar fragments, with a fine-grained matrix composed mostly of clay minerals. The measured Chemical Index of Alteration (CIA) values for cataclasite and weathered cataclasite are 47–49 and 60–67, respectively. Measurements of hydraulic properties show that weathered cataclasite has higher porosity and permeability compared with unweathered cataclasite. Physical and chemical weathering are interpreted to have increased the fracture density of the weathered cataclasite and enhanced the dissolution of vein minerals, respectively. These processes have not only contributed to the higher permeability and porosity of the weathered (cf. unweathered) cataclasite but have also resulted in a loss of cohesion. When cohesion is lost due to weathering, distinguishing between cataclasite and fault breccia becomes challenging. Our study demonstrates that the cohesion-based classification of fault rocks becomes limited for fault rocks with CIA value more than 60.

Quaternary Faulting along the Southernmost Part of Yangsan Fault in Geumsan-ri, Yangsan-si, SE Korea

Quaternary Faulting along the Southernmost Part of Yangsan Fault in Geumsan-ri, Yangsan-si, SE Korea

Near-surface termination of upward-propagating strike-slip ruptures on the Yangsan Fault, Korea

We present a new example of the termination of strike-slip paleoearthquake ruptures in near-surface regions on the Yangsan Fault, Korea, based on multi-scale structural observations. Paleoearthquake ruptures occur mostly along the boundary between the inherited fault core and damage zone (N10–20°E/> 75°SE). The ruptures propagated upward to the shallow subsurface along a < 3-cm-wide specific slip zone with dextral-slip sense, along which the deformation mechanism is characterized mainly by granular flow in near-surface region. The ruptures either reach the surface or are terminated in unconsolidated sediment below the surface. In the latter case, the rupture splays show westward bifurcation, and their geometry and kinematics show a change to NNW-strike with low-angle dip and dextral-reverse oblique-slip sense in the strata. We suggest that the upward termination of the contractional strike-slip ruptures is controlled by the inherited fault geometry that is unfavorable with respect to the stress field (ENE–WSW σHmax) at basement depths in terms of movement on the fault, and the lack of extension of the fault into shallow subsurface; a depth-dependent change in stress from σHmax > σv > σHmin to σHmax > σHmin > σv at depth of a ~ 200 m; and the physical properties of unconsolidated sediment, which have low inter-granular cohesion, resulting in distributed deformation.

Fault-related basins as carbon reservoirs: Soil CO2 emissions in the SE Korean Peninsula

Carbon dioxide (CO2) is one of the main components of greenhouse gases, and there is a great concern about emissions mainly from human activities. However, long term CO2 emissions during the Earth’s history are largely related to natural emissions by geological factors. Natural CO2 emissions are mainly at highly permeable passages below the surface (e.g., volcanoes or faults). Unlike volcanoes, which actively release mantle-derived volatiles, faults can be affected by CO2 of more diverse origins and are relatively lacking in research. Here, we note that it is important for CO2 emissions that faults as channels with high permeability take topographical control to form sedimentary basins and produce mature soils. To this end, we performed CO2 flux measurements in the Yangsan Fault System (YFS), Republic of Korea. As this fault is an active fault, topographical variations are clear and accessible. In the YFS, high spring CO2 fluxes (119.5 g m−2 d-1 to 77,699.5 g m−2 d-1) were observed in Sector 1, and high soil CO2 fluxes (0.5 g m−2 d-1to 1,240 g m−2 d-1) were observed along the Hyeongsan River in Sector 2. The carbon isotope composition indicates that the mantle contributes to fault-related spring CO2 (δ13C = -14.03 ‰ to −7.44 ‰), and soil CO2 comes from shallow biogenic sources (δ13C = –22.82 ‰ to −13.53 ‰) deposited in fault-forming basins. In addition, the helium isotope ratios indicative of the mantle contribution (3He/4He = 1.86 to 6.02 Ra) are shown in the gas samples of the springs. Furthermore, in a post-earthquake survey, we found temporal changes in soil CO2 flux values near the epicenter, which may be related to the earthquake. A simple calculation of overall CO2 emissions suggests that significant amounts of CO2 (6.2 Mt yr−1) are being emitted along the YFS. Therefore, this study reports both large-scale structural degassing and biological CO2 emissions from fault zones, providing implications for the role of sedimentary basins and soil types formed in fault zones.

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

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.

Tectonic evolution of the Yangsan Fault, SE-Korea, by gravity field interpretation

SUMMARY To estimate the tectonic displacement history of the Yangsan Fault (YSF) in the Cretaceous Gyeongsang Basin (GB), SE-Korea, gravity field measurements were implemented and interpreted. A total of 8000 ground-measured gravity data were compiled and deployed to calculate the Bouguer and residual gravity field. The residual field shows that the mean value in the southern segment of the YSF is very similar to that of the northern segment, meanwhile that of the central segmentation is significantly lower than those of the other segmentations. This implies that the crustal structure and petrophysical properties of the central segment differ significantly from those of the other segments. Applying dip curvature analysis to enhance the image of the residual gravity field, we find that (1) the Gaum fault system (GF) in the western and middle part of the GB extends up to the YSF, where A-type granite outcrops are observed. (2) The middle- and eastern segments of the GF that formed before tectonic motion of the YSF are revealed in turn in areas east of the YSF, which were now covered by the younger sedimentary basin. (3) The middle segment of the GF which occupies between the YSF and the Yeonil tectonic line (YTL) has been displaced approximately 25 km southward from the main GF trace. (4) The easternmost segment is revealed buried in the eastern side of the YTL, which is displaced southward about 18 km from the main GF trace. Comparing all the available geoscientific data sets, we conclude that the right-lateral tectonic movement of the YSF, and the deeply buried middle segment of the GF remained stationary, while the most eastern segment of the GF is reversely moved to the north through left-lateral strike movement of the YTL.

Correlation of paleoearthquake records at multiple sites along the southern Yangsan Fault, Korea: Insights into rupture scenarios of intraplate strike-slip earthquakes

The construction of spatiotemporal models of earthquake occurrence for intraplate areas is challenging due to the low deformation rates in these areas. In this study, we conducted paleoseismological investigations along the southern Yangsan Fault (SYF), a typical low-deformation-rate fault, on the Korean Peninsula. The SYF is distinct from the northern Yangsan Fault (NYF), and the boundary between them is located at the junction between the NNE-striking YF and another major structure, the NNW-striking Ulsan Fault (UF), which branches off from the YF. Paleoseismological trenches at four sites along the SYF indicate that this fault section has not ruptured during the Holocene, in contrast to the NYF and UF. In detail, surface ruptures along the studied section of the SYF occurred during three different time periods, as inferred from stratigraphy and radiocarbon dating: 74 to 49 ka at two sites, 39 to 35 ka at another site, and 28,000 cal yr BP (or 30 ka considering the OSL age) to 16 ka at all sites. These results suggest two alternative rupture scenarios for the timing of paleoearthquakes along the studied fault section during the Late Pleistocene: (1) full rupture along the entire studied section during each earthquake event, or (2) multiple partial ruptures along the two structurally distinguishable parts of the studied fault section, that is, the Wolsan–Miho and Inbo north–Inbo sections. We conclude that geometric discontinuities of the long-lived YF system in the Korean Peninsula intraplate region have played an important role in controlling recent spatiotemporal rupture behavior.

Monitoring of Possible Activities of Yangsan Fault Zone Using GNSS

After the Gyeongju earthquake in 2016 and the subsequent one in Pohang the following year, there is an imminent necessity to evaluate the risk of earthquakes accurately as well as respond to the risks on the Korean peninsula. For this purpose, the existence and movement of a fault should be investigated in the area. In this study, we calculated the displacement of the crust around the mass production fault using GNSS (Global Navigation Satellite System) data and analyzed the deformation characteristics by applying the method of stress calculation. The Yangsan Fault Zone has been analyzed with a total of 24 GNSS stations between 2018 and 2021. Data processing was conducted with Bernese GNSS Software, which requires high-precision orbit, satellite clock, ionosphere information for high-precision position estimation. By accumulating daily solutions over the three years to produce the final solution with the velocity of the stations, the Yangsan Fault Zone moved about 32 mm per year southeast on average. Based on the results, the movements of the stations on either side of the Faults are almost the same. Stress analysis of the Yangsan Fault Zone showed a large east–west expansion during 2018–2019 but decreased in stress afterwards, thus it is evaluated to be relatively stable compared to the past. However, due to the nature of crustal variation continuous monitoring research with long-term data processing should be followed, which will be discussed in further research.

규장질 누적암과 용융체의 불완전 분리를 통한 고-실리카 화강암의 형성에 대한 예비연구: 경주 일대 양산단층 동부의 우백질 화강암

규장질 누적암과 용융체의 불완전 분리를 통한 고-실리카 화강암의 형성에 대한 예비연구: 경주 일대 양산단층 동부의 우백질 화강암

Active Fault Trace Identification Using a LiDAR High-Resolution DEM: A Case Study of the Central Yangsan Fault, Korea

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.

Relationship between hydraulic conductivity and occurrence of fault rocks in Yangsan fault zone, Korea

Relationship between hydraulic conductivity and occurrence of fault rocks in Yangsan fault zone, Korea

"경상남·북도 논매기소리 공간분포와 전파 특성에 관한 연구 - 지형요소를 중심으로 -"

In this study, the spatial distribution and diffusion characteristics of the Chingching-i, Sangsa and Ipmal in Gyeongnam and Gyeongbuk provinces were analyzed using geomorphic elements. By examining the drainage network, we found that the Chingching-i is dominant along the Nakdong river, Wangpi stream, Hyeongsan river, Hwang river and Namgang, The Sangsa was widespared along the Nakdong river, Miryang river, Hwang river, Yangsan stream. The Ipmal appeared along the flow path of the Nakdong river, Naeseong stream, and Yangsan stream. A lineament analysis indicated that the chingching-i, Sangsa, and Ipmal are generally distributed along the NE-SW direction, coinciding with the strike of the Sobaek Mountains, the NS and NNE-SSW directions, coinciding with the strike of the Taebaek Mountains, and the Yangsan Fault zone. The whole intersection between these lineaments acted as a medium for smooth spreading of the sounds to neighboring regions. The findings of the present research can be used as basic data for regional classifiying the Gyeongsang Province using the spatial distribution characteristics of rice-paddy weeding songs, and it will be possible to build a spatial database.

A multidisciplinary approach to characterization of the mature northern Yangsan fault in Korea and its active faulting

A multidisciplinary approach to characterization of the mature northern Yangsan fault in Korea and its active faulting

Long‐Term Weakening Processes and Short‐Term Seismic Slip Behavior of an Intraplate Mature Fault Zone: A Case Study of the Yangsan Fault, SE Korea

AbstractAn intraplate tectonic fault evolves with repeated seismic cycles that may exhibit multi‐mode slip behaviors (continuous aseismic sliding, slow slip with silent earthquakes, and earthquakes resulting from stick‐slip frictional instability). Here, we show long‐term (geological time scale) fault zone weakening processes and short‐term (seismic cycle scale) fault behavior of the Yangsan Fault, SE Korea, based on structural and mineralogical observations of an across‐strike fault zone sequence retrieved by inclined borehole drilling. Since the Late Cretaceous, physical and chemical weakening processes have formed a wide and complex fault zone characterized by interconnected clay‐rich fault core strands and fractured lenses. The deformation is more concentrated in the eastern block (Cretaceous sedimentary rock with felsic dikes) of the fault zone than in the western block (Paleogene granite) of the fault zone. The asymmetrical deformation pattern is controlled by the distinct properties of the different host rocks and differential fluid‐assisted reaction softening involving hydrothermal processes. Of the five main strands and numerous subsidiary strands in the wide fault zone, strand S1 between the sedimentary rock and granite has accommodated the largest displacements. In particular, the smectite‐rich, &lt;2‐cm‐wide principal slip zone within S1 has acted as the major pathway for past seismic slip. Our findings consider that slow deformation in the sedimentary rocks formed the asymmetrical wide fault zone over long geological time, whereas that the preferential propagation of repeated seismic slip events propagated preferentially along the narrow principal slip zone of S1.