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The Permo-Triassic adakitic magmatism in the southern Korean Peninsula preserves important tectonomagmatic records along the East Asian continental margin. In this study, we present SHRIMP/LA–MC–ICPMS U-Pb zircon ages and Hf isotope signature with whole-rock geochemical compositions of the Middle Permian to Middle Triassic granitoid gneiss-granitoid suites and the Middle to Late Triassic plutonic rocks in the southeastern Korean Peninsula. The former yields three age groups of ca. 272–263 Ma, ca. 258–251 Ma and ca. 243–240 Ma, respectively. The latter group yields ca. 237–216 Ma ages, indicating a long term magmatism that lasted from the Middle Permian to late Triassic. The granitoid gneiss-granitoid suites have chemical compositions similar to high silica adakitic rocks, showing high SiO2 (59.55–73.97 wt.%), Na2O (3.55–5.30 wt.%), Sr/Y (30–401), and La/YbN (11–173), and low MgO (0.18–1.82 wt.%), Y (2–14 ppm) and YbN (2–7). These rocks are peraluminous with high Ba and Sr, and show relatively high K2O contents and K2O/Na2O ratios (> 0.7), with positive correlation between La/YbN vs. Sr/Y ratios and high initial Sr ratios. These features reflect different contribution of the slab-derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the Middle Paleoproterozoic lower crustal basement of the Yeongnam Massif. On the contrary, the Triassic alkaline magmatism in the Yeongnam Massif is alternatively interpreted either by a tectonic switch to the extension-dominated arc system or by a delamination of an overthickened arc. The results from this study offer important evidence for a common subduction-accretion system existed between the North and South China Cratons and microcontinents between them along margins of the East Asian continental blocks, with different plate interaction in different locations generating distinct magmatic suites.

The sediments of the Cretaceous Gyeokpori Formation in south-western South Korea accumulated in a lake in which mainly siliciclastic rocks were deposited, with some interbedded volcaniclastics. The nearby volcanic activity resulted in unstable lake margins inducing a dominance of gravity-flow deposits. The high sedimentation rate facilitated soft-sediment deformation on the sloping margin. The deposition of numerous gravity-flow deposits resulted in a vertically heterolithic stratification. The slumps are composed of different lithologies, which is expressed in different types of deformation due to the difference in cohesion between sandy and mussy layers within the slumps. Coarser-grained (cohesionless) slumps tend to show more chaotic deformation of their lamination or layering. The difference in slumping behaviour of the cohesive and non-cohesive examples is explained and modelled. A unique soft-sediment deformation structure is recognized. This structure has not been described before, and we call it ‘envelope structure’. It consists of a conglomerate mass that has become entirely embedded in fine-grained sediment because slope failure took place and the fine-grained material slumped down with the conglomerate ‘at its back’. The cohesive laminated mudstone formed locally slump folds that embedded the non-cohesive overlying conglomerate unit, possibly partly due to the bulldozing effect of the latter. This structure presumably can develop when the density contrast with the underlying and overlying deposits is exceptionally high. The envelope structure should be regarded as a special – and rare – type of a slumping-induced deformation structure.

Cretaceous volcano-sedimentary basins and successions in the Korean Peninsula are located along NE-SW- and NNE-SSW-trending sinistral strike–slip fault systems. Soft-sediment deformation structures (SSDS) of lacustrine sedimentary strata occur in the Wido, Buan, and Haenam areas of the southwestern Korean Peninsula. In this study, systematic geological, geochronological, and geochemical investigations of the volcanic-sedimentary successions were conducted to constrain the origin and timing of SSDS-bearing lacustrine strata. The SSDS-bearing strata is conformably underlain and overlain by volcanic rocks, and it contains much volcaniclastic sediment and is interbedded with tuffs. The studied SSDSs were interpreted to have formed by ground shaking during syndepositional earthquakes. U-Pb zircon ages of volcanic and volcaniclastic rocks within the studied volcano-sedimentary successions were ca. 87–84 Ma, indicating that active volcanism was concurrent with lacustrine sedimentation. Geochemical characteristics indicate that these mostly rhyolitic rocks are similar to subduction-related calc-alkaline volcanic rocks from an active continental margin. This suggests that the SSDSs in the study area were formed by earthquakes related to proximal volcanic activity due to the oblique subduction of the Paleo-Pacific Plate during the Late Cretaceous.

Bleached rocks are commonly formed from CO2-saturated water leakage to the surface. It could provide opportunities to understand the mechanisms and controlling factors associated with injected and sequestrated CO2 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 CO2 leakage in oil reservoirs or CO2 sequestration sites located in a reservoir-cap rock system of sedimentary basins.

Geological disposal of High-Level Radioactive Waste (HLRW) is considered to be one of the best disposal methods that can stably and semi-permanently isolate high-level radioactive waste from the biosphere. In this study, three types of potential host rocks for HLRW disposal were selected and the hydrogeological characteristics were investigated using deep drilling cores collected at about 50 m intervals in the borehole of a depth of 1 km. The rocks used in this study were granites and gneiss which are crystalline rock, and mudstone which is a sedimentary rock. The results of the study showed that the average porosity of granite was 0.48% and the permeability ranged from 7.87 × 10-19 m2 to 1.39 × 10-21 m2 except for samples outside the measurement limit (4.04 × 10-22 m2). The average porosity of gneiss was 0.49% and the permeability ranged from 3.62 × 10-18 m2 to 4.58 × 10-22 m2. The average porosity of mudstones was 3.62% and the values of permeability for most mudstone samples were lower than the measurement limit. For SEM-EDS analysis, many microcracks were observed in the crystalline rock samples having high permeability. On the other hand, there were almost no microcracks in crystalline rock samples having low permeability, and even if there were cracks, the cracks were filled with fillers such as clay minerals. These results indicate that the presence of microcracks or the filling of cracks in crystalline rocks has a significant effect on the flow of groundwater through the host rock.

This study attempted to use unmanned aerial vehicle (UAV) photogrammetry for structural mapping at limited exposure outcrops in the west coast area of Buan, South Korea. The west coast area of Buan has a large tidal range, and there are restrictions for traditional structure mapping. High spatial resolution (about 4.5 cm per pixel) UAV images were obtained at low tide from a selected study site. The UAV survey identified 50 brittle structures (fractures and faults that were divided into three groups) and changes in the bedding trace. The bedding trace demonstrates various directional verging of the fold geometry that indicates slump-fault structures. While more research is still necessary, this study demonstrated that UAV mapping techniques are very useful for geological structural analysis in coastal areas.

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.

During and shortly after the 2017 Pohang Earthquake (Mw 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground’s susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes (Mw > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea.

In the southwestern part of the Korean Peninsula, Cretaceous volcanic rocks occur along a NE–SW-trending, sinistral strike-slip fault (Hamyeol Fault). Based on their spatial distribution, the volcanic rocks are classified into three lithostratigraphic units: the Buan, the Seonunsan, and the Beopseongpo Volcanics. These volcanics are composed of various types of pyroclastic, sedimentary, and lavas/intrusive rocks. SHRIMP U Pb ages of zircon crystals were isolated from each unit. For the Buan Volcanics, Cheonmasan Tuff = 87.23 ± 0.92 Ma; Udongje Tuff = 86.79 ± 0.71 Ma; Seokpo Tuff = 87.30 ± 0.99 Ma; and Yujeongje Tuff = 86.66 ± 0.93 Ma. For the Seonunsan Volcanics, Gyeongsusan Tuff = 84.9 ± 1.1 Ma and Yeongije Tuff = 86.61 ± 0.67 Ma. For the Beopseongpo Volcanics, Seongsan Tuff = 87.73 ± 0.89 Ma and Gyema Rhyolite = 86.2 ± 1.7 Ma. The ages correspond well to recent mapping results of volcanic rocks in the southwest and south parts of the Korean Peninsula. In addition, the age data are comparable to those of the Aioi and Arima volcanic rock groups in southwestern Japan. This suggests that regional volcanic activity in the Japanese Islands and the southwestern part of the Korean Peninsula is related, and results from magmatism together with crustal deformation due to slab rollback of the Izanagi Oceanic Plate underneath the Eurasian Plate.

The western margin of the Gyeonggi massif, southern Korean Peninsula, has preserved N–S trending Neoproterozoic and sporadic Late Mesoproterozoic metaigneous rocks. Here we present the results from systematic field mapping, sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb dating, and whole-rock geochemical analyses of the Mesoproterozoic and Early Neoproterozoic metaplutonic rocks in the Hongseong area, together with previously published data from the western Gyeonggi massif. The SHRIMP ages of these rocks are categorized into three groups: (1) Late Mesoproterozoic (ca. 1.25–1.15 Ga), (2) Early Neoproterozoic (ca. 900–770 Ma), and (3) late Early Neoproterozoic (ca. 762–730 Ma). The geochronological and geochemical features of the Late Mesoproterozoic rocks suggest that they were possibly formed in association with convergent plate motion. The Early and late Early Neoproterozoic rocks are interpreted to arc-related orogenic and rift-related post-orogenic environments, respectively. These age results and the tectonic signatures provide insight into the convergence process along the margins of the Rodinia supercontinent.

Bleached rocks are commonly formed from CO2-saturated water leakage to the surface. This provides an opportunity to understand the controlling factors of fluid flow in the subsurface. This study examined the relationships between bleaching patterns and geologic features or elements. 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 with 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 fluid leakage in oil reservoirs or CO2 sequestration sites located in a reservoir-cap rock system of sedimentary basins.

The Gyeokpori Formation in the Buan volcanic area primarily contains siliciclastic rocks interbedded with volcanoclastics. These sediments are characterized by a variety of soft-sediment deformation structures (SSDS). The SSDS in the Gyeokpori Formation are embedded in poorly sorted conglomerates, slump folds are also present in the formation. The deformation mechanisms and triggers causing the deformation are not yet clear. In the present study, the trigger of the SSDS in the Gyeokpori Formation was investigated using facies analysis. This included evaluation of the reworking process of both cohesive and non-cohesive sediments. The analysis indicates that the SSDS are directly or indirectly associated with the alternation of conglomerates and mud layers with clasts. These layers underwent non-cohesive and cohesive deformation, respectively, which promoted SSDS formation. The slump folds were controlled by the extent of cohesive and non-cohesive deformation experienced by the sediment layers in the slope environment. The SSDS deformation style and morphology differ, particularly in the case of reworking by slump activity. This study contributes to the understanding of lacustrine slope-related soft-sediment deformation structures.

The Cretaceous tectonomagmatism of the Korean Peninsula was examined based on geochemical and geochronological data of the Cretaceous plutonic rocks, along with distribution of volcano-sedimentary nonmarine N- to NE-trending fault bounded sedimentary basins. We conducted sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb ages and whole-rock geochemical compositions of 21 Cretaceous plutonic rocks, together with previously published data, from the central to southern Korean Peninsula. Four age groups of plutonic rocks were identified: Group I (ca. 119–106 Ma) in the northern to central area, Group II (ca. 99–87 Ma) in the central southern area, Group III (ca. 85–82 Ma) in the central to southern area, and Group IV (ca. 76–67 Ma) in the southernmost area. These results indicate a sporadic trenchward-younging trend of the Cretaceous magmatism in the Korean Peninsula. The Group I, II, and III rocks are dominated by high-K calc-alkaline I-type rocks with rift-related A-type granitoids. In contrast, the Group IV rocks are high-K calc-alkaline I-type plutonic rocks with no A-type rocks. The geochemical signatures of the entire groups indicated LREEs (light rare earth elements) enrichments and negative Nb, Ta, and Ti anomalies, indicating normal arc magmatism. A new tectonic model of the Cretaceous Korean Peninsula was proposed based on temporal and spatial distribution of the Cretaceous plutons represented by four age groups; 1) magmatic quiescence throughout the Korean Peninsula from ca. 160 to 120 Ma, 2) intrusions of the I- and A-type granitoids in the northern and central Korean Peninsula (Group I plutonic rocks from ca. 120 to 100 Ma) resulted from the partial melting of the lower continental crust due to the rollback of the Izanagi plate expressed as the conversion from flat-lying subduction to normal subduction. The Gyeongsang nonmarine sedimentary rift basin in the Korean Peninsula and adakite magmatism preserved in the present-day Japanese Islands supported the slab rollback followed by steepening of the Izanagi plate with an injection of upwelling of the hot asthenosphere into the mantle wedge. 3) Alternating shallow (from ~100 to 85 Ma) to steep (from ~85 to 65 Ma) subduction resulted in the migration of the normal arc magmatism in the southern Korean Peninsula, expressed as the intruded I- and A-type (Group III) and I-type granitoids (Group IV), respectively. The tectonomagmatism of the Korean Peninsula showed the unique style of evolution, different from those of South China and Japanese Islands.

The Neoproterozoic metasedimentary successions and igneous suites in the central Korean Peninsula provide important insights into the tectonic evolution of East Asia. Here we report detailed detrital zircon U Pb age data from the Neoproterozoic metasedimentary successions as well as geochemical data on the early Neoproterozoic rift-related plutonic rocks. Our results together with the available data from the central Korean Peninsula, lead to the following inferences. (1) Regional sedimentation in the early Neoproterozoic (ca. 1000–920 Ma) as a result of the late Paleoproterozoic to early Neoproterozoic intracratonic rifting. (2) Arc magmatism in the southern periphery of the central Korean Peninsula in the early Neoproterozoic (ca. 913–895 Ma and ca. 865–770 Ma). (3) Back-arc magmatism in the inland area of the central Korean Peninsula in the early Neoproterozoic (ca. 888–852 Ma). (4) Magmatism and sedimentation in the early Neoproterozoic (ca. 765–720 Ma) due to early Neoproterozoic back-arc and intracratonic rifting. The early-Neoproterozoic geological and tectonic events in the central Korean Peninsula correlate with those in the southeastern part of the North China Craton. The spatial and temporal similarities and discrepancies in the early Neoproterozoic geological records of the Sino-Korean continent mark the tectonic evolution within a continental inland (the southeastern part of the North China Craton) and a continental margin (the central Korean Peninsula).

Our research is focused on the bleaching patterns indicating natural CO2-saturated water leakage to the surface, which provides the understanding of controlling factors on fluid flow processes. To examine the relationships between bleaching patterns and geologic characteristics, we investigated the characteristics of bleaching patterns around major faults (Moab and Salt Wash Faults) based on field observations in the exhumed reservoir-cap rock systems at SE Utah, USA. According to the results of our scanline survey, the deformation bands frequently observed in fault damage zones and in bleached layers compared with unbleached layers. Although almost all fault zones act as conduits for fluid flow, some fault zones filled with clay-rich gouges can impede fluid flow.

Although the widths of fault damage zones commonly show a positive correlation with displacements, these relationships also show a somewhat scattered distribution. We believe that one of the fundamental reasons for this problem is strongly related to subjective definitions and inconsistent uses of the term ‘damage zone’. Thus, firstly we classify damage zones into along-fault, around-tip and cross-fault damage zones based on descriptive views of an arbitrary fault exposure as well as their tridimensional locations around a segmented fault system. Secondly, we propose an advanced field technique and data acquisition method to more accurately define a damage zone using the distribution of cumulative fracture frequency. We tested this method on new field and borehole observations as well as previously published data to identify damage zone boundaries, and express them as a change in slope gradients of the cumulative distribution of deformation structures. The results show how this slope change can be a useful criterion in accurately defining the width of damage zones and some internal properties of fault zones. We argue that this damage zone classification and definition method should be adopted and used to prevent discrepancies in field data. This will help us to gain a better understanding of fault damage zone properties and their scaling with fault displacement.

Sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb ages and whole-rock chemical compositions of Early to Middle Jurassic plutons from the central to southern Korean Peninsula are reported to investigate the effect of paleo-Pacific plate subduction preserved along the continental margin. Twenty-one plutonic rocks from the Yeongnam massif (i.e., Sunchang and Namwon plutons), the Okcheon belt (Jeongup, Boeun, and Mungyeong plutons), the northeast (Gangreung pluton), and the Gyeonggi massif (Gonam, Anheung, and Ganghwa plutons) have age ranges from ca. 189–186 Ma to 177 Ma, 177–166 Ma, and 177–173 Ma, respectively. Most plutonic rocks have chemical compositions similar to adakites, showing high SiO 2 (45.62–74.96 wt.%), low MgO (0.01–2.84 wt.%), high Na 2 O (2.65–4.83 wt.%), high Sr/Y and La/Yb, low Y and Yb, as well as low HFSEs (Nb and Ta), but initial Sr ratios (0.7048–0.7262), K 2 O (0.50–5.88 wt.%), and K 2 O/Na 2 O (0.34–2.1) were unlikely to have been formed by melting of either a thickened and/or delaminated lower continental crust, or an altered oceanic crust. These suggest that the “adakitic” plutonic rocks in this region resulted from partial melting of an enriched mantle source metasomatized by dewatering from a delaminated flat-slab. The spatial distributions of this continental adakitic plutonic belt, based on the present study, together with previously reported geochronological results, indicate that magmatic pulses gradually migrated toward the continent across the Korean Peninsula as a result of slab shallowing caused by periodic slab buckling. The similar geochronological and geochemical characteristics, petrogenesis and tectonic setting of the plutonic belt spanning the Korean Peninsula, Japan, eastern China, and eastern Russia indicate a possible link to an active subduction system that existed during the Early to Middle Jurassic, although the products of the plate subduction might differ in different locations along the East Asian continental margin.

Neoproterozoic arc magmatism in or around the Korean Peninsula provides important insights into the history of the Rodinia supercontinent. Here we report the petrology, zircon U-Pb ages, geochemistry, and Hf isotope data from the Early Neoproterozoic (ca. 913–895 Ma) igneous complexes (gabbro, diorite and granitic dyke) in the northern part of the Gogunsan Islands along the southwestern margin of the Hongseong–Imjingang Belt in the central–western Korean Peninsula. The gabbro and diorite- yielded zircon U–Pb ages of ca. 913 Ma, and ca. 909–899 Ma, respectively. The granitic dykes within this complex show ages of ca. 903–895 Ma. The gabbro-diorite, and granite belong to the subalkaline series, and are characterized by large ion lithophile element (LILE) enrichments, Nb–Ta troughs, and depletion in P and Ti anomalies similar to magmatism in the continental arc setting. The initial 176Hf/177Hf ratios and eHf(t) values obtained of zircon grains are in the ranges of 0.282132–0.282268 and –2.7 to 2.3 for gabbro, 0.282010–0.282363 and –6.4 to 6.0 for diorite, and 0.282071–0.282285 and –5.0 to 2.6 for granitic dykes, suggesting juvenile crust production with mixing of older crust materials. In combination with previously published U-Pb ages and geochemical features of Late Paleoproterozoic, Mesoproterozoic, and Early Neoproterozoic rift-related rocks in and around the central–western Korean Peninsula, the Early Neoproterozoic arc magmatism reported in this study provides clear evidence for a tectonic transition from the disruption of the Columbia supercontinent to the amalgamation and disruption of Rodinia supercontinent.

Ko, K. and Lee, H.-J., 2019. Detecting geological structures in coastal areas with unmanned aerial vehicle photogrammetric surveys. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 362-368. Coconut Creek (Florida), ISSN 0749-0208.This study attempted to use unmanned aerial vehicle (UAV) photogrammetry for structural mapping at limited exposure outcrops in the west coast area of southwestern Korea. The west coast area of the Korean Peninsula has a large tidal range, and there are restrictions for traditional structure mapping. A study site was selected, and high spatial resolution images (< 5 cm per pixel) were obtained at low tide. The UAV survey identified 50 brittle structures (fractures and faults that were divided into three groups) and changes in the bedding trace. The bedding trace demonstrates various directional verging of the fold geometry that indicates slump-fault structures. While more research is still necessary, this study demonstrated that UAV mapping techniques are very useful for geological structural analysis in coastal areas.

The purpose of this work is to gain a better understanding of the interrelationships between geological structures and slope failure in sedimentary rocks. In the studied slopes, construction-related slope failure could only be observed on the south-dipping slopes. This indicates that slope stability may be dependent on the angular relationships between the dip direction of bedding and the orientation of the slope. Slope failure continued, post-construction, around large fault zones in the studied outcrop; these fault damage zones are, however, not easily recognized in the field. Here we suggest a new method that uses accumulated fracture density to precisely identify fault damage zones. Multiple-faced slopes are now increasingly being exposed during large-scale construction projects in South Korea. This multiple-faced slope analysis indicates that the stability of a slope should be evaluated by identifying domains, through the analysis of possible slopes and their angular relationships with bedding and other discontinuities, prior to construction. Therefore, careful consideration of geological structures such as bedding and other discontinuities, and their angular relationships during the design of cuttings through sedimentary rocks, will increase the efficiency of construction and enable the safe construction of more stable slopes that will retain their stability after construction.