Dong-Eun Kim

Accurate and precise geochronological constraints on marine terrace surfaces are essential for understanding the development of shoreline responses to tectonic uplift and climate change. In particular, high-resolution digital elevation models and numerical dating methods are necessary to establish such constraints on terrace formation. This study aimed to constrain the age of formation of marine terrace T2 in the region around the active Quaternary Eubchun Fault on the eastern coast of the Korean Peninsula. OSL dating and ¹⁰ Be depth-profile analysis of marine deposits reveal that T2 was abandoned (subaerially exposed) at approximately 71–67 and 62–60 ka, respectively. These age constraints show that the terrace was deposited during a high-sea-level stage (from OSL ages) and subsequently abandoned from ¹⁰ Be depth-profile age. Through detailed stratigraphic observations combined with the abandonment age, we characterized the process of marine terrace development. In addition, by combining the abandonment age with a high-resolution digital elevation model derived from data obtained from an unmanned aerial vehicle, we determined a precise uplift rate of 0.44 mm/yr. The calculated uplift rate is higher than regional uplift rates (0.2–0.3 mm/yr) and is ascribed to the vertical movement of reactivated Quaternary faults in the study area. In summary, climate forcing led to the formation and abandonment of the terrace, whereas subsequent Late Pleistocene tectonic uplift raised the terrace higher compared with other terraces along the eastern coast of the Korean Peninsula.

A comprehensive, interdisciplinary study was carried out to investigate the characteristics of the 1967 magnitude 7.1 earthquake along the right-lateral strike fault in Mogod, Mongolia. This fault consists of three segments—two strike faults and a reverse fault spanning from north to south. Recent research revealed a 25 ka cycle in the movement of the reverse fault segment located in the south (Bollinger et al., 2021).To understand two remaining faults, four excavation surveys (T1, T2, T3, T4) were conducted along the two northern segments. Optically Stimulated luminescence (OSL) was used to track the deposition period in unconsolidated sedimentary layers where surface ruptures occurred, aiding in estimating the recent earthquake of the fault. An additional excavation survey was conducted near the river crossing the fault (at location T4) to determine the thalweg for evaluating geological displacement over the geological timescale.The excavation results revealed Quaternary surface ruptures in three trenches with OSL sampling. A total of 51 samples were respectively collected from Trench T2 (24 samples), T3 (18 samples), and T4 (9 samples). The Quaternary sediment layers have been deposited since the Last Glacial Maximum (LGM), around ~20 ka. Excavation sites (3 upstream and 4 downstream) intersecting the fault line (T4) aimed to assess displacement caused by seismic activity.In summary, seismic movements resulting in surface ruptures were detected in the northern two segments around the 20 ka. Further analysis would provide a more precise earthquake recurrence cycle, potentially revealing the timing of subsequent seismic events. Furthermore, completion of the identifying the thalweg, it is expected to reveal the slip rate over geological time scales.

Quantifying today's topography can provide insights into landscape evolution and its controls, since present topography represents a cumulative expression of past and present surface processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that was reactivated as a reverse fault around 5 Ma. The UFZ strikes NNW–SSE and dips eastward. This study investigates the relative tectonic activity along the UFZ and the landscape evolution of the hanging-wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-averaged denudation rates and bedrock incision rates, topographic metrics, and a landscape evolution model. Five geological segments were identified along the fault, based on their relative tectonic activity and fault geometry. We simulated four cases of landscape evolution to investigate the geomorphic processes and accompanying topographic changes in the study area in response to fault movement. Model results reveal that the geomorphic processes and the patterns of topographic metrics (e.g., χ anomalies) depend on inherited topography (i.e., the topography that existed prior to reverse fault reactivation of the UFZ). On the basis of this important model finding and additional topographic metrics, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, so this segment underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma, and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates the utility of topographic metrics as reliable criteria for resolving fault segments. Together with landscape evolution modeling, topographic metrics provide powerful tools for examining the influence of inherited topography on present topography and for the elucidation of tectono-geomorphic histories.

Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.

Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.

Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.

Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.

Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using ¹⁰Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.

A pre-existing landform is created by weathering and erosion along the bedrock fault and the weak zone. A neotectonic landform is formed by neotectonic movements such as earthquakes, volcanoes, and Quaternary faults. It is difficult to clearly distinguish the landform in the actual field because the influence of the tectonic activity in the Korean Peninsula is relatively small, and the magnitude of surface processes (e.g., erosion and weathering) is intense. Thus, to better understand the impact of tectonic activity and distinguish between pre-existing landforms and neotectonic landforms, it is necessary to understand the development process of pre-existing landforms depending on the bedrock characteristics. This study used a two-dimensional numerical landscape evolution model (LEM) to study the spatio-temporal development of landscape according to the different erodibility under the same factors of climate and the uplift rate. We used hill-slope indices (i.e., relief, mean elevation, and slope) and channels (i.e., longitudinal profile, normalized channel steepness index, and stream order) to distinguish the difference according to different bedrocks. As a result of the analysis, the terrain with high erosion potential shows low mean elevation, gentle slope, low stream order, and channel steepness index. However, the value of the landscape with low erosion potential differs from that with high erodibility. In addition, a knickpoint came out at the boundary of the bedrock. When researching the actual topography, the location around the border of difference in bedrock has only been considered a pre-existing factor. This study suggested that differences in bedrock and various topographic indices should be comprehensively considered to classify pre-existing and active tectonic topography.