• Journal of the Korean earth science society
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• v.40 no.1
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• pp.56-67
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• 2019

In this study, we analyzed the intensity attenuation for M 6.0, 6.5, and 7.0 earthquakes using the broadband strong ground motion simulation platform based on the physical seismic modeling developed by the US Southern California Earthquake Center (SCEC). The location of the earthquake was assumed to be near the epicenter of the 2016 M 5.8 Gyeongju earthquake, but two of the representative US regional models provided by the SCEC strong ground motion simulation platform were used for the propagation model. One is the Central and Eastern United States (CEUS) model representing the intraplate region, and the other is the LA Basin model representing the interplate region. Five modeling methodologies are presented in the version 16.5 of the simulation platform, and Song and Exsim models were used in this study. In the analysis, we found that different intensity attenuation patterns can be observed with the same magnitude of earthquakes, especially depending on the region (CEUS vs LA Basin). Given the same magnitude and distance, the instrumental intensity in the CEUS region (intraplate) could be larger by a unit of 2 than that in the LA Basin region (interplate). Given the difference of intensity attenuation patterns observed in the study, it is important to know the regional intensity attenuation characteristics to understand the accurate level of seismic hazard imposed in the Korean Peninsula. This study also shows the level of the uncertainty of intensity attenuation if region specific attenuation characteristics are not considered.

• Explosives and Blasting
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• v.39 no.2
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• pp.1-14
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• 2021

Recently, with the development of high-performance processing devices such as GPGPU, a three-dimensional dynamic analysis technique that can replace expensive rock material impact tests has been actively developed in the defense and aerospace fields. Experimentally observing or measuring fracture processes occurring in rocks subjected to high impact loads, such as blasting and earth penetration of small-diameter missiles, are difficult due to the inhomogeneity and opacity of rock materials. In this study, a three-dimensional dynamic fracture process analysis technique (3D-DFPA) was developed to simulate the fracture behavior of rocks due to impact. In order to improve the operation speed, an algorithm capable of GPGPU operation was developed for explicit analysis and contact element search. To verify the proposed dynamic fracture process analysis technique, the dynamic fracture toughness tests of the Straight Notched Disk Bending (SNDB) limestone samples were simulated and the propagation of the reflection and transmission of the stress waves at the rock-impact bar interfaces and the fracture process of the rock samples were compared. The dynamic load tests for the SNDB sample applied a Pulse Shape controlled Split Hopkinson presure bar (PS-SHPB) that can control the waveform of the incident stress wave, the stress state, and the fracture process of the rock models were analyzed with experimental results.

• Tunnel and Underground Space
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• v.33 no.1
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• pp.57-69
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• 2023

In this study, we simulated induced seismicity in the Groningen natural gas reservoir using 2D hydro-mechanical coupled discrete element modelling (DEM). The code used is PFC2D (Particle Flow Code 2D), a commercial software developed by Itasca, and in order to apply to this study we further developed 1)initialization of inhomogeneous reservoir pressure distribution, 2)a non-linear pressure-time history boundary condition, 3)local stress field monitoring logic. We generated a 2D reservoir model with a size of 40 × 50 km² and a complex fault system, and simulated years of pressure depletion with a time range between 1960 and 2020. We simulated fault system failure induced by pressure depletion and reproduced the spatiotemporal distribution of induced seismicity and assessed its failure mechanism. Also, we estimated the ground subsidence distribution and confirmed its similarity to the field measurements in the Groningen region. Through this study, we confirm the feasibility of the presented 2D hydro-mechanical coupled DEM in simulating the deformation of a complex fault system by hydro-mechanical coupled processes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.187-196
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• 2008

An earthquake of magnitude 5.0 occurred at Ssang-gye-sa, a Buddhist temple in Jirisan, located near the southern border of the Korean peninsula on 4 July 1936. It resulted in severe damage of several buildings and structures in Ssang-gye-sa. Particularly, the top component of a five-story stone pagoda in the temple was tipped over and fell down during the earthquake. This earthquake damage case would be usefully applied to estimating the intensity of ground motion in the Korean peninsula, a moderate seismicity region, where strong motion has never been recorded with the exception of historic seismic events. In order to estimate the local site effects and the corresponding ground motion at Ssang-gye-sa site, intensive site investigations including borehole drilling and in-situ seismic tests such as crosshole and SASW tests were performed in the temple area. Based on the site characteristics, site-specific seismic response analyses using various input motions were conducted for a representative Ssang-gye-sa site by means of both one-dimensional equivalent-linear and nonlinear methods with six input rock outcrop acceleration levels ranging from 0.044g to 0.220g. The resultant site-specific seismic responses indicated the amplified ground motions in the short-period range near the site period of Ssang-gye-sa. Furthermore, the intensity on rock outcrop of the 1936 Jirisan earthquake was estimated by making a comparison between the site responses analysis results in this study and the full-scaled seismic test of pagoda model in the prior study.

• Journal of The Korean Association For Science Education
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• v.35 no.1
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• pp.37-52
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• 2015

In this study, assessment items to examine geocognition on plate tectonics were developed and applied to middle and high school students and college students. Conceptual constructs on plate tectonics are Earth interior structure, specific geomorphology, and geologic phenomena at each plate boundary. Construct for geocognition included temporal reasoning, spatial reasoning, retrospective reasoning, and system thinking. Pictorial data in each item were all obtained from GeoMapApp. Students' responses to the items were analyzed and measured cross-sectionally by Rasch model, which distinguishes persons' ability levels based on their scores for all items and compared them with item difficulty. By Rasch model analysis, Wright maps for middle and high school students and college students were obtained and compared with each other. Differential Item Functioning analysis was also implemented to compare students' item responses across school grades. The results showed: 1) Geocognition on plate tectonics was an assessable construct for middle and high school students in current science curriculum, 2) The most distinguished geocognition factor was spatial reasoning based on cross sectional analysis across school grades, 3) Geocognition on plate tectonics could be developed towards more sophisticated level through scaffolding of relevant instruction and earth science content knowledge, and 4) Geocognition was not a general reasoning separated from a task content but a content-specific reasoning related to the content of an assessment item. We proposed several suggestions for learning progressions for plate tectonics and national curriculum development based on the results of the study.

• Economic and Environmental Geology
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• v.8 no.2
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• pp.73-87
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• 1975

Regional unconformities have been used as boundaries of major stratigraphic units in Korea. The term "synthem" has already been propsed for formal unconformity-bounded stratigraphic units of maximum magnitude (ISSC, 1974). The unconformity-based classification of the strata in the cratonic area in Korea comprises in ascending order the Kyerim, $Sangw{\check{o}}n$, $Jos{\check{o}}n$, $Py{\check{o}}ngan$, Daedong, and $Ky{\check{o}}ngsang$ Synthems, and the Cenozoic Erathem. The unconformites separating them from each other are either orogenic or epeirogenic (and vertical tectonic). The sub-$Sangw{\check{o}}n$ unconformity is a non-conformity above the basement complex in Korea. The unconformities between the $Sangw{\check{o}}n$, $Jos{\check{o}}n$, and $Py{\check{o}}ngan$ Synthems are disconformities denoting late Precambrian and Paleozoic crustal quiescence in Korea. The unconformities between the $Py{\check{o}}ngan$, Daedong, and $Ky{\check{o}}ngsang$ Synthems are angular unconformities representing Mesozoic orogenies. The bounding unconformities of the $Ky{\check{o}}ngsang$ Synthem involve non-conformable parts overlying the Jurassic and late Cretaceous granitic rocks.

• Economic and Environmental Geology
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• v.34 no.5
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• pp.471-483
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• 2001

The pH values of the mine and surface water from the Tohyun mine creek were higher compared with those of groundwater, and 2nd round samples in same sites were even alkaline. The stream and mine waters belong to the characteristics of (Ca+Mg)-(SO$_4$) and (Ca+Mg)-(HCO$_3$) types, and groundwaters have to the (Ca+Mg+Na+K)-(HCO$_3$+SO$_4$) type. As the 2nd samples. concentrations of mostly anions are increasing compared with the forder samples. However, the mostly cation concentrations are decreasing. The hydrogeochemistry indicate that water quality is different chemical characteristics and evolution trends. The range of $\delta$D and $\delta$$^{18}$ valutes (relative to SMOW) in the waters are shown in -62.2 to -70.1$\textperthousand$, and -8.1 to -9.4$\textperthousand$. The values are plowed parallel to $\delta$D=8$\delta$$^{18}$ O+ (6$\pm$4). The d values of groundwater show 2.4, which is lower than the surface (5.2) and mine (7.6) waters. Strontium concentra titans range from 0.025 to 11.844 mg/$\ell$ in all kinds of water samples, but the groundwater has the highest contents The $^{87}$ Sr/$^{86}$ Sr ratios (0.7115 to 0.7129) show more lightened to the groundwater. The $\delta$$^{18}$ O value, Ca and Sr contents are decreased with $^{87}$ Sr/$^{86}$ Sr increasing, because it is support to the altitude effects of the sampling sites rather than a water-rock interaction of environmental isotope. Using computer code of WATEQ4F, saturation indices of albite, Quartz, gibssite and gypsum are calculated to be soluble. The calcite and dolomite show super saturation state, however, clay mineral species are plotted boundary between undersaturation and supersaturation. In the Tohyun mine creek, reaction materials with ore wastes arid precipitation have influence upon increasing EC and TDS of the waters independent of pH. The SO$_4$ concentrations in the mine water is 181.845 mg/$\ell$. This is abruptly increase in surface water and then detected 249.727 mg/$\ell$ in the groundwater. As a results of the calculated sulfate mineral solubilities, the sulfate ions became saturation states an above 150 mg/$\ell$ concentrations.

• Economic and Environmental Geology
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• v.38 no.6 s.175
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• pp.607-622
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• 2005

This study was carried out in order to evaluate where the soil loss was mainly occurred, .and to verify how riverbed sediments in the tributaries of the Seomjin River were related to their source rocks distributed in Sunchang area. The study area including the Seomjin River with 4 tributaries of Kyeongcheon, Okgwacheon, Changjeong-cheon and Ipcheon was divided into 10 watershed. The RUSLE (Revised Universal Soil Loss Equation) was estimated for all the grids (10 m cells) in the corresponding watershed. The amount of soil loss per unit area was calculated as follows: dry fold (53,140.94 tons/ha/year), orchard (25,063.38 tons/ha/year), paddy field (6,506.7 tons/ha/year) and Idlest (6,074.36 tons/ha/year). The differences of soil loss per unit area appear to be depends on areas described earlier. Soil erosion hazard zones were generally distributed within dry fields. Several thematic maps such as land use maps, topographical maps and soil maps were used as a data to generate the RUSLE factors. The amount of soil loss, computed by using the RUSLE, showed that soil loss mainly occurred at the regions where possible source rocks were distributed along the stream. Based on the this study on soil loss and soil erosion hazard zone together with chondrite-normalized REE patterns that were previously analyzed in same study area, a closed relationship between riverbed sediments and possible source rocks is formed. Especially in the Okgwacheon that are widely distributed by various rocks, chondrite-normalized REE pattern derived from the riverbed sediments, source rock and soil is expected to have a closed relationship with the distribution of soil loss.

• Economic and Environmental Geology
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• v.39 no.3 s.178
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• pp.235-253
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• 2006

We interpreted marine seismic profiles in conjunction with swath bathymetric and magnetic data to investigate rifting to breakup processes at the Korean margin leading to the separation of the Japan Arc. The Korean margin is rimmed by fundamental elements of rift architecture comprizing a seaward succession of a rift basin and an uplifted rift flank passing into the slope, typical of a passive continental margin. In the northern part, rifting occurred in the Korea Plateau, a continental fragment extended and partially segmented from the Korean Peninsula, that provided a relatively broader zone of extension resulting in a number of rifts. Two distinguished rift basins (Onnuri and Bandal Basins) in the Korea Plateau we bounded by major synthetic and smaller antithetic faults, creating wide and symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. In contrast, the southern margin is engraved along its length with a single narrow rift basin (Hupo Basin) that is an elongated asymmetric half-graben. Rifting at the Korean margin was primarily controlled by normal faulting resulting from extension in the west and southeast directions orthogonal to the inferred line of breakup along the base of the slope rather than strike-slip deformation. Although rifting involved no significant volcanism, the inception of sea floor spreading documents a pronounced volcanic phase which seems to reflect slab-induced asthenospheric upwelling as well as rift-induced convection particularly in the narrow southern margin. We suggest that structural and igneous evolution of the Korean margin can be explained by the processes occurring at the passive continental margin with magmatism intensified by asthenospheric upwelling in a back-arc setting.

• Economic and Environmental Geology
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• v.50 no.2
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• pp.117-128
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• 2017

Occurrence characteristics and existing forms of U-Th containing minerals in KURT (KAERI Underground Research Tunnel) granite are investigated to understand long-term behavior of radionuclides in granite considered as a candidate rock for the geological disposal of high-level radioactive waste. KURT granite primarily consists of quartz, feldspar and mica. zircon, REE(Rare Earth Element)-containing monazite and bastnaesite are also identified. Besides, secondary minerals such as sericite, microcline and chlorite including quartz vein and calcite vein are observed. These minerals are presumed to be accompanied by a post-hydrothermal process. U-Th containing minerals are mainly observed at the boundaries of quartz, feldspar and mica, mostly less than $30{\mu}m$ in size. Quantitative analysis results using EPMA (Electron Probe Micro-Analyzer) show that 74.2 ~ 96.5% of the U-Th containing minerals consist of $UO_2$ (3.39 ~ 33.19 wt.%), $ThO_2$ (41.61 ~ 50.24 wt.%) and $SiO_2$ (15.43 ~ 18.60 wt.%). Chemical structure of the minerals calculated using EPMA quantitative analysis shows that the U-Th minerals are silicate minerals determined as thorite and uranothorite. The U-Th containing silicate minerals are formed by a magmatic and hydrothermal process. Therefore, KURT granite formed by a magmatic differentiation is accompanied by an alteration and replacement owing to a hydrothermal process. U-Th containing silicate minerals in KURT granite are estimated to be recrystallized by geochemical factors and parameters such as temperature, pressure and pH owing to the hydrothermal process. By repeated dissolution/precipitation during the recrystallization process, U-Th containing silicate minerals such as thorite and uranothorite are formed according to the variation in the concentrated amount of U and Th.