• Korean Journal of Mineralogy and Petrology
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• v.35 no.4
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• pp.485-505
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• 2022

On November 15, 2017, a Mw 5.4 Pohang Earthquake occurred at about 4 km hypocenter in the Heunghae area, and caused great damage to Pohang city, Korea. In the Heunghae area, which is the central part of the Pohang Basin, the Cretaceous Gyeongsang Supergroup and the Late Cretaceous to Early Paleogene Bulguksa igneous rocks as basement rocks and the Neogene Yeonil Group as the fillings of the Pohang Basin, are distributed. In this paper, structural and geological researches on the crustal deformations (folds, faults, joints) in the Pohang Basin and the coseismic ground deformations (sand volcanoes, ground cracks, pup-up structures) of Pohang Earthquake were carried out, and the deformation history of the Pohang Basin and characteristics of the coseismic ground deformations were considered. The crustal deformations were formed through at least five deformation stages before the Quaternary faulting: forming stages of the normal-slip (Gokgang fault) faults which strike (N)NE and dip at high angles, and the high-angle joints of E-W trend regionally recognized in Yeonil Group and the faults (sub)parallel to them, and the conjugate normal-slip faults (Heunghae fault and Hyeongsan fault) which strike E-W and dip at middle or low angles and the accompanying E-W folds, and the conjugate strike-slip faults dipped at high angles in which the (N)NW and E-W (NE) striking fault sets show the (reverse) sinistral and dextral strike-slips, respectively, and the conjugate reverse-slip faults in which the NNE and NNW striking fault sets dip at middle angles and the accompanying N-S folds. Sand volcanoes often exhibit linear arrangements (sub)parallel to ground cracks in the coseismic ground deformations. The N-S or (N)NE trending pop-up structures and ground cracks and E-W or (W)NW trending ground were formed by the reverse-slip movement of the earthquake source fault and the accompanying buckling folding of its hanging wall due to the maximum horizontal stress of the Pohang Earthquake source. These structural activities occurred extensively in the Heunghae area, which is at the hanging wall of the earthquake source fault, and caused enormous property damages here.

• Journal of Soil and Groundwater Environment
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• v.11 no.3
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• pp.20-30
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• 2006

Hydrogeochemistry of deep geothermal water (temperature: $42.2-47.9^{\circ}C$) at Heunghae, Pohang was evaluated using core logging, temperature and electrical conductivity (EC) logging before and after pumping tests, chemical analysis of geothermal water with depth, and observation of water quality variations during pumping tests. The geology of the area is composed of highly fractured marine sedimentary rocks. The hydrogeochemistry of geothermal water varies with drilling depth, distance from the coast, and pumping duration. According to the temperature and EC variations during 4 times of pumping tests, main aquifer of the area is considered as the fractured zones (540 to 900 m) developed in rhyolitic rocks. The high content of Na and $HCO_3$ in geothermal water can be explained by the inflow of deep groundwater from inland regulated by dissolution of silicates and carbonates. High TDS, Na and Cl concentrations indicate that the geothermal water was also strongly affected by seawater. The molar ratios of Na:Cl ($0.88{\sim}2.14$) and Br:Cl ($21.0{\sim}24.9{\times}10^{-4}$) deviate from those of seawater (0.84 and $34.7{\times}10^{-4}$, respectively), suggesting that water-rock interaction also plays an important role in the formation of water quality.

• Journal of Soil and Groundwater Environment
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• v.10 no.6
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• pp.45-55
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• 2005

The geothermal research has been carried out on the Heunghae, Pohang geothermal area know as having geo-heat-flow area in the Korean peninsula. This study results so far indicate that geothermal water in the area is in peripheral waters of hydrothermal area and is not in equilibrium with the reservoir rock. The average oxygen and hydrogen stable isotope values are as follows: deep groundwater $(average:\;{\delta}^{18}O=-10.1\%_{\circ},\;{\delta}D=-65.8\%_{\circ})$, intermediate groundwater (average: $(average:\;{\delta}^{18}O=-8.9\%_{\circ},\;{\delta}D=-59.6\%_{\circ})$, shallow groundwater $(average:\;{\delta}^{18}O=-8.0\%_{\circ},\;{\delta}D=-53.6\%_{\circ})$, surface water $(average:\;{\delta}^{18}O=-7.9\%_{\circ},\;{\delta}D=-53.3\%_{\circ})$ respectively. Deep groundwaters was originated from a local meteoric water recharged from distant, topographically high mountain region and not affected by the sea water. High temperature zone inferred from water geothermometers is around D-1, D-5, D-6, 1-04 well zones. The estimated enthalpy from Silica-enthalpy mixing model is near 410 kJ/kg, which corresponds to the temperature of $98^{\circ}C$, and in consistent with the result of Na-K and K-Mg geothermometer.

• The Korea Swine Journal
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• v.29 no.8 s.336
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• pp.156-160
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• 2007

마산지역은 항구도시로 교통과 교역이 흥성한 경남의 대표도시이다. 뿐만 아니라 도농복합도시로 예부터 양돈이 흥해 양돈을 시작한 지 대부분 20~30년 이상이 된 경남지역 양돈산업의 터주대감 중에 하나이다. 지난 7월19일에는 '창립32주년'을 기념하여 전 회원이 참석한 가운데 기념행사를 개최하기도 했다. 마산지부는 오래된 역사만큼이나 양돈 생산성 향상과 개선을 위해 최선의 노력을 기울이고 있다. 이를 위해 마산지부 회원들은 해양매출 저감에 노력하는 한편, 가축분뇨 자원화를 통한 분뇨처리 시스템 구축과 지역 대표 돼지고기 브랜드 사업을 적극 추진하여 지역 양돈산업의 재도약을 위해 매진하고 있었다.

• Journal of the Korean earth science society
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• v.43 no.1
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• pp.188-198
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• 2022

Some deep faults do not reach the ground surface and are seldom recognized. Gokgang Fault area in the east of the Heunghae area of the Pohang basin has been selected to confirm the feasibility of the Horizontal-to-Vertical Spectral Ratio (HVSR) approach to identify blind faults. Densely spaced microtremor data have been acquired along two lines in the study area and processed to obtain resonance frequencies. An empirical relationship between the resonance frequency and the bedrock depth was proposed using borehole data available in the study area. Resonance frequencies along two lines were then converted to bedrock depths. The resulting depth profiles show significant lateral variations in the bedrock depth. As expected, considerable variation in the resonance frequency is observed near the Gokgang fault. The depth profiles also present additional significant variations in the resonance frequencies and the bedrock depths. The feature is presumably related to a blind fault that is previously unknown. Therefore, this case study confirms the feasibility of the HVSR technique to identify faults otherwise not recognized on the surface.

• Journal of the Korean association of regional geographers
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• v.22 no.3
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• pp.703-713
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• 2016

This study documents the altitude of paleo-shoreline and formation age of the $1^{st}$ marine terrace emerged around Heunghae-eup Pohang City (South Korea). As a result, the $1^{st}$ terrace representing 10 m of the paleo-shoreline was formed at MIS 5c around 100,000 BP and was influenced repetitive sedimentation of sea-wave till regression of MIS 5a. The result is recognized as a definite truth for the $1^{st}$ terrace in the eastern coast of the Korean peninsula based on synthetic reviews of previous studies and cross-validation of absolute age data. Furthermore, this study deduces a sea stand at MIS 5c from the geomorphological contrast method, but precise determination of paleo-shoreline of the $2^{nd}$ terrace should be required to estimate that of MIS 5c.

• The Journal of Engineering Geology
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• v.15 no.4 s.42
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• pp.391-405
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• 2005

Chemical and isotopic analysis for stream water, shallow groundwater, intermediate groundwater and deep groundwater was carried out to grasp hydrogeochemical characteristics of groundwater in the Heunghae area, Pohang city. Water type of stream water and shallow groundwaters is typified as Ca-Cl type, intermediate groundwater is $Na-HCO_3$, and deep groundwater is prominent in Wa-Cl type. $HCO_3^-\;and\;SiO_2$ in shallow groundwater are originated from weathering of silicate minerals, whereas those of deep groundwaters are resulted from weathering of carbonate minerals. Ca and Mg ions in both shallow and deep groundwaters are resulted from weathering of calcite and dolomite. $SO_4^{2-}$ in shallow groundwater is originated mainly from pyrite oxidation. As well depth increases, pH and TDS increase, but Eh and DO decrease. Alkali metal contents(K, Na, Li) increases as well depth increases, but alkali earth metal(Mg, Ca) and hi concentrations increase as well depth decreases. Anions, halogen elements(F, Cl, Br), and $HCO_3$ contents increase as well depth increases. The average stable isotope value of the groundwater of each depth is as follows; deep groundwater: ${\delta}^{18}O=-10.1\%o,\;{\delta}D=-65.8\%_{\circ}$, intermediate groundwater: ${\delta}^{18}O=-8.9\%_{\circ},\;{\delta}D=-59.6\%_{\circ}$, shallow groungwater : ${\delta}^{18}O=-8.0\%_{\circ},\;{\delta}D=-53.6\%_{\circ}$, surface water : ${\delta}^{18}O=-7.9\%_{\circ},\;{\delta}D=-53.3\%_{\circ}$ respectively.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.559-569
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• 2022

This study investigated the acidification and mixing with seawater of groundwater, stream water, and reservoir water in the Hunghae area of Pohang City, as well as the source of water expelled to the stream by liquefaction induced by the Pohang earthquake on 15 November 2017. Geologically, the area consists of Tertiary sedimentary rocks. We collected six samples of groundwater, five of reservoir water, four of stream water, two of liquefaction water, and one of seawater to analyze the chemical composition and stable isotopes (𝛿D and 𝛿¹⁸O). Gogkang Stream flows eastward through the central part of the study area into the East Sea. The groundwater and reservoir water in the lower part of the stream are acidic (pH < 4), have a Ca(Mg)-SO₄ composition, and high concentrations of Al, Fe, and Mn, likely due to the oxidation of pyrite in Tertiary rocks. The groundwater in the upper part of the stream have a Ca(Na)-HCO₃(Cl) composition, indicating the mixing of seawater with the stream water. The 𝛿D and 𝛿¹⁸O isotope data indicate the isotopic enrichment of reservoir water by evaporation. Based on the chemical and isotopic data, it is inferred that the two samples of liquefaction water originated from alluvium water in a transition zone with stream water, and from deep and shallow groundwaters that has been infiltrated by seawater, respectively.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.459-474
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• 2009

By the analysis of discontinuity at the outcrop and lineament on the satellite image, the joints have deeply relationship with the lineaments. The joint spaces at the drilling core are mostly 1~20 cm but at the rhyolite which is distributed near fault they have more closely. These volcanic rocks belong to the subalkaline series tuff, rhyolite, basalt in the study area from the diagram of $Nb/Y-Zr/TiO_2$. The composition diagram of Hf/3-Th-Nb/16 show destructive plate-margin basalt and their differentiates. The environment of formation of volcanics are normal continental arc. Most of LREE show high enriched pattern but HREE show depleted pattern. The K/Ar age of intermediate volcanics, tuff, rhyolite, crystal tuff are 55.3Ma, 77.25 Ma~91.22Ma, 63.16~64.39Ma, 54.49 Ma respectively.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.173-184
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• 2018

Geologic structures related to the latest event in the evolution around Gyeongsang Basin are mainly associated with the Yangsan Fault. In particular, the structures in the northern part of the Yangsan Fault are mainly observed in the region between Bogyeongsa Temple and Danguri. Such structures are also clustered in the vicinity of the Yangsan Fault, exhibiting similar geometric and kinematic patterns. In general, N-S and NE-SW trending fractures and tectonogeomorphic lineament are mainly eastward dipping reverse faults, such that the blocks in the east of the structures moved west or northwest. The reverse faults are segmented by NW trending fractures that accommodate strike-slip movements. The reverse faults and geomorphotectonic lineaments related to the latest event of deformation in the northern part of the Yangsan Fault show a westward convex patterns. We infer that these structures were initially normal faults that formed during a NW-SE extensional environment and were later reactivated during an E-W compressional one. Such a deformation pattern is also well developed around Pohang-Heunghae area based on the tectonogeomorphic analysis, which appears to be closely related to the Pohang Earthquake (15 Nov. 2017), and its development of the surface rupture and highly damaged zones.