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  • Research Paper 2024-02-29

    0 171 43

    Teleseismic Travel Time Tomography for the Mantle Velocity Structure Beneath the Melanesian Region

    Jae-Hyung Lee, Sung-Joon Chang

    Econ. Environ. Geol. 2024; 57(1): 1-15

    Abstract : The Melanesian region in the western Pacific is dominated by complex plate tectonics, with the largest oceanic plateau, the Ontong-Java plateau, and a hotspot, the Caroline Islands. To better understand the complex geodynamics of the region, we estimate P- and S-velocity models and δ (VP/VS) model by using relative teleseismic travel times measured at seismometers on land and the seafloor. Our results show high-velocity anomalies in the subduction zones of the Melanesian region to a depth of about 400 km, which is thought to be subducting Solomon Sea, Bismarck, and Australian plates along plate boundaries. Along subduction zones, positive δ (VP/VS) anomalies are found, which may be caused by partial melting due to dehydration. A broad high-velocity anomaly is observed at 600 km depth below the Ontong-Java plateau, with a negative δ (VP/VS) anomaly. This is thought to be a viscous and dry remnant of the Pacific plate that subducted at 45-25 Ma, with a low volume of fluids due to dehydration for a long period in the mantle transition zone. Beneath the Caroline Islands, a strong low-velocity anomaly is obseved to a depth of 800 km and appears to be connected to the underside of the remnant Pacific plate in the mantle transition zone. This suggests that the mantle plume originating in the lower mantle has been redirected due to the interaction with the remnant Pacific plate and has reached its current location. The mantle plume also has a positive δ (VP/VS) anomaly, which is thought to be due to the influence of embedded fluids or partial melting. A high-velocity anomaly, interpreted as an effect of the thick lithosphere beneath the Ontong-Java plateau, is observed down to 300 km depth with a negative δ (VP/VS) anomaly, which likely indicate that little fluid remains in the melt residue accumulated in the lithosphere.

  • Research Paper 2024-02-29

    0 187 45

    Characteristics of Ground-Penetrating Radar (GPR) Radargrams with Variable Antenna Orientation

    Yoon Hyung Lee, Seung-Sep Kim

    Econ. Environ. Geol. 2024; 57(1): 17-23

    Abstract : Ground penetrating radar (GPR) survey is a geophysical method that utilizes electromagnetic waves reflecting from a boundary where the electromagnetic property changes. As the frequency of the antenna is about 25 MHz ~ 1 GHz, it is effective to acquire high resolution images of underground pipe, artificial structure, underground cavity, and underground structure. In this study, we analyzed the change of signals reflected from the same underground objects according to the arrangement of transceiver antennas used in ground penetrating radar survey. The antenna used in the experiment was 200 MHz, and the survey was performed in the vertical direction across the sewer and the parallel direction along the sewer to the sewer buried under the road, respectively. A total of five antenna array methods were applied to the survey. The most used arrangement is when the transmitting and receiving antennas are all perpendicular to the survey line (PR-BD). The PR-BD arrangement is effective when the object underground is a horizontal reflector with an angle of less than 30°, such as the sewer under investigation. In this case study, it was confirmed that the transmitter and receiver antennas perpendicular to the survey line (PR-BD) are the most effective way to show the underground structure. In addition, in the case where the transmitting and receiving antennas are orthogonal to each other (XPOL), no specific reflected wave was observed in both experiments measured across or parallel to the sewer. Therefore, in the case of detecting undiscovered objects in the underground, the PR-BD array method in which the transmitting and receiving antennas are aligned in the direction perpendicular to the survey line taken as a reference and the XPOL method in which the transmitting and receiving antennas are orthogonal to each other are all used, it can be effective to apply both of the above arrangements after setting the direction to 45° and 135°.

  • Research Paper 2024-02-29

    0 193 50

    Petrographic Study of Mn-bearing Gondite (Birimian) of Téra Area in the Leo-Man Shield (West African Craton) in Niger.

    Hamidou GARBA SALEY, Moussa KONATÉ, Olugbenga Akindeji OKUNLOLA

    Econ. Environ. Geol. 2024; 57(1): 25-39

    Abstract : The Téra manganese deposit represents the most significant manganese mineralization discovered in Niger up today. The main host rocks of this ore are gondites, which are a garnet and quartz rich metamorphic rocks. The supergene weathering developed an alteration profile on these gondites. This study aims to identify the mineralogical composition of gondites and associated rocks, in order to highlight the origine of rocks and the manganese enrichment.
    The methodological approach adopted involved a field study followed by polarizing microscopic analysis using transmitted and reflected lights. Additionally, quantitative X-ray diffraction (XRD) analysis was performed to assess the manganese ore minerals present in the gondite and associated rocks, including mica schists, amphibolites, and quartzites. The petrographic study revealed a paragenesis characterized by the presence of kyanite, staurolites, garnets and plagioclases that are generally poikiloblasts with quartz and opaque minerals inclusions, emphasizing the internal schistosity which is planar, helicitic or microfolded. These features indicate a prograde metamorphism until high-pressure amphibolite facies conditions. These conditions are followed by greenschist facies conditions marked by calcite, epidote, muscovite, chlorite and muscovite assemblage which emphasizes the vertical tectonics. Depending on the alteration process, the manganese ore exhibit a granular texture at the bottom of the gondite hills, transitioning to a colloform texture towards the top, passing through the epigenization and replacement texture. The XRD analysis further revealed that the studied rocks originated from a volcano-sedimentary complex, characterized by alternating marly, arenaceous and pelitic sequences associated with submarine exhalations.

  • Research Paper 2024-02-29

    0 156 70

    Structural Geometry of a Regional-scale Overturned Fold in the Daecheong Island, Central-western Korean Peninsula

    Jeong-Yeong Park, Deung-Lyong Cho, Seung Hwan Lee, Yujung Kwak, Seung-Ik Park

    Econ. Environ. Geol. 2024; 57(1): 41-50

    Abstract : This study reports the structural geometry and folding mechanism of a regional-scale overturned fold in the Daecheong Island, central-western part of the Korean Peninsula. Based on low-hemisphere stereographic and down-plunge projections using data from a detailed field survey, we classify the regional-scale fold as an open overturned fold shallowly plunging toward NE. The asymmetric and symmetric parasitic folds in the limb and hinge zones indicate layer-parallel shortening prior to flexural-flow folding. Fold dating must be required to decipher the orogenic process causing the regional-scale overturned fold in the Daecheong Island.

  • Research Paper 2024-02-29

    0 143 56

    Study on the Seismic Random Noise Attenuation for the Seismic Attribute Analysis

    Jongpil Won, Jungkyun Shin, Jiho Ha, Hyunggu Jun

    Econ. Environ. Geol. 2024; 57(1): 51-71

    Abstract : Seismic exploration is one of the widely used geophysical exploration methods with various applications such as resource development, geotechnical investigation, and subsurface monitoring. It is essential for interpreting the geological characteristics of subsurface by providing accurate images of stratum structures. Typically, geological features are interpreted by visually analyzing seismic sections. However, recently, quantitative analysis of seismic data has been extensively researched to accurately extract and interpret target geological features. Seismic attribute analysis can provide quantitative information for geological interpretation based on seismic data. Therefore, it is widely used in various fields, including the analysis of oil and gas reservoirs, investigation of fault and fracture, and assessment of shallow gas distributions. However, seismic attribute analysis is sensitive to noise within the seismic data, thus additional noise attenuation is required to enhance the accuracy of the seismic attribute analysis. In this study, four kinds of seismic noise attenuation methods are applied and compared to mitigate random noise of poststack seismic data and enhance the attribute analysis results. FX deconvolution, DSMF, Noise2Noise, and DnCNN are applied to the Youngil Bay high-resolution seismic data to remove seismic random noise. Energy, sweetness, and similarity attributes are calculated from noise-removed seismic data. Subsequently, the characteristics of each noise attenuation method, noise removal results, and seismic attribute analysis results are qualitatively and quantitatively analyzed. Based on the advantages and disadvantages of each noise attenuation method and the characteristics of each seismic attribute analysis, we propose a suitable noise attenuation method to improve the result of seismic attribute analysis.

  • Research Paper 2024-02-29

    0 150 45

    Displacement of Dongducheon and Wangsukcheon Fault Observed by Gravity Field Interpretation

    Sungchan Choi, Sung-Wook Kim, Eun-Kyeong Choi, Younghong Shin

    Econ. Environ. Geol. 2024; 57(1): 73-81

    Abstract : To estimate the tectonic displacement of the Chugaryeong Fault System (CFS), gravity surveys were conducted along the Dongducheon fault (DF) and the Wangsukcheon fault (WF). A total of 1,100 stations for the DF and WF regions have been added to the current gravity database. The results of the gravity interpretation indicate that (1) the dextral displacement of the DF is about 3,000 m, similar to the tectonic displacement (2,900-3,100 m) shown in the geological map. (2) The dextral displacement of the WF is about 3,200 m. (3) Taken together, the tectonic displacement of the CFS is estimated to be about 3,000 m on average. To investigate more accurate tectonic displacement of the CFS, further gravity surveys is planned for the Pocheon fault, Gyeonggang fault, and Inje fault.

  • Research Paper 2024-02-29

    0 140 45

    Abstract : According to the IEA (2022), global rechargeable battery demand is expected to reach 1.3 TWh in 2040. EV batteries will account for about 80% of this demand, and used EV batteries are expected to be discharged after 30 years. Used EV batteries can be recycled and reused to create new value. They can also resolve one of the most vulnerable parts of the battery supply chain: raw material insecurity. In this study, we analyzed the amount of used batteries generated by EV in Korea and their potential for reuse and recycling. As a result, it was estimated that the annual generation of used batteries for EV began to increase to more than 100,000 in '31 and expanded to 810,000 in '45. In addition, it was found that the market for recycling EV batteries in '45 could be expected to be equivalent to the production of 1 million batteries, and the market for reuse could be expected to be equivalent to the production of 36 Gwh of batteries. On the other hand, according to the plan standard disclosed by the recycling company, domestic used EV batteries can account for 11% of the domestic recycling processing capacity (pre-treatment) ('30). So it will be important to manage the import and export of used batteries in terms of securing raw materials.

  • Research Paper 2024-02-29

    0 122 47

    Reconsideration of the Natural Monument Geummubong Petrified Tree Fern Fossil Site, Ghilgok, Korea

    Seung-Ho Jung, Dal-Yong Kong

    Econ. Environ. Geol. 2024; 57(1): 93-105

    Abstract : Chilgok Geummubong tree fern fossil site is the type locality where tree fern stem fossils (Cyathocaulis naktongensis) were first discovered by Tateiwa in 1925. Recognized for its academic value, it was designated as a natural monument in the 1930s during the Japanese colonial period, and preserved and managed for over 90 years. However, at the time of discovery, the stratigraphic level of tree fern fossils could not be located because the fossils were fragments detached from the rock body, and thus the Geummubong area where the conglomerate/sandstone layers of the Nakdong Formation are distributed, has been designated as a cultural heritage area. Only in the 2000s, when tree fern fossils were directly recovered from the outcrops near the designated area, the sedimentary rock facies containing the fossils were interpreted, and the anatomical characteristics of the Mesozoic tree fern fossils could be described and identified as a species level. Such studies are, in these days, redefining classification criteria done by Japanese paleontologist, Ogura. That is, Korean researchers pointed out that the classification criteria of the tree fern fossils (Cyathocaulis) reported early from Chilgok were ambiguous, and the possibility that the two species were the same species was suggested. In addition, it is necessary to reorganize designated areas as a way to resolve social conflicts and civil complaints caused by various regulations that have continued for a long time.

Feb 29, 2024 Vol.57 No.1, pp. 1~91

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