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Deformation-induced right-side-up pseudo-stratigraphy of the early Paleozoic Joseon Supergroup in the southeastern Danyang area, South Korea 韩国丹阳东南部早古生代朝鲜超群的变形诱导右旋假地层学
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-04-18 DOI: 10.1007/s12303-024-0008-2
Tae-Hoon Uhmb, Jin-Han Ree, Hyeong Soo Kim

The formations in the early Paleozoic Joseon Supergroup (mainly carbonates with subordinate siliciclastics) within the Taebaeksan Basin in the Danyang area, South Korea, show an apparent right-side-up homoclinal stratigraphy without repetition or omission of any formation, and it was therefore thought that the NW-dipping formation boundaries are primary depositional contacts. Our detailed examination revealed, however, that the formation boundaries are reverse-slip shear zones parallel to the second-generation foliation (S2) crenulating transposed S0//S1 foliation and that WNW-dipping bedding planes (S0) are only locally preserved. The most penetrative regional planar structure in the area is the NNW-dipping first-generation foliation (S1) that is defined by compositional layering and is parallel to the axial planes of isoclinal F1 folds. Isoclinal to close F1 folds occur on both the mesoscopic and macroscopic scale, whereas tight to close F2 folds occur locally only on the mesoscopic scale. D1 deformation presumably involved a NNW-SSE horizontal contraction and resulted in the buckle folding and transposition of S0. D2 deformation involved a NW-SE contraction, probably at a high angle to the S0//S1 transposed layers, and produced passive shear folding of S0//S1 with S2 crenulation cleavages as discrete shear surfaces. Shearing deformation was strongly localized along some S2 foliation planes, resulting in reverse shear zones that represent the current ‘pseudo’-formation boundaries. Based on zircons U-Pb ages, we suggest that the Okdong Fault was initiated from an unconformable boundary between the Precambrian basement gneiss and overlying sediments of the Paleozoic Taebaeksan Basin, probably during the Middle Jurassic.

韩国丹阳地区太白山盆地内早古生代朝鲜超群的地层(主要为碳酸盐岩,其次为硅质岩)显示出明显的右旋同向地层,没有重复或遗漏任何地层,因此人们认为西北倾的地层边界是主要的沉积接触点。然而,我们的详细研究发现,地层边界是与第二代折线(S2)平行的反向滑动剪切带,该剪切带呈圆弧状转置 S0//S1 折线,仅在局部地区保留了向西北倾斜的基底面(S0)。该地区最具穿透力的区域平面结构是北西倾第一代褶皱(S1),它是由成分层理确定的,与等轴F1褶皱的轴向平面平行。等卷至闭合的F1褶皱出现在中观和宏观尺度上,而紧密至闭合的F2褶皱仅出现在局部中观尺度上。D1 变形可能涉及 NNW-SSE 水平收缩,并导致 S0 的倒扣褶皱和转位。D2变形涉及西北-东南收缩,可能与S0//S1转位层呈高角度,并产生了S0//S1的被动剪切褶皱,S2的齿状裂隙成为离散的剪切面。剪切变形沿着一些 S2 褶皱平面强烈局部化,形成了代表当前 "伪 "构造边界的反向剪切带。根据锆石的 U-Pb 年龄,我们认为 Okdong 断层是由前寒武纪基底片麻岩与古生代太白山盆地上覆沉积物之间的不整合边界引发的,可能发生在中侏罗世。
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引用次数: 0
Classification of terrestrial impact craters based on morphometric parameters using remote sensing data: a case study of Jeokjung-Chogye impact crater, South Korea 利用遥感数据根据形态参数对陆地撞击坑进行分类:韩国 Jeokjung-Chogye 撞击坑案例研究
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-04-18 DOI: 10.1007/s12303-024-0007-3
Habimana Emmanuel, Jaehyung Yu, Lei Wang, Sung Hi Choi, Gilljae Lee, Digne E. Rwabuhungu R

This study aims to develop an automated impact crater classification machine learning (ML) method based on the morphometric parameters extracted from SRTM DEM. The training and testing dataset comprises data from 52 confirmed, well preserved, and moderately eroded impact craters and a recently discovered impact crater in Korea, Jeokjung Chogye Basin (JCB). The morphometric parameters including rim diameter, floor diameter, and wall width of complex craters and simple craters were tested by Mann Whitney U test and One Sample Wilcoxon signed rank test. The tests showed that those parameters can statistically separate the two types of craters. The Random Forest model classified them with an accuracy of 88.6% and a Kappa coefficient of 0.67, where rim diameter, floor diameter, and wall width were identified as variables with the highest Gini indices. Complex craters are characterized by a large flat diameter and wide wall width compared to simple craters with parabolic bases. The difference is caused by the impact energy when the craters were formed. The study confirmed that using machine learning, the complex craters and simple craters can be separated by checking the SRTM elevation model with machine learning methods. The morphometric parameters of JCB impact crater indicated that the crater is highly a complex crater concluded by both statistical tests and machine learning algorithm.

本研究旨在开发一种基于从 SRTM DEM 提取的形态参数的自动撞击坑分类机器学习(ML)方法。训练和测试数据集包括 52 个已确认的、保存完好的和中度侵蚀的撞击坑数据,以及韩国最近发现的一个撞击坑--Jeokjung Chogye Basin(JCB)的数据。对复杂陨石坑和简单陨石坑的边缘直径、底面直径和壁宽等形态参数进行了曼-惠特尼 U 检验和单样本 Wilcoxon 符号秩检验。检验结果表明,这些参数能在统计学上将两类陨石坑区分开来。随机森林模型对它们进行分类的准确率为 88.6%,卡帕系数为 0.67,其中边缘直径、底面直径和壁宽被认为是基尼指数最高的变量。与具有抛物线基底的简单陨石坑相比,复杂陨石坑的特点是平面直径大、壁宽。造成这种差异的原因是陨石坑形成时的撞击能量。研究证实,利用机器学习方法,通过检查 SRTM 高程模型,可以将复杂陨石坑和简单陨石坑区分开来。通过统计检验和机器学习算法,JCB 撞击坑的形态参数表明该撞击坑属于高度复杂的撞击坑。
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引用次数: 0
Geochronology and geochemistry of the polyphase mafic rocks in the North Liaohe Group, Jiao-Liao-Ji Belt, North China Craton: implications for petrogenesis and tectonic evolution 华北克拉通胶辽冀带北辽河组多相岩浆岩的地质年代和地球化学:对岩石成因和构造演化的影响
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-04-18 DOI: 10.1007/s12303-024-0009-1
Lixiang Zhao, Minxia Ma, Ye Qian, Haoran Li, Lingyun Sun, Jinlei Sun, Yanjie Shen, Fengyue Sun

The Jiao-Liao-Ji Belt (JLJB) is one of the Paleoproterozoic orogenic belts within the North China Craton (NCC), whose tectonic evolution is still controversial due to multiple magmatic/metamorphic events after its formation. To tackle this controversy, we conducted petrological, geochronological, geochemical and zircon Hf isotopic studies for the meta-mafic rocks from the North Liaohe Group (NLG) in the central JLJB. 207Pb/206Pb weighted average ages of 1849 ± 36 Ma and 1853 ± 13 Ma indicate that the protoliths of the amphibolites in the Shisixian area formed at ca. 1.85 Ga. Geochemically, the amphibolites belong to tholeiitic series; while the meta-gabbros can be divided into the low-Ti and high-Ti types: the former belongs to calc-alkaline series, whereas the latter belongs to tholeiitic series. The high-Ti rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs; e.g., Ba, K and Pb), and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs; e.g., Nb, Ta, P and Ti). These rocks display slightly positive εHf(t) values (+1.40 to +2.02). The low-Ti meta-gabbros were most likely derived from the partial melting of the enriched lithospheric mantle in the spinel stability field, which was metasomatized by subduction-related fluids and/or melts with significant contamination of crustal material, while the amphibolites and high-Ti meta-gabbros were derived from partial melting of depleted asthenospheric mantle in the spinel stability field, which was metasomatized by limited subduction-related fluids and/or melts, coupled with fractional crystallization. The lithological and geochemical characteristics show that the low-Ti meta-gabbros formed in a magmatic arc environment, the high-Ti rocks formed in the later stage of a back-arc basin; while the amphibolites formed in a post-collisional extensional environment. Combined with literature data, we suggest that the JLJB experienced a process from subduction, collision, to extension: At ca. 2.2–2.1 Ga back-arc basin opened via southward subduction of an oceanic plate followed by northward subduction at ca. 2.1–1.91 Ga, and subsequently closed to form the JLJB at ca. 1.91 Ga, which led to the Longgang-Nangrim continental collision, and post-collision extension occurred at ca. 1.85 Ga along with the collapse of the collisional orogen.

焦辽冀带是华北克拉通(NCC)中的古新生代造山带之一,由于其形成后发生了多次岩浆/变质事件,其构造演化至今仍存在争议。针对这一争议,我们对金陵拗陷中部北辽河组的元杂岩进行了岩石学、地质年代学、地球化学和锆石Hf同位素研究。207Pb/206Pb加权平均年龄分别为1849±36Ma和1853±13Ma,表明石西县地区闪长岩的原岩形成于约1.85Ga。1.85 Ga。在地球化学上,闪长岩属于透辉岩系列;而元辉长岩可分为低钛和高钛类型:前者属于钙碱性系列,后者属于透辉岩系列。高钛岩石富含轻稀土元素(LREEs)和大离子亲岩元素(LILEs;如Ba、K和Pb),而贫含重稀土元素(HREEs)和高场强元素(HFSEs;如Nb、Ta、P和Ti)。这些岩石的εHf(t)值略微偏正(+1.40 至 +2.02)。低钛元辉长岩很可能来自于尖晶石稳定场中富集的岩石圈地幔的部分熔融,这些地幔在与俯冲有关的流体和/或熔体的作用下发生了变质作用,并受到大量地壳物质的污染;而闪长岩和高钛元辉长岩则来自于尖晶石稳定场中贫乏的星体层地幔的部分熔融,这些地幔在有限的与俯冲有关的流体和/或熔体的作用下发生了变质作用,再加上碎裂结晶作用。岩石学和地球化学特征表明,低钛元辉长岩形成于岩浆弧环境,高钛岩石形成于后弧盆地后期,而闪长岩则形成于碰撞后延伸环境。结合文献数据,我们认为JLJB经历了从俯冲、碰撞到延伸的过程:在约 2.2-2.1 Ga 时,通过一个大洋板块向南俯冲打开了弧后盆地,随后在约 2.1-1.91 Ga 时向北俯冲,随后在约 1.91 Ga 时闭合形成了 JLJB。约 1.91 Ga 时,龙岗-南岭大陆发生碰撞,碰撞后的延伸发生在约 1.85 Ga 时,同时发生了塌陷。随着碰撞造山带的塌陷,碰撞后的延伸发生在约1.85 Ga。
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引用次数: 0
Liquefaction assessment using alternative approaches: a case study of Ho Chi Minh City stratigraphy 使用替代方法进行液化评估:胡志明市地层案例研究
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-03-27 DOI: 10.1007/s12303-024-0006-4
Nhat-Phi Doan, Duy Triet Doan, Van Nam Nguyen, Sung-Sik Park

Liquefaction has been known as a phenomenon in which the shear strength and stiffness of saturated soil are reduced by the generation of pore water pressure under earthquake loading. Consequently, liquefaction-induced settlement can result in severe damage including building cracks or slope failure, which pose a threat to human lives and properties. In the current Vietnamese standard TCVN 9386:2012, liquefaction potential hazard is often evaluated using the simplified method, which solely identifies the areas with a high risk of liquefaction. Prediction of Safety Factor (FS), Settlement (S), Liquefaction Potential Index (LPI), and Liquefaction Severity Number (LSN) has not received sufficient attention to a completeness standard. This study assesses the liquefaction of the site at Ho Chi Minh City, Vietnam by using four conventional methods: the simplified procedure, linear equivalent analysis, loosely-coupled effective stress analysis, and fully-coupled effective stress analysis based on standard penetration test (SPT) data in Ho Chi Minh Metropolitan City. A class of seismic events that are compatible with the design response spectrum in the Vietnamese standard TCVN 9386:2012 is used as input ground motion at the bedrock. According to the results of different methods, maps of ground settlement, LPI, and LSN are proposed as useful references for construction works on such soils, which may have a high potential for liquefaction and subsidence.

众所周知,液化是指在地震荷载作用下,饱和土壤的剪切强度和刚度因孔隙水压力的产生而降低的一种现象。因此,液化引起的沉降会导致严重破坏,包括建筑物开裂或斜坡坍塌,对人类生命和财产构成威胁。在现行的越南标准 TCVN 9386:2012 中,液化潜在危害通常采用简化方法进行评估,该方法仅确定液化风险较高的区域。安全系数 (FS)、沉降 (S)、液化潜势指数 (LPI) 和液化严重度数 (LSN) 的预测尚未得到足够的重视,因此尚未形成完整的标准。本研究根据胡志明市的标准贯入试验 (SPT) 数据,采用四种常规方法评估了越南胡志明市场地的液化情况:简化程序、线性等效分析、松散耦合有效应力分析和完全耦合有效应力分析。基岩处的输入地面运动采用了与越南标准 TCVN 9386:2012 中的设计反应谱相一致的一类地震事件。根据不同方法的结果,提出了地面沉降、LPI 和 LSN 图,作为在此类土壤上进行建筑工程的有用参考,因为此类土壤可能具有较高的液化和沉降潜力。
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引用次数: 0
Petrology and geochemistry of the Az Zabirah south zone bauxite deposit at Al Ba’itha mine, north-central Saudi Arabia 沙特阿拉伯中北部 Al Ba'itha 矿区 Az Zabirah 南区铝土矿的岩石学和地球化学研究
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-03-14 DOI: 10.1007/s12303-023-0046-1
Mahmoud A. Galmed, Hisham A. Gahlan, Habes A. Ghrefat, Essam A. Mohamed, Khaled M. Al Kahtany

In the central north of Saudi Arabia, outcrop samples from the Cretaceous bauxite profile deposits in the Az Zabirah area were subjected to a comprehensive evaluation aimed at investigating their petrographical and geochemical characteristics using X-ray diffraction analysis (XRD), Scanning electron microscope (SEM) coupled with Energy dispersive (EDS) analysis, and X-ray fluorescence spectrometer (XRF) analysis. These bauxite deposits in the Az Zabirah area comprises of three main zones: the South zone, the Central zone, and the North zone. Petrologically, the bauxite samples predominantly consist of oolitic to pisolitic grains that are bound together by a matrix comprising bauxitic materials, iron oxides, calcite, and/or kaolinite. Mineralogical investigations indicate that the primary mineral composition of the bauxite includes gibbsite, boehmite, diaspore (kaolinite), hematite, quartz, and calcite. XRF showed that the dominant chemical components of the bauxite samples are Al2O3, SiO2, and Fe2O3. When considering the collective data from the rare earth elements (REEs) analysis (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and chemical weathering indices such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Weathering Index of Parker (WIP), it becomes evident that the Az Zabirah South Zone bauxite laterite profile at Al Ba’itha mine was formed under the influence of significant and persistent weathering conditions. The findings and methods used in this study are considered beneficial and valuable as they support mineral exploration in arid and semi-arid environments.

对沙特阿拉伯中北部 Az Zabirah 地区白垩纪铝土剖面矿床的露头样本进行了全面评估,旨在利用 X 射线衍射分析 (XRD)、扫描电子显微镜 (SEM) 结合能量色散 (EDS) 分析以及 X 射线荧光光谱仪 (XRF) 分析,研究其岩石学和地球化学特征。Az Zabirah 地区的这些铝土矿藏包括三个主要区域:南区、中区和北区。从岩石学角度来看,铝土矿样本主要由鲕粒到鲕粒组成,这些鲕粒被由铝土矿材料、氧化铁、方解石和/或高岭石组成的基质结合在一起。矿物学研究表明,铝土矿的主要矿物成分包括辉绿岩、波长石、透辉石(高岭石)、赤铁矿、石英和方解石。XRF 显示,铝土矿样品的主要化学成分是 Al2O3、SiO2 和 Fe2O3。在考虑稀土元素(REEs)分析(La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb 和 Lu)和化学风化指数(如化学蜕变指数(CIA))的综合数据时,需要考虑以下因素:(a) 铝土矿样品的化学成分;(b) 铝土矿样品的化学成分;(c) 铝土矿样品的化学成分、根据这些指数,可以明显看出 Al Ba'itha 矿区 Az Zabirah 南区红土铝土矿剖面是在显著而持久的风化条件影响下形成的。本研究的发现和使用的方法被认为是有益和有价值的,因为它们有助于在干旱和半干旱环境中进行矿产勘探。
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引用次数: 0
The Hakcheon-Chogok Megaturbidite in the Miocene Pohang-Youngduk Basin, SE Korea: high-gradient slope failure probably triggered by a giant tsunami wave 韩国东南部中新世浦项-永都盆地的白川-乔谷巨型砾岩:可能由巨型海啸波引发的高梯度斜坡崩塌
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-03-12 DOI: 10.1007/s12303-024-0004-6
Junghee Son, Soonmi Cho, In Gul Hwang

In ancient records, discrimination of specific triggering events from sediment gravity flow deposits is very difficult, due to multiple interactions between triggering events and similar sedimentary characteristics. For this study, we introduce the Hakcheon-Chogok Megaturbidite (HCM) in the Miocene Pohang-Youngduk Basin (PYB), providing an opportunity to differentiate the triggering events. This megaturbidite is over 70 m thick in the proximal part and less than 4 m thick in the distal part. The diachronous stratigraphic position and distinct coarser sediments than those of the underlying and overlying successions suggest a large-scale slope failure of the fine-grained foreset (more than 2 km3). The occurrence of exotic granitic boulders, originating from the basement rock, more than 1 km west of the present fan-apex, is indicative of extreme sea-level run-up. The dispersal pattern and paleocurrent direction suggest that the HCM flowed to the northeast, irrespective of the local depositional slope which show a radial distribution from the fan-apex. The distribution pattern almost perpendicular to the strike of the NW-SE trending transfer fault suggests that the HCM was triggered by a reflection flow of giant tsunami wave, resulting in a large-scale failure of high-gradient (> 15° in slope angle) fandelta slope.

在古代记录中,由于触发事件与类似沉积特征之间存在多种相互作用,因此很难从沉积重力流沉积中分辨出具体的触发事件。在这项研究中,我们引入了中新世浦项-营都盆地(PYB)的白川-乔谷特大扰动岩(HCM),为区分触发事件提供了机会。该特大扰动岩近端厚度超过 70 米,远端厚度不足 4 米。地层位置的不同步性以及明显比底层和上覆岩层更粗的沉积物表明,细粒前置岩(超过 2 km3)发生了大规模的斜坡崩塌。在现扇形顶点以西 1 公里多的地方,出现了源自基底岩石的外来花岗岩巨石,这表明海平面急剧上升。散布模式和古水流方向表明,河姆渡向东北方向流动,与当地的沉积斜坡无关,而当地的沉积斜坡显示出从扇形顶点开始的放射状分布。几乎垂直于 NW-SE 走向转移断层走向的分布模式表明,HCM 是由巨型海啸波的反射流引发的,导致高坡度(坡角 15°)扇形斜坡的大规模崩塌。
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引用次数: 0
A new lithostratigraphic scheme of the Ordovician Jeongseon Formation of the Yongtan Group in the Taebaeksan Basin and sequence stratigraphic analysis with discussion on basin geometry 太白山盆地龙潭组奥陶纪旌善层新地层方案和层序地层分析及盆地几何学讨论
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-03-12 DOI: 10.1007/s12303-024-0005-5

Abstract

Lithostratigraphy of the Yongtan Group is newly established based on detailed sedimentologic and stratigraphic studies on recently exposed, less deformed, relatively continuous outcrops and comprehensive review of previous studies, mainly focusing on the Jeongseon Formation which occupies most of the group spatially and stratigraphically. The Yongtan Group is divided into the Jeongseon, Haengmae, and Hoedongri formations in ascending order, and all the units are assigned to the Ordovician. The Jeongseon Formation is divided into three members based on lithology. Eleven sedimentary facies are recognized in the Jeongseon Formation and organized into five facies associations (FAs), FA1 (tidal flat), FA2 (inner-ramp), FA3 (shoal), FA4 (mid-ramp), and FA5 (ramp-slope to outer-ramp). The formation is interpreted to have been deposited on a homoclinal ramp. The Yongtan Group is divided into two supersequences separated by type 1 sequence boundary and the lower and middle members of the Jeongseon Formation belong to Supersequence I and the Upper Member to Supersequence II which includes the Haengmae and Hoedongri formations. The relative sea-level curve inferred from sequence stratigraphic analysis suggests that the formation evolved through two depositional stages in accordance with second-order sea-level changes separated by the boundary between the Sauk and Tippecanoe sequence, and the curve is greatly similar to that of the Taebaek and Yeongwol groups. The southeastward thickening of FA3 and northwestward prevalence of shale-rich facies suggest that topographic highs and lows were present in the Taebaeksan Basin and a slope might have developed along the carbonate platform during the early stage of deposition. The correlation and lateral thickness variation of the facies associations additionally suggest that the basin was deeper toward the northwestern part of the Jeongseon area. The deepening is likely attributed to the weakening of the productivity of the carbonate factory during the early Ordovician.

摘要 根据对新近出露、变形较小、相对连续的露头进行的详细沉积学和地层学研究,以及对以往研究的全面回顾,新建立了龙潭组的岩石地层学,主要侧重于在空间和地层上占据龙潭组大部分的贞善层。龙潭组从高到低依次分为旌善层、幸前层和会东里层,所有单元均归入奥陶系。旌善地层根据岩性分为三个单元。旌善地层共有 11 个沉积面,分为五个面系(FA):FA1(滩涂)、FA2(内斜坡)、FA3(浅滩)、FA4(中斜坡)和 FA5(斜坡至外斜坡)。根据解释,该地层沉积于同轴斜坡上。龙潭组被划分为两个超序,以第 1 型序列边界分隔,贞善地层的中下部成员属于超序 I,上部成员属于超序 II,其中包括 Haengmae 和 Hoedongri 地层。根据层序地层分析推断出的相对海平面曲线表明,该地层根据二阶海平面变化经历了两个沉积阶段,以Sauk层序和Tippecanoe层序的边界为分界,该曲线与Taebaek组和Yeongwol组的曲线极为相似。FA3向东南方向增厚,富含页岩的岩层向西北方向盛行,这表明太白山盆地存在地形高低起伏,在沉积早期可能沿着碳酸盐平台形成了斜坡。此外,岩相的相关性和横向厚度变化也表明,盆地在贞善地区西北部的深度较深。盆地变深的原因可能是奥陶纪早期碳酸盐工厂生产力的减弱。
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引用次数: 0
New insights on seismic activity in the southeastern Korean Peninsula from the Gyeongju Hi-density Broadband Seismic Network (GHBSN) 庆州高密度宽带地震网络(GHBSN)对朝鲜半岛东南部地震活动的新认识
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-03-07 DOI: 10.1007/s12303-024-0003-7
Dabeen Heo, Tae-Seob Kang, Minook Kim, Byeong Seok Ahn, Hobin Lim, Jaeseoung Han, Kwang-Hee Kim, Junkee Rhie, YoungHee Kim, Jin-Han Ree

The 2016 magnitude (MW) 5.5 Gyeongju earthquake, which occurred in Korea near assumed epicenters of several substantial historical earthquakes and Quaternary fault segments, underscores the importance of seismic hazard assessment in the region. However, uncertainties about potential seismic sources make evaluating the potential for a moderate-to-large earthquake challenging. Microearthquake monitoring through a dense seismic network can provide crucial insights into the regional seismic characteristics. An extensive temporary seismic array known as the Gyeongju Hi-density Broadband Seismic Network (GHBSN) was established to investigate microearthquake activity in the southeastern Korean Peninsula. This included the zone of aftershocks from the 2016 Gyeongju earthquake sequence. The GHBSN comprises 200 broadband stations located at approximately 4.5 km intervals in an area of approximately 60 × 60 km2 around the epicenter of the mainshock. A total of 4,773 events were detected from November 2017 to December 2021, including 3,935 events within the GHBSN. The detected events were categorized into five seismic regions excluding quarry blasting sites, that is, the 2016 Gyeongju earthquake region, eastern part of the Ulsan Fault, 2017 Pohang earthquake region, eastern offshore Gyeongju, and western part of the Miryang Fault. A local magnitude scale was developed for the southeastern Korean Peninsula using events detected through the GHBSN. This reflects the distance attenuation and site conditions of the GHBSN stations for earthquakes. An event catalog was created using two automatic detection methods based on the measurement of the energy ratio. This provided high-resolution hypocenter parameters at a completeness magnitude (MC) of 0.0 despite the seismic environment of the network being exposed to high cultural noise. The Gutenberg-Richter b-value was estimated as 0.82 ± 0.02 for all events and 1.01 ± 0.02 for those inside GHBSN. This implies that the seismicity reflects a representative intraplate seismic environment. Testing the obtainability of the focal mechanism solutions showed that the GHBSN outperformed the regional network. Depending on the relationship between the magnitude and frequency of earthquakes, a relatively large number of small earthquakes can provide detailed information on the geometric properties of the causative faults and the state of the acting stress. High-precision microearthquake observation and analysis through GHBSN could provide an unprecedented opportunity with seismic datasets to understand the seismogenesis of the southeastern Korean Peninsula, including the zone of aftershocks of the 2016 Gyeongju earthquake.

2016 年韩国庆州发生 5.5 级地震,震中靠近历史上几次大地震的假定震中和第四纪断层段,凸显了该地区地震灾害评估的重要性。然而,由于潜在震源的不确定性,评估中到大型地震的可能性具有挑战性。通过密集的地震网络进行微震监测,可以为了解区域地震特征提供重要信息。为调查朝鲜半岛东南部的微震活动,建立了一个广泛的临时地震阵列,即庆州高密度宽带地震网络(GHBSN)。其中包括 2016 年庆州地震序列的余震区。GHBSN 由 200 个宽带台站组成,这些台站位于主震震中周围约 60 × 60 平方公里区域内,间隔约 4.5 公里。从 2017 年 11 月到 2021 年 12 月,共探测到 4,773 个事件,其中 3,935 个事件发生在 GHBSN 范围内。探测到的事件被划分为五个地震区域(不包括采石场爆破点),即 2016 年庆州地震区域、蔚山断层东部、2017 年浦项地震区域、庆州东部近海以及秘阳断层西部。利用 GHBSN 探测到的事件,为朝鲜半岛东南部制定了当地震级表。这反映了 GHBSN 地震站的距离衰减和现场条件。利用基于能量比测量的两种自动检测方法创建了事件目录。这提供了高分辨率的次中心参数,尽管网络的地震环境受到高文化噪声的影响,但完整度(MC)为 0.0。所有地震事件的古腾堡-里希特 b 值估计为 0.82 ± 0.02,GHBSN 内部地震事件的古腾堡-里希特 b 值估计为 1.01 ± 0.02。这意味着地震活动反映了具有代表性的板内地震环境。测试焦点机制解的可获得性表明,GHBSN 的性能优于区域网络。根据地震震级和频率之间的关系,相对大量的小地震可以提供有关致震断层几何特性和作用应力状态的详细信息。通过 GHBSN 进行高精度微震观测和分析,可为了解朝鲜半岛东南部(包括 2016 年庆州地震余震区)的地震发生情况提供前所未有的地震数据集机会。
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引用次数: 0
Geospatial technologies for estimating post-wildfire severity through satellite imagery and vegetation types: a case study of the Gangneung Wildfire, South Korea 通过卫星图像和植被类型估算火灾后严重程度的地理空间技术:韩国江陵野火案例研究
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-02-29 DOI: 10.1007/s12303-023-0045-2
Liadira K. Widya, Chang-Wook Lee

Wildfires have caused natural environmental damage that has contributed to deforestation, consequently demonstrating a significant influence on atmospheric emissions. Wildfires occur frequently in South Korea, especially during the spring season. This study assessed post-wildfires areas in Gangneung, South Korea, on April 11, 2023, which were generated by implementing remote sensing technology and statistical analysis. Remote sensing and classification techniques, including PlanetScope, have been developed for identifying wildfire-damaged areas. The method for classifying post-wildfire mapping estimation includes the utilization of deep learning approaches, especially using the U-Net architecture. Therefore, the assessment of wildfire severity can be conducted using Sentinel-2 and Sentinel-5P imagery in addition to an analysis of the vegetation type and air pollutant within the affected region. In the present study, Sentinel-2 imagery was to generate spectral indices, including the differenced normalized burn ratio (dNBR), differenced normalized difference moisture index (dNDMI), differenced soil adjusted vegetation index (dSAVI), and differenced normalized vegetation index (dNDVI). Sentinel-5P imagery was utilized to produce carbon monoxide (CO) column number densities. The estimation of wildfire areas was conducted using a PlanetScope classified image with the U-Net classifier, which was evaluated based on the overall accuracy value of 95% and kappa accuracy of 0.901. The wildfire severity level was shown by dNBR, which was correlated with the parameters, including RBR, dNDMI, dSAVI, dNDVI, and CO. The statistical analysis demonstrated a significant and positive correlation between the wildfire severity and the parameters. Moreover, the average of vegetation indices (NDMI, SAVI, and NDVI) before and after a wildfire were found to decrease by vegetation type, including 17.55% in mixed barren land areas, 17.49% in other grasses, 24.71% in mixed forest land, 22.48% in coniferous land, 13.48% in fields, and 4.29% in paddy fields. On the basis of the results, these estimates can be employed to identify the level of damage caused by wildfires to vegetation and air quality.

野火对自然环境造成破坏,导致森林砍伐,从而对大气排放产生重大影响。韩国经常发生野火,尤其是在春季。本研究通过遥感技术和统计分析,对 2023 年 4 月 11 日韩国江陵的野火后地区进行了评估。包括 PlanetScope 在内的遥感和分类技术已被开发用于识别野火灾区。对野火后绘图估算进行分类的方法包括利用深度学习方法,特别是使用 U-Net 架构。因此,除了对受影响区域内的植被类型和空气污染物进行分析外,还可利用哨兵-2 和哨兵-5P 图像对野火严重程度进行评估。在本研究中,哨兵-2 图像用于生成光谱指数,包括差分归一化燃烧比(dNBR)、差分归一化差异水分指数(dNDMI)、差分土壤调整植被指数(dSAVI)和差分归一化植被指数(dNDVI)。哨兵-5P 图像用于生成一氧化碳 (CO) 柱数密度。利用 PlanetScope 分类图像和 U-Net 分类器对野火区域进行了估算,根据 95% 的总体准确率和 0.901 的 kappa 准确率进行了评估。野火严重程度由 dNBR 表示,dNBR 与 RBR、dNDMI、dSAVI、dNDVI 和 CO 等参数相关。统计分析表明,野火严重程度与参数之间存在显著的正相关。此外,不同植被类型在野火前后的植被指数(NDMI、SAVI 和 NDVI)平均值均有所下降,其中混交荒地下降 17.55%,其他草地下降 17.49%,混交林地下降 24.71%,针叶林地下降 22.48%,田地下降 13.48%,水田下降 4.29%。根据这些估算结果,可以确定野火对植被和空气质量的破坏程度。
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引用次数: 0
Skarn alteration and Fe-Zn-Pb mineralization at the Wondong deposit in the Taebaeksan Basin, South Korea 韩国太白山盆地 Wondong 矿床的矽卡岩蚀变和铁-锌-铅成矿作用
IF 1.2 4区 地球科学 Q2 Earth and Planetary Sciences Pub Date : 2024-02-23 DOI: 10.1007/s12303-024-0002-8

Abstract

Skarn and Fe-Zn-Pb mineralization at the Wondong deposit located in the Taebaeksan Basin of the central-eastern region of Korean Peninsula occurs along the contact between the Upper Cretaceous quartz-feldspar porphyry (QFP) and carbonate rocks of the Ordovician Makgol Formation. The QFP is relatively fresh and has a sharp contact with the garnet skarn. Skarn is dominant in the carbonate rocks but is rare in the QFP. It consists almost of grandite throughout the skarn but has mineralogical zonation of proximal garnet, intermediate pyroxene, and distal wollastonite with increasing distance from the contact between the QFP and garnet skarn. Garnet becomes Fe-rich, and pyroxene tends to be enriched in Fe and Mn toward the marble front. Massive Fe mineralization, replacing garnet skarn, is restricted proximal to the QFP. In contrast, although the Zn-Pb mineralization is found in all areas it mostly occurs in the carbonate rocks beyond the skarn. Zinc-Pb mineralization occurred as stockwork and vein in the QFP and the garnet skarn consists of sphalerite, galena, Al-rich garnet, and calcite with a minor quantity of arsenopyrite. In contrast, the carbonate replacement of the Zn-Pb mineralization beyond skarn consists of sphalerite, pyrrhotite, galena, diopsidic pyroxene, and calcite with minor minerals such as arsenopyrite, löellingite, and chalcopyrite. Sphalerite, principal ore mineral, becomes darker and Fe- (up to 34.4 mol% FeS) and Mn-rich (up to 1.5 mol% MnS) with increasing distance from the QFP. Arsenopyrite is closely associated with sphalerite tends to be decreased in As away from the QFP. All sulfide minerals from Zn-Pb mineralization in the Wondong deposit have δ34S values ranging from 2.9 to 5.9‰, which are attributed to the magmatic source. In addition, the narrow range and subtle variation of the δ34S values for all sulfides throughout the Wondong deposits are not interpreted to be involved in the mixing of multiple sulfur sources. Geological, petrographic, mineralogical, and isotopic geochemical investigations show that the early skarn was formed in an environment of high fluid: rock ratios at the contact between the QFP and Makgol Formation and it was dominated by grandite, indicating the oxidizing nature of the skarn-forming fluids. The ore deposition began after the formation of the main garnet dominated skarn. The ore-forming fluids responsible for Zn-Pb mineralization are characterized by a less oxidizing nature, as defined by comparatively Al-enriched garnet in vein type mineralization in and around the QFP. Farther, the fluids producing the carbonate replacement of the Zn-Pb mineralization are unlikely to be engaged in external effects such as mixing with multiple sulfur sources even though it travels over long distance.

摘要 位于朝鲜半岛中东部太白山盆地的 Wondong 矿床的矽卡岩和铁-锌-铅矿化现象发生在上白垩统石英-长石斑岩(QFP)与奥陶纪 Makgol 组碳酸盐岩的接触带。石英-长石斑岩相对较新,与石榴石矽卡岩有尖锐的接触。矽卡岩在碳酸盐岩中占主导地位,但在 QFP 中却很少见。在整个矽卡岩中,矽卡岩几乎都是英安岩,但随着距离矽卡岩与石榴石矽卡岩接触点的距离增加,矽卡岩的矿物分带也随之增加,由近端石榴石、中间辉石和远端硅灰石组成。石榴石变得富含铁,而辉石的铁和锰含量则趋向于向大理岩前沿富集。大量铁矿化取代了石榴石矽卡岩,但仅限于 QFP 附近。与此相反,尽管锌铅矿化在所有地区都有发现,但主要出现在矽卡岩以外的碳酸盐岩中。锌-铅矿化以网脉和脉石的形式出现在 QFP 中,石榴石矽卡岩由闪锌矿、方铅矿、富铝石榴石和方解石以及少量的砷黄铁矿组成。与此相反,矽卡岩以外的锌铅矿化的碳酸盐置换物由闪锌矿、黄铁矿、方铅矿、二侧辉石和方解石组成,还有少量的砷黄铁矿、络菱铁矿和黄铜矿等矿物。闪锌矿是主要的矿石矿物,随着与 QFP 的距离增加,颜色变深,富含铁(FeS 含量高达 34.4 摩尔)和锰(MnS 含量高达 1.5 摩尔)。黄铜矿与闪锌矿密切相关,其砷含量在远离钦定边界点的地方呈下降趋势。翁东矿床锌铅矿化的所有硫化物矿物的δ34S值在2.9-5.9‰之间,这与岩浆源有关。此外,整个翁东矿床所有硫化物的δ34S值范围狭窄且变化微妙,不能解释为涉及多种硫源的混合。地质、岩相、矿物学和同位素地球化学研究表明,早期矽卡岩是在 QFP 与 Makgol 地层接触处的高流体岩石比环境中形成的,以英安岩为主,表明矽卡岩形成流体的氧化性质。矿石沉积始于以石榴石为主的矽卡岩形成之后。造成锌铅矿化的成矿流体具有氧化性较低的特点,这一点从 QFP 及其周边地区矿脉型矿化中相对富含铝的石榴石可以看出。更进一步说,产生锌铅矿化碳酸盐置换的流体不太可能受到外部影响,如与多种硫源混合,即使流体经过很远的距离。
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