Numerical simulation of hydro-mechanical constraints on the geometry of a critically tapered accretionary wedge

송인선,고희재 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.3

A critically tapered active accretionary wedge was simulated using a numerical analysis of plastic slip-line theory to understand the mechanics of morphologic evolution. The concept of critical state soil mechanics was applied to describe the entire wedge area overlying a basal décollement fault. Presuming a condition of two-dimensional plane strain along the compressional direction, we obtained the numerical solution of conjugate plastic slip lines at a critical state of stress defined by the Coulomb yield criterion. The velocity vectors were obtained by applying the associate flow rule with the boundary conditions at the upper surface of the wedge. Finally, the detachment was determined from the effective stress condition inside the wedge and the sliding friction coefficient along the fault. Our numerical simulations demonstrate that the morphology of a critically tapered wedge is dependent on the frictional strengths of both the wedge materials and the basal fault. The critical taper angle decreases with increasing internal friction angle and decreasing basal friction coefficient. The results also revealed that the pore pressure controls the morphology of the accretionary wedge for cohesive sediments but not for non-cohesive materials. The effect of pore pressure on the morphology of a critically tapered accretionary wedge becomes more significant as the cohesion increases. Assuming that the cohesion is very low, we could infer the ranges of strengths that most observed wedge geometry data have 0.3–0.6 for the basal friction coefficient and ~35–45° for the internal friction angle of the wedge materials.

Identification of aquifer system in the whole Red River Delta, Vietnam

Duong Du Bui,Akira Kawamura,Thanh Ngoc Tong,Hideo Amaguchi,Naoko Nakagawa,Yoshihiko Iseri 한국지질과학협의회 2011 Geosciences Journal Vol.15 No.3

The Red River Delta is one of two biggest deltas in Vietnam. People living in the delta depend entirely on groundwater for their domestic water. However, the aquifer system in the whole Red River Delta remains poorly understood due to the lack of available data. Recently, we were nominated to construct a hydrogeological database. Using these valuable data contained in this database, this paper comprehensively analyzed the best number of 778 boreholes including well logs and their hydrogeological parameters obtained from pumping tests for the first time in order to identify the entire aquifer system and characterize hydrogeological conditions in the whole delta for potential groundwater resources. Great efforts have been made to establish and analyze hydrogeological maps, cross sections, and contour maps of main aquifers’ thickness and transmissivity. As for the results, we found that groundwater mainly exists in Quaternary unconsolidated sediments as porous water forming the topmost Holocene unconfined aquifer (HUA) and the shallow Pleistocene confined aquifer (PCA) sandwiching the Holocene-Pleistocene aquitard (HPA), while cleft and karst water exist in consolidated Neogene formations and Mesozoic rocks constituting the Neogene water bearing layer (NWL) and Mesozoic fractured zones (MFZ), respectively. PCA is almost entirely distributed over the delta. It serves as the highest groundwater potential and the most important aquifer for water supply. HUA is also widely distributed about 88% over the delta and has a high groundwater potential. NWL and MFZ, placed below PCA but exposed on the surface outside the delta, are minor sources for local domestic water supply only. These findings are indispensable for further groundwater analyses needed to ensure the sustainable groundwater development for the high-security water requirements in the delta, but have never been completed sufficiently before due to the unavailability of large-scale basic data sets

Sedimentation rates in Bera Lake (Peninsular Malaysia) using 210Pb and 137Cs radioisotopes

Mohammadreza Gharibreza,John Kuna Raj,Ismail Yusoff,Zainudin Othman,Wan Zakaria Wan,Mohammad Aqeel Ashraf 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

The evolutionary environmental history of Bera Lake was studied using the fallout radioisotopes137Cs and 210Pb. 317Cs horizons in the all ten studied cores showed a constant rate of 210Pb supply along all distinctive layers in each core. The lithology of layers significantly affected the variation of 210Pb value with depth. The chronology of Bera Lake sediment was conducted using the Constant Rate of Supply (CRS) model. The 1963 fallout maximum 137Cs from atmospheric testing of nuclear weapons found in all selected master cores at the depth of 40 cm. The mean pre-1950 sediment accumulation rate was ranged between 0.06 ± 0.02 and 0.16 ± 0.2 g cm–2 y–1. Environmental impacts of five deforestation projects performed from 1972 to 1995 at the catchment area, contributed significantly toward increasing the sedimentation rate within Bera Lake. Besides the 137Cs horizons, the charcoal horizon at the lower contact of white sandy mud revealed the datum of maximum deforestation in the study area. 210Pb dates using the CRS model correlated historical sediment fluxes to anthropogenic changes in Bera Lake catchment area. Organic-rich sediments deposited mostly at the top of the Bera Lake sediment columns with a mean rate of 0.2 ± 0.1 g cm–2 y–1 since 1994. High biomass productivity of mature oil palm plantations, which were developed in the catchment area, dictated organic-rich deposit distribution. This study highlighted capability of radioisotopes to reconstruct long-term (100–150 years) history of a natural lake at a tropical area where surrounding catchment has extensively deforested over the recent decades.

Analyzing groundwater change on a volcanic island caused by the impact of the M9 Sumatra earthquake

Jae-Yeol Cheong,함세영,김상현,Soo-Hyoung Lee,우남칠,김규범 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

Changes in groundwater level have been recognized by the earthquakes at various epicentral distances. The M9 Sumatra earthquake resulted in changes in the groundwater level, electrical conductivity, and temperature in monitoring wells on Jeju Island, South Korea. In regions of different groundwater type (basal, lower parabasal, upper parabasal, and high-level groundwater), the changes in the groundwater levels at 25 monitoring wells ranged between 4.0 and 49.5 cm; changes in the electrical conductivity at six monitoring wells ranged between 1 and 27,975 mS/cm; and the changes in water temperature at three wells ranged between 0.02 and 1.37 ûC. The irregular groundwater level changes at different locations on the island due to the earthquake reflect various interactions between hydrological properties and seismological processes. The impact of the earthquake was successfully recognized via transfer function modeling between the time series of groundwater level and the tidal oscillation. On the basis of the theoretical aquifer response to the earthquake, storage coefficient estimates for aquifers, which could not be determined from the single-well pumping tests, were determined to be within the range of 1.22•10–4–3.51•10–6.

Sedimentation and seafloor mound formation in the southern slope of the Ulleung Basin, East Sea, Korea, since the Last Glacial Maximum

박장준,유동근,In kwon Um,이상훈,우경식 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

Detailed analysis of core sediments and acoustic characteristics of Chirp sub-bottom profiles from a submarine ridge in the southern slope of the Ulleung Basin, East Sea, Korea, reveals changes in sedimentary processes and deformation of sedimentary sequence induced by seafloor mound formation since the Last Glacial Maximum (LGM). The core sediments consist generally of four sedimentary facies which represent hemipelagic sedimentation under a poorly-oxygenated bottom-water condition during the LGM (crudely laminated mud), shoreface erosion and seaward transport off the shelf break during the post-glacial transgression (bioturbated sandy mud or muddy sand), hemipelagic sedimentation under generally well-oxygenated bottom-water condition after the sea-level rise (bioturbated mud), and episodic precipitation of authigenic carbonates by methane venting since the LGM (authigenic carbonate-bearing mud), respectively. The formation of authigenic carbonate-bearing mud facies and associated accumulation of near-seafloor gas hydrates might have led to up-warping of the sediment cover since the LGM that resulted in the seafloor mounds protruding along the crest line of the ridge. The effects of up-warping by expansion of the subsurface gas hydrates are firstly manifested in this paper by the abrupt lateral changes in the sedimentary facies distribution and uplifted acoustic reflectors between the mounds and the background seafloor.

Ore geology, and H, O, S, Pb, Ar isotopic constraints on the genesis of the Lengshuibeigou Pb-Zn-Ag deposit, China

Changming Wang,Xinyu He,Changhai Yan,Wende Lü,Weizhi Sun 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

The Lengshuibeigou Pb-Zn-Ag deposit is located in the Qinling superlarge metallogenic belt, China. The Pb-Zn-Ag orebodies are hosted in the Proterozoic Luanchuan Group. The ore types are hydrothermal veins and skarns type. The ore-forming process can be divided into three stages: (1) quartz-pyrite; (2) quartz-sulphide; and (3) quartz-carbonate. This paper used stable and radiogenic isotopes to study the characteristics of the Lengshuibeigou Pb-Zn-Ag deposit. The temperature and salinity of fluids tend to decrease from the early skarn and quartz- pyrite stages to the late quartz-carbonate stage. The ranges of 18OH2O (SMOW) and DH2O (SMOW) values of the ore-forming fluids range from –0.03 to +4.97‰ and from –83.00 to –72.00‰, respectively. The 34SV-CDT values of pyrite, sphalerite and galena from the skarn-type and hydrothermal-type vein ores range from +0.34 to +5.88‰, which is similar to those of porphyry-type Mo-W deposits in the area, but is different from those in the strata. The sulphur in both types of ores may have been derived from magmatic sources. The ranges of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios in the sulphide ores are 17.457–17.765, 15.423–15.606 and 37.712–39.012, respectively, which are comparable with those of feldspars in porphyry granites in the Nannihu ore field and less radiogenic than those in the host strata. These new data support the likelihood that the fluids and metals associated with Lengshuibeigou Pb-Zn-Ag deposit were carried by the porphyry magmatic system. The 40Ar/39Ar plateau age of 137.9 ± 0.4 Ma age obtained from the Lengshuibeigou Pb-Zn-Ag deposit is likely its mineralization age. This paper is useful not only for interpretation of the genesis of the magmatic-hydrothermal deposits but also significant for mineral exploration in the area especially for finding large deposits in large magmatic districts where various types of base metal deposits might occur.

Geochemical analyses on bituminous carbonate reservoir in Alberta, Canada: focusing on the GC/GC-MS results of bitumen

박명호,Jiyoung Choi,길영우,권이균,김지훈 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

The geochemical study on bituminous carbonate reservoir in Alberta has been performed to document the organic geochemical characteristics of the Grosmont Formation using two drilling cores (SAL 03-34 and SAL 08-01), especially focusing on the GC and GC-MS analyses. The results of GC and GC-MS analyses for the extracted organic matter (EOM) showed that all samples have been severely undergone a biodegradation process. However, the GC-MS data have displayed a little variation among the samples, which may be due to degree/type of biodegradation and the type of microbial activity. Triterpane biomarkers are present in low amounts, and steranes in even lesser amounts. Source and maturity assessments from both biomarkers are limited due to the lack of peaks by advanced biodegradation. The demethylated hopanes, which are typical of biodegraded oils, are not seen in these samples but they are apparently not unusual for the Athabasca tar sands, probably due to the specific type of post-emplacement microbial activity. Triterpanes biomarkers illustrate that a highly anoxic hypersaline source environment has contributed to the original oils, at the same time having anoxic marine carbonate/marl character. There is also tenuous evidence for a post-Triassic source according to the tricyclic terpane ratios. The steranes similarly indicate a marine, possibly carbonate-influenced source. Some of the aromatic compounds could also indicate a marine and anoxic hypersaline sourcing. The available peak ratios and patterns of EOM by GC-MS suggest high maturity, and aromatic parameters infer condensate window level with a vitrinite reflectance equivalent range of ~0.9–1.2%. This could explain the remaining relatively light n-alkanes in the saturated GC chromatograms.

Relocation of earthquakes beneath the East Sea of Korea: uncertainty of hypocentral parameters caused by refracted waves

Yeong-Ah Kang,김우한,강태섭 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

In addition to direct waves, refracted (head) waves such as Pn and Sn have been used to determine hypocentral locations, especially when the number of direct waves is inadequate to determine the hypocentral parameters of local earthquakes. However, refracted waves tend to increase errors and the non-uniqueness problems of hypocentral parameters compared with direct waves, if the true velocity structure is not known. Beneath the East Sea of Korea (Japan Sea), conditions for determining hypocentral parameters of earthquakes are unfavorable. To estimate these parameters, this study applied the computational algorithm VELHYPO, which uses the best-fitting velocity model obtained from the results of grid searching methods. The accuracy of hypocentral parameters obtained from direct and different combinations of refracted waves was examined using a synthetic data set. The accuracy tests indicated that hypocentral parameters determined by direct waves alone tend to be more accurate and reliable than those determined by direct and refracted waves combined. The accuracy of hypocentral parameters increases as the grade of the weighting factor for refracted waves decreases when compared with that for direct waves. We relocated 72 earthquakes that occurred beneath the East Sea by applying VELHYPO and giving a lower weighting factor grade to refracted waves than to direct waves. The relocated epicenter distribution shows a close relationship with the regional fault distribution. We compared the hypocentral parameters determined by this study and the Korea Institute of Geoscience and Mineral Resources.

Reevaluation of Th and U concentrations in marine sediment reference materials using isotope dilution MC-ICP-MS: towards the analytical improvements in dose rate estimation for luminescence dating

최정헌,류종식,신형선,김정민,정창식 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

The thorium and uranium concentrations of four marine sediment reference materials (CRMs NIST 1646a, NRCC HISS-1, MESS-3 and PACS-2) were determined using isotope dilution-multiple collector-inductively coupled plasmas-mass spectrometry (ID-MC-ICP-MS), aiming at helping the assessment of reliability in dose rate estimation for luminescence dating. Quintuplicate analyses of the CRMs revealed their intrinsic heterogeneity in the concentration of both elements (up to 23% and 8% for thorium and uranium, respectively, in 2s standard error level) for individual sub-samples of about 100 mg. The thorium and uranium concentrations of all CRMs determined in this study were significantly lower (up to 45%) than the provided or reported informative values, requiring reevaluation of their reference concentrations. The use of informative thorium and uranium concentrations in these CRMs as standard values for elemental analysis of unknown samples will result in overestimated dose rates, and thus age underestimation when applied to luminescence dating techniques.

Characteristics and provenance of hazardous trace elements in soil from a typical agricultural region in eastern Anhui, China

Lu Wei,Guijian Liu,Dun Wu 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.5

With the purpose of investigate the characteristics and provenances of the hazardous trace elements (HTEs) in a typical agricultural land in the undulating plain area of eastern Anhui province, China, a total of 1170 soil samples were collected. Six HTEs, including Cd, Cr, Hg, Ni, Pb, and As, were determined. Statistical methods including box plot, Pears on correlation analysis, principal component analysis, and cluster analysis, were conducted to illustrate the provenances of HTEs. Results indicate that Cd and Hg were influenced by human activities (such as traffic transportation for Cd and Pb, and chemical pesticides for Hg). Cr, Ni, and As mainly originated from the parent materials (e.g., red detrital rocks, carbonate rocks, and late Pleistocene loess). Pb is of dual provenances of both human activity and parent material. In a word, regarding highly toxic HTEs, the soil in the study area is almost free from pollution, and only a small amount of soil samples contains slightly higher contents of As, Cd and Pb.