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.

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.

Origin of volcaniclastics in the central part of a pull-apart basin, the Cretaceous Eumsung Basin, Korea

양우헌 한국지질과학협의회 2013 Geosciences Journal Vol.17 No.2

There are coarse-grained deposits, especially composed entirely of volcaniclastics in the central part of the Cretaceous Eumsung Basin (Eumseong Basin), far away from the basinal margins. Primary volcanic masses are not exposed on the surface in the adjacent areas. For unraveling the origin of the volcaniclastics, subsurface magnetotelluric as well as surface sedimentological data were examined. Two resistivity profiles of crossed lines ES2 and ES9 represent subsurface basinal and basin-fill structures of the Eumsung Basin. In the basin fills, four high-resistivity bodies of A, B, C, and D were found. Considering the basin-scale structure and forming process of the pull-apart Eumsung Basin, it is reasonable to infer that these isolated high-resistivity bodies formed as a result of volcanic intrusion/extrusion into/upon the basin-fill. Therefore, the coarse-grained volcaniclastic deposits in the central part of the Eumsung Basin can be interpreted as the product of syn-sedimentary deposition of volcaniclastic material that was shed from an exposed part of subsurface volcanics in a relatively short distance.

Some large values of in-situ stress and related engineering geological problems in China

Yanjun Shang,박형동,Yongyue Shi,Guangxiang Yuan,Yuanchun Sun 한국지질과학협의회 2010 Geosciences Journal Vol.14 No.2

In recent years, different methods have been applied to in-situ stress estimation for stability analysis of increasing large-scale tunnels in China. It was found that some extraordinary stress values are mostly associated with, although not a necessity of, engineering geological problems such as collapse, rock burst and squeezing. This paper focuses on finding the relationship among abnormal in-situ stress component values. The exposure in ground surface with unloading and erosion contributes a lot to relatively higher horizontal stress and lateral coefficient values of igneous and metamorphic rocks, while this situation is not the case for sedimentary rocks. Comparing stress data and connecting some abnormal values with typical case examples for better understanding and estimating stress is the main feature of this paper.

Source parameters for small–moderate earthquakes in Marmara Region (Turkey)

Tahir Serkan Irmak,Evrim Yavuz,Hamdullah Livaoğlu,Erman Şentürk,Emre Y. Sahin 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.5

The main aim of this study is to investigate the self-relation and self-similarity of earthquakes in and around the Marmara Sea (NW Turkey) by using these obtained source parameters. With this purpose, spectral source parameters for 77 small to moderate earthquake (3.5 ≤ ML ≤ 5.2) that occurred during 2004–2018 have been determined from P and S wave spectra according to Brune’s source model by using regional broadband seismograms. The average ratio of P/S wave corner frequency is found to be 1.3 that suggesting higher corner frequency for P wave. The static stress drops range from 0.1 and 136 MPa with a median value of 9.8 MPa (98 bars). The high stress drops for these events can indicate high frictional strength and low strain-rate of the faults. Similarly, the low values of the stress drop can indicate a general weakness of the faults in the study area. There is no clear dependence between the seismic moment and the static stress drop in the analyzed events but some events which have lower seismic moment value also have lower stress drop. Obtaining results indicated the corner frequency decreases with increasing of the seismic moment. Also, a slight depth dependence of the corner frequency has been observed for the analyzed events. Shallower events have larger corner frequency value than deeper events. Also, a clear depth dependence of the stress drop values has not been observed. However, the depth dependence of the seismic moment is seen more clearly. Our results indicated that the deeper events have larger seismic moment values in the study area. In spite of scattering in small events, a linear relationship between local magnitude (ML) and moment magnitude (MW) could be obtained as MW = 1.4261(± 0.31) + 0.6399(± 0.08)ML from P waves spectra and MW = 0.0136(± 0.21) + 0.9883(± 0.05)ML from S wave spectra and calculated MW values are consistent with waveform inversion (centroid moment tensor – CMT) results. These relationships may be useful for seismic hazard studies in the study area.

Petrological characteristics of lithospheric mantle beneath Nui Nua and Ba Ria areas, southern Vietnam

Cong Nguyen,길영우 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.5

Spinel peridotites from the Nui Nua and Ba Ria volcanic suites of southern Vietnam were investigated to interpret mantle processes and geochemical evolution of the lithospheric mantle beneath southern Vietnam. Spinel peridotites from both study areas consist of lherzolites and harzburgites displaying porphyroclastic textures. The spinel peridotites may have experienced a low degree (1–13%) of fractional melting. The variation of light rare earth elements (LREEs) and other incompatible elements in clinopyroxenes indicates that most of the spinel peridotites have undergone silicate metasomatism. The spinel peridotite xenoliths of both areas originated at depths between 35 and 52 km with equilibrium temperatures ranging from 714–1211 °C (±15 °C). Correlations between Sr, Nd, and Pb isotopic compositions of the clinopyroxenes suggest that the spinel peridotites originated from mixing of depleted (DM) and enriched (EM2) mantle sources. The spinel peridotites from Nui Nua gave a Pb-Pb isochron age of 3.6 ± 0.3 Ga which suggests the formation time of lithospheric mantle beneath southern Vietnam due to initial melt extraction.

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.

Detection of surface anomalies through fractal analysis and their relation to morphotectonics (High Zagros belt, Iran)

Mahnaz Shiran,Mohammad Ali Zangeneh Asadi,Paolo Mozzi,Hamed Adab,Abolghasem Amirahmadi 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.5

Fractal geometry is considered as a new method for quantitative analysis and explanation of surface complexities and roughness in self-similar or self-affine landforms. In the present study, the surface fractal dimensions were investigated by a cellular model by covering divider method and remote sensing data, in a complex morphotectonic region in terms of tectonic, geological, and geomorphological structures along the margin of the High Zagros Belt. Results of this study indicated that surface anomalies can be detected by cellular fractal model due to variations at the boundary of lithological units and structural zones, and along faults that can change the characters of the fractal dimension of landforms. Investigation of wavelet analyses on two profiles of study area shows that the amplitude and frequency of the fractal dimension is related to lithological and structural zones boundaries, and to the presence of faults. In this study, the lowest fractal dimension is associated with the integrated units of Mesozoic orbitolina limestone on the border of the two structural zones of Sanandaj-Sirjan and High Zagros belt. However, the presence of friable and erodible Quaternary formations increases the fractal dimension. There is an inverse relationship between the fractal dimension and elevation and Terrain Ruggedness Index, indicating that mountains have lower fractal dimensions than lowlands. The results of the present study show that fractal dimensional changes in topographically complex zones depend on the interaction of a set of lithological, tectonic, and geomorphological factors, and allow for a systematic quantitative analysis of landforms.

Fusion of hydrologic and geophysical tomographic surveys

Tian-Chyi Jim Yeh,Cheng-Haw Lee,Kuo-Chin Hsu,Jet-Chau Wen 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.2

In this paper, we argue the need for high-resolution characterization of the subsurface and discuss difficulties of traditional characterization approaches to meet this need. Necessary and sufficient conditions are then presented for well-posedness of groundwater inverse problems associated with identifying spatially distributed parameters. Non-uniqueness and large uncertainty in model calibration are subsequently attributed to difficulties in collecting information to meet these conditions. Using an example, we show that a tomographic survey can make problems of identification of spatially distributed parameters better posed. We subsequently present some recent advances in hydrologic/geophysical characterization of the subsurface using information fusion based on tomographic survey concepts. This paper includes hydraulic and electrical resistivity tomographic surveys as well as fusion of hydraulic and resistivity tomography and fusion of hydraulic and tracer tomography