Evaluation of the processes affecting vertical water chemistry in an alluvial aquifer of Mankyeong Watershed, Korea, using multivariate statistical analyses

Vertical variations of redox chemistry and groundwater quality were investigated in an alluvial aquifer beneath an agricultural area, in which deep groundwaters are free of NO₃, Fe, and Mn problems that are frequently encountered during the development of alluvial groundwaters. This study was performed to identify and evaluate vertical chemical processes attenuating these chemical species in the study area. For this study, the processes affecting groundwater chemistry were identified by factor analysis (FA) and the groundwater samples collected from six multilevel samplers were hierarchically classified into three different redox zones by cluster analysis (CA) based on the similarity of geochemical features. FA results indicated three major factors affecting the overall water chemistry: agricultural activities (factor 1), redox reactions (factor 2), and remnant seawater (factor 3). The groundwater quality in the study area was revealed to be controlled by a series of different redox reactions, resulting in different redox zones as a function of depth. It was also revealed that the low Fe and Mn levels in the groundwater of the deeper part are associated with sulfate reduction, which led to precipitation of Fe as iron sulfide and adsorption of Mn on it.     

Morphological characteristics and distribution of Pleuronectidae (Pisces) eggs in the western margin of the East Sea

Seven species of Pleuronectidae (Platichthys stellatus, Kareius bicoloratus, Pseudopleuronectes herzensteini, Microstomus achne, Glyptocephalus stelleri, Hippoglossoides dubius, and Limanda punctatissima) were identified based on eggs collected from the western margin of the East Sea (east coast of Korea), using DNA barcoding. The eggs of P. herzensteini and G. stelleri were relatively widely distributed along the east coast of Korea, whereas those of P. stellatus and K. bicoloratus were narrowly distributed; in particular, the eggs of P. stellatus were restricted to areas near bays. The eggs, which share common morphological characteristics (such as a homogeneous yolk and smooth membrane) were divided into three groups according to egg size: group A (more than 1.60 mm in egg diameter, including genera Hippoglossoides and Microstomus), group B (1.00–1.60 mm, including genera Kareius, Glyptocephalus, and Platichthys), and group C (less than 1.00 mm, including genera Limanda and Pseudopleuronectes). This paper provides an overview of the morphological characteristics of the eggs of the family Pleuronectidae collected from the east coast of Korea. Our approach to the analysis of eggs, based on DNA barcoding, morphological characteristics, and geographic distributions, provides a rapid and accurate basis for identifying spawning areas and spawning periods, thus facilitating the assessment and management of fisheries stocks and resources.     

Population dynamics of the solitary ascidian <Emphasis Type="Italic">Herdmania momus</Emphasis> (Savignyi, 1816) in Jeju Island,Korea

In 2007–2008, a population outbreak of the solitary ascidian Herdmania momus was observed along the coasts of Jeju Island and the ascidians became the top dominant species in macrobenthic communities. We conducted field experiments on population dynamics and demographic parameters including seasonal density fluctuation, vertical distribution, recruitment patterns, mortality, and growth rate. Recruitment continued year-round except in April following the lowest water temperature season in February. Population density was highest in August-October, concomitantly with the peak in recruitment, related to the highest water temperature. The lowest density was observed in February-April when the water temperature was lowest. In April all individuals disappeared from all permanent plots, resulting in a maximum life span of 10–12 months. Individuals of newly recruited H. momus grew to have an adult size of 4–6 cm in only 3–4 months. Higher densities were observed in the shallower areas (5 m) compared to the deeper zones. More recruitment occurred on vertical slopes than horizontal substrates, but substrate pre-occupancy caused no difference in recruitment. This is the first report on H. momus population-level investigation in Korea, which provides valuable baseline information on the current status of population demography and their potential community-level influence on Jeju coasts.     

Application of an artificial neural network for a direct estimation of atmospheric instability from a next-generation imager

Atmospheric instability information derived from satellites plays an important role in short-term weather forecasting,especially the forecasting of severe convective storms. For the next generation of weather satellites for Korea's multi-purpose geostationary satellite program, a new imaging instrument has been developed. Although this imaging instrument is not designed to perform full sounding missions and its capability is limited, its multi-spectral infrared channels provide information on vertical sounding. To take full advantage of the observation data from the much improved spatiotemporal resolution of the imager, the feasibility of an artificial neural network approach for the derivation of the atmospheric instability is investigated.The multi-layer perceptron model with a feed-forward and back-propagation training algorithm shows quite a sensitive response to the selection of the training dataset and model architecture. Through an extensive performance test with a carefully selected training dataset of 7197 independent profiles, the model architectures are selected to be 12, 5000, and 0.3 for the number of hidden nodes, number of epochs, and learning rate, respectively. The selected model gives a mean absolute error,RMSE, and correlation coefficient of 330 J kg~(-1), 420 J kg~(-1), and 0.9, respectively. The feasibility is further demonstrated via application of the model to real observation data from a similar instrument that has comparable observation channels with the planned imager.     

Uncoupled analysis of stabilizing piles in weathered slopes

This paper describes a simplified numerical approach for analyzing the slope/pile system subjected to lateral soil movements. The lateral one-row pile response above and below the critical surface is computed by using load transfer approach. The response of groups was analyzed by developing interaction factors obtained from a three-dimensional nonlinear finite element study. An uncoupled analysis was performed for stabilizing piles in slope in which the pile response and slope stability are considered separately. The non-linear characteristics of the soil–pile interaction in the stabilizing piles are modeled by hyperbolic load transfer curves. The Bishop's simplified method of slope stability analysis is extended to incorporate the soil-pile interaction and evaluate the safety factor of the reinforced slope. Numerical study is performed to illustrate the major influencing parameters on the pile-slope stability problem. Through comparative studies, it has been found that the factor of safety in slope is much more conservative for an uncoupled analysis than for a coupled analysis based on three-dimensional finite element analysis.     

Thrust geometries in unconsolidated Quaternary sediments and evolution of the Eupchon Fault, southeast Korea

Abstract The Korean peninsula is widely regarded as being located at the relatively stable eastern margin of the Asian continent. However, more than 10 Quaternary faults have recently been discovered in and reported from the southeastern part of the Korean Peninsula. One of these, the Eupchon Fault, was discovered during the construction of a primary school, and it is located close to a nuclear power plant. To understand the nature and characteristics of the Quaternary Eupchon Fault, we carried out two trench surveys near the discovery site. The fault system includes one main reverse fault (N20°E/40°SE) with approximately 4 m displacement, and a series of branch faults, cutting unconsolidated Quaternary sediments. Structures in the fault system include synthetic and antithetic faults, hanging‐wall anticlines, drag folds, back thrusts, pop‐up structures, flat‐ramp geometries and duplexes, which are very similar to those seen in thrust systems in consolidated rocks. In the upper part of the fault system, several tip damage zones are observed, indicating that the fault system propagates upward and terminates in the upper part of the section. Pebbles along the main fault plane show a preferred orientation of long axes, indicating the fault trace. The unconformity surface between the Quaternary deposits and the underlying Tertiary andesites or Cretaceous sedimentary rocks is displaced by this fault with a reverse movement sense. The stratigraphic relationship shows normal slip sense at the lower part of the section, indicating that the fault had a normal slip movement and was reversely reactivated during the Quaternary. The inferred length of the Quaternary thrust fault, based on the relationship between fault length and displacement, is 200–2000 m. The current maximum horizontal compressive stress direction in this area is generally east‐northeast–west‐southwest, which would be expected to produce oblique slip on the Eupchon Fault, with reverse and right‐lateral strike‐slip components.     

Lateral and consolidation behaviors of seabed-type breakwater for very soft ground

A seabed-type of breakwater applicable to very soft ground without the need for soil improvement is newly developed. This type of soft-ground breakwater is expected to ensure sufficient lateral resistance and prevent excessive consolidation settlement due to self-weight of the breakwater. In this paper, lateral and consolidation behaviors of soft-ground breakwater were investigated by performing model tests and finite element simulations. The results revealed that the bottom wall and buoyant box, which are the main features of soft-ground breakwater, contribute to the increase in lateral resistance and to the control of the consolidation settlements, respectively, and that Terzaghi's consolidation theory could be conservatively adopted in deriving the consolidation settlements of soft-ground breakwater proposed herein.     

Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.     

Rainfall intensity-duration thresholds for landslide prediction in South Korea by considering the effects of antecedent rainfall

This study was conducted to determine the rainfall intensity-duration thresholds (ID curves) for landslide prediction by considering the effects of antecedent rainfall. Data for the time and location of landslides that occurred in South Korea from 1999 to 2016 were collected. Overall, 231 landslide histories from 1999 to 2013 were used to determine the rainfall thresholds, and 12 landslide histories from 2014 to 2016 were used to verify the proposed rainfall thresholds. Probabilistic ID curves were proposed to reflect the influence of other factors except rainfall, and ID curves for various inter-event time definitions (IETDs) were suggested to analyze the variation in the ID curves with the effects of antecedent rainfall. The results suggest that the IETD indicates the duration for which the antecedent rainfall affects the ground condition. It was also found that the ID curve for 12 h of the IETD was the most reliable of the verification procedures using the receiver operating characteristic (ROC) plot and threat score (TS).