Landforms and landscape evolution in the Skardu,Shigar and Braldu Valleys,Central Karakoram

The Central Karakoram, which includes K2 in Pakistan, is one of the most rapidly rising areas on Earth and exhibits complex topography and extreme relief. Impressive valley fills and glacial landforms are present throughout the valleys. The dynamics of landscape evolution of the region are currently not well understood. Consequently, the landforms were mapped and assessed in the Skardu, Shigar, and Braldu valleys, to elucidate the spatio-temporal scale dependencies of surface processes active in the region. These valleys were examined using geomorphic field methods, remote sensing, geomorphometry, and terrestrial cosmogenic nuclides (TCNs) surface exposure dating. The glaciers in this region have oscillated considerably throughout the Late Quaternary, and four glacial stages have been recognized including at least six glacial advances. Surface processes readjusted after glacier retreat, and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms, while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley. Glacier geochronology and late Holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late Quaternary.     

2D acoustic‐elastic coupled waveform inversion in the Laplace domain

Although waveform inversion has been intensively studied in an effort to properly delineate the Earth's structures since the early 1980s, most of the time‐ and frequency‐domain waveform inversion algorithms still have critical limitations in their applications to field data. This may be attributed to the highly non‐linear objective function and the unreliable low‐frequency components. To overcome the weaknesses of conventional waveform inversion algorithms, the acoustic Laplace‐domain waveform inversion has been proposed. The Laplace‐domain waveform inversion has been known to provide a long‐wavelength velocity model even for field data, which may be because it employs the zero‐frequency component of the damped wavefield and a well‐behaved logarithmic objective function. However, its applications have been confined to 2D acoustic media. We extend the Laplace‐domain waveform inversion algorithm to a 2D acoustic‐elastic coupled medium, which is encountered in marine exploration environments. In 2D acoustic‐elastic coupled media, the Laplace‐domain pressures behave differently from those of 2D acoustic media, although the overall features are similar to each other. The main differences are that the pressure wavefields for acoustic‐elastic coupled media show negative values even for simple geological structures unlike in acoustic media, when the Laplace damping constant is small and the water depth is shallow. The negative values may result from more complicated wave propagation in elastic media and at fluid‐solid interfaces. Our Laplace‐domain waveform inversion algorithm is also based on the finite‐element method and logarithmic wavefields. To compute gradient direction, we apply the back‐propagation technique. Under the assumption that density is fixed, P‐ and S‐wave velocity models are inverted from the pressure data. We applied our inversion algorithm to the SEG/EAGE salt model and the numerical results showed that the Laplace‐domain waveform inversion successfully recovers the long‐wavelength structures of the P‐ and S‐wave velocity models from the noise‐free data. The models inverted by the Laplace‐domain waveform inversion were able to be successfully used as initial models in the subsequent frequency‐domain waveform inversion, which is performed to describe the short‐wavelength structures of the true models.     

Consolidation settlement properties of seashore landfills for municipal solid wastes in Korea

The large amount of wastes is generated in metropolitan area where population is heavily concentrated. As a result, treatment of wastes became a social problem and geotechnical problems related to landfill have emerged in Korea. Settlement behavior of waste landfill is similar to behavior of peat that possesses relatively small time-dependent secondary compression alongside large initial compression. A number of researchers published their own settlement computations. However, accurate computation method for waste-reclaimed landfill has yet to be determined as the settlement mechanism is very complicated. Hence, it is important to examine the accurate settlement behavior of reclaimed ground by comparing the material properties from laboratory test and field monitoring and comparing the results with the theoretical equation. This study determines the consolidation coefficients according to the change of organic contents through the total volume reduction in fresh waste layer and initial void ratio change and examines the feature of settlement in each load stage. Moreover, the article attempts to investigate the characteristics of consolidation of the relevant reclaimed landfill and to determine the suitability of the equation by comparing the variables in theoretical equations obtained from the laboratory test and field monitoring. Moreover, to verify the compression characteristics of the waste-reclaimed landfill upon loading, consolidation test results were analyzed to conduct index study on the consolidation characteristics of the waste-reclaimed landfill.     

A study of the three-dimensional groundwater flow system in an upland area of Japan

A three-dimensional finite difference model was developed to study the groundwater flow system in an upland area bordering a lake. For a general perspective of the groundwater flow system, a steady state three-dimensional flow was employed. Having determined the flow net by using a three-dimensional model, the flow volumes under natural conditions have been used to establish the parameter values and for the analyses of flow patterns. Further, to study the effects of human impact and precipitation on groundwater flow conditions in a small area, a transient three-dimensional simulation was performed. Environmental tritium was used to trace the regional groundwater movement to verify the three-dimensional mathematical model. Results obtained using the three-dimensional mathematical model approach and tritium concentration analyses were in close agreement. The results demonstrated that the groundwater flow system should be analysed using a three-dimensional geometric concept of groundwater movement.     

Factors causing dynamic variations in the saltwater–freshwater transition zone in a beach aquifer, Mangsang, South Korea

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.     

Evaluation of Simulated CO_2 Concentrations from the CarbonTracker-Asia Model Using In-situ Observations over East Asia for 2009–2013

The CarbonTracker(CT) model has been used in previous studies for understanding and predicting the sources, sinks, and dynamics that govern the distribution of atmospheric CO_2 at varying ranges of spatial and temporal scales. However, there are still challenges for reproducing accurate model-simulated CO_2 concentrations close to the surface, typically associated with high spatial heterogeneity and land cover. In the present study, we evaluated the performance of nested-grid CT model simulations of CO_2 based on the CT2016 version through comparison with in-situ observations over East Asia covering the period 2009–13. We selected sites located in coastal, remote, inland, and mountain areas. The results are presented at diurnal and seasonal time periods. At target stations, model agreement with in-situ observations was varied in capturing the diurnal cycle. Overall, biases were less than 6.3 ppm on an all-hourly mean basis, and this was further reduced to a maximum of 4.6 ppm when considering only the daytime. For instance, at Anmyeondo, a small bias was obtained in winter, on the order of 0.2 ppm. The model revealed a diurnal amplitude of CO_2 that was nearly flat in winter at Gosan and Anmyeondo stations, while slightly overestimated in the summertime. The model's performance in reproducing the diurnal cycle remains a challenge and requires improvement. The model showed better agreement with the observations in capturing the seasonal variations of CO_2 during daytime at most sites, with a correlation coefficient ranging from 0.70 to 0.99. Also, model biases were within-0.3 and 1.3 ppm, except for inland stations(7.7 ppm).     

Marine-Derived Fungi in Korea

Ocean Science Journal - Studies on marine fungi (termed as ‘marine-derived fungi’ in this paper) have been significantly increasing worldwide because of the critical role displayed by...     

Origin and patterns of the Upper Paleolithic industries in the Korean Peninsula and movement of modern humans in East Asia

Assemblages classified as ‘Upper Paleolithic’ in the Korean peninsula are diverse in their composition, including not only some blade industries but also conventional ones continued from earlier Paleolithic periods. This has often been explained as the result of an indigenous development. However, the ‘heterogenic’ character of Upper Paleolithic industries is the result of the continuing influx of modern human populations via two different routes: (1) from Siberia and (2) from southern China. Blade technology from Siberia appeared in the Korean peninsula around 35 000 BP and coexisted with core and flake stone industries carried by modern humans from southern China and Southeast Asia throughout the Upper Paleolithic. This explanation is based on the current observation of patterns of Upper Paleolithic industries in East Asia. Blade industries have been found only in the northern part of East Asia while none have been reported in southern China, although modern Homo evidently dispersed via two different routes from the Near East. The ‘North-South Model’ of Modern Homo migrations into the Korean peninsula is supported by a genetic analysis of the Y-chromosome of the modern population in this region. Continuing influx of modern human population from both origins to the peninsula can explain the consistent presence of Upper Paleolithic industries that appear heterogenic.