Underwater Explosion (UWE) Analysis of the ROKS Cheonan Incident

The underwater explosion (UWE) resulting in the sinking of the South Korean warship, ROKS Cheonan occurred on March 26 2010. Raw data was analyzed from several 3-component stations—Baengyeong-do Korea Meteorological Administration (KMA) station (BAR), Ganghwa KMA station (GAHB), Incheon Incorporated Research Institutions for Seismology (IRIS) station (INCN), the short-period station—Deokjeok-do KMA station (DEI), as well as from the seismo-acoustic array Baengyeong-do Korea Institute of Geoscience and Mineral Resources (KIGAM) station (BRDAR). The ROKS Cheonan incident has been investigated by both the Multinational Civilian-Military Joint Investigation Group (Ministry of National Defense, 2010) and Hong (Bull Seism Soc Am 101:1554–1562, 2011). Their respective methods and conclusions are also presented in this study. One of the main differences between their findings and ours is that we deducted that the fundamental bubble frequency was 1.01 Hz with a subsequent oscillation of 1.72 Hz. Also, in contrast to findings by the MCMJIG and Hong, our analysis shows the first reverberation frequency to be 8.5 Hz and the subsequent one to be ≈25 Hz. The TNT-equivalent charge weight (seismic yield) and seismic magnitude were estimated from an observed bubble frequency of 1.01 Hz and the analytical model of a bubble pulse. From the data analyzed, we deducted that the seismic yield would be about 136 kg of TNT, which is equivalent to the individual yield of a large number of land control mines (LCM) which were abandoned in the vicinity of the ROKS Cheonan incident by the Republic of Korea (ROK) Navy in the 1970s (Ministry of National Defense 2010). Also, whereas both the MCMJIG and HONG estimated the local magnitude at 1.5, our findings came to the conclusion of a local magnitude of approximately 2.04 based on the bubble frequency of 1.01 Hz measured on the vertical component of BAR station data considering the empirical relationship between charge weight (TNT yield) and underwater explosion magnitude. Strong high-frequency signals collected at the 3-component BAR station approximately 30 s after P-wave arrivals and infrasound records at BRDAR clearly indicate powerful acoustic phases and N-waves caused by a relatively shallow UWE. T-phases are also observed on seismograms and spectra at 15–17 Hz on the DEI, GAHB, and INCN stations.     

Generalized Lyzenga's Predictor of Shallow Water Depth for Multispectral Satellite Imagery

Multispectral satellite remote sensing can predict shallow-water depth distribution inexpensively and exhaustively, but it requires many in situ measurements for calibration. To extend its feasibility, we improved a recently developed technique, for the first time, to obtain a generalized predictor of depth. We used six WorldView-2 images and obtained a predictor that yielded a 0.648 m root-mean-square error against a dataset with a 5.544 m standard deviation of depth. The predictor can be used with as few as two pixels with known depth per image, or with no depth data, if only relative depth is needed.     

Mercury-water interactions in the estuarine environment

Examination of mercury-water interactions in the estuarine environment reveals that, while locally mercury concentration in estuarine waters may reflect external influence on the estuarine system, the interactions of the heavy metal with soluble and insoluble water components greatly influence the transport of the metal and its impact on the biota in natural waters. In connection with transformation of mercury in aquatic ecosystems, the role played by methylation in spatial and temporal mobilization of mercury is viewed in wider perspective. This throws light on metal concentration and dispersion and the need for monitoring them in any realistic environmental management design.     

Metagenomic characterization of viral communities in Goseong Bay,Korea

In this study, seawater samples were collected from Goseong Bay, Korea in March 2014 and viral populations were examined by metagenomics assembly. Enrichment of marine viral particles using FeCl₃ followed by next-generation sequencing produced numerous sequences. De novo assembly and BLAST search showed that most of the obtained contigs were unknown sequences and only 0.74% of sequences were associated with known viruses. As a result, 138 viruses, including bacteriophages (87%), viruses infecting algae and others (13%) were identified. The identified 138 viruses were divided into 11 orders, 14 families, 34 genera, and 133 species. The dominant viruses were Pelagibacter phage HTVC010P and Roseobacter phage SIO1. The viruses infecting algae, including the Ostreococcus species, accounted for 9.4% of total identified viruses. In addition, we identified pathogenic herpes viruses infecting fishes and giant viruses infecting parasitic acanthamoeba species. This is a comprehensive study to reveal the viral populations in the Goseong Bay using metagenomics. The information associated with the marine viral community in Goseong Bay, Korea will be useful for comparative analysis in other marine viral communities.     

Temperature dependence of the magnetic rotation process of kaolinite microcrystals containing paramagnetic impurity ions dispersed in liquid medium

Temperature dependencies of magnetic rotation were measured in micron-sized silicates dispersed in ethanol for two different samples of kaolinite. Magnetic rotation proceeded by balance between thermal agitation energy and magnetic anisotropy energy. Measurements were performed between 195 and 343 K. The field intensity required to achieve magnetic alignment of microcrystals increases with temperature, because of the temperature dependence of paramagnetic anisotropy, and the temperature dependence of thermal agitation energy. The results indicate that the values of magnetic anisotropy of nonmagnetic materials might partially derive from the paramagnetic moments, which derive from paramagnetic impurity ions. The present experiment provides a technical basis for determining the precise values of diamagnetic anisotropy ()_DIA from minerals which have a concentration of paramagnetic ions and do not form a single crystal large enough to allow bulk measurements. The values of ()_DIA can be obtained by extrapolating the –T relations, which follow the Curie law, to the temperature limits.     

Deep convection in a lake triggered by wind: Two-dimensional numerical experiments with a nonhydrostatic model

We have investigated the fundamental processes of deep convection in a lake at high latitudes triggered by wind during spring or autumn and the associated deep water formation, executing vertically two-dimensional numerical experiments with a nonhydrostatic model. The water column in which a relatively cold mixed layer overlies a relatively warm layer becomes unstable, when the Ekman convergence on the shore due to along-shore wind deepens the mixed layer below the compensation depth, where water densities in both layers becomes equal to each other because of the thermobaric effect. At the onset of deep convection, the critical Rayleigh number agrees with that predicted by the linear theory. The onset time of deep convection is inversely proportional to the magnitude of wind stress. On the other hand, the onset time is minimal when water temperature in the mixed layer _m is 3.1°C because a change of _m has two effects oppositely acting on the stability of the water column. After the first onset, deep convection occurs intermittently for a few days. The sinking of the mixed layer water occurs in a thermal-like shape, and its amount is 4184% of the time-integrated Ekman transport when _m 3°C while it decreases to less than 10% for _m lower than 1.5°C. The present process can explain 30% of the amount of deep water renewal which is expected from the observation in Lake Baikal.     

An Application of Hydraulic Tomography to a Large‐Scale Fractured Granite Site,Mizunami, Japan

While hydraulic tomography (HT) is a mature aquifer characterization technology, its applications to characterize hydrogeology of kilometer‐scale fault and fracture zones are rare. This paper sequentially analyzes datasets from two new pumping tests as well as those from two previous pumping tests analyzed by Illman et al. (2009) at a fractured granite site in Mizunami, Japan. Results of this analysis show that datasets from two previous pumping tests at one side of a fault zone as used in the previous study led to inaccurate mapping of fracture and fault zones. Inclusion of the datasets from the two new pumping tests (one of which was conducted on the other side of the fault) yields locations of the fault zone consistent with those based on geological mapping. The new datasets also produce a detailed image of the irregular fault zone, which is not available from geological investigation alone and the previous study. As a result, we conclude that if prior knowledge about geological structures at a field site is considered during the design of HT surveys, valuable non‐redundant datasets about the fracture and fault zones can be collected. Only with these non‐redundant data sets, can HT then be a viable and robust tool for delineating fracture and fault distributions over kilometer scales, even when only a limited number of boreholes are available. In essence, this paper proves that HT is a new tool for geologists, geophysicists, and engineers for mapping large‐scale fracture and fault zone distributions.     

Generation of greenhouse effect gases from different landfill types

Recently much attention is focussed on the problems of global warming due to greenhouse effect gases, notably carbon dioxide and methane. Because these gases cause important problems to the global environment, their generation from landfill sites containing solid wastes has drawn attention and their environmental impact is causing concern.

Generally, the gases associated with a greenhouse effect include carbon dioxide, methane and nitrous oxide. However, there are no general basic data available concerning gases generated from biodegradation of solid wastes in landfill sites. Specifically, no assessment has been made concerning greenhouse effect gases from different landfill types.

This paper proposes a quantitative model for estimating the gasification rate by different landfill types. The model is based on measurement data for a long-term material balance for an aerobic landfill and an anaerobic landfill, obtained with two types of large-scale lysimeters.

This paper will also give an estimate for the amount of greenhouse effect gases by for different types of landfill and propose countermeasures for their reduction.     

Water and sediment quality, partial mass budget and effluent N loading in coastal brackishwater shrimp farms in Bangladesh

The present study aimed to quantify the water and sediment quality and growth and production parameters and to establish nutrient budgets for an average of five selected semi-intensive shrimp ponds in Bangladesh over a growing cycle. Physico-chemical parameters of water and sediments were measured and analyzed by standard methods. Gross yield (kg ha-1) of shrimp was calculated from the stocking and harvesting data. Finally, a partial nutrient mass budget for N and P was calculated. Most of the parameters of water and sediments correlated significantly with each other suggesting a high degree of interactions between different parameters in the system. Significantly higher concentrations of all species of nitrogenous nutrients were recorded in the effluent waters than that entering into the ponds. Therefore, a high loading and net output of nitrogenous nutrients in effluent waters was documented. The study also indicated a net discharge of solids and minerals through effluent loading. However, significantly lower concentrations of phosphorus in the effluent water indicated a net retention and trapping of phosphatic nutrients in the environment. Total production ranged between 532.0 and 697.0 kg ha-1 cycle-1 and P. monodon production between 484.0 and 562.0 kg ha-1 cycle-1. Ponds gained nitrogen primarily from intake water (55%) and fertilizers (29%), and nitrogen was lost primarily from water exchange (78%) and harvested shrimp (12%). Phosphorus gain occurred mostly from intake water (52%) and fertilizers (25%), and phosphorus was lost primarily from water exchange (52%) and harvested shrimp (3.3%). About 10% of input nitrogen and 44% of phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in the system. On average, 78 g N was discharged to and 25 g P was removed from the surrounding water by the system for each kilogram of shrimp produced. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 74% and 40%, respectively. It was concluded that semi-intensive systems serve as net supplier of N to and net remover of P from the surrounding water.