A method to develop the input parameter database for site-specific debris flow hazard prediction under extreme rainfall

The predictive hazard analysis at a detailed scale for debris flow runout analysis can be improved significantly through reliable estimation of the input parameters. In this study, a method for database establishment of input parameters at a site-specific scale was laid out for the predictive-based debris flow hazard assessment under extreme rainfall. The adoption of the DAN-3D code necessitated the estimation of three main input parameters: initial volume, bulk basal frictional angle, and growth rate. The initial volume was assessed using a 3D coupled finite element seepage and limit equilibrium-based slope stability analysis. An artificial neural network-based model was developed using 27 debris flow events for predicting the basal bulk frictional angle and consisted of eight factors: plan curvature, profile curvature, percentage of fine content, D₅₀, initial unit weight, initial volume, relative relief ratio, and channel length. Finally, the growth rate was estimated using the previously assessed initial volume, soil depth, and the approximate runout length. The proposed method was validated by application to the Raemian slope in the Woomyeon mountain region, Seoul, for the extreme rainfall event of 27 July 2011. The analysis yielded a final volume of 53,067.9 m³, a velocity upon arrival on the road of 26.81 m/s, and an approximately 0.5-m debris thickness concentrated near the Raemian apartments. The comparison of the predicted debris flow path and debris flow velocity with the actual event demonstrates good similarity and provides a conservative estimate of the volume. This study therefore illustrates the importance of an input parameter database in providing a reliable debris flow runout hazard assessment.     

Deformation microstructures of olivine and pyroxene in mantle xenoliths in Shanwang,eastern China,near the convergent plate margin,and implications for seismic anisotropy

Deformation microstructures, including lattice-preferred orientations (LPOs) of olivine, enstatite, and diopside, in mantle xenoliths at Shanwang, eastern China, were studied to understand the deformation mechanism and seismic anisotropy of the upper mantle. The Shanwang is located across the Tan-Lu fault zone, which was formed due to the collision between the Sino-Korean and South China cratons. All samples are spinel lherzolites and wehrlites, and LPOs of minerals were determined using scanning electron microscope/electron backscattered diffraction. We found two types of olivine LPO: type-B in spinel lherzolites and type-E in wehrlites. Enstatite showed two types of LPO (types BC and AC), and diopside showed four different types of LPO. Observations of strong LPOs and numerous dislocations in olivine suggest that samples showing both type-B and -E LPOs were deformed in dislocation creep. The seismic anisotropy of the P-wave was in the range of 2.2–11.6% for olivine, 1.2–2.3% for enstatite, and 2.1–6.4% for diopside. The maximum seismic anisotropy of the shear wave was in the range 1.93–7.53% for olivine, 1.53–2.46% for enstatite, and 1.81–6.57% for diopside. Furthermore, the thickness of the anisotropic layer was calculated for four geodynamic models to understand the origin of seismic anisotropy under the study area by using delay time from shear wave splitting, and S-wave velocity and anisotropy from mineral LPOs. We suggest that the seismic anisotropy under the study area can be most likely explained by two deformation modes that might have occurred at different times: one of deformed lherzolites with a type-B olivine LPO by lateral shear during/after the period of the Mesozoic continental collision between the Sino-Korean and South China cratons; and the other deformed the wehrlites with a type-E olivine LPO by horizontal extension during the period of change in absolute plate motion in relation to the westward-subducting Pacific plate.     

Non-parametric simulations-based conditional stochastic predictions of geologic heterogeneities and leakage potentials for hypothetical CO2 sequestration sites

The present study focuses on understanding the leakage potentials of the stored supercritical CO₂ plume through caprocks generated in geostatistically created heterogeneous media. For this purpose, two hypothetical cases with different geostatistical features were developed, and two conditional geostatistical simulation models (i.e., sequential indicator simulation or SISIM and generalized coupled Markov chain or GCMC) were applied for the stochastic characterizations of the heterogeneities. Then, predictive CO₂ plume migration simulations based on stochastic realizations were performed and summarized. In the geostatistical simulations, the results from the GCMC model showed better performance than those of the SISIM model for the strongly non-stationary case, while SISIM models showed reasonable performance for the weakly non-stationary case in terms of low-permeability lenses characterization. In the subsequent predictive simulations of CO₂ plume migration, the observations in the geostatistical simulations were confirmed and the GCMC-based predictions showed underestimations in CO₂ leakage in the stationary case, while the SISIM-based predictions showed considerable overestimations in the non-stationary case. The overall results suggest that: (1) proper characterization of low-permeability layering is significantly important in the prediction of CO₂ plume behavior, especially for the leakage potential of CO₂ and (2) appropriate geostatistical techniques must be selectively employed considering the degree of stationarity of the targeting fields to minimize the uncertainties in the predictions.     

Application of electrical resistivity tomography (ERT) technique to detect underground cavities in a karst area of South Korea

Recently, the electrical resistivity tomography (ERT) technique has been increasingly applied to underground cavity detection filled with groundwater and/or clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in a karst area in Korea. Numerical ERT modeling and inversion were carried out to select appropriate field survey parameters. Two geological structures, similar to those that exist in the field survey area, were modeled: a sinkhole model and a vein-type structure. Electrode configurations using pole–pole, pole–dipole, dipole–pole, and dipole–dipole arrays were tested with the two geologic models and compared. The numerical modeling showed that the resistivity distribution of the ERT tomogram using the pole–dipole array produced the best representation of the two models. The pole–dipole and pole–pole array configurations were applied in an ERT field survey using six boreholes. The field ERT results show that cavity areas filled with clay or groundwater appeared as low-resistivity anomalies in the limestone formation. This was particularly evident in the inclined vein-type structures attributed to fracture zones, where the field data were similar to the modeling results. Therefore, the ERT technique could be effectively used for detecting underground limestone cavities under similar geological conditions as those at our study area.     

Runoff characteristics of non-point pollutants caused by different land uses and a spatial overlay analysis with spatial distribution of industrial cluster: a case study of the Lake Sihwa watershed

To characterize a runoff pattern of non-point pollutants in relation with different land uses in a watershed, a monitoring activity and field measurements were carried out and data points were recorded during the rainfall events for 2 years. The study area includes industrial, urban, and rural sectors, which can represent a model case for the runoff study. Each sector was monitored with methodology and parameters including partial event mean concentration, first flush effect, mass first flush ratios, and correlation analysis. The Banwol Industrial Outfall No. 4 (4TG), an industrial area, showed a strong first flush effect, indicating that pollutants such as suspended solids, chemical oxygen demand, total nitrogen, and total phosphorus, were discharged at the early stage of a storm. An MFF₃₀ analysis of the runoff revealed a mean pollutant load was over 50 %. In the Ansan Stream, an urban area, a strong first flush effect did not appear; however, the concentrations of pollutants reached a peak some time later during a storm event. Then, the concentrations of pollutants quickly reduced. On the other hand, Jangjunbo and Munsan Stream, rural areas, did not exhibit the first flush effects, and when considering the value of MFF₃₀, 30 % or fewer pollutants on average were discharged at the initial stage of a storm. This means most of pollutants were streamed out at the later time of a storm event. The monitoring results found that the runoff characteristics of non-point pollutants in industrial, urban, and rural areas were distinctly different and site-specific. Therefore, each watershed management plan should be prepared to meet its own characteristics. Also, this kind of data can be an important base in designing and sizing a regional wastewater treatment facility to treat pollutants from a contaminated watershed.     

Parameters controlling the quality of the Hamra Quartzite reservoir,southern Hassi Messaoud,Algeria: insights from a petrographic,geochemical, and provenance study

Petrographic and geochemical analysis of the Hamra Quartzite reservoir in the southern periphery of the Hassi Messaoud field has been undertaken. The aim is to identify the quality of these sandstones as well as their tectonic setting and possible provenance. Petrographic analysis reveals that the studied reservoir is constituted of fine- to coarse-grained sandstones in which quartz forms the principal framework mineral. The main cement phases identified in this reservoir are quartz, illite, and carbonate, precipitated in that order. The principal diagenetic factors controlling the reservoir quality are quartz overgrowths, formation of authigenic clays, and the precipitation of carbonate cement. The Hamra Quartzite reservoir is considered mature from a compositional point of view as it consists predominantly of quartz arenites. Geochemically, these sandstones have a high SiO₂ content (93.28–98.79 wt%). The Hamra Quartzite deposits appear to be derived from deeply weathered (under warm–humid climate conditions) granitic–gneissic terrains or recycled sedimentary source areas. A passive margin origin is the most likely tectonic setting for the depositional environment of these arenites. The reservoir quality is strongly influenced by the relationship between the clay content and mineralogy. The combined effect of quartz overgrowth and the plugging of pores by illite have reduced both porosity and permeability. As a result, economically viable oil production in this area will depend most strongly on the combination of matrix and fracture porosity.     

Ensemble of ground subsidence hazard maps using fuzzy logic

Hazard maps of ground subsidence around abandoned underground coal mines (AUCMs) in Samcheok, Korea, were constructed using fuzzy ensemble techniques and a geographical information system (GIS). To evaluate the factors related to ground subsidence, a spatial database was constructed from topographic, geologic, mine tunnel, land use, groundwater, and ground subsidence maps. Spatial data, topography, geology, and various ground-engineering data for the subsidence area were collected and compiled in a database for mapping ground-subsidence hazard (GSH). The subsidence area was randomly split 70/30 for training and validation of the models. The relationships between the detected ground-subsidence area and the factors were identified and quantified by frequency ratio (FR), logistic regression (LR) and artificial neural network (ANN) models. The relationships were used as factor ratings in the overlay analysis to create ground-subsidence hazard indexes and maps. The three GSH maps were then used as new input factors and integrated using fuzzy-ensemble methods to make better hazard maps. All of the hazard maps were validated by comparison with known subsidence areas that were not used directly in the analysis. As the result, the ensemble model was found to be more effective in terms of prediction accuracy than the individual model.     

Interbed Modeling to Predict Wellbore Damage for Big Hill Strategic Petroleum Reserve

Oil leaks were found in wellbores of Caverns 105 and 109 at the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interbed between the caprock bottom and salt top. A three-dimensional finite element model, which allows each cavern to be configured individually, was constructed to investigate horizontal and vertical displacements in each well as it crosses the various interbeds. The model contains interfaces between each lithology and a shear zone (fault) to examine the interbed behavior in a realistic manner. This analysis results indicate that the casings of Caverns 105 and 109 failed, respectively, from shear stress that exceeded the casing shear strength due to the horizontal movement of the salt top relative to the caprock and tensile stress due to the downward movement of the salt top from the caprock. The wellbores of Caverns 114 and 104, located at the far end of the field and near the fault, respectively, are predicted to fail by shear stress in the near future. The wellbores of inmost Caverns 107 and 108 are predicted to fail by tensile stress in the near future. The salt top subsides because the volumes of caverns in the salt dome decrease with time due to salt creep closure, while the caprock does not subside at the same rate as the salt top because the caprock is thick and stiff. This discrepancy yields deformation of the well.     

Effects of Light,Salinity and Temperature on Germination Characteristics of Surfgrass,Phyllospadix japonicus and P. iwatensis Seeds

Ocean Science Journal - Surfgrass (Phyllospadix spp.) is a marine flowering plant that attaches to the bedrock of the Pacific Ocean, where the tide is fast and the waves are strong. In Korea, two...     

Current Structure and Volume Transport in the Jeju Strait Observed for a Year with Multiple ADCP Moorings

Ocean Science Journal - The seasonal and spatial variation of the current structure and volume transport across the Jeju Strait (JS) is described based on an analysis of the data from five bottom...