Continuous Observation of Groundwater and Crustal Deformation for Forecasting Tonankai and Nankai Earthquakes in Japan

In 2006, we started construction of an observation network of 12 stations in and around Shikoku and the Kii Peninsula to conduct research for forecasting Tonankai and Nankai earthquakes. The purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to Tonankai and Nankai earthquakes. Construction of the network of 12 stations was completed in January 2009. Work on two stations, Hongu-Mikoshi (HGM) and Ichiura (ICU), was finished earlier and they began observations in 2007. These two stations detected strain changes caused by the slow-slip events on the plate boundary in June 2008, although related changes in groundwater levels were not clearly recognized.     

Deep-learning based projection of change in irrigation water-use under RCP 8.5

Stream water-use is essential for both agricultural and hydrological management and yet not many studies have explored its non-stationarity and nonlinearity with meteorological variables. This study proposed a deep-learning based model to estimate agricultural water withdrawal using hydro-meteorological variables, which projected the changes of agricultural water withdrawal influenced by climate change of future. The relationships between meteorological variables and stream water-use rate (WUR) were quantified using a deep belief network (DBN). The influences of precipitation, potential evapotranspiration, and monthly averaged WUR on the performance of the developed DBN model were tested. As a result, this DBN with potential evapotranspiration (PET) provided better performances than precipitation to estimate the WUR. The PET of multi-model scenarios for Representative Concentration Pathways 8.5 would be increased as time goes by, and thus leads to increase WUR estimated by DBN in three basins, located in South Korea during the future period. On the contrary, water availability expected to decrease compared to the current. Therefore, managing water-uses and improving efficiencies can be prepared for the change in agricultural water-use by climate change in the future.     

Potential extents for ENSO-driven hydrologic drought forecasts in the United States

The relationship between the El Niño-Southern Oscillation (ENSO) and hydrologic variability in the United States is investigated using Empirical Orthogonal Function (EOF)/Principal Component Analysis (PCA). The multivariate ENSO index (MEI) is utilized to identify strong coherences associated with multiple months (1-, 2-, 4-, 6-, 12-, 24-, 48-month) of the Log-Standardized Hydrologic Drought Index (LSHDI) in the conterminous states for the period 1950–2005. Based on 56 years of monthly streamflow data for 102 forecast climate divisions, this research explores the spatial and temporal variation of hydrologic responses corresponding to ENSO events. Preliminary results show that a potential predictor of the dominant streamflow modes in the northern Great Plains is identified from streamflows in western Arizona. Also, positive relationships between hydrologic drought and El Niño were found in the Pacific Northwest (Washington, Oregon, and northern California), whereas negative relationships were detected in southern California and the northern Great Plains. These findings will provide useful insights to help improve streamflow forecast potential and capabilities, and minimize the impacts of hydrologic events (e.g. floods and droughts) associated with ENSO events.     

Stability Assessment of a Pit Slope Under Blast Loading: A Case Study of Pasir Coal Mine

In Pasir mine, coal seams and host rocks of varying thickness have been uniquely deposited with an average dip angle of 85°. The host rocks are weak and mainly composed of mudstone and sandstone comprising of 90–95% of the total pit volume. The thickness of coal seams and host rocks ranges from sub-metric to few tenths of meter. The overall safe pit slope angle was evaluated to be 27° for mining depth of 50–150 m. Several slopes failure incidents have occurred in the mine causing considerable disruption in production and monetary loss. It is envisaged that slope failures may be triggered due to blasting conducted in steeply dipping stratified deposit. In order to investigate the causes of slope failures, peak particle velocity (PPV) and accelerations at various locations from the blast site have been measured. In addition, finite element models of pit slope have been analyzed by applying static or gravity loading as well as blasting or dynamic loading. This paper elaborates the results of in situ measurements of ground vibration and numerical investigation and suggests possible causes of slope failures in Pasir mine.     

Spatial polychaeta habitat potential mapping using probabilistic models

The purpose of this study was to apply probabilistic models to the mapping of the potential polychaeta habitat area in the Hwangdo tidal flat, Korea. Remote sensing techniques were used to construct spatial datasets of ecological environments and field observations were carried out to determine the distribution of macrobenthos. Habitat potential mapping was achieved for two polychaeta species, Prionospio japonica and Prionospio pulchra, and eight control factors relating to the tidal macrobenthos distribution were selected. These included the intertidal digital elevation model (DEM), slope, aspect, tidal exposure duration, distance from tidal channels, tidal channel density, spectral reflectance of the near infrared (NIR) bands and surface sedimentary facies from satellite imagery. The spatial relationships between the polychaeta species and each control factor were calculated using a frequency ratio and weights-of-evidence combined with geographic information system (GIS) data. The species were randomly divided into a training set (70%) to analyze habitat potential using frequency ratio and weights-of-evidence, and a test set (30%) to verify the predicted habitat potential map. The relationships were overlaid to produce a habitat potential map with a polychaeta habitat potential (PHP) index value. These maps were verified by comparing them to surveyed habitat locations such as the verification data set. For the verification results, the frequency ratio model showed prediction accuracies of 77.71% and 74.87% for P. japonica and P. pulchra, respectively, while those for the weights-of-evidence model were 64.05% and 62.95%. Thus, the frequency ratio model provided a more accurate prediction than the weights-of-evidence model. Our data demonstrate that the frequency ratio and weights-of-evidence models based upon GIS analysis are effective for generating habitat potential maps of polychaeta species in a tidal flat. The results of this study can be applied towards conservation and management initiatives for the macrofauna of tidal flats.     

Sediment mounds and other sedimentary features related to hydrate occurrences in a columnar seismic blanking zone of the Ulleung Basin, East Sea, Korea

A mound related to a cold vent in a columnar seismic blanking zone (CSBZ) was formed around site UBGH1-10 in the central Ulleung Basin (2077 m water depth), East Sea, Korea. The mound is 300–400 m wide and 2–3 m high according to multi-beam bathymetry, 2–7 kHz sub-bottom profiler data, and multi-channel reflection seismic data. Seafloor topography and characteristics were investigated using a remotely operated vehicle (ROV) around site UBGH1-10, which is located near the northern part of the mound. The origin of the mound was investigated through lithology, mineralogy, hydrate occurrence, and sedimentary features using dive cores, piston cores, and a deep-drilling core. The CSBZ extends to ∼265 ms two-way traveltime (TWT) below the seafloor within a mass-transport deposit (MTD) unit. Gas hydrate was entirely contained 6–141 m below the seafloor (mbsf) within hemipelagic deposits intercalated with a fine-grained turbidite (HTD) unit, characteristically associated with high resistivity values at site UBGH1-10. The hydrate is commonly characterized by veins, nodules, and massive types, and is found within muddy sediments as a fracture-filling type. Methane has been produced by microbial reduction of CO₂, as indicated by C₁/C₂₊, δ¹³CCH4, and δD₄CH analyses. The bowl-shaped hydrate cap revealed at 20–45 ms TWT below the seafloor has very high resistivity and high salinity, suggesting rapid and recent gas hydrate formation. The origin of the sediment mound is interpreted as a topographic high formed by the expansion associated with the formation of the gas hydrate cap above the CSBZ. The lower sedimentation rate of the mound sediments may be due to local enhancement of bottom currents by topographic effects. In addition, no evidence of gas bubbles, chemosynthetic communities, or bacterial mats was observed in the mound, suggesting an inactive cold vent.     

Seasonal and spatial variations in water chemistry and nitrate sources in six major Korean rivers

Seasonal and spatial variations in water chemistry and contaminant sources were investigated in six major rivers in South Korea that vary widely in drainage area and length. The dissolved-load content of the rivers varied seasonally, and some dissolved ions such as Cl^? and NO₃ ^? showed large spatial differences in all of the rivers. The water type changed from Ca–HCO₃ in the upper reaches to Na–Cl–NO₃ in the lower reaches, indicating anthropogenic contamination in the lower reaches. Compared with two relatively pristine rivers (the Sumjin and Mankyung rivers), the other four rivers, which flow through agricultural and urban areas, registered much higher Cl^? and NO₃ ^? concentrations. Statistical analysis showed that seasonal and spatial variations in water chemistry occurred in all the rivers. The nitrogen and oxygen isotopes of dissolved nitrate indicated that the rivers flowing through urban and agricultural areas were significantly affected by manure, sewage, or both.     

Characterizing Excavation Damaged Zone and Stability of Pressurized Lined Rock Caverns for Underground Compressed Air Energy Storage

In this paper, we investigate the influence of the excavation damaged zone (EDZ) on the geomechanical performance of compressed air energy storage (CAES) in lined rock caverns. We conducted a detailed characterization of the EDZ in rock caverns that have been excavated for a Korean pilot test program on CAES in (concrete) lined rock caverns at shallow depth. The EDZ was characterized by measurements of P- and S-wave velocities and permeability across the EDZ and into undisturbed host rock. Moreover, we constructed an in situ concrete lining model and conducted permeability measurements in boreholes penetrating the concrete, through the EDZ and into the undisturbed host rock. Using the site-specific conditions and the results of the EDZ characterization, we carried out a model simulation to investigate the influence of the EDZ on the CAES performance, in particular related to geomechanical responses and stability. We used a modeling approach including coupled thermodynamic multiphase flow and geomechanics, which was proven to be useful in previous generic CAES studies. Our modeling results showed that the potential for inducing tensile fractures and air leakage through the concrete lining could be substantially reduced if the EDZ around the cavern could be minimized. Moreover, the results showed that the most favorable design for reducing the potential for tensile failure in the lining would be a relatively compliant concrete lining with a tight inner seal, and a relatively stiff (uncompliant) host rock with a minimized EDZ. Because EDZ compliance depends on its compressibility (or modulus) and thickness, care should be taken during drill and blast operations to minimize the damage to the cavern walls.