The South Yellow Sea Basin is the largest sedimentary basin in the Yellow Sea. The Gunsan Basin in the central eastern part of the Northern South Yellow Sea Basin comprises the Western, Central, and Eastern Subbasins. The Eastern Subbasin marks the eastern margin of the South Yellow Sea Basin. Interpretation of multi-channel seismic profiles and balanced cross-section restoration of depth-converted seismic profiles reveal the structural characteristics and evolution of the Eastern Subbasin. The subbasin comprises three groups of faults: NW-SE, NE-SW, and NNE-SSW trending faults. The subsidence pattern of the subbasin, derived from the cross-section restoration analysis, indicates five distinguished evolution phases: (i) rapid subsidence in the Late Cretaceous, (ii) slow subsidence from the Paleocene to the Eocene, (iii) accelerated subsidence in the Oligocene, (iv) alternation of the uplift and subsidence in the Early Miocene, and (v) gradual subsidence since the Middle Miocene. The main and moderate subsidence can be explained by the combination of extension in the SE and NE-SW directions that formed double duplex structures. We suggest that the NW oblique subduction of the Pacific Plate under the NE Asia margin induced both extension toward the trench and dextral strike-slip parallel to the margin. The extension toward the trench caused SE transtension in a local pull-apart setting, whereas the dextral strike-slip parallel to the margin caused NE-SW extension, inducing more significant subsidence. The combined processes resulted in the progressive development of nested duplex structures. The evolution of the Eastern Subbasin is not compatible with previously suggested models for the western part of the South Yellow Sea Basin including foreland basin formation and transtension induced by branch faults of the Tan-Lu Fault.

The geological evolution of the SE continental margin of the Korean Peninsula resulted from crustal extension with back-arc rifting to spreading (from the Late Oligocene to the Middle Miocene) and crustal shortening with back-arc closing (from the Middle Miocene to the present), associated with the separation of the SW Japan Arc. Earthquakes occur more frequently in this region compared to other offshore regions of the Korean Peninsula; among them, the Mw 5.0 earthquake that occurred in 2016 is the largest event ever recorded instrumentally. We investigate the geological structure of the epicentral area of the Mw 5.0 earthquake and address neotectonic activity at the margin. Seismic reflection profiles reveal abundant faults in the epicentral area that make up strike-slip fault systems. A fault system encompassing the epicenter of the Mw 5.0 earthquake is suggested as the source structure, with its attitude consistent with the focal mechanism solution. We propose that the Mw 5.0 earthquake occurred due to the reactivation of an extensional fault created during back-arc rifting which currently induces dextral slip under the ENE–WSW-oriented compressional stress field in and around the Korean Peninsula. The maximum magnitude of earthquakes expected at the margin is estimated as no higher than Mw 6.0. Restoration of seismic profiles indicates that the current stress field was established after 5.5 Ma. The S-wave velocity structure of the uppermost mantle shows asthenospheric upwelling elongated along the continental margin, which may be considered an important regional source of the current stress field by inducing convection in the uppermost mantle toward the Korean Peninsula lithosphere.

Fourth-order sequences in the northern central Miocene Gulf of Mexico are typically at or below seismic resolution and embedded in deformed strata with lateral thickness variations, making it difficult to image the corresponding paleo-depositional surfaces. Stratal or proportional slicing, involving proportionally slicing between two bounding reference horizons, can overcome these difficulties. However, if the target horizon can be readily interpreted, its horizon slice can provide the most accurate image. In this study, we first improved the resolution of the seismic data from the northern central Gulf of Mexico by bandwidth extension. Then, we autotracked a Miocene fourth-order sequence (M4) through the 50-Hz isofrequency volume obtained by the generalized spectral decomposition of the bandwidth-exteneded data. The horizon slice along M4 through the bandwidth-extended data provides a better image for incised-fluvial valleys and distributary channels compared with the stratal slice of the original data reported by earlier work. The corendered image of the variance and amplitude horizon slices further highlights the depositional features of M4. The horizon slice of M4 through the acoustic impedance volume, computed from inversion, shows that the incised-fluvial-valley fill is characterized by low impedance, suggesting good reservoir quality and that the distributary-channel fill is characterized by low to moderate impedance, suggesting fair to good reservoir quality. The definition of the horizon slice includes both the slice along the target horizon and those parallel to the reference horizon. We propose to call the slice along the target horizon a "horizon slice" and to use the term "horizon-parallel slices" for any slices parallel to an interpreted horizon.

A study on the laws, systems and development cases of urban regeneration in Japan, which are prior to urban regeneration and urban development, foresaw the development measures of urban residential regeneration projects in Korea. To this end, Japan’s Special Act on Urban Regeneration was compared with Korea’s Urban Regeneration Act, which was enacted in 2013. In particular, the Private Urban Regeneration Project, which is being embodied in Japan’s Special Act on Urban Regeneration, proposed the need to revise the Urban Regeneration Act as it did not specify support and deregulation in Korea In order to find out the need for a private-centered urban development project, Japan’s representative Odaiba, Rock Peak Hills, and Evisgarden Place development projects were analyzed. As a measure to revitalize urban housing regeneration projects in Korea, firstly, it was suggested that private participation for private capital and technology inducement is needed, secondly, urban-based and central-town urban regeneration projects linked to regional economy and job creation should be promoted, and third, that competitiveness should be secured through complex urban housing regeneration projects.The purpose of this study is to analyze the development of the Urban Regeneration Act and the Urban Regeneration Act in Japan.

In this case study, we geomodeled the Upper Cretaceous Second Wall Creek Sand (SWCS) of the southern Teapot Dome field, Wyoming, USA, using public domain seismic and well-log data. The SWCS is an at-or-below seismic-resolution (about 20 m), fluvial-deltaic reservoir and has been the most productive in the field. The goemodeling procedure consisted of structural modeling of the depth 3-D grid (30 m x 30 m x 1 m cells) and petrophysical modeling for porosity and net-to-gross (N/G). The seismic data were enhanced by spectral balancing to resolve the SWCS. Facies modeling was not necessary because a facies analysis of gamma-ray logs and lithofacies and stratigraphic-discontinuity seismic attributes suggests a uniform facies. The porosity and N/G were modeled by neural network multi-attribute transform (NN-MAT). NN training included the absolute and relative impedances and three representative isofrequencies in addition to the conventional amplitude-and frequency-based attributes. The modeled porosity varies from less than 8% to over 18% with an average of 16.7% which agrees with the reported averages. The modeled N/G values range from about 0.2 to over 0.8 with an average of 0.7 which is greater than the reported average (0.5). The porosity and N/G models may not be optimal because only a few wells and a small number of the time samples for the thin reservoir interval were used in NN training. The geomodeling workflow presented in this study is optimized for thin reservoirs and can be used when facies modeling is difficult because NN-MAT computes petrophysical properties without being guided by facies models.

We made deterministic estimations of the gas-hydrate and in-place gas resource volumes in a small area in the northwestern Ulleung Basin, East Sea (Japan Sea) from 3-D pre-stack seismic data and well-log and core data from the UBGH2-6 well. We modeled the P-impedance (I-p) logs at the well for 0%-100% pore-space gas-hydrate saturation from the P-wave velocity (Vp) and density logs modeled by the simplified three-phase Biot-type equation (STPBE). Then, the I-p volume for the gas-hydrate-bearing zone (GHBZ) was constructed by pre-stack inversion and divided into 28 layers. The porosity and mineralogy along these layers were assumed to be uniform, respectively, to the porosity log upscaled to the layers and the sediment constituents at the well determined from the core samples. Next, the pore-space gas-hydrate saturation at every time sample of each layer was found by matching the I-p value of the time sample to the modeled I-p logs upscaled to the layers. The gashydrate saturation volume with a cell size of 25 m x 6.25 m x 1 ms was obtained from the product of the porespace gas-hydrate saturation volume and the porosity volume. The gas-hydrate saturation volume was converted into the depth volume based on the V-p value at each cell found by matching the pore-space gas-hydrate saturation of the cell to the modeled V-p logs. The estimated total gas-hydrate and gas resource volumes are about .43 x 10(s) m(3) and about 1.38 x 10(11) m(3), respectively.

Earthquakes occur frequently in the continental shelf and slope area of the Korean Peninsula in the East Sea (Japan Sea) although they are mostly not large in magnitude. This area constitutes the eastern Korean margin, marking a transitional structure from rifted continental crust to oceanic crust that resulted from lithospheric extension into breakup in a back-arc. We reviewed how the crustal structure of the eastern Korean margin was emplaced to understand its correlation with the present seismicity. Back-arc extension that caused rifting and breakup at the Korean margin took place sequentially from the northern to southern parts in the Late Oligocene through the Early Miocene. The stress regime of the Korean margin switched from extension to compression in the Middle Miocene, resulting from the collision of the Philippine Sea Plate with the Japan Arc. The structural lineations at the Korean margin inherited from backarc rifting and breakup are interpreted to be prone to earthquakes by showing a close spatial correlation with ongoing seismicity. The changing geometry of the estimated locus of breakup at the Korean margin that follows a curvilinear path appears to induce diverse focal mechanisms of the earthquakes under the present compressive stress field.

Prospective shale plays require a combination of good reservoir and completion qualities. Total organic carbon (TOC) is an important reservoir quality and brittleness is the most critical condition for completion quality. We analyzed seismically-derived brittleness and TOC to investigate the prospectivity of the Horn River Group shale (the Muskwa, Otter Park, Evie shales) of a shale-gas field in the western Horn River Basin, British Columbia, Canada. We used the λρ-μρ brittleness template, constructed from the mineralogy-based brittleness index (MBI) and elastic logs from two wells, to convert the λρ and μρ volumes from prestack seismic inversion to the volume for the brittleness petrotypes (most brittle, intermediate, and least brittle). The probability maps of the most brittle petrotype for the three shales were generated from Bayesian classification, based on the λρ-μρ template. The relationship between TOC and P-wave and S-wave velocity ratio (VP/VS) at the wells allowed the conversion of the VP/VS volume from prestack inversion to the TOC volume, which in turn was used to construct the TOC maps for the three shales. Increased TOC is correlated with high brittleness, contrasting with the commonly-held understanding. Therefore, the prospectivity of the shales in the study area can be represented by high brittleness and increased TOC. We propose a shale prospectivity index (SPI), computed by the arithmetic average of the normalized probability of the most brittle petrotype and the normalized TOC. The higher SPI corresponds to higher production rates in the Muskwa and Evie shales. The areas of the highest SPI have not been fully tested. The future drilling should be focused on these areas to increase the economic viability of the field.

In high-resolution, shallow-water seismic surveys, correction for water-column height variations caused by tides, weather, and currents is an important part of data processing. In this study, we present a very simple method of correction for profile-length (i.e., long-wavelength) water-column height variations for high-resolution seismic data using a reference bathymetric grid. First, the difference between the depth of the seafloor picked from seismic data and the bathymetry from the bathymetric grid is computed at the locations where the shot points of seismic profiles and the bathymetric grid points are collocated or closest. Then, the results are gridded and smoothed to obtain the profile-length water-column height variations for the survey area. Next, the water-column height variations for each seismic profile are extracted from the smoothed grid and converted to two-way traveltimes. The corrections for the remaining mis-ties at the intersections, computed within a circular region around each tie shot point, are added to the corrections for the water-column height variations. The final, mistie corrected water-column height corrections are loaded to the SEGY trace header of seismic data as a total static. We applied this method to the sparker data acquired from the shallow-water area off the western-central part of Korea where the tidal range is over 7 m. The corrections for water-column height variations range from -10 to 4 m with a median value of about -2 m. Large corrections occur locally between and near the islands probably due to the amplification and shortening in tidal wavelength caused by rapid shoaling toward the islands.

Through a detailed analysis of seismic profile and vibra-/drilling-core sediments (up to 25.5 m long) with AMS C-14 ages from a tidal flat in the mid-western coast of Korea, we reconstruct development of coastal sedimentary sequences in response to sea-level changes for more than about 150 ka, and reveal effect of irregular, complex underlying topography in the Holocene coastal sedimentation. Unit I overlying rock basement and the lower part of Unit II consist of fluvial sediments deposited during sea-level lowstands prior to interglacial period of Eemian Stage (MIS 5e). During the sea-level highstand of MIS 5e, muddy tidal sediments between 7.40 and 10.76 m deep below the present tidal-flat surface were deposited in the upper to middle part of Unit II. The study area had been subaerially exposed for a long duration from MIS 5e to ca. 10 ka. During this period, the muddy tidal sediments in Unit II had been underwent oxidization and significant erosion by fluvial process, forming irregular and complex morphology of the upper boundary of Unit II with a large topographic relief (up to ca. 7 m) even over a short (ca. 560 m) distance. On the upper boundary of Unit II, topographic highs could act as barriers for weakening wave effects from ca. 8-9 ka to 3-4 ka (period of relatively rapid sea-level rise), depositing muddy tidal sediments (Unit III-B). As the muddy tidal sediments (Unit III-B) filled the irregular, complex underlying morphology, surface topography was nearly flat without barriers around about 3-4 ka. Since then, the nearly flat surface morphology without barriers, together with relatively slow sea-level rise and direct exposure of strong onshore winter waves/storms, could promote to deposit wave-/storm-driven sandy sediments (Unit III-A). This study suggests that change in surface morphology could affect stratigraphic evolution of the Holocene coastal sequence by variation in depositional regime. (c) 2017 Elsevier Ltd and INQUA. All rights reserved.

The Yellow Sea Bottom Cold Water (YSBCW) is a large cold water mass lying in the deep part of the Yellow Sea during the warm season. We acquired multichannel seismic (MCS) data using an air gun source to image the structure of the YSBCW. The MCS data recorded reflections from sea water. The recognition of these reflections was confirmed by finite-difference seismic modeling in the frequency-domain. The seismic section from MCS data enabled discrimination of water masses distinctly separated by reflecting horizons. The structure of the water masses is fairly consistent with temperature-depth variations obtained using expandable bathythermograph (XBT) casts. The YSBCW is imaged as the lowermost water mass, maximally 40 m thick, that extends as a lens-like form along the sea bottom under the warm mixed layer. The correlation of XBT measurements and the seismic section indicates a rapid decrease in temperature from around 11 to 8 °C in the uppermost part of the YSBCW. A transition zone between the mixed layer and the underlying YSBCW is also defined. This transition zone has fairly uniform thickness of 14–18 m and marks an interval of rapid temperature drop, indicating vigorous thermal mixing. Our study demonstrates that MCS profiling is a useful and reliable tool for imaging fine structures in the shallow Yellow Sea.

The East Sea (Japan Sea) is a semi-enclosed back-arc basin that is thought to preserve a significant record of tectonic evolution and paleo-climatic changes of Eastern Asia during the Neogene. We use here 2-D regional multi-channel seismic reflection profiles and borehole data from Expedition 346 of the Integrated Ocean Drilling Program (IODP) to provide new constraints on the geological history of the Eastern South Korea Plateau (ESKP). The ESKP represents a structurally-complex basement high in the southwestern East Sea which formed during rifting of the back-arc basin. Our new observations show that the ESKP is composed of numerous horsts and grabens controlled by NE-trending normal faults. The acoustic basement is blanketed by Oligocene to recent sediments that have preferentially accumulated in topographic lows (up to 1.5 km thick) and have been cored during Expedition 346 at Site U1430 close to the southern margin of the ESKP. Seismic profiles in the ESKP reveal three units separated by regional unconformities. These seismic units closely correspond to IODP lithostratigraphic units defined at Site U1430, where biostratigraphic data can be used to constrain the timing of three main evolutionary stages of the ESKP. Stage 1 was related to rifting in the late Oligocene and middle Miocene, terminated by a regional uplift leading to an erosional phase in the middle Miocene. Stage 2 was associated with subsidence in the middle and late Miocene and uplift and accompanying erosion or non-deposition in the latest late Miocene. Stage 3 (Pliocene to present) recorded overall uniform hemipelagic-pelagic subsidence of the ESKP with short-lived tectonically-induced uplifts in the late middle Miocene and latest Miocene-early Pliocene. The three stages of evolution of the ESKP closely correlate to sedimentary changes since the Oligocene and suggest a direct control of regional/local tectonics on sedimentation patterns in the southwestern East Sea, with secondary influence of regional climatic and paleo-oceanographic processes.

The NNE-trending dextral Yangsan fault is a>190-km-long structure in the Korean Peninsula traced to the southeastern coast. The scarcity of Quaternary deposits onland precludes any detailed investigation of the Quaternary activity and structure of the Yangsan fault using seismic reflection profiling. We acquired offshore high-resolution seismic profiles to investigate the extension of the Yangsan fault and constrain its Quaternary activity using stratigraphic markers. The seismic profiles reveal a NNE-trending fault system consisting of a main fault and an array of subsidiary faults that displaced Quaternary sequences. Stratigraphic analysis of seismic profiles indicates that the offshore faults were activated repeatedly in the Quaternary. The up-to-the-east sense of throw on the main fault and plan-view pattern of the fault system are explained by dextral strike-slip faulting. The main fault, when projected toward the Korean Peninsula along its strike, aligns well with the Yangsan fault. We suggest that the offshore fault system is a continuation of the Yangsan fault and has spatial correlation with weak but ongoing seismicity.

The Ulleung Basin, East (Japan) Sea, is well-known for the occurrence of submarine slope failures along its entire margins and associated mass-transport deposits (MTDs). Previous studies postulated that gas hydrates which broadly exist in the basin could be related with the failure process. In this study, we identified various features of slope failures on the margins, such as landslide scars, slide/slump bodies, glide planes and MTDs, from a regional multi-channel seismic dataset. Seismic indicators of gas hydrates and associated gas/fluid flow, such as the bottom-simulating reflector (BSR), seismic chimneys, pockmarks, and reflection anomalies, were re-compiled. The gas hydrate occurrence zone (GHOZ) within the slope sediments was defined from the BSR distribution. The BSR is more pronounced along the southwestern slope. Its minimal depth is about 100 m below seafloor (mbsf) at about 300 m below sea-level (mbsl). Gas/fluid flow and seepage structures were present on the seismic data as columnar acoustic blanking zones varying in width and height from tens to hundreds of meters. They were classified into: (a) buried seismic chimneys (BSC), (b) chimneys with a mound (SCM), and (c) chimneys with a depression/pocicmark (SCD) on the seafloor. Reflection anomalies, i.e., enhanced reflections below the BSR and hyperbolic reflections which could indicate the presence of gas, together with pockmarks which are not associated with seismic chimneys, and SCDs are predominant in the western-southwestern margin, while the BSR, BSCs and SCMs are widely distributed in the southern and southwestern margins. Calculation of the present-day gas-hydrate stability zone (GHSZ) shows that the base of the GHSZ (BGHSZ) pinches out at water depths ranging between 180 and 260 mbsl. The occurrence of the uppermost landslide scars which is below about 190 mbsl is close to the range of the GHSZ pinch-out, The depths of the BSR are typically greater than the depths of the BGHSZ on the basin margins which may imply that the GHOZ is not stable. Close correlation between the spatial distribution of landslides, seismic features of free gas, gas/fluid flow and expulsion and the GHSZ may suggest that excess pore pressure caused by gas hydrate dissociation could have had a role in slope failures. (C) 2016 Elsevier Ltd. All rights reserved.

Seismic reflection data from the Ulleung Basin, East Sea, provide extensive evidence for Plio-Quaternary mass transport deposits (MTDs). We identified 23 MTDs embedded in 7 MTD bearing seismic units (U1–U7, from oldest to youngest) and estimated their geometric characteristics and source areas. The thicknesses and volumes of these MTDs range between 25 m and 392 m, and 13 km3–550 km3, respectively. The depth of the acoustic basement below sea level varies between about 100 m in the western margins to over 5900 m in the central part of the basin and highlights eight structural highs in the central and southern parts of the basin. These structural highs had a major role in controlling the pathway and distribution of the MTDs in the basin. In general, the thickest MTD units are sourced from the southern parts of the basin and the volume of these MTDs has remained relatively constant throughout the Plio-Quaternary. The seismic reflection data also reveal about 50 m high slide/slump scars formed on the seafloor by the latest submarine landslides which mainly concentrate on the southern and western margins of the basin. High-sedimentation rates and pore pressure build-up are likely the predominant factor controlling initiation of slope failures in the southern margin. Tectonics and gas hydrates likely play a role, too. The initial water depth of submarine landslides and volume and runout of the MTDs originating from the southern margin imply significant geohazard to the region.

Rock physics serves as a useful tool for seismic reservoir characterization and monitoring by providing quantitative relationships between rock properties and seismic data. Rock physics models can predict effective moduli for reservoirs with different mineral components and pore fluids from well-log data. The distribution of reservoirs and fluids for the entire seismic volume can also be estimated from rock physics models. The first part of this report discusses the Voigt, Reuss, and Hashin-Shtrikman bounds for effective elastic moduli and the Gassmann fluid substitution. The second part reviews various contact models for moderate-to high-porosity sands. In the third part, constant-cement model, known to work well for the sand that gradually loses porosity with deteriorating sorting, was applied to the well-log data from an oil field in the North Sea. Lastly, the rock physics template constructed from the constant-cement model and the results from the prestack inversion of 2D seismic data were combined to predict the lithology and fluid types for the sand reservoir of this oil field.

Collocated cokriging (CCK) and neural-network multi-attribute transform (NN-MAT) are widely used in the prediction of reservoir properties because they can integrate sparsely-distributed, high-resolution well-log data and densely-sampled, low-resolution seismic data. CCK is a linear-weighted averaging method based on spatial covariance model. NN-MAT, based on a nonlinear relationship between seismic attributes and log values, treats data as spatially independent observations. In this study, we analyzed 3-D seismic and well-log data from the Second Wall Creek Sand of the Teapot Dome field, Wyoming, USA to investigate: (1) how CCK and NN-MAT perform in the prediction of porosity and (2) how the number of wells affects the results. Among a total of 64 wells, 25 wells were selected for CCK and NN-MAT and 39 wells were withheld for validation. We examined four cases: 25, 20, 15, and 10 wells. CCK overpredicted the porosity in the validation wells for all cases likely due to the strong influence of high values, but failed to predict very large porosities. Overprediction of CCK porosity becomes more pronounced with decreasing number of wells. NN-MAT largely underpredicted the porosity for all cases probably due to the band-limited nature of seismic data. The performance of CCK appears to be not affected significantly by the number of wells. Overall, NN-MAT performed better than CCK although its performance decreases continuously with decreasing number of wells.