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Thromboembolism is one of the major complications during coil embolization of an aneurysm, which usually causes familiar neurological deficits, such as, weakness, aphasia, etc. We report a rare complication by thromboembolism after coil embolization causing hemiballism. A 69-year-old female presented with unruptured posterior communicating artery aneurysm and was treated by coil embolization. After the procedure, the patient showed global aphasia and right hemiparesis, and there were small multiple, scattered infarctions on the left middle cerebral artery territory. The neurologic deficit subsided after five days, but hemballism occurred thereafter. There was no other medical history to explain the hemiballism. The patient was treated with clonazepam and antiepileptics and the hemiballism subsided at postoperative day 20. We report a case of rare complication, hemiballism, during coil embolization.

The synovial cyst of the spine may be caused by degenerative changes or instability of the spine. The most common site of spinal synovial cyst is the lumbar spine. If conservative management is failed, the operation must be considered. So far, microscopic cyst removal has been considered a treatment of choice. Recently, biportal endoscopic surgery is now becoming increasingly common in spine surgery and has the advantage of minimizing damage to related structures such as muscle, bone, and nerve. There was a case in which the synovial cyst of the L4–5 level was successfully removed through a biportal endoscopic surgery, so we would like to report it with a literature review.

Objective : In March 2020, World Health Organization declared a global pandemic caused by a novel coronavirus (SARS-CoV-2). The disease caused by this virus is called COVID-19. Due to its high contagiousness, many changes have occurred in overall areas of our daily life including hospital use by patients. The aim of this study was to investigate the impact of COVID-19 on volume of spine surgery in South Korea using the National Health Insurance database and compare it with the volume of a homologous period before the pandemic.Methods : Data of related to spine surgery from January 2019 to April 2021 were obtained from the National Health Insurance and Health Insurance Review and Assessment Service database. Primary outcomes were total number of patients, rate of patients per 100000 population, and total number of procedures. The number of patients by hospital size was also analyzed.Results : COVID-19 outbreaks occurred in South Korea in March, August, and December of 2020. Compared to the previous year, the total number of patients who underwent spinal surgery showed a decrease for 2–3 months after the first and second outbreaks. However, it showed an increasing trend after the third outbreak. The same pattern was observed in terms of the ratio of the number of patients per 100000 population. Between 2019 and 2021, the mean number of spine surgeries per month tended to increase. Mean annual medical expenses increased over the years (p=0.001). When the number of spine surgeries was analyzed by hospital size, proportion of tertiary general hospital in 2021 increased compared to those in 2019 and 2020 (vs. 2019, p=0.012; vs. 2020, p=0.016). The proportion of general hospital was significantly decreased in 2020 compared to that in 2019 (p=0.037).Conclusion : After the COVID-19 outbreak, patients tended to postpone spinal surgery temporarily. The number of spinal surgeries decreased for 2–3 months after the first and second outbreaks. However, as the ability to respond to the COVID-19 pandemic at the hospital and society-wide level gradually increased, the number of spine surgeries did not decrease after the third outbreak in December 2020. In addition, the annual number of spine surgeries continued to increase. However, it should be noted that patients tend to be increasingly concentrated in tertiary hospitals for spinal surgery.

The deep core samples (site name: 21ESDP-203, drilled depth: 200.3m) collected from the southeastern shelf (Korea strait) of Korea were used to characterize physical property with sedimentary depth. Laboratory analysis (i.e., velocity and physical properties) was conducted on core samples. The physical property data were readily classified in good agreement with the lithological units alternating sandy mud and muddy sand with sedimentary depth. Based on compressional wave velocity data, the geoacoustic units are divided by 11 units with sedimentary depth. In particular, the upper sediments above 15 meter are characterized by high compressional wave velocity (greater than 1700 m/s) and high wet bulk density (∼2.2g/cm3 in maximum). Whereas, the porosity is very low (25% in minimum). This is due to the abundance of sandy sediments in this interval. The shear wave velocities of sediments are calculated from the compressional wave velocity and the effect of burial depth (Hamilton, 1980). The range of shear wave velocity is from 267 to 1345 m/s. However, most of data are less than 400 m/s. The velocity ratio (Vp/Vs) and the velocity gradient with sedimentary depth are calculated and estimated. The patterns are slightly different from those of Hamilton (1980). These results suggest that the physical properties are not only controlled by lithology and compaction caused by dewatering with burial depth, but also by different sedimentary environment after deposition.

This study focus on the depositional environment of the Hupo Basin shelf. We used sedimentary facies, grain size, textures, sediment color, as well as optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) age data. A long sediment core (19ESDP-101, about 120 m) has been interpreted to be the product of shallow water contourites. The sediments in the core are divided into seven sedimentary facies grouped into four facies associations (FA): FA1) contourite drift, FA2) contourite drift and channel transition, FA3) contourite channel and drift transition, and FA4) contourite channel. FA1 resulted from the interaction between hemipelagic fallout, low-density gravity flow, and sedimentation under low velocity bottom currents. Compared to FA1, both FA 2 and FA3 are indicative of higher velocity bottom currents, owing to their relative increase in grain size and the presence of subtle indicators of bed-load transport. FA 4 portrayed massive to slightly bedded sand, representing a contourite channel environment with high-energy conditions. The sedimentary facies stacking patterns observed at the study area site suggested that the depositional processes changed at the area where the core was optained. Therefore, the FA stacking pattern suggests the lateral migration of the contourite depositional system and continuous flow of the North Korean Cold Current (NKCC). Fluctuations in the bottom current activity, related to the intensification and deceleration of the NKCC, have caused fluctuations between contouritic and hemipelagic dominated periods. Our findings and interpretations can serve as a much needed reference for shallow-water contourite recognition in modern environments.

Endoluminal reconstruction of an intracranial aneurysm using flow-diverting devices, such as the pipeline embolization device (PED), is a new treatment modality with good clinical outcomes. The device was originally indicated for challenging cases, such as wide-necked large or giant aneurysms, and is gaining popularity as a reliable treatment for nearly all intracranial aneurysms. The overall complication rate of flow-diverting devices use is 17.0%, including occlusion of side-branching or perforating arteries, rerupture of the aneurysm, in-stent thrombosis, and, rarely, stent migration. We report a rare complication of the PED: delayed migration of the PED after successful stent implantation during treatment of an unruptured vertebral artery dissecting aneurysm, which resulted in rupture of the aneurysm. Further, we discuss technical steps that can be taken to prevent this potential complication.

The depositional environments of the Jeju Strait shelf since the last interglacial period are analyzed using sedimentary structures, grain size textures, sediment color, and optically-stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) ages of vibro-cores. The shelf deposits can be divided into 12 sedimentary facies grouped into four depositional units: 1) shelf sand, 2) estuarine sand/mud, 3) fluvial sand/mud, and 4) shelf sand/mud. Each unit is separated by a sharp and unconformable erosion boundary. Unit 1 shows massive to slightly bedded sandy shells with oyster fragments, representing a shelf environment during sea-level highstand. The OSL date of the base of the unit is 124.4 ± 10.0 ka. Unit 2 is characterized by thin periodic parallel laminated mud, suggesting tidal signatures in tidal flats. Sediments are typically moderate brownish, suggesting extreme weathering after deposition. The OSL dates of this unit range from 81.1 ± 5.3 to 74.2 ± 4.7. Unit 3 consists of lower cross-bedded sand and laminated mud with fining-upward successions. It is interpreted as the product of channel deposits in a fluvial environment during a sea-level falling. The OSL ages of Unit 3 range from 50.6 ± 2.9 to 26.1 ± 1.6 ka, belonging to the Weichselian glacial period. The uppermost unit (Unit 4) is composed of homogeneous mud and massive sand with molluscan shell fragments in the modern shelf environment during sea-level highstand. OSL and 14C-AMS ages range from 0.32 ± 0.02 to 11.2 ± 0.1 ka. Consequently, the late Pleistocene-Holocene sedimentary facies in this area consist of marine and non-marine environments, which mainly correspond to sea-level changes.

Thirty-two core samples were collected from the continental shelf area of the South Sea, Korea. They have been used to characterize physical properties in relation to sedimentary units (interpreted from seismic and core data) and to interpret physical property variation as a function of burial depth. The physical property data were readily classified into sedimentary units: Units S1, S2, S3, S4, and S5, in descending order. The variations in physical properties reflect well the relative characteristics of sedimentary units (equivalent to seismic units). Moreover, the relationships between physical properties are well grouped by each sedimentary unit. In addition, the distributions of physical properties match well with the grain size distribution and bathymetry of the study area. In particular, the lithology (e.g., grain size) plays an important role in the variation of physical properties. These results suggest that the physical properties of these sediments are mainly controlled by depositional processes in the vicinity of the paleo-Seomjin River, and that sea-level change specifically was a dominant sedimentary processes in the study area during the Quaternary. In particular, the physical properties of Unit S2 do not show transitional characteristics between Units S1 and S3, although it belongs to the transition zone in sequence order. This finding is attributed to the fact that compared with the sediments of Units S1 and S3, Unit S2 is composed of more coarse-grained sediments with abundant shell fragments.

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley reveals that the Nakdong River valley deposits, approximately 60 - 70 m thick, consist of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuary, coastal/shoreface, and delta. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed approximately before 12 ka. The transgressive systems tract (TST) can be divided into two depositional systems (Unit II and III). The river-derived sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 6 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the recent deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 6 ka.

Because of the increase in coastal erosion problems, many studies have been conducted to prevent coastline retreat by developing low-cost, highly effective countermeasures. We developed the artificial coral reefs (ACRs) method as part of this research trend. To verify its coastal protection performance, we carried out performance tests on its wave attenuation and beach sand capture ability, which are the key barometers for this newly developed technology. In this study, three different types of methods, including natural beach, TTP, and ACRs, were used to determine the coastal protection efficiency under both ordinary and storm wave conditions. Based on the results of this study, ACRs were found to have the best wave attenuation performance and captured more than 20% of the total erosion area. This means the ACR method can be applied as a reliable countermeasure to protect a coastal zone.

This study investigates sediment transport and depositional processes from a newly collected dataset comprising sub-bottom chirp profiles, multibeam bathymetry, and sediment cores from the northeastern continental margin of Korea in the East Sea (Japan Sea). Twelve echo-types and eleven sedimentary facies have been defined and interpreted as deposits formed by shallow-marine, hemipelagic sedimentation, bottom current, and mass-movement processes. Hemipelagic sedimentation, which is acoustically characterized by undisturbed layered sediments, appears to have been the primary sedimentary process throughout the study area. The inner and outer continental shelf (

An uncharted field of sand waves was discovered in a low-relief submarine canyon incised in the outer shelf on the southeastern continental margin of the Korean Peninsula in water depths of 180–190 m. We characterize the nature and origin of the waves and the sand forming them using sub-bottom chirp profiles, eXpendable bathythermograph (XBT) profile, multibeam echosounder (MBES) data, and sediment samples from four piston cores. Two types of sand waves characterized by distinct height versus wavelength relationships were found in the study area. The sand waves in the upper, narrower part of the shelf-incised canyon are sinuous-crested, with amplitudes of 0.3–2.1 m (mean: ~1 m) and wavelengths of 10–45 m (mean: ~24 m). Their asymmetry indicates migration upslope in a southwesterly direction, opposite to the surface currents. In contrast, the lower part of the canyon that is wider and closer to the margin of the continental shelf hosts nine long (ca. 1 km) curvilinear-crested sand waves with symmetrical crests; these waves likely reflect transient bedforms forming under fluctuating current conditions.\ud\udThe sediment of the sand waves consists of a variable mixture of siliciclastic and carbonate materials. The carbonate fraction (~22–55%; mean: ~34%) is derived mainly from the remains of bryozoans, bivalves, echinoderms, foraminifers, gastropods, and serpulids. Six bioclasts were dated by the radiocarbon method between ca. 41.3 and 11.8 ka BP. These relatively old ages and palaeontological data supports reworking from a shallow-marine environment during the last glacial transgression and limited sedimentation/sediment supply in the study area. The siliciclastic fraction (~44–79%; mean: ~37%) is composed of rounded to subrounded quartz and feldspar of moderate to good sorting and a mean grain size of ~1.3 phi (medium sand). The uppermost ~30 cm of all the sand wave cores reveals a decrease in the grain size of the siliciclastic fraction coupled with an increase in the carbonate/siliciclastic ratio, suggesting episodic sediment reworking and migration of the sand waves in response to fluctuating bottom currents. The coarser sediment that forms the core of the sand waves records bedload transport during periods of stronger currents. Finer carbonate-rich pelagic sediment (i.e., plankton) accumulated at the top of the sand waves during periods of weaker bottom currents. Significantly, our results show that the grain size and mineralogy of the sediment composing the sand waves are controlled by changes in hydrodynamic conditions. Our study provides novel geomorphological evidence for the influence of SW-flowing cold-water incursions (Korean Strait Bottom Cold Water) on the seafloor sediments.

Sequence analysis of high-resolution seismic profiles and sediment data from the Jeju Strait reveals that the shelf deposits form a depositional sequence consisting of a set of lowstand, transgressive, and highstand systems tracts deposited since the LGM. Six seismic units, each with different seismic facies and geometry, constitute three systems tracts. During the LGM, most of the continental shelf was exposed, resulting in sub-aerial erosion associated with paleo-channel incision, forming incised-channel fill (unit 1). The paleo-river may have supplied abundant terrigenous sediments to the study area around the paleo-river mouth. As the shelf flooded, these sediments were trapped within the paleo-estuary and formed estuarine deposits (unit 2). As transgression continued, the near-surface sediments were reworked and redistributed by shelf erosion, resulting in a thin transgressive sand sheet (unit 3) covering a large area of the shelf. Based on age dates and sea-level curves, a transgressive sand ridge (unit 4) formed during the stillstand or very slow rise period (13.7–11.5 ka BP). The Heuksan mud belt (HMB; unit 5), which is one of the prominent mud deposits located in the western part of the study area, can be divided into two subunits (5a and 5b). The lower part of the HMB (unit 5a) corresponds to shelf mud deposited during transgression. In contrast, the upper part of HMB (unit 5b) consists of recent shelf mud that was deposited during the highstand (after ∼7 cal kyr BP). The Seomjin subaqueous delta (unit 6), which consists exclusively of homogenous mud, was deposited after the sea-level highstand. Unit 6 indicates a transition from proximal to distal facies around the Seomjin River mouth. A single depositional sequence on the Jeju Strait shelf was mainly controlled by the complex interplay between bottom morphology, a varying sediment supply, and high-amplitude (∼130 m) sea-level changes, along with hydrodynamic conditions.

Three drill core samples collected from the Heuksan Mud Belt off SW Korea have been used to characterize sediment properties in relation to seismic units and to interpret geotechnical properties as a function of burial depth. The physical property data were readily classified into seismic units: Unit I, Subunit II-a, Subunit II-b, Subunit III-a, Subunit III-b, and Pre-LGM (last glacial maximum), in descending order. Thus, the variations in physical properties reflect the relative characteristics of the seismic units. Moreover, the relationships between physical properties are well grouped by each seismic unit. These results suggest that the physical properties of these sediments are mainly controlled by depositional processes related to sea-level change as one of dominant sedimentary processes in the study area. Interestingly, the shear strength and velocity of Subunit II-b are characterized by cyclic variation. These characteristic patterns are likely related to periodic variation in sedimentary environments (e.g., wave- or tide-dominated environments) in the study area. Clay fabric investigations with depth using scanning electron microscopy are characterized by different clay particle arrangements (e.g., from edge-to-edge to face-to-face contact with depth) owing to compaction effect caused by overburden pressure with depth. The geotechnical properties of the Heuksan Mud Belt suggest that the shallow regions are apparently over consolidated probably due to the flocculated fabrics at shallow depths and that the regions have moderate compressibilities in spite of the high mud content in the sediments.

This study is the first attempt at describing and interpreting incised-channels on the continental shelf of the South Sea, Korea. The distribution, pattern, shape, and infilling of submerged channels incised across the continental shelf of the South Sea have been investigated based on approximately 1940 line-km of chirp and sparker data. The incised-channel system of the paleo-Seomjin River on the continental shelf is approximately 109 km long, 800–5000 m wide, and is more than 890 km2 in area. Meandering and straight types of channel are dominant on the inner shelf, with a change to straight and braided planforms on the mid to outer shelf. Sparker seismic data suggest the paleo-channels formed under fluvial systems when the shelf was exposed during the Last Glacial Maximum (LGM). Channel fills are divided into five types, based on erosional surfaces and internal seismic reflectors: (I) transparent to semi-transparent incised channel fill; (II) parallel to sub-parallel incised channel fill; (III) complex incised channel fill; (IV) divergent incised channel fill; and (V) chaotic incised channel fill. The acoustically transparent facies of the channel fill type (Type I) suggest the presence of basin muddy deposits in a low energy environment, which were dominant in the inner shelf. These muddy sediments were likely during a period of higher sea level during the Holocene transgression. Types II, III, and IV are characterized by onlap, downlap, and wave or tidal ravinement surfaces, respectively, indicating that they were deposited during a transgressive stage, which type V represent basal incision surface. The evolution of paleo Seomjin River has been strongly controlled by sea level change and sediment transport processes since the LGM.

Objective In respect of the health and safety of the public, universal access to health care is an issue of the greatest importance. The geographic distribution of doctors is one of the important factors contributing to access to health care. The aim of this study is to assess the imbalances in the geographic distribution of neurosurgeons across Korea. Methods Population data was obtained from the National Statistical Office. We classified geographic groups into 7 metropolitan cities, 78 non-metropolitan cities, and 77 rural areas. The number of doctors and neurosurgeons per 100000 populations in each county unit was calculated using the total number of doctors and neurosurgeons at the country level from 2009 to 2015. The density levels of neurosurgeon and doctor were calculated and depicted in maps. Results Between 2009 and 2015, the number of neurosurgeons increased from 2002 to 2557, and the ratio of neurosurgeons per 100000 populations increased from 4.02 to 4.96. The number of neurosurgeons per 100000 populations was highest in metropolitan cities and lowest in rural areas from 2009 to 2015. A comparison of the geographic distribution of neurosurgeons in 2009 and 2015 showed an increase in the regional gap. The neurosurgeon density was affected by country unit characteristics (p=0.000). Conclusion Distribution of neurosurgeons throughout Korea is uneven. Neurosurgeons are being increasingly concentrated in a limited number of metropolitan cities. This phenomenon will need to be accounted when planning for a supply of neurosurgeons, allocation of resources and manpower, and the provision of regional neurosurgical services.

The KISAP (Korea Institute of Geoscience and Mineral Resources Seafloor Acoustic Probe) was developed to obtain in situ compressional wave velocity and attenuation profiles for seafloor sediments. The instrument comprises recording channels receivers, and an acoustic source, and can be attached to a corer or a probe. Here we report experiments comparing KISAP in situ velocity to laboratory velocity of co-located piston cores. KISAP data matched laboratory data (corrected for temperature and pressure) reasonably. KISAP can be used to collect in situ acoustic data, and can be effectively used to calibrate previous laboratory data to in situ data.

Laboratory measurements of sound velocity in unconsolidated marine sediment were performed to establish specific correction curves between temperature and sound velocity. Cores from the Hupo Basin ...

This paper is a review of stratigraphic architectures and evolution history of late Pleistocene lowstand deposits on the outer shelf of Korea Strait. Located between the southeastern tip of the Korean Peninsula and the Tsushima Island, the Korea Strait is a seaway connecting the East Sea with the East China Sea. Detailed analysis of high-resolution seismic profiles and sediment data give a good evidence for the existence of three superimposed wedge-shaped sedimentary units that thicken seaward. The individual sedimentary wedges are characterized by seaward dipping and complex sigmoid-oblique prograding reflection configurations with some chaotic or hummocky reflectors. On the basis of distribution and external geometry, these sedimentary wedges are interpreted as a “shelf-margin or shelf-edge delta”, mainly related to falling and lowstand sea level. Occurrence of this delta type is a common constitute of the Quaternary shelf in the Korea Strait. Although the entire units have not been fully dated, it is believed that these wedges were deposited during late Pleistocene sea-level lowstands. Repeated falls and lowstands of sea level (isotopic stages 8, 6 and 2/4) resulted in the formation of lowstand prograding wedges along the present shelf margin and trough region, having been separated from the inner shelf deposits. During subsequent episodes of sea-level rise (isotopic stages 8/7, 6/5, and 2/1), the upper part of sedimentary wedges was eroded, and thin covered by thin transgressive sands. Consequently, the late Pleistocene sequences on the shelf margin and trough region in this area mainly consist of a succession of stacked lowstand prograding wedges formed during the regression and lowstand of sea level.

High-resolution seismic data (Chirp and Sparker profiles) were used to investigate the sequence stratigraphy and evolution of the continental shelf of the South Sea, Korea, since the Last Glacial Maximum (LGM). Approximately 1950 km of chirp and sparker profiles were acquired. Along with seismic profiling, 30 piston core samples were collected and two previous long drill cores (SSDP-103 and 104) were tied to the seismic data. Our data show nine types of seismic facies on the basis of seafloor morphology and sub-bottom acoustic characters. Based on the analysis of seismic profiles, shelf deposits of the South Sea accumulated after the onset of the LGM can be divided into five sedimentary units; S1 to S5, from top to bottom. Correlation between sediment cores and seismic data suggests that Unit S5 is an incised channel fill formed by fluvial or coastal sediments during the early transgressive stage, accompanied by backstepping of the shoreline. Unit S4 is a transgressive sand layer reflecting the deposition of coarse sediments due to the strong currents and tides, following the rapid retreat of the coastline. Unit S3 represents paleo channel- and basin-fill deposits formed in estuary or delta environments near the inner continental shelf. Unit S2 forms an inner shelf transgressive sand layer including sand ridges. Unit S1 is interpreted as the most recent mud formed during the sea level highstand stage when the sea-level rise ended. Our results show that the sedimentary evolution of the continental shelf of the South Sea, since the LGM, has been closely related to the sea-level changes. The distribution of paleo-channels is associated with the paleo-Seomjin River, local sediment supply, and continental shelf erosion.

A total of 157 piston and box core samples were collected and analyzed to characterize physical properties and geoacoustic provinces of surficial sediments in the southwestern part of the Ulleung Basin in the East Sea. The results and distribution patterns of surficial sediment texture, physical and acoustic properties reflect well the sedimentary environment like distribution and composition of sediment in the study area. The inner shelf and basin slope in this study are dominated by fine-grained sediments and show high porosity and water content, with low bulk density and velocity as well. The trough of the Korea Strait and outer shelf, which is composed of coarse-grained sediments, shows low porosity and water content and high bulk density and velocity. Based on in-situ velocity and sediment properties, the study area is divided into five provinces: (1) Province IA is hemi-pelagic mud partially mixed with intermittent sandy sediments which are derived from the outer shelf due to slide/slump or mass flows (in-situ velocity: 1445 m/s, mean grain size: 8.4Φ, porosity: 84%, and bulk density: 1.24 g/cm3), (2) Province IB is covered with muddy sediments that were deposited during the Holocene (in-situ velocity: 1445 m/s, mean grain size: 7.9Φ, porosity: 78%, and bulk density: 1.35 g/cm3), (3) Province II is marked by mixed recent and relict sediments (in-situ velocity: 1477 m/s, mean grain size: 6.1Φ, porosity: 68%, and bulk density: 1.53 g/cm3), (4) Province III is dominated by coarse-grained relict sediments formed during the Pleistocene (in-situ velocity: 1564 m/s, mean grain size: 3.8Φ, porosity: 54%, and bulk density: 1.77 g/cm3), and (5) Province IV consists of coarser sediments than Province III (in-situ velocity: 1671 m/s, mean grain size: 3.0Φ, porosity: 46%, and bulk density: 1.91 g/cm3). The compressional wave velocity, mean grain size, and bulk density increase from Province IA to Province IV, whereas the porosity and water content decrease from Province IA to Province IV. Variability of the physical and acoustic properties tends to follow the general trend of the mean grain size. The classification of each province using the in-situ velocity corrected with the temperature and pressure provides a better reflection of the sediment properties and sedimentary environment.

The Korea Strait is a seaway connecting the East Sea with the East China Sea. The Plio-Quaternary stratigraphy and sedimentation on the Korea Strait shelf was studied using a dense network of high-resolution, single-channel seismic reflection profiles. The shelf sequences above the acoustic basement consist of seven depositional sequences separated by erosional unconformities corresponding to falls in sea level. Individual sequences are characterized by well-stratified and complex sigmoid-oblique prograding reflection configurations, reflecting a history of upbuilding and outbuilding in response to repetitive transgressive and regressive events driven by sea level changes. During the regression to lowstand of sea level, lowstand prograding wedges were formed seaward along the present shelf margin, whereas during the highstand of sea level, as in the present condition, highstand deposits were deposited in the inner shelf along the coast. However, as the subsequent regression began, the inner-shelf highstand deposits were severely eroded out and/or formed a condensed section. Volumetrically, the forced regressive and lowstand systems tracts are the most important components of the Korea Strait. Consequently, the Plio-Quaternary sequence in this area consists of a succession of stacked progradational lowstand wedges, mainly formed during the regression and lowstand of sea level.

잔디혹응애(Aceria zoysiae)는 잔디에 중요한 해충의 하나로 특히 한국잔디에 피해가 심하다. 본연구에서는 자생 채집 잔디 유전자원 보존원에서 잔디혹응애 저항성 잔디 개체의 선발을 위하여 잔디혹응애 피해를 조사하였다. 온실에서 295 계통의 자생지 채집 잔디를 대상으로 잔디혹응애 피해율을 조사한 결과, 잔디혹응애 피해는 잔디 종과 채집 계통별로 차이가 있었다. 잔디혹응애 피해가 가장 많은 잔디 초종은 들잔디와 중지였다. 들잔디가 97.6%의 개체들이 잔디혹응애 피해를 받았으며 중지와 갯잔디가 각각 87.7, 81.1%의 개체들이 잔디혹응애 피해를 받았다. 2개체의 왕잔디도 잔디혹응애 피해가 있었지만 일부 개체들은 온실과 야외에서 잔디혹응애 피해가 없었다. 야외에서 잔디혹응애 피해는 5월부터 발생하여 7월이후 급증하였다. 본 조사에서 잔디혹응애의 피해가 없는 잔디계통들은 향후 잔디혹응애 관리에 활용될 수 있을 것이다.

Aphanisticus congener is a newly recorded buprestid (Coleoptera) insect pest of turfgrass in Korea. This buprestid pest was initially found from turfgrass conservation site in a greenhouse in Jinju, Gyeongnam province, Korea in July, 2014. The Aphanisticus in the family Buprestidae is a leaf miner. A. congener is the close species of A. aeneus which was firstly reported as sugarcane leaf sucker in India. A. congener was active from early July to late August in the greenhouse. Damage by the insect led to drying out and browning of turfgrass leaf because larva fed on cell sap of leaves and adult fed on leaf surface. A. congener damaged Zoysia japonica, Z. sinica, Conodon dactylon, and Poa pratensis when adults were artificially released into potted turfgrasses in the laboratory. In green house, A. congener damaged Z. japonica, Z. macrostachya, Z. matrella, Z. sinica, Conodon dactylon, and hybrid zoysiagrass. However, no damage symptoms were observed from the same turfgrass accessions in the nearby field of the greenhouse. Thus, the new coleopteran pest may be a warm-adapted pest for turfgrass, damaging turfgrass leaf only in warmer conditions.

Submarine landslides form very complex depositional and erosional features on the seafloor, and their dynamics and triggering processes are yet to be understood completely. Numerous studies are being undertaken both because of the scientific significance but also for their potential harm to seafloor infrastructure and coastal areas. This study investigates the styles and causes of landsliding along the western margin of the Ulleung Basin in the East Sea, based on multiple sparker, subbottom profiler, multibeam echosounder and sediment core datasets collected in 2015. The bathymetric analyses indicate that the southern slope of the Ulleung Basin has experienced at least seven submarine failures. These failures left clear arcuate-shaped scarps that initiated at water depths of ~600 m. The observed headwall scarps have heights that exceed 60 m and appear to be the result of retrogressive-type failures. Seismic reflection data clearly image the basal sliding surface that is characterized by a prominent high-amplitude reflector. Chaotic-to-transparent seismic facies occur immediately downslope of the headwall scarps; these represent ~20 m thick landslide deposits. Gravity cores taken from areas adjacent to the scars suggest that these slides are older than ca. 97 ka. Interpretation of the present data shows that faults appear to cut recent sediments upslope of scarps, and that the slope may still be in an active phase of failure. Seismic data also image various overpressurized gases and/or gas fluids, as evidenced by the occurrence of pockmarks and seismic chimneys in upslope or adjacent areas of the scarps. Hence, earthquakes associated with tectonic activity and development of fluid overpressure may have acted as the main conditioning factor for destabilizing the slope sediments. Geotechnical stability analyses indicate that the sampled slope sediments are exceptionally stable under present-day conditions, even under seismic loading. This finding points to additional forces such as excess pore pressure caused by gas fluids at the times of slide emplacement.

Analysis of high-resolution seismic profiles and sediment data from the eastern Yellow Sea reveals that the late Quaternary deposits comprise six seismic units, interpreted as transgressive and highstand systems tracts formed since the LGM. Each unit was deposited during distinctive portions of the sea-level curve associated with hydrodynamic conditions. During the LGM (>19 ka BP), the study area was completely exposed, resulting in subaerial erosion associated with paleo-channel incision by the Huanghe and Korean Rivers. As the shelf was flooded, the incised channels were backfilled fluvial or coastal sediments, forming incised channel-fill deposits (SU1). The paleo-river may have supplied abundant terrigenous sediments to the study area around the paleo-river mouth and adjacent area. These sediments were trapped within the paleo-estuary and formed SU2, regarded as an estuarine deposit. Two types of serial sand ridges (SU3 and SU5) which correspond to transgressive deposits developed. SU3 on the southern part, west of Jeju Island (80–110 m deep) is regarded as a moribund-type mainly formed during the early to middle stage of transgression. These are thought to have ceased growing and remobilizing. In contrast, SU5 (occurring 30–50 m deep off the Korean Peninsula) is generally regarded as active sand ridges deposited during the late stage of transgression and is partly modified by modern tidal currents. As the transgression continued, the near-surface sediments were reworked and redistributed by shelf erosion, resulting in a thin veneer of transgressive sands (SU4). The uppermost unit (SU6) formed the Heuksan Mud Belt (HMB), which is one of the most prominent mud deposits in the Yellow Sea. The lower part of the HMD corresponds to shelf-mud deposited during the late stage of transgression, whereas the upper part consists of a recent shelf-delta developed after the highstand sea level at about 7 ka BP.

21 pages, 16 figures, 2 tables, Submarine landslides are common geomorphological features of continental margins. Some of the largest submarine landslides occurred on low-angle (< 4°), sediment-starved margins, yet their preconditioning and trigger mechanisms are still largely unconstrained. The southwestern continental margin of the East Sea (between 37.5°N and 38.0°N), Korea, occupies a narrow shelf (< 10 km), is characterized by low sedimentation rates (~3–7 cm /ka) with an average gradient of less than 2°. Here, we investigate submarine landslides using newly collected datasets including multibeam echosounder (MBES), chirp sub-bottom profiler, multichannel seismic (MCS) data and ten piston cores. MBES data from the margin reveal at least four major submarine landslides initiated at depths of 400 m to over 600 m. These landslides left clear headwall scarps on the seafloor with reliefs reaching over ~130 m and extend for over 40 km. MCS data show that some of the failures have resulted in the complete disintegration of the failed mass, while others have resulted in the deposition of well-defined hummocky debris flows. Sediments recovered downslope of the headwall scarps contain slides and debris flow deposits and turbidites that are overlain by bioturbated hemipelagic layers. Radiocarbon dating from hemipelagic units overlying MTDs within the headwall scarps reveal that major failures occurred at ca. 11 to 19 ka, coinciding with the time of the Last Glacial Maximum (LGM) to early deglaciation. Since then, hemipelagic sedimentation has prevailed throughout the sediment starved slope. Slope stability analyses based on geotechnical properties of sediments indicate that all areas are stable under static, and even stable under loads derived from earthquakes in instrumental records, but there were probably earthquakes in pre-historical records (i.e., with a longer recurrence interval) of potentially significant larger magnitude. We suggest that the preferential occurrence of major failures adjacent to the major faults on the lower slope may ultimately be tectonic-controlled although other factors may have contributed as well. Our work shows that coarse-grained clastic sediments are abundant in the shallow subsurface and that these higher-permeability units, often identified as weak layers, would focus fluid flow and could act as slip planes for slope failure. Our data also indicate that tectonic steepening and gas charging are other key parameters for controlling instability in sediment-starved margins, This study was supported by the project entitled “Geological survey in the Korean Peninsula and publication of the geological maps (GP2020-009)” of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science and ICT. The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund through grant CTM2015-70155-R (project INSIGHT) are also acknowledged, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka.

Hong, S.-H.; Chun, S.S.; Kim, J.-C.; Lee, G.-S.; Yoon, H.-H., and Yoo, D.-G., 2020. Sedimentary facies and depositional environment of long sediment cores from the Nakdong incised valley fills, southeastern Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 511–515. Coconut Creek (Florida), ISSN 0749-0208.Two deep-drilled cores were obtained from the Nakdong River delta in 2016. Based on the sediment structure, composition and texture, the deposits can be divided into four depositional units: I) fluvial sediments, II) estuarine sediments, III) coastal sediments, and IV) delta sediments. The lowermost Unit I is about 25 m thick and comprised clast-supported gravel and massive sand. The age dates of the upper part of Unit 1 is 49.7 ± 5.3 ka. Unit II consists of thin silt laminations that vary rhythmically in thickness, suggesting tidal influences in the estuarine environment. The age dates of this unit range from 10.9 ± 0.18 to 9.6 ± 0.11. Unit III is composed of cross-bedded sand, which contains peat materials and shell fragments and is interpreted to rapidly deposited sand bars in coastal environment. The age of Unit III had 9.7 ± 0.18 ka. Unit IV is composed of extremely bioturbated sandy mud and cross-laminated sand. The age dates of Unit IV ranges from 7.4 ± 0.5 to 0.8 ± 0.09 ka, the deposits belonging to the Holocene. These results indicate that depositional units in the study area consists of fluvial deposits of forced regression formed during the MIS 3, estuarine to tidal flat deposits during deglacial transgression, prograding delta deposits during postglacial periods.