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Variations in mineralogy and chemical composition, layer structures, redox states of Fe and Mn, and microbial diversity are closely linked to the biogeochemical process when a ferromanganese crust layer forms. A sample collected from the Magellan Seamount (OSM11), in the western Pacific, was characterized in five well-defined layers, top to bottom (L1–5). Fe-vernadite occurs in all layers, compared to detritus quartz, feldspar, goethite, and hematite in L1 and L3, and carbonate fluorapatite (CFA) in L4–5. The relatively high concentrations of Ca and P in L4–5, and Fe, Co, and Si in L1 and L3 correspond to the mineralogical variations in the crust layer. Disappearance of elongated voids along the convex growth line is likely due to void filling precipitation of CFA in L4–5, resulting in the void reduction (31.6 to 6.0%). The oxidation states of Fe in Fe-vernadite measured by electron energy loss spectroscopy (EELS) ranges from 36 to 63% of Fe3+/Fetot, and a layer where CFA appeared (L4) contains a more reductive form of Fe (Fe3+/Fetot = 36–48%). Presence of Fe- (coxC) and Mn-oxidizing gene (cumA), particularly displaying a strong PCR band of coxC in L2–3, indicates a dominant oxidizing condition. Direct evidence of microbial activity in Fe - and Mn-oxide precipitation with various redox conditions was identified in the focused ion beam-sectioned microfossil. Particularly, a spectrum image displaying a more reducing form of Fe around the voids previously occupied by microorganisms, strongly supports that microorganisms play an important role in the redox reaction in the growth of a crust.

The Dokdo and Ulleung islands (Korea) are volcanic islands in the East Sea (Sea of Japan), formed in the late Cenozoic. These volcanic islands, in the back-arc basin of the Japanese archipelago, provide important information about magma characteristics in the eastern margin of the Eurasian plate. The origin of the Dokdo and Ulleung intraplate volcanism is still controversial, and the role of fluids, especially water, in the magmatism is poorly understood. Here, we comprehensively analyzed the melt inclusions (10&ndash, 100 m in diameter) hosted in clinopyroxene phenocrysts of trachyte, trachyandesite, and trachybasalt. In particular, we observed Ti-magnetite and amphibole which were crystallized as daughter mineral phases within melt inclusions, suggesting that Ti-magnetite was formed in an oxidized condition due to H2O dissociation and H2 diffusion. The Ti-magnetite exhibited compositional heterogeneities of MgO (average of 8.28 wt %), Al2O3 (average of 8.68 wt %), and TiO2 (average of 8.04 wt %). The positive correlation of TiO2 with Cr2O3 is probably attributed to evolutionary Fe&ndash, Ti-rich parent magma. Correspondingly, our results suggested hydrous and oxidized magmatism for the Dokdo and Ulleung volcanic islands.

Microbial interaction with minerals are significantly linked with depositional conditions during glacial and interglacial periods, providing a unique redox condition in the sedimentary process. Abiotic geophysical and geochemical properties, including sedimentary facies, magnetic susceptibility, grain size, clay mineralogy, and distribution of elemental compositions in the sediments, have been widely used to understand paleo-depositional environments. In this study, microbial abundance and diversity in the core sediments (6.7 m long) from the northeastern slope of Dokdo Island were adapted to characterize the conventionally defined sedimentary depositional units and conditions in light of microbial habitats. The units of interglacial (Unit 1, &lt, 11.5 ka) and late glacial (Unit 2, 11.5&ndash, 14.5 ka) periods in contrast to the glacial period (Unit 3, &gt, 14.5 ka) were distinctively identified in the core, showing a sharp boundary marked by the laminated Mn-carbonate (CaM) mud between bioturbated (Unit 1 and 2) and laminated mud (Unit 3). Based on the marker beds and the occurrence of sedimentary facies, core sediments were divided into three units, Unit 1 (&lt, 11.5 ka, interglacial), Unit 2 (11.5&ndash, 14.5 ka, late glacial), and Unit 3 (&gt, 14.5 ka, glacial), in descending order. The sedimentation rate (0.073 cm/year), which was three times higher than the average value for the East Sea (Sea of Japan) was measured in the late glacial period (Unit 2), indicating the settlement of suspended sediments from volcanic clay in the East Sea (Sea of Japan), including Doldo Island. The Fe and Mg-rich smectite groups in Unit 2 can be transported from volcanic sediments, such as from the volcanic island in the East Sea or the east side of Korea, while the significant appearance of the Al-rich smectite group in Unit 1 was likely transported from East China by the Tsushima Warm Current (TWC). The appearance of CaM indicates a redox condition in the sedimentary process because the formation of CaM is associated with an oxidation of Mn2+ forming Mn-oxide in the ocean, and a subsequent reduction of Mn-oxide occurred, likely due to Mn-reducing bacteria resulting in the local supersaturation of Mn2+ and the precipitation of CaM. The low sea level (&minus, 120 m) in the glacial period (Unit 3) may restrict water circulation, causing anoxic conditions compared to the late glacial period (Unit 2), inducing favorable redox conditions for the formation of CaM in the boundary of the two units. Indeed, Planctomycetaceae, including anaerobic ammonium oxidation (ANAMMOX) bacteria capable of oxidizing ammonium coupled with Mn-reduction, was identified in the CaM layer by Next Generation Sequencing (NGS). Furthermore, the appearance of aerobic bacteria, such as Alphaproteobacteria, Gammaproteobacteria, and Methylophaga, tightly coupled with the abundance of phytoplankton was significantly identified in Unit 1, suggesting open marine condition in the interglacial period. Bacterial species for each unit displayed a unique grouping in the phylogenetic tree, indicating the different paleo-depositional environments favorable for the microbial habitats during the glacial and interglacial periods.

Extensive intraplate volcanism in the East Asia regions, including Dokdo and Ulleungdo (DU), occurred due to the extensional stress field during the Cenozoic era. However, the origin of magmatism is still controversial. Here we report new results of helium isotopes in olivine and clinopyroxene phenocrysts as well as major and trace element compositions from the DU basalts in order to determine the origin of the DU magmas and provide insights into Cenozoic mantle dynamics in East Asia. The DU volcanic islands were formed by magmatism after opening of the East Sea (Sea of Japan), a back-arc basin behind the Japanese arc, and are currently located in the Ulleung basin, one of sub-basins of the East Sea. The 3He/4He ratios range from 5.7 to 5.9 Ra for Dokdo and 4.5 to 6.0 Ra for Ulleungdo, respectively, similar to the sub-continental lithospheric mantle (SCLM) range of East Asia (4.6 to 7.7 Ra). Helium isotope compositions indicate that the depleted asthenosphere or the lower mantle plume might not be the direct source of the DU magmas. Also, there is no geochemical evidence that the DU magmas were influenced by subduction-derived components or the HIMU mantle source. Hence, we argue that SCLM provided enriched geochemical features in the DU basalts, contrary to basalts from other back-arc basins composed of the oceanic crust. In this respect, it is likely that the extended SCLM may still remain beneath the Ulleung basin. Our helium isotope and trace element mixing model shows the mixing trend between the metasomatized lithospheric melts and the asthenospheric melts. In addition, the presence of the low-velocity zone beneath the surface of the DU volcanoes in seismic tomography implies that the magmas were formed through the lithospheric melting due to the hot asthenospheric upwelling. Therefore, our study shows that the DU volcanism was mainly contributed by SCLM and that the lithosphere-asthenosphere interaction was the main mechanism that led to the Cenozoic magmatism in East Asia.

Most pollen analysis in Korea has focused on the Holocene Epoch, because pre-last glacial maximum terrestrial archives suitable for palynological study in the Korean Peninsula are limited. Thus, to verify the responses of vegetation to climate changes over the orbital timescales, analysis of pollen in marine sediments is needed. Here, we present the pollen record of hemipelagic sediments of core DD09-ST21 obtained from the northern Ulleung Basin in the East Sea. The palynofloral assemblages were dominated by warm temperate broadleaved trees and boreal conifers during interglacial and glacial periods, respectively. We also demonstrated that bisaccate pollen and herbaceous pollen in the palynological sequence can be used as indicators of the variation in the East Asian winter monsoon (EAWM) intensity during the last glacial period and freshwater inflow into the East Sea, respectively. During glacial periods, the EAWM intensified in response to weakening of the summer insolation at 60° N, while freshwater influx into the East Sea decreased due to a decrease in precipitation.

Volcano #1 is a large submarine stratovolcano with a summit caldera in the south central part of the Tonga Arc. We collected and analyzed multichannel seismic profiles in conjunction with magnetic data from Volcano #1 to investigate the structure of the intracaldera fill and processes of caldera formation. The intracaldera fill, exhibiting stratified units with a maximum thickness of 2 km, consists of at least four seismic units and a thick wedge of landslide debris derived from the caldera wall. The structural caldera floor, deepening toward the northwestern rim, suggests asymmetric collapse in the initial stage, which, in turn, appears to have contributed to the creation of a caldera elongated to the northwest by enhancing gravitational instability along the northwestern caldera boundary. Occasional, but repeated, eruptions resulted in a thick accumulation of the intracaldera fill and further subsidence in the mode of piston collapse. Magnetization lows are well-defined along the structural rim of the caldera that is interpreted as the inner principal ring fault. The magnetization lows indicate sites of submarine hydrothermal vents that caused an alteration of magnetic minerals. Faults recognized on the outer slope of the volcano are interpreted to be involved in hydrothermal fluid circulation.

In the northeastern part of the Ulleung Back-Arc Basin, the East Sea, the Dokdo volcano anomalously emerges, rising abruptly from the sea floor (~2,100 m below sea level). It is lying as a cluster of emerged small islets surmounting a larger submerged volcanic edifice. In order to investigate the detailed bathymetry and morphologic characteristics around the volcano's underwater guyot type summit, we carried out multi-beam surveys from 2006 to 2011 and analyzed the data. From the near islets to ~30 m depth, the flank slopes are very steep and irregular, overlain by sunken rocks, indicating partial erosion and talus formation due to waves, currents and weathering. The area from ~30 m to ~80 m depth shows gentle rises and falls, with a modest slope. Below ~80 m, the bathymetry gradually transitions to a relatively flat undulation with a smooth slope, extending to offshore areas. The bathymetry and the seafloor image from backscattering data show that there are small islets of the Dokdo volcano and a rocky sea bottom elongated from the islets, probably originating from residual parts of the eroded and collapsed main crater of the volcano. The seafloor images identify typical rocky bottoms, like rocky protrusions, and less sediment around the survey area, except for some areas with shallow sand sedimentary deposits. The stepped slopes of the study area are interpreted to be wave-cut submarine terraces rather than terraces from other origins, based on their relatively flat morphology and lack of sediments. The submarine terraces suggest a repetition of sea level changes (transgressions and regressions) in the Quaternary.

We studied the detailed bathymetry and the geophysical characteristics of the summit of the Dokdo volcano using mutibeam echosounding and geophysical survey data. The bathymetry around the main east and west islets of the Dokdo volcano shows very shallow within about 10 m water depth. From near islets to about 30 m b.s.l., the shallow water area has very steep slope and many irregular sunken rocks. The area from about 30 m to about 80 m b.s.l. shows gentle rises and falls, and less steep slope. The area from 80 m b.s.l. has gradually flat undulation and smooth slope seabaed and is extended to offshore. The main islets of the Dokdo volcano and the rocky sea bottom elongated from the islets might be the residual part of the eroded and collapsed main crater of the Dokdo volcano. The bathymetry and the seafloor image(from backscattering) data show small craters, assumed to be formed by the eruption of later volcanism. The seafloor images propose that, except some areas with shallow sand sedimentary deposits, there are typical rocky bottom such as rocky protrusions and lack of sediments in the main morphology of the survey area. The stepped slopes of the seabed are deduced to be submarine terraces. The several prominent submarine terraces are found at the summit of the Dokdo volcano, suggesting repetition of sea level changes(transgressions and regressions) in the Quaternary. The results of the magnetic anomaly and the analytic signal have a good coherence with other geophysical consequences regarding to the location of the residual crater.

We study the deep structure of Korean Peninsula by estimating Moho depth and crustal thickness from using land and oceanic topography and free-air gravity anomaly data. Based on Airy-Heiskanen isostatic hypothesis, the correlated components between the terrain gravity effects and free-air gravity anomalies by wavenumber correlation analysis(WCA) are extracted to estimate the gravity effects that will be resulted from isostatic compensation for the area. With the resulting compensated gravity estimates, Moho depth that is a subsurface between the crust and mantle is estimated by the inversion in an iterative method with the constraints of 20 seismic depth estimates by the receiver function analysis, to minimize the uncertainty of non-uniqueness. Consequently, the average of the resulting crustal thickness estimate of Korean Peninsula is 32.15 km and the standard deviation is 3.12 km. Moho depth of South Korea estimated from this study is compared with the ones from the previous studies, showing they are approximately consistent. And the aspects of Moho undulation from the respective study are in common deep along Taebaek Mountains and Sobaek Mountains and low depth in Gyeongsang Basin relatively. Also, it is discussed that the terrain decorrelated free-air gravity anomalies inferring from the intracrustal characteristics of the crust are compared to the heat flow distributions of South Korea. The low-frequency components of terrain decorrelated Free-air gravity anomalies are highly correlated with the heat flow data, especially in the area of Gyeongsang basin where high heat flow causes to decrease the density of the rocks in the lower crust resulting in lowering the Moho depth by compensation. This result confirms that the high heat sources in this area coming from the upper mantle by Kim et al. (2008).

Gravity and Magnetic survey data were analyzed to investigate the geophysical characteristics and regional geological structures of the southwestern Yellow Sea. The set of data about the southwestern part of the Yellow Sea in Korea was one collected by the Korea Ocean Research and Development Institute (KORDI) in 2003, 2004, and 2005. The Yellow Sea has a few basins and the study area also includes parts of the Heuksan Basin and the East China Sea Basin. The bathymetry of the study area ranges from about ?40 m southwestward near China to about 150 m northeastward near Korea. The bathymetry has the gentle rise and fall and the smooth slope. The gravity anomalies, from sea surface gravity and satellite gravity data, reflect the basement rocks rather than the smooth bathymetry. The gravity anomalies are higher on Northeastern part of the study area and lower over the South of the Heuksan Basin. The analytic signal from the Bouguer anomaly shows higher anomalous zones near the boundaries of the basins. The magnetic anomalies and the analytic signal, from the magnetic data, suggest that the complex anomalies on the Northern part are attributed to the volcanic intrusions and that the smooth patterns in the Southern part are based on the lack of the intrusions. The power spectrum analysis of the Bouguer anomalies and the magnetic anomalies indicate that the depth to the Moho discontinuity varies from about 30.2 to 28.3 km and that the depths of the basement rocks and the Eocene discontinuity range from about 8.4 to 8 km and from about 1.5 to 1.7 km, respectively. The inversion of the Bouguer anomaly shows that the Moho depth to the Western part of the study area near China is slightly deeper than the Eastern part near Korea. The result of 2-D gravity modeling has a good coherence with the results of the analytic signal, the power spectrum analysis, and the inversion.

The isostatic compensation and loading sequence of the Dokdo seamounts on the Ulleung Basin in the East Sea are studied by a flexure model using gravity and bathymetric data. The Dokdo seamounts comprise Dokdo (Dok Island), lying as a cluster of emerged small islets surmounting a large submerged volcanic edifice, and two voluminous tablemounts, Simheungtaek and Isabu. In spite of their similarity in topographic expression, a large difference of about 50 mGal between the observed gravity anomaly peaks over Dokdo and the Isabu Tablemount implies different amounts of compensation. A comparison between the observed and calculated gravity anomalies of the seamounts shows that the flexural compensation investigated in this study predicts well the observed data. The flexure model suggests that the Dokdo seamounts might be composed of high-density volcanic rocks. Modeling results show that the flexural rigidity or effective elastic thickness of the lithosphere under Dokdo is stronger or thicker than that under the Isabu Tablemount. It implies that the age of lithosphere at the time of loading for Isabu was younger than that for Dokdo. The effective elastic thicknesses associated with the Dokdo seamounts approximately follow 200–400 °C isotherms in the cooling plate model. The results of this study and the former age dating of Dokdo suggest that the Isabu Tablemount was formed first, followed by Dokdo after the opening of the East Sea ceased.

The East Sea including the area of this study is identified as a typical back-arc sea located in the backside of the Circum-Pacific volcanic and earthquake belt. Previous studies reported that the East Sea has begun to open by tensile force and formed its current shape. In this study, we investigate the regional tectonic structure of the East Sea using ship-borne gravity, magnetic, and satellite gravity data. The result of three-dimensional depth inversion shows that Moho depth of the study area is approximately 13-25km and inversely proportional to the thickness of the crust. In addition, as approaching to the center of the Ulleung Basin (UB), the thickness of the crust of the UB becomes thinner due to the extension caused by tensile force which had opened the East Sea.

In the Ulleung Basin, East Sea, the Dok Do seamount group comprises Dok Do (Dok Island), consisting of very small islets/rocks and a large submerged volcanic edifice, and two voluminous tablemounts, Simheungtaek and Isabu. We attempted to reconstruct the evolution of these seamounts, using virtual geomagnetic poles (VGPs) determined by the least-squares and the seminorm magnetization methods, with 1,500 m upward continued magnetic anomalies. The VGPs of Dok Do with normal dipole anomaly, and of Simheungtaek with normal dipole anomaly are located near the present magnetic pole. The VGP of Isabu with normal dipole anomaly is located at low latitude, presumably due to overprints of reversals in the Tertiary, and the distortion of magnetization and structures associated with volcanism after its formation. In contrast to the tablemounts, magnetic anomalies over Dok Do are a combination of both normal polarity and reversed polarity dipoles in the northern hemisphere, indicating that Dok Do has had at least two major eruptions, one during normal and another during reversed polarity intervals. From these results, and information on the ages of the seamounts (either published radiometric ages of subaerial volcanic rocks, or ages reconstructed in terms of reported elastic thickness incorporated into an existing cooling plate model), we tentatively propose that (1) Isabu formed first, during a normal polarity interval after the opening of the East Sea had ceased; (2) this was followed by an initial and subsequent large eruption of Dok Do during a normal polarity and a reversed polarity interval after about 5 Ma; and (3) the formation of Simheungtaek occurred in between that of Isabu and Dok Do in a normal polarity interval. The pattern of normal/reversed magnetization is not inconsistent with the geomagnetic polarity timescale for at least the last 5 Ma. Nevertheless, precise ages of formation would need verification by additional geophysical/geochemical constraints. Evaluating various possible models explaining the successive formation of the Dok Do seamounts, we currently favor fracturing and volcanism related to compression-induced weakening of the extensional field from the late Miocene to Pliocene after the opening of the East Sea.

Magnetic surveys of sites contaminated with unexploded ordnance (UXO) locate ferromagnetic sources and discriminate between UXO and some non-UXO (clutter) that can be left in place. High-pass, two-dimensional (2-D) intra-inversion filtering (IIF) is introduced as a partial solution to the vexing problem of overlapping fields of UXO, clutter, and geologic sources. IIF can severely distort target fields while ameliorating effects of overlapping fields. The filter applied to the input data is also applied to unit dipole fields that are used in the inversion algorithm to extract the position, strength, and orientation of the best-fit magnetic dipole. A least-squares converging grid-search inversion, with successive passes using smaller dipole search volumes, is more efficient than an exhaustive search. Between passes, a polynomial is fit to objective function values and the next search volume is centered on the node nearest the minimum of the polynomial. Intra-inversion gradient estimation improves some inver...

A geophysical mapping was performed for Hwasan caldera which is located in Euisung Sub-basin of the southeastern part of the Korean Peninsula. In order to overcome the limitation of the previous studies, remote sensing technic was used and dense potential data were obtained and analyzed. First, we analyzed geological lineament for target area using geological map, digital elevation model (DEM) data and satellite imagery. The results were greatly consistent with the previous studies, and showed that N-S and NW-SE direction are the most dominant one in target area. Second, based on the lineament analysis, highly dense gravity data were acquired in Euisung Sub-basin and an integrated interpretation considering air-born magnetic data was made to investigate the regional structure of the target area. The results of power spectrum analysis for the acquired potential data revealed that the subsurface of Euisung Sub-basin have two density discontinuities at about 1 km and 3-5 km depth. A 1 km depth discontinuity is thought as the depth of pyroclastic sedimentary rocks or igneous rocks which were intruded at the ring vent of Hwasan caldera, while a 3-5 km depth discontinuity seems to be associated with the depth of the basin basement. In addition, three-dimensional gravity inversion for the total area of Euisung Sub-basin was carried out, and the inversion results indicated two followings; 1) Cretaceous Palgongsan granite and Bulguksa intrusion rocks, which are located in southeastern part and northeastern part of Euisung Sub-basin, show two major low density anomalies, 2) pyroclastic rocks around Hwasan caldera also have lower density when compared with those of neighborhood regions and are extended to 1.5 km depth. However, a poor vertical resolution of potential survey makes it difficult to accurately delineate the detailed structure caldera which has a vertically developed characteristic in general. To overcome this limitation, integrated analysis was carried out using the magnetotelluric data on the corresponding area with potential data and we could obtain more reasonable geologic structure.

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.

Detailed investigations on both submarine and subaerial volcaniclastic deposits around Dokdo were carried out to identify geomorphologic characteristics, stratigraphy, and associated depositional processes of Dokdo caldera. Dokdo volcano has a gently sloping summit (about 11km in diameter) and relatively steep slope (basal diameter is about 20-25 km) rising above sea level at about 2,270m. We found ragged, elliptical-form of Dokdo caldera with a diameter of about 2km estimated by Chirp (3-11 kHz) sub-bottom profile data and side scan sonar data for the central summit area of Dokdo volcano. We interpreted that the volcaniclastic deposits of Dokdo unconformably consist of the Seodo (west islet) and the Dongdo(east islet) formations based on internal structure, constituent mineral composition, and bedding morphology. The Seodo Formation mainly consisted of massive or inversely graded trachytic breccias (Unit S-I), overlain by fine-grained tuff (Unit S-II), which is probably supplied by mass-wasting processes resulting from Dokdo caldera collapse. The Dongdo Formation consists of alternated units of stratified lapilli tuff and inversely graded basaltic breccia (Unit D-I, Unit D-III, and Unit D-V), and massive to undulatory-bedded basaltic tuff breccias (Unit D-II and Unit D-IV) formed by a repetitive pyroclastic surge and reworking processes. Although, two islets of Dokdo are geographically near each other, they have different formations reflecting their different depositional processes and eruptive stages.

Understanding the crustal structure of the Ulleung basin (Tsushima basin) in the southwestern Japan sea (East sea of Korea) is important for reconstructing the opening tectonics of the Japan sea. A Korea and Russia collaborative seismic experiment was carried out in 1991 to investigate the crustal structure of this basin using ocean bottom seismometers (OBSs) and large capacity air guns. The results of the experiment reveal that the Ulleung basin is floored by distinctive upper and lower crustal layers with velocities typical of layers 2 and 3. The lower crust, however, is unusually thick (7–8 km) and the Moho lies flat at 15–16 km depths. Though similar to the Yamato basin in crustal thickness, the Ulleung basin has a much thicker sedimentary sequence and a slightly thinner lower crust in the center. Geophysical evidence, thus, shows that the crust under the Ulleung basin has velocity range and crustal layering falling closer to those of normal oceanic crust than the Yamato basin. The formation mechanism of the thicker than normal lower crust should be clarified to better understand the complex opening process in the southern Japan sea.

A method of modifying a zero-dc symmetric filter to obtain an edge-adaptive gapped gradientnulling (EAGGN) filter is developed and tested on sparse magnetic field data. These data were obtained in a magnetic field survey on Chongcho Lake in the Republic of Korea to determine possible dredging hazards or impediments including possible unexploded ordnance (UXO). The data are interpolated to a regular grid but only grid points proximate to the observed field stations are flagged for use in inversion. The least-squares inversion simultaneously estimates a modeled magnetic dipole, dc-bias and, optionally, a constant-gradient background (regional) field. The EAGGN filter is applied as a preinversion filter here, but is also useful as an intra-inversion filter for other applications including UXO surveys. Bull’s eye plots present a stereographic projection of a dipole’s orientation onto a plane perpendicular to the earth’s field. These help visualize the deviation of a magnetic dipole’s orientation from the direction of the earth’s field. Deviations of less than 60 deg are consistent with UXO that have been shock demagnetized by firing or impact.

Ocean satellite altimetry-implied free-air gravity anomalies have had the shortest wavelengths removed during the processing to generate the optimal solution between multiple radar altimeter missions. ERS-1 168-day mission altimetry was residualized to a reference geoid surface generated by integrating Anderson and Knudsen’s free-air gravity anomalies for the Barents Sea. The altimetry tracks were reduced and filtered to extract the shortest wavelengths (between 4 and 111 km) from both ascending and descending tracks, respectively. These data were recombined using existing quadrant-swapping techniques in the wavenumber domain to generate a correlated, high frequency gravity field related to the local geologic sources. This added-value surface adjusted the reference free-air gravity anomalies to better reflect features in the gravity field at a wavelength related to the distance between altimetry ground tracks.

This study aims to investigate possible source and long-term distributional patterns of coastal sands in the high slope-gradient, wave-dominated coast with no large rivers, eastern Korea. Chirp (2–7 kHz) seismic profiles show that the coastal sand deposits, the uppermost transparent layer, are up to 7.1 m thick off small, mountainous stream mouths, and thins laterally, showing a radial distribution from the stream mouths with a slightly SE-skewed elongated (i.e., alongshore) geometry. These features suggest that the terrigenous coarse sediments emptied by the streams during the summer flash flooding season have been a major source to the adjacent coastal sands. Hydrodynamic measurements with benthic tripod systems indicate that alongshore currents occurring during episodic storms play a significant role in the displacement of the coastal sands toward the southeast, resulting in the slightly SE-skewed elongated (i.e., alongshore) distributional geometry of the sands.