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Abstract: Long wavelength gravity anomalies derived from satellite data have limitations of spatial resolution and accuracy. To complement these weak points, combined datasets merged with shipborne/land gravity data and satellite data are generally compiled using global spherical harmonic, rectangular harmonic, or spherical cap harmonic analysis etc. However, each method also has a different resolution and accuracy. In this study, gravity anomalies and geoid undulations of South Korea and its vicinity are calculated using the spherical cap harmonic method, and the results are compared with those of GGM02C and EGM2008. Absolute and relative geoid height differences between GPS/leveling data and the results of various other methods show that the method used in this study has the lowest RMS error (0.271m vs 0.344–0.416m) and standard deviation (0.236m vs 0.309–0.362m). This implies that the spherical cap harmonic method has better resolution and accuracy than the other methods. The short wavelength gravity anomalies derived from the spherical cap harmonic coefficients are used to estimate the sediment thickness of the Ulleung Basin, which is poorly known. The sediment thickness of the Ulleung Basin is about 5km at the center of the basin, and about 12km at the southern margin. [Copyright &y& Elsevier]

Results of numerous geological and geophysical surveys of the East China Sea Shelf Basin (ECSSB), mainly from the southwestern part, indicate that the basin was formed by rifting processes due to the subduction of the Pacific and Philippine Sea plates at the paleo-Ryukyu margin during the Late Cenozoic. However, dominantly negative anomalies in the northeastern part of the ECSSB and absence of direct evidence for the subduction-related volcanic activity mean that this interpretation is equivocal. New seismic reflection data show volcanic edifices, sills and dikes are common on and around the Hupijiao Rise. Recovered drill-hole cutting samples of Early and Middle Miocene (14.55 to 17.59 Ma) basalt from a well on the Rise have magnetic susceptibilities of 9.6 mSI and natural remnant magnetization of 3.6 A/m. These data are combined with information about the extent of volcanic edifices and the magnetic properties of sediments and granite-gneiss basement to model the magnetization distribution on the Hupijiao Rise using a Fast Fourier Transform (FFT) routine. The results suggest that the NRM of the volcanic edifices have been acquired primarily during geomagnetically-reversed polarity. Modeling predicts that the reversed polarity of basalt (Q-ratio = 9.84) is the main reason for negative magnetic anomalies on the northeastern part of the ECSSB. In addition, geochemical analysis indicates that the basalts sampled from the Hupijiao Rise are related to OIB (Ocean Island Basalt)-type volcanism. These analyses suggest a crustal thinning and asthenosphere upwelling event occurred in this region during the Miocene. [ABSTRACT FROM AUTHOR]

Abstract: 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 50mGal 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. [Copyright &y& Elsevier]

We analyzed the unsymmetrical fault characteristics of resistive superconducting-fault-current-limiters (SFCL) based on YBCO thin films with the unbalanced faults such as a single line-to-ground fault, a double line-to-ground fault, and a line-to- line fault in a three-phase system. The unsymmetrical rates of fault phases were 6.4, 9.2, 8.8 at the fault onset, but decreased by 1.4, 1.5,3.7 after 50 ms in the fault types, respectively. The positive sequence current I¹ was the highest in a double line-to-ground fault, immediately after the fault onset, but that of a line-to-line fault was the highest after 50 ms. This means the current limiting effect was the worst in a line-to-line fault, due to the unbalanced quench between the SFCL units. The negative sequence currents I² of a single and double line-to-ground faults were relatively low, except for the quench instant, because of the rapid interruption of fault currents by the SFCL. The zero sequence current I0 was similar to the behavior of the negative sequence current. Finally, the positive sequence resistance Z¹ was reduced remarkably immediately after the fault but gradually approached the balanced positive sequence resistance prior to the system fault, except during a line-to-line fault. The simultaneous quench between the SFCL units was important for low line-to-line fault currents. [ABSTRACT FROM AUTHOR]