Shear wave velocity and attenuation structure for the shallow crust of the southern Korean peninsula from short period Rayleigh waves

We analyzed the short period Rayleigh waves from the first crustal-scale seismic refraction experiment in the Korean peninsula, KCRUST2002, to determine the shear wave velocity and attenuation structure of the uppermost 1 km of the crust in different tectonic zones of the Korean peninsula and to examine if this can be related to the surface geology of the study area. The experiment was conducted with two large explosive sources along a 300-km long profile in 2002. The seismic traces, recorded on 170 vertical-component, 2-Hz portable seismometers, show distinct Rayleigh waves in the period range between 0.2 s and 1.2 s, which are easily recognizable up to 30–60 km from the sources. The seismic profiles, which traverse three tectonic regions (Gyeonggi massif, Okcheon fold belt and Yeongnam massif), were divided into five subsections based on tectonic boundaries as well as lithology. Group and phase velocities for the five subsections obtained by a continuous wavelet transform method and a slant stack method, respectively, were inverted for the shear wave models. We obtained shear wave velocity models up to a depth of 1.0 km. Overall, the shear wave velocity of the Okcheon fold belt is lower than that of the Gyeonggi and Yeongnam massifs by  0.4 km/s in the shallowmost 0.2 km and by 0.2 km/s at depths below 0.2 km. Attenuation coefficients, determined from the decay of the fundamental mode Rayleigh waves, were used to obtain the shear wave attenuation structures for three subsections (one for each of the three different tectonic regions). We obtained an average value of Q_β^− 1 in the upper 0.5 km for each subsection. Q_β^− 1 for the Okcheon fold belt ( 0.026) is approximately three times larger than Q_β^− 1 for the massif areas ( 0.008). The low shear wave velocity in the Okcheon fold belt is consistent with the high attenuation in this region.     

Neo-Proterozoic rift-related syenites (Northern Damara Belt, Namibia): Geochemical and Nd–Sr–Pb–O isotope constraints for mantle sources and petrogenesis

Major element, trace element and Nd–Sr–Pb–O isotope data for a suite of Neo-Proterozic, pre-orogenic, rift-related syenites from the Northern Damara orogen (Namibia) constrain their sources and petrogenesis. New U–Pb ages obtained on euhdreal titanite of inferred magmatic origin constrain the age of intrusion of the Lofdal and Oas syenites to ca. 750 Ma compatible with previous high-precision zircon analyses from the Oas complex. Major rock types from Lofdal and Oas are mildly sodic nepheline-normative and quartz-normative syenites and were primarily generated by fractional crystallization from a mantle-derived alkaline magma. Primitive samples from Lofdal and Oas show depletion of Rb, K and Th relative to Ba and Nb together with variable negative anomalies of P and Ti on a primitive mantle-normalized diagram. Evolved samples from Oas develop significant negative Ba, Sr, P and Ti anomalies and positive U and Th anomalies mainly as a function of crystal fractionation processes. The lack of a pronounced negative Nb anomaly in samples from Lofdal suggests that involvement of a crustal component is negligible. For the nepheline-normative samples from Lofdal, the unradiogenic Sr and radiogenic Nd isotope composition and low δ¹⁸O values suggest derivation of these samples from a moderately depleted lithospheric upper mantle with crustal-like U/Pb ratios (⁸⁷Sr/⁸⁶Sr: 0.7031–0.7035, ε Nd: ca. + 1, δ¹⁸O: 7‰, ²⁰⁶Pb/²⁰⁴Pb: ca.18.00, ²⁰⁷Pb/²⁰⁴Pb: 15.58–15.60). Primitive samples of the Oas quartz-normative syenites have identical isotope characteristics (⁸⁷Sr/⁸⁶Sr: 0.7034, ε Nd: ca. + 1, δ¹⁸O: 6.5‰, ²⁰⁶Pb/²⁰⁴Pb: ca.18.00, ²⁰⁷Pb/²⁰⁴Pb: 15.59) whereas more differentiated samples have higher ⁸⁷Sr/⁸⁶Sr ratios (0.709–0.714), slightly higher δ¹⁸O values (7.0–7.1‰), less radiogenic ε Nd values (− 1.1 to − 1.4) and more radiogenic ²⁰⁶Pb/²⁰⁴Pb ratios up to 18.27. These features together with model calculations using Sr–Nd–Pb isotopes suggest modification of a primary syenite magma by combined AFC processes involving ancient continental crust. In this case, high Nb abundances of the parental syenite liquid prevent the development of significant negative Nb anomalies that may be expected due to interaction with continental crust.     

Three-dimensional hydrodynamic-eutrophication model (HEM-3D): application to Kwang-Yang Bay, Korea

The purpose of this paper is twofold: to describe the water quality model of Three-Dimensional Hydrodynamic-Eutrophication Model (HEM-3D) and to present an application of HEM-3D to a coastal system in Korea. HEM-3D, listed as a tool for the development of Total Maximum Daily Load by US Environmental Protection Agency, is a general-purpose modeling package for simulation of the flow field, transport, and eutrophication processes throughout the water column and of diagenetic processes in the benthic sediment. This paper describes the water quality model of HEM-3D with emphasis on its unique features. Excessive loadings of organic wastes have significantly deteriorated water quality conditions of Korean coastal waters. This paper presents an application of HEM-3D to Kwang-Yang Bay, a coastal system in Korea, which is one of the first water quality modeling efforts for Korean coastal waters accompanied by a relatively comprehensive field program. The current status of data availability for water quality modeling in Korea is discussed.     

Pathways of organic matter through food webs of diverse habitats in the regulated Nakdong River estuary (Korea)

The benthic macroinvertebrates of the Nakdong River estuary were sampled at three different habitats: two salt marsh (Scirpus triqueter and Phragmites australis) beds and a bare intertidal flat. Fishes were sampled in the main channel. The trophic importance of marsh vascular plants, microphytobenthos, and riverine and channel particulate organic matter to macroinvertebrate and fish production was studied using stable carbon and nitrogen isotope tracers. There was a dramatic change in coverage of macrophytes (salt marshes and seagrass) after the construction of an estuarine barrage in 1987 in the Nakdong River estuary, with the S. triqueter bed increasing, the P. australis bed decreasing, and Zostera marina habitats being nearly lost. Although the invertebrate δ¹³C were within a narrower range than those of the primary producers, the values varied considerably among consumers in these habitats. However, the isotope signatures of consumers showed similarities among different habitats. Cluster analysis based on their isotopic similarity suggested that the isotope variability among species was related more to functional feeding groups than to habitats or taxonomic groups. While δ¹³C values of suspension feeders were close to that of the channel POM (mainly phytoplankton), other benthic feeders and predators had δ¹³C similar to that of microphytobenthos. Isotopic mixing model estimates suggest that algal sources, including microphytobenthos and phytoplankton, play an important role in supporting the benthic food web. Despite the huge productivity of emergent salt marshes, the contribution of the marsh-derived organic matter to the estuarine food webs appears to be limited to some nutrition for some invertebrates just within marsh habitats, with little on the bare intertidal flats or in the channel fish communities. Isotope signatures of the channel fishes also confirm that algal sources are important in supporting fish nutrition. Our findings suggest that benthic and pelagic microalgae made a large contribution to consumer diets, while marsh plants may not have a large role in supporting food webs in this estuarine system.     

Marine-Derived Fungi in Korea

Ocean Science Journal - Studies on marine fungi (termed as ‘marine-derived fungi’ in this paper) have been significantly increasing worldwide because of the critical role displayed by...     

Petrology and geotectonic significance of salic rocks preceding ophiolites in the Eastern Vardar Zone,Greece

Summary In the eastern Vardar Zone of Greece, Na-dominant salic rocks are intimately associated with ophiolites, constituting a NW-trending, about 8 km thick belt along the western margin of the Serbomacedonian Massif. Though of different ages and metamorphic histories, both contrasted lithologic units display similar lateral variations. The salic rocks vary from a hypabyssal tonalite-trondhjemite series in the NW into granophyres and submarine volcanics in the SE. The juxtaposed ophiolites change in the same direction from tectonite peridotites overlain or intruded by mafic-ultramafic cumulates into sheeted dykes and submarine volcanics. The salic rocks were formed by multi-staged fractional melting of a mafic source and correspond chemically to the low-K andensite rhyolite series. The geological and chemical evidence points at an immature island-are setting for the salic rocks above a NE-dipping subduction zone. The lateral variations in their mode of occurrences probably reflect progressive attenuation of the continental crust. The corresponding variations displayed by the juxtaposed ophiolites may have resulted from a change in the plate motion from conservative in the NW to constructive in the SE.

---

Petrologie und geotektonische Bedeutung der den Ophiolithen vorausgegangenen salischen Gesteine in der östlichen Vardar-Zone, Griechenland

Zusammenfassung In der östlichen Vardar-Zone von Griechenland bilden Na-betonte salische Gesteine und Ophiolithe einen NW-streichenden, ca. 8 km mächtigen Gürtel entlang des westlichen Randes des Serbomazedonischen Massivs. Trotz verschiedenen Alters und unterschiedlicher metamorpher Beanspruchung zeigen die beiden lithologischen Einheiten gleiche laterale Variationen. Die salischen Gesteine wechsein von Tonaliten und Trondhjemiten im NW zu Granophyren und submarinen Vulkaniten im SE. Die tektonisch angrezenden, etwas jügeren Ophiolithe variieren in der gleichen Richtung von Tektonit-Peridotiten und den überlagrenden oder intrudierenden mafisch-ultramafischen Kumulaten zu einem Gangstockwerk und submarinen, vorwiegend basischen Vulkaniten. Die salischen Gesteine sind durch ein mehrphasiges fraktioniertes Aufschmelzen mafischen Materials entstanden und entsprechen chemisch der K-armen Reihe von basischem Andesit bis Rhyolith. Als Bildungsort weisen die geologischen und chemischen Kriterien auf einen inmaturen Inselbogen oberhalb einer nach NE gerichteten Subduktionszone während des Mittleren Juras hin. Veränderungen in den Ausbildungsformen der salischen Gesteine gehen offensichtlich auf ein progressives Verdünnen der kontinentalen Kruste zurück. Entsprechende Veränderungen in den gegenübergestellten Ophiolithen lassen sich durch Veränderungen in der Plattenbewegung von konservativ im NW zu konstruktiv im SE erklären.

---

---

With 12 Figures     

Effect of water and stress on the lattice-preferred orientation of olivine

The influence of water and stress on the lattice-preferred orientation (LPO) of olivine aggregates was investigated through large strain, shear deformation experiments at high pressures and temperatures (P = 0.5–2.1 GPa, T = 1470–1570 K) under both water-poor and water-rich conditions. The specimens are hot-pressed synthetic olivine aggregates or single crystals of olivine. Water was supplied to the sample by decomposition of a mixture of talc and brucite. Deformation experiments were conducted up to γ (shear strain)  6 using the Griggs apparatus where water fugacity was up to  13 GPa at the pressure of 2 GPa. The water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at P = 0.5–2 GPa was  400–1200 ppm H/Si. Several new types of LPO in olivine are found depending on water content and stress. Samples deformed in water-poor conditions show a conventional LPO of olivine where the olivine [100] axis is subparallel to the shear direction, the (010) plane subparallel to the shear plane (type-A). However, we identified three new types (type-B, C, and E) of LPO of olivine depending on the water content and stress. The type-B LPO of olivine which was found at relatively high stress and/or under moderate to high water content conditions is characterized by the olivine [001] axis subparallel to the shear direction, the (010) plane subparallel to the shear plane. The type-C LPO which was found at low stress and under water-rich conditions is characterized by the olivine [001] axis subparallel to the shear direction, the (100) plane subparallel to the shear plane. The type-E LPO which was found under low stress and moderate water content is characterized by the olivine [100] axis subparallel to the shear direction, the (001) plane subparallel to the shear plane. Observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the dislocations in water-poor samples (type-A) are curved and both b =  [100] and b = [001] dislocations have a similar population. Numerous subgrains are seen in water-poor samples in backscattered electron images. In contrast, water-rich samples (both type-B and type-C) contain mostly b = [001] dislocations and dislocations are straight and sub-grain boundaries are rare compared to those in water-poor samples. These observations suggest that (1) dominant slip systems in olivine change with water fugacity (and stress) and (2) grain boundary migration is enhanced in the presence of water. Seismic anisotropy corresponding to the fabrics under water-rich condition is significantly different from that under water-poor condition. Consequently, the relationship between seismic anisotropy and flow geometry in water-rich regions is expected to be different from that in water-poor regions in which type-A fabric dominates (i.e., the lithosphere). A few cases are discussed including anisotropy in the subduction zone and in the deep upper mantle.     

Post-subduction margin structures along Boyd Strait, Antarctic Peninsula

The Pacific margin of the Antarctic Peninsula to the southwest of the Hero Fracture Zone (HFZ) is a former subducting margin which became inactive following the arrival of ridge crest segments of the Antarctic–Phoenix ridge at the margin during the Tertiary. In contrast, the part of the margin to the northeast of the HFZ remains active. Tertiary convergence was approximately perpendicular to the margin and ongoing motion is thought to have the same orientation. A new seismic reflection profile running along Boyd Strait, just northeast of the landward projection of the HFZ, shows major structural components similar to those typically observed along the margin to the southwest of the HFZ. In order of increasing proximity to the margin, these components are: the inner shelf, the shelf basin, the mid-shelf basement high (MSBH), and the outer shelf. The continuation of the post-subduction margin structures to the active margin suggests that the boundary between crust with passive and active margins characteristics is not sharply defined. Our postulated scenario for tectonic evolution along Boyd Strait is that: (1) before the arrival of the last ridge crest segment to the southwest of the HFZ, the inner shelf and the shelf basin were part of a Cretaceous–Tertiary arc and forearc area, (2) after the arrival, thermal effects resulting from interaction of the ridge crest with the margin just southwest of the HFZ lead to the formation of the MSBH to the northeast, but MSBH uplift in Boyd Strait did not prevent concurrent cross-shelf sediment transport contributing to development of an extensive outer shelf on the seaward flank of the MSBH, (3) Recent extension in Bransfield Strait, a marginal basin to the northeast of the landward projection of the HFZ, has caused about 10 km of seaward deflection in the strike of the part of the MSBH to the northeast of the projection of the HFZ.     

Finite-element computation of wave impact load due to a violent sloshing

A nonlinear sloshing problem is numerically simulated. During excessive sloshing, the sloshing-induced impact load can cause a critical damage on the tank structure. Recently the problem becomes an important research topic in LNG (Liquefied Natural Gas) Tanker and FPSO (Floating Production Storage Offloading) design. In this study, the wave impact load on the structure is obtained numerically by imposing the exact nonlinear free surface conditions and compared with that predicted by Morison's formula. As a theoretical model, a three-dimensional free surface flow in a tank is formulated in the scope of potential flow theory with the exact nonlinear free-surface conditions. A finite-element method based on Hamilton's principle is employed as a numerical method. The problem is treated as an initial-value problem. The nonlinear problem is numerically solved through an iterative scheme at each time step.