Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping

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.     

Investigation of motions of catamarans in regular waves—I

In this paper an analytical technique based on the two-dimensional Green function method associated with a cross-flow approach for taking viscous effects into account to estimate the motion response of catamarans in the frequency domain is presented. In order to validate this method, the numerical results are compared with experimental values obtained for two different catamarans (ASR5061 [Wahab, R., Pritchett, C. and Ruth, L.C. 1971. On the behaviour of the ASR catamaran in waves. Marine Technology, 8, 334–360] and Marintek [Faltinsen, O., Hoff, J.R., Kvalsvold, J. and Zhao, R. 1992. Global loads on high speed catamarans. 5th Int. Symp. on Practical Design of Ships and Mobile Units, University of Newcastle-upon-Tyne, 1.360–1.373]).In the second part of the paper the tests carried out with a third catamaran configuration at the Hydrodynamics Laboratory of the University of Glasgow are presented to evaluate the non-linear effects. These test results cover different speeds and wave heights at a wide range of wave frequencies. The paper concludes that the two-dimensional method correlates very well with measurements of small amplitude motions. For large amplitude motion tests, the non-linear effects become significant when the model speed and wave amplitudes increase. The peak values of heave and pitch motions measured around the resonance frequency are smaller than those obtained from the linear theory.     

High Performance Concrete and Its Typical Mixes

- With the modern development of chemical and mineral admixtures, it is now possible to produce much higher performance concrete than before. Higher performance does not only mean higher strength, but also better durability, lower risk of thermal cracking and higher dimensional stability etc. The three most effective admixtures for producing high performance concrete are superplastieizer, pulverized fuel ash and condensed silica fume. This paper outlines the properties of these materials and presents some practical guidelines for their usage.     

A method for estimating specimen tangent stiffness for hybrid simulation

Researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness matrix of a test specimen in hybrid simulations employing implicit and mixed‐integration schemes. However, the computation of the tangent stiffness matrix during testing has proved to be challenging, particularly for test specimens with more than one degree of freedom (dof). This paper presents a new methodology that is more straightforward and simpler than existing techniques for computing the tangent stiffness matrix of a multi‐dof test specimen. The proposed method is combined with the operator‐splitting method (OSM), and the capabilities, advantages and limitations of the new formulation are demonstrated through several examples. The accuracy, stability, and error propagation characteristics of the modified OSM are also studied theoretically as well as numerically. The research results show that the proposed algorithm provides results that are better than those produced via the regular OSM alone, especially for damped structures undergoing highly inelastic behavior during testing. Copyright © 2008 John Wiley & Sons, Ltd.     

Following up the afterglow:strategy for X-ray observation triggered by gravitational wave events

The multi-messenger observation of coalescing compact binary systems promises great scientific treasure.However,synthesising observations from both gravitationa...     

Slip monitoring of a dip-slope and runout simulation by the discrete element method: a case study at the Huafan University campus in northern Taiwan

Slope failure is a widely observed phenomenon in the mountainous areas in Taiwan due to rainy climatic and fragile geological conditions. Landslides easily occur after intense rainfall, especially from typhoons, and, accordingly, cause a great loss of human life and property. At the northern end of the Western Foothill belt in northern Taiwan, Huafan University is founded on a dip-slope about 20° toward the southwest composed of early Miocene alternations of sandstone and shale. Data from continuous monitoring using inclinometers and groundwater gauges reveal that 6–10 mm/month of slope creeping occurs, and a potential sliding surface is then detected about 10–40 m beneath the slope surface. To understand the potential runout process of the dip-slope failure at the campus, particle flow code 3D models based on a discrete element method are applied in this study. Results of the simulation reveal a critical value of the friction coefficient to be 0.13 and that more than 90% of the campus buildings will slide down in 100 s when the friction coefficient is reduced to half the critical value. The weakening of the shear zone due to the rise of groundwater during rainstorms is assumed to be the main factor. Some suggestions for preventing landslide disasters are to construct catchpits to drain runoff and lower the groundwater table and to install a sufficient number of ground anchors and retaining walls to stabilize the slope.     

Incorporation of internal fluctuations in a meandering plume model of concentration fluctuations

A meandering plume model that explicitly incorporates the effects of small-scale structure in the instantaneous plume has been formulated. The model requires the specification of two physically based input parameters; namely, the meander ratio,M, which is dependent on the ratio of the meandering plume dispersion to the instantaneous relative plume dispersion and, a relative in-plume fluctuation measure,k, that is related inversely to the fluctuation intensity in relative coordinates. Simple analytical expressions for crosswind profiles of the higher moments (including the important shape parameters such as fluctuation intensity, skewness, and kurtosis) and for the concentration pdf have been derived from the model. The model has been tested against some field data sets, indicating that it can reproduce many key aspects of the observed behavior of concentration fluctuations, particularly with respect to modeling the change in shape of the concentration pdf in the crosswind direction.List of Symbols C Mean concentration in absolute coordinates - C _r Mean concentration in relative coordinates - C₀ Centerline mean concentration in absolute coordinates - C _r,0 Centerline mean concentration in relative coordinates - f Probability density function of concentration in absolute coordinates - f _c Probability density function of plume centroid position - f _r Probability density function of concentration in relative coordinates - i Absolute concentration fluctuation intensity (standard deviation to mean ratio) - i _r Relative concentration fluctuation intensity (standard deviation to mean ratio) - k Relative in-plume fluctuation measure:k=1/i _r ² - K Concentration fluctuation kurtosis - M Meander ratio of meandering plume variance to relative plume variance - S Concentration fluctuation skewness - x Downwind distance from source - y Crosswind distance from mean-plume centerline - z Vertical distance above ground - Instantaneous (random) concentration - Crosswind dispersion ofnth concentration moment about zero - _ny Mean-plume crosswind (absolute) dispersion - _y Plume centroid (meandering) dispersion in crosswind direction - _y,c Instantaneous plume crosswind (relative) dispersion - Normalized mean concentration in absolute coordinates:C/C ₀ - Particular value taken on by instantaneous concentration,      

Dating cleavage formation in slates and phyllites with the 40Ar/39Ar laser microprobe: an example from the western New England Appalachians, USA

Determinations of the absolute age of cleavage formation can provide fundamental information about the evolution of orogenic belts. However, when applied to cleavages in slates and phyllites, conventional dating methods are complicated by problems related to mineral separation and the presence of multiple cleavage generations. In situ high-spatial-resolution ⁴⁰Ar/³⁹Ar laser microprobe geochronology and microstructural observations indicate that the age of cleavage formation in slates and phyllites can be constrained by analysing zones of tightly packed cleavage domains. Three regionally developed cleavages (S₂, S₃, and S₄) are present in the northern Taconic Allochthon of Vermont and New York. Representative samples were studied from a variety of localities where these cleavages, which are defined by white micas, are well developed. In the suite of samples, only S₃ and S₄ are expressed as domains that are sufficiently wide and spatially isolated in thin section to permit quantitative ⁴⁰Ar/³⁹Ar geochronology. Mean ⁴⁰Ar/³⁹Ar laser microprobe ages for these domains are 370.7 ± 1.0 Myr for S₃ and 345.5 ± 1.7 Myr for S₄. Because estimates of the Ar closure temperature for white micas are substantially higher than the inferred growth temperatures of the micas defining S₃ and S₄, these values are interpreted as periods since cleavage formation. This interpretation is consistent with independent geochronological constraints on the age of the Acadian orogeny in the region.