Finite-element Simulation of Seismic Ground Motion with a Voxel Mesh

— Accurate simulation of seismic ground motion for three-dimensionally complex topography and structures is one of the most important goals of strong motion seismology. The finite-element method (FEM) is well suited for this kind of simulation, since traction-free conditions are already included in the formulation, and the Courant condition is less strict than for the finite-difference method (FDM). However, the FEM usually requires both large memory and computation time. These limitations can be overcome by using a mesh consisting of voxels (rectangular prisms) with isotropy built into the explicit formulation of the dynamic matrix equation. Since operators in the voxel FEM are the combinations of ordinary FDM operators and additional terms, the method keeps accuracy of the same order as FDM and the terms relax the Courant condition. The voxel FEM requires a similar amount of memory and only takes 1.2～1.4 times longer computation time. The voxel mesh can be generated considerably faster than the popular tetrahedral mesh. Both ground motions and static displacements due to a point or line source can be calculated using the voxel FEM approach. Comparisons with the reflectivity method and theoretical solutions demonstrate the successful implementation of the method, which is then applied to more complex problems.     

Improving integrity of RC beam-column joints with deficient beam rebar anchorage

In recent earthquakes in developing countries, severe damage was observed on reinforced concrete buildings. This study focuses on exterior beam-column joints with substandard beam rebar anchorage and seismic strengthening by installing wing walls. First, a series of experiments was conducted to investigate the seismic behavior of exterior joints with substandard beam rebar anchorage representing typical Bangladeshi buildings. Two 0.7-scaled exterior joint specimens were tested, and these specimens showed beam rebar anchorage failure and/or joint shear failure. Prior to strengthening of the joint, a series of pullout tests was conducted on postinstalled bonded anchors in low-strength concrete for strengthening design. Then, an experiment was performed to apply the strengthening method by wing walls to one of the exterior joint specimens to improve the integrity, and this method was intended to prevent the failure of beam rebar anchorage. The strengthening method is proposed to extend the development length of beam longitudinal bars by considering the embedment length along the wing walls. The test results verified the effectiveness and applicability of the proposed strengthening method to upgrade exterior RC beam-column joints with deficient beam rebar anchorage.     

Size distribution of urban blocks in the Tokyo Metropolitan Region: estimation by urban block density and road width on the basis of normative plane tessellation

The size distribution of urban blocks is important for the characterisation of urban block patterns and is known to follow several parametric statistical distributions. However, it has not previously been analysed on the basis of a normative plane tessellation and in terms of urban block density and mean road width. In this article, we formulate the size distribution of Voronoi cells using the gamma distribution estimated by urban block density and mean road width. We found that (1) both log-normal and gamma distributions can be good candidates for the size distribution of urban blocks at the scale of a region that consists of regular urban blocks and that has a uniform road width; and (2) the size distribution of urban blocks depends on the balance between pattern and width improvement effects. Based on one study region in Tokyo, if the pattern improvement effect is more prominent than the width improvement effect, the mode of urban block sizes tends to be larger than if it is not. These findings are expected to provide scientific support for urban planning (e.g. land readjustment projects).     

The reversible effect of temperature on the chemical composition of interstitial water of marine sediment

The reversibility of the temperature effect on the chemical composition of interstitial waters of three deep-sea sediment samples was examined between 2 and 25°C for Cl, Na, K, Mg, Ca, Si, B, Mn and alkalinity. When the temperature of sediment samples was returned from 25°C to the initial value of 2°C, most chemical species gave nearly their initial concentrations. However, for alkalinity and in one case for magnesium, it took another three to four hours to reach their initial concentrations.     

Sulfate reduction and sulfur fixation in sediment of a historically meromictic lake,Lake Suigetsu,Japan

Vertical distributions of sulfate, hydrogen sulfide, and iron (II) concentrations in interstitial waters and of sulfur content in sediment have been studied in a sediment core (73 cm long) from a meromictic lake, Lake Suigetsu, which changed from fresh-water to brackish conditions in 1664 A.D. The diatom assemblage of the sediment has also been analyzed. A boundary between high (>1.5%) and low (<0.2%) sulfur contents is found at a depth of 52 cm in the core. In the high sulfur layer (above 52 cm), the maximum sulfur content is 6.8% at 35 to 37 cm. The diatom assemblage, however, indicates that the boundary between fresh-water and brackish sediments lies at 40 cm. The hydrogen sulfide and iron (II) profiles in the interstitial waters indicate a sink for these chemical species near a depth of 40 cm. The discrepancy between the chemically-defined boundary at 52 cm and the paleontologically-defined boundary at 40 cm seems to be due to the downward migration of hydrogen sulfide and deposition of iron sulfide after the lake became brackish.     

Diagenetic deposition of manganese in sediment of a historically meromictic lake,Lake Suigetsu,Japan

Vertical profiles of manganese concentration in interstitial waters and of manganese and iron contents in five chemically-separated fractions of sediments have been studied in a sediment core (73 cm long) from a meromictic lake, Lake Suigetsu, which changed from freshwater to brackish conditions in 1664 A.D. The interstitial waters show a minimum manganese concentration of 0.13 ppm near a depth of 10 cm and a maximum of 26 ppm near 65 cm in the core. A predominant amount of manganese, up to 0.17%, is found in the hydrogen peroxide-soluble fraction of sediments in layers above a depth of 52 cm. It is suggested that the manganese is included in stable iron sulfides such as pyrite. Manganese, which diffuses upward from the lower layer, is thought to be deposited along with stable iron sulfide during diagenetic formation of the latter near a depth of 10 cm in the core.     

江西永平铜矿花岗质岩石的岩石结构、地球化学特征及其成矿意义

江西永平铜矿位于华南怀玉山-北武夷山铜铅锌多金属成矿带内,是赣东北地区除了德兴铜矿外的另一个大型铜矿基地.该矿区存在两种类型的花岗质岩石,一种是花岗岩;另一种是英安斑岩.英安斑岩具有典型斑状结构和石英眼结构,而花岗岩则具有单向固结结构.在化学成分上,两者属于高钾的钙碱性系列岩石,英安斑岩贫硅、富Al、Fe、Mg、Ca,以及具有较大的Na2O/K2O(0.02～0.64)等特点;而花岗岩富硅、贫Al、Ca,以及富碱和具有较小的Na2O/K2O(0.02～0.03)等特点.两种类型的岩石具有一致的REE配分曲线.它们均富集大离子亲石元素(Ba、Rb、K),亏损高场强元素(Th、Nd、Ta、Ti)以及元素Sr和P,显示了与俯冲作用有关的岩浆作用.在结构和化学成分上,花岗岩则类似于美国Climax斑岩钼(铜)矿成矿斑岩的性质(如具有单向固结结构、较高的分异指数、富Si、贫Al、Ca、富Na2O K2O以及K2ONa2O).与英安斑岩有关的蚀变作用主要有夕卡岩化、黑云母化、白云母化、绿泥石化和萤石化,而与花岗岩有关的蚀变作用主要是白云母化和萤石化;相应地,与英安斑岩有关的成矿作用主要为铜,而与花岗岩有关的成矿作用则主要为钼.2件辉钼矿样品的Re-Os年龄分别为156.7±2.8Ma和155.7±3.6M8,表明与花岗岩有关的钼成矿作用发生在156Ma左右.本文认为,永平铜钼矿的成矿地球动力学背景应是由挤压向伸展的转换环境.     

Diagenetic behavior of manganese in Tokyo Bay sediment

To understand the behavior of manganese in diagenetic processes in sediments of an enclosed bay which is similar to those of an estuary, chemical analyses have been carried out on both sediment and interstitial water of a core sample collected from Tokyo Bay. The results suggest that redistribution of manganese takes place within the sediment as a result of the dissolution of buried manganese oxides and hydroxides under reducing condition, the downward diffusion of Mn²⁺ through the interstitial water toward lower layers and then the precipitation of carbonate. The carbonate formed in the sediment contains managanese carbonate probably as a solid solution between calcitic calcium carbonate and manganese carbonate.     

Generation of greenhouse effect gases from different landfill types

Recently much attention is focussed on the problems of global warming due to greenhouse effect gases, notably carbon dioxide and methane. Because these gases cause important problems to the global environment, their generation from landfill sites containing solid wastes has drawn attention and their environmental impact is causing concern.

Generally, the gases associated with a greenhouse effect include carbon dioxide, methane and nitrous oxide. However, there are no general basic data available concerning gases generated from biodegradation of solid wastes in landfill sites. Specifically, no assessment has been made concerning greenhouse effect gases from different landfill types.

This paper proposes a quantitative model for estimating the gasification rate by different landfill types. The model is based on measurement data for a long-term material balance for an aerobic landfill and an anaerobic landfill, obtained with two types of large-scale lysimeters.

This paper will also give an estimate for the amount of greenhouse effect gases by for different types of landfill and propose countermeasures for their reduction.     

Volume transport of the Soya Warm Current revealed by bottom-mounted ADCP and ocean-radar measurement

The vertical structure of the Soya Warm Current (SWC) was observed by a bottom-mounted acoustic Doppler current profiler (ADCP) in the region of the SWC axis near the Soya Strait during a 1-year period from May 2004. The ADCP data revealed a marked seasonal variability in the vertical structure, with positive (negative) vertical shear in summer and fall (winter and spring). The volume transport of the SWC is estimated on the basis of both the vertical structure observed by the ADCP and horizontal structure observed by the ocean radars near the strait. The transport estimates have a minimum in winter and a maximum in fall, with the yearly-averaged values in the range of 0.94–1.04 Sv (1 Sv = 10⁶ m³ s⁻¹). These lie within a reasonable range in comparison to those through other straits in the Japan Sea.