Long-term measurement of temperature variabilities off Mindanao Island by the ocean acoustic tomography

Oceanic variabilities off Mindanao Island, Philippines where the North Equatorial Current branches into the Kuroshio and the Mindanao Current were measurerd for a period from 14 Feb.–1 Jun. 1992 by the oceean acoustic tomography (OAT). From the beginning of April, the travel time of acoustic rays propagating over a horizontal distance of about 250km, through the depth range of 80–4700 m around the underwater sound channel began to decrease, implying a warming of water. This variability was also confirmed with the results of temperature measurement at the sites where a sound source and receiver were located. The TOGA/TAO array data show that the OAT experiment was done when the 1991–1992 El Nino was at a decaying stage and the resulting warming-up of water occurred at the western Pacific. This study provides us a first evidence of ENSO-related variabilities detected by the OAT.     

Prediction of long-period ground motions from huge subduction earthquakes in Osaka,Japan

There is a high possibility of reoccurrence of the Tonankai and Nankai earthquakes along the Nankai Trough in Japan. It is very important to predict the long-period ground motions from the next Tonankai and Nankai earthquakes with moment magnitudes of 8.1 and 8.4, respectively, to mitigate their disastrous effects. In this study, long-period (>2.5 s) ground motions were predicted using an earthquake scenario proposed by the Headquarters for Earthquake Research Promotion in Japan. The calculations were performed using a fourth-order finite difference method with a variable spacing staggered-grid in the frequency range 0.05–0.4 Hz. The attenuation characteristics (Q) in the finite difference simulations were assumed to be proportional to frequency (f) and S-wave velocity (V _s) represented by Q = f · V _s / 2. Such optimum attenuation characteristic for the sedimentary layers in the Osaka basin was obtained empirically by comparing the observed motions during the actual M5.5 event with the modeling results. We used the velocity structure model of the Osaka basin consisting of three sedimentary layers on bedrock. The characteristics of the predicted long-period ground motions from the next Tonankai and Nankai earthquakes depend significantly on the complex thickness distribution of the sediments inside the basin. The duration of the predicted long-period ground motions in the city of Osaka is more than 4 min, and the largest peak ground velocities (PGVs) exceed 80 cm/s. The predominant period is 5 to 6 s. These preliminary results indicate the possibility of earthquake damage because of future subduction earthquakes in large-scale constructions such as tall buildings, long-span bridges, and oil storage tanks in the Osaka area.     

Interpretation of Mineral Zoning in Submarine Hydrothermal Ore Deposits in Terms of Coupled Fluid Flow‐Precipitation Kinetics Model

Major minerals (sulfates, sulfides, quartz) are distributed in different parts of submarine hydrothermal ore deposits. For instance, the abundance of barite increases stratigraphically upwards in the massive orebodies of the Kuroko deposits (black and yellow ores), while quartz is abundant in the lower parts (siliceous ore). The different distribution of barite and quartz in the Kuroko deposits can not be accounted for by thermochemical equilibrium calculations based on the precipitation due to mixing of ascending hydrothermal solutions with ambient cold seawater. In the present study, a coupled fluid flow‐precipitation kinetics model was used to calculate the amounts of quartz, barite, and anhydrite precipitated from a hydrothermal solution mixed with seawater, assuming reasonable values for temperature, precipitation rate, fluid flow velocity, mineral surface area/fluid mass ratio (A/M), and initial concentrations of hydrothermal solution and seawater before mixing occurred. The results indicate that barite precipitates more efficiently than quartz from discharging fluids with relatively higher flow velocity, lower temperatures and under the condition of lower A/M ratios on the seafloor (black ore), whereas quartz precipitates more effectively from solutions with lower flow velocity, higher temperatures and higher A/M ratios beneath the seafloor (siliceous ore) and in the orebody (barite ore, ferruginous chert ore). Anhydrite precipitates in shallow sub‐seafloor environments with lower precipitation rates and higher A/M ratios than barite and higher precipitation rates and lower A/M ratios than quartz. These results explain the observed occurrences of barite, anhydrite, and quartz in the Kuroko deposits. Namely, barite is abundant in black ore and barite ore which formed above the seafloor, anhydrite formed in high‐permeability tuff breccias, and quartz formed in low permeability dacite intrusive bodies in the sub‐seafloor environment.     

Volatilization properties of gasoline components in soils

Understanding the volatilization properties of gasoline components in soils is of fundamental importance in the field of geoenvironments. A series of experiments were performed to investigate the effects of temperature, soil water content, soil organic matter content, as well as mean particle size on volatilization rate of total petroleum hydrocarbons (TPH) and the paraffin (n-paraffin and isoparaffin), olefin, naphthene, and aromatic (PONA) components in four typical Japanese soils. The results of this study can be summarized as follows. (1) Volatilization rate of gasoline in a soil is concentration-dependent; extensive volatilization occurs above a certain threshold, while volatilization becomes very slow below this threshold. (2) Compared to other factors, temperature and soil organic matter content have greater effects on volatilization rate of gasoline in soils. The volatilization rate is proportional to temperature, but inversely related to soil organic matter content. (3) The characteristics of time-dependent decreases of TPH and PONA components in soils are similar. The volatilization rate of olefin is higher than those of other components. In addition, volatilization of olefin is also more sensitive to temperature as well as organic matter content.     

Comparison of community structures between particle-associated and free-living prokaryotes in tropical and subtropical Pacific Ocean surface waters

The subtropical and tropical regions of the Pacific Ocean are less productive than other oceanic regions. Although particle association should be an important strategy for heterotrophic prokaryotes to survive in such environments, we have little information on particle-associated (PA) prokaryotes in these regions. The specific aim of this study was to determine bacterial and archaeal community structures in the PA assemblage in comparison to the free-living (FL) assemblage in the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and an eastern equatorial region of the Pacific Ocean. Community profiles and phylogenetic identities were obtained by denaturing gradient gel electrophoresis, 454-pyrosequencing, and cloning followed by Sanger sequencing of 16Sr RNA gene amplicons. The distribution patterns of some abundant groups in three regions and two lifestyles (PA and FL) are shown in this study. Also, the PA community structures of bacteria differed from the FL ones and exhibited higher diversity than the FL ones, while the archaeal community structures did not show significant differences between PA and FL assemblages. We found that specific phylotypes of Gammaproteobacteria and Flavobacteria were abundant in PA bacterial assemblages, suggesting that they prefer to attach and consume particulate organic matter. In summary, the surface seawater PA assemblages represent very different bacterial and archaeal community structures between three different oceanic regions, each of which had distinct PA and FL community structures. These results imply that environmental factors determine microbial community structures.     

A new evolutionary scenario of intermediate-mass star-formation revealed by multi-wavelength observations of OMC-2/3

We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust continuum and H¹³CO⁺(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H¹³CO⁺(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations, we detected six molecular outflows associated with the dense gas envelopes traced by H¹³CO⁺(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence. We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic scenario of IM star/disk formation.     

Scientific role of ACA for low-mass star-formation study

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS (J=7–6) and HCN (J=4–3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ∼2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.     

The population trend and the population problems in recent Japan

All data obtained from vital statistics and the fertility survey indicate that the population of Japan will have a heavy burden of increasing old ages in the near future, because the attitude toward the number of children among Japanese women is to have fewer children (but not to have no children) and because it is anticipated that this attitude will not last for a good number of years in the future. This is one of issues discussed in recent Japan as population problems in the Aging Society.Another issue is population problems in the High Density Society. This issue is discussed in relation to unbalanced land utilization, air and water pollution, destruction of village life etc., brought about by the over-congestion in the metropolitan areas areas and depopulation in rural areas.One of the aims involved in the regional development plan of Japan is to solve the problems occured by the uneven distribution of population. The Third Comprehensive National Development Plan published in 1977 states that the central aim of this plan is to undertake the reorganization of population distribution by the development of attractive local cities, towns and villages where enough educational and employment opportunities are provided to make a best use of the desirable characteristics of the region, maintaining the present profitable feature of the areas and comfortable living conditions for people.The original of this article is the paper submitted to the International Conference on Population Problems and National Development, held at Seoul, Korea in November, 1978, sponsored by the Institute of Population Problems, Seoul, Korea.     

Equivalent linear method considering frequency dependent characteristics of stiffness and damping

Equivalent linear dynamic response analysis of ground is based on complex moduli and Fourier series expansion; therefore, it is not an equivalent method but an approximate method. Two deficiencies in the conventional equivalent linear method represented by SHAKE are described first. The maximum shear strength is overestimated, resulting in overestimation of the peak acceleration under a strong ground motion, and the amplification is underestimated at high frequency. The latter sometimes results in underestimation of the peak acceleration under weak ground shaking, and gives an incident wave with unrealistic large accelerations or a divergence of analysis in deconvolution analysis under strong ground motion. Both deficiencies are shown to come from the same cause, i.e. computing the effective strain as a constant fraction of the maximum strain. Since this is a key concept of the equivalent linear analysis, one cannot overcome both deficiencies at the same time in the conventional method. An apparent frequency dependence in stiffness and damping is shown to appear in the dynamic response, although soil itself does not show frequency dependent characteristics. Following this observation, the effective strain is expressed in terms of frequency from the similarity concept of the strain–frequency relationship between time domain and frequency domain. This enables the reduction of both deficiencies at the same time, resulting in a marked improvement in the equivalent linear analysis. The accuracy of the proposed method is examined by the simulations of three vertical array records during large earthquakes. The proposed method always gives much better prediction than conventional equivalent linear methods for both convolution and deconvolution analyses, and it is confirmed to be applicable at more than 1% shear strain.     

Pressure dependence of electrical conductivity of (Mg,Fe)SiO<Subscript>3</Subscript> ilmenite

The electrical conductivity of (Mg_0.93Fe_0.07)SiO₃ ilmenite was measured at temperatures of 500–1,200 K and pressures of 25–35 GPa in a Kawai-type multi-anvil apparatus equipped with sintered diamond anvils. In order to verify the reliability of this study, the electrical conductivity of (Mg_0.93Fe_0.07)SiO₃ perovskite was also measured at temperatures of 500–1,400 K and pressures of 30–35 GPa. The pressure calibration was carried out using in situ X-ray diffraction of MgO as pressure marker. The oxidation conditions of the samples were controlled by the Fe disk. The activation energy at zero pressure and activation volume for ilmenite are 0.82(6) eV and −1.5(2) cm³/mol, respectively. Those for perovskite were 0.5(1) eV and −0.4(4) cm³/mol, respectively, which are in agreement with the experimental results reported previously. It is concluded that ilmenite conductivity has a large pressure dependence in the investigated P–T range.