N-body simulation of giant molecular clouds in a galaxy

We madeN-body simulation of Giant Molecular Clouds in a model galaxy and confirmed that their random motion is generated and accelerated by purely gravitational interaction among them in some 10^7–8 yr. The results of the present simulation agree well with those of the previous theoretical calculation by Fukunaga (1984a, b).Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Geological and geophysical studies of the Nojima Fault from drilling: An outline of the Nojima Fault Zone Probe

Abstract The Nojima Fault Zone Probe was designed to study the properties and recovery processes of the Nojima Fault, which moved during the Hyogo-ken Nanbu earthquake ( M _JMA7.2) of 1995. Three holes, 500 m, 800 m and 1800 m deep, were drilled into or near the fault zone by the Disaster Prevention Research Institute, Kyoto University. The 500 m and 800 m holes were drilled in November 1995, and in December 1996 the last hole reached its final depth of 1760 m. The significant results are: (i) Geological and geophysical reconstruction of the structure and evolution of the Nojima Fault was obtained; (ii) the maximum compression axis was found to be perpendicular to the fault, approximately 45° to the regional compression stress axis; (iii) micro-earthquakes (m = –2 to +1) were induced by water injections 1–3 km from the injection points in the 1800 m hole; (iv) the fault zone was measured to be 30 m wide from microscopic studies of core samples. Instruments such as three-component seismometers, crustal deformation instruments, and thermometers were installed in the holes.     

Warped temperature profiles observed in the sediment of geothermally active areas in the Japan Sea— A hypothesis of double diffusive sinking

Some temperature profiles observed in sea floor sediments of the Japan Sea, west of the northern part of Honshu, show distinct gradients changing with depth, for which we use the term warping. Using a simplified model, this warping can be attributed to an abrupt temperature change in the bottom water just above the sediment. The bottom water temperature change might be explained by the hypothesis that warm and salt surface water in the region sank to the sea bottom, through colder and less saline water, maintaining a relatively warmer temperature than the bottom water which originates from ordinary lateral intrusion.     

Monitoring and simulation of water, heat, and CO2 fluxes in terrestrial ecosystems based on the APEIS-FLUX system

The Integrated Environmental Monitoring (IEM) project, part of the Asia-Pacific Environmental Innovation Strategy (APEIS) project, developed an integrated environmental monitoring system that can be used to detect, monitor, and assess environmental disasters, degradation, and their impacts in the Asia-Pacific region. The system primarily employs data from the moderate resolution imaging spectrometer (MODIS) sensor on the Earth Observation System- (EOS-) Terra/Aqua satellite, as well as those from ground observations at five sites in different ecological systems in China. From the preliminary data analysis on both annual and daily variations of water, heat and CO2 fluxes, we can confirm that this system basically has been working well. The results show that both latent flux and CO2 flux are much greater in the crop field than those in the grassland and the saline desert, whereas the sensible heat flux shows the opposite trend. Different data products from MODIS have very different correspondence, e.g. MODIS-derived land surface temperature has a close correlation with measured ones, but LAI and NPP are quite different from ground measurements, which suggests that the algorithms used to process MODIS data need to be revised by using the local dataset. We are now using the APEIS-FLUX data to develop an integrated model, which can simulate the regional water, heat, and carbon fluxes. Finally, we are expected to use this model to develop more precise high-order MODIS products in Asia-Pacific region.     

Dynamics of relativistic jets

We discuss the structure and relativistic kinematics that develop in three spatial dimensions when a moderately hot, supersonic jet propagates into a denser background medium and encounters resistance from an oblique magnetic field. Our simulations incorporate relativistic MHD in a four-dimensional spacetime and clearly show that (a) relatively weak, oblique fields (at 1/16 of the equipartition value) have only a negligible influence on the propagating jet and they are passively pushed away by the relativistically moving head; (b) oblique fields in equipartition with the ambient plasma provide more resistance and cause bending at the jet head, but the magnitude of this deflection and the associated backflow are small compared to those identified by previous studies. The new results are understood as follows: Relativistic simulations have consistently shown that these jets are effectively heavy and so they do not suffer substantial momentum losses and are not decelerated as efficiently as their nonrelativistic counterparts. In addition, the ambient magnetic field, however strong, can be pushed aside with relative ease by the beam, provided that the degrees of freedom associated with all three spatial dimensions are followed self-consistently during the simulations. The effect is analogous to pushing Japanese “noren” or vertical Venetian blinds out of the way while the slats are allowed to bend and twist in 3-D space. Applied to relativistic extragalactic jets from blazars, the new results are encouraging since superluminal outflows exhibit bending near their sources and their environments are profoundly magnetized – but observations do not provide support for irregular kinematics such as large-scale vortical motions and pronounced reverse flows near the points of origin.     

Interfacial energies for quartz and albite in pelitic schist

Interfacial energies of quartz/quartz (qz/qz), albite/albite (ab/ab), and quartz/albite (qz/ab) boundaries in low-grade pelitic schist were determined based on measured values of dihedral angles. Three kinds of microstructures were investigated, and the interfacial energies were obtained in two independent ways. (1) Relative values of interfacial energy were calculated from dihedral angles formed at quartz and albite triple junctions. (2) Subgrain boundary energy was calculated using the Read-Shockley theory for a boundary connected to an intergranular pore. Dihedral angles formed at the corners of intergranular pores were measured. From the interfacial tension balance equation, the value of the qz/qz grain boundary energy was then obtained. (3) Dihedral angles formed at intersections of either pericline or albite twin boundaries with either ab/ab or qz/ab boundaries were measured. The twin boundary energy was calculated based on a previously derived equation using Landau potential, twin wall thickness, and critical temperature for a phase transition in albite. With a modified interfacial tension balance equation for a twin boundary fixed to a facet orientation, the interfacial energies of ab/ab and qz/ab boundaries were obtained. Energies obtained by methods of (2) and (3) are in good agreement. The interfacial energies for qz/qz, ab/ab, and qz/ab boundaries obtained in this study are 270뀶, 300끞, and 250끀 mJ/m², respectively.     

Geothermal constraints on the hydrological regime of the TAG active hydrothermal mound, inferred from long-term monitoring

During August 1994 to March 1995, a period that included ODP Leg 158 drilling, bottom-water and sub-bottom temperatures were continuously logged by a long-term temperature monitoring system ‘Daibutsu’ at the base of the central black-smoker complex (CBC) and within the low heat flow zone at the TAG hydrothermal mound on the Mid-Atlantic Ridge. The temperature of hydrothermal fluid at CBC was also measured with a small high-temperature probe ‘Hobo’. Bottom-water temperature variations measured with Daibutsu at both sites have predominant semi-diurnal periods, causing the sub-bottom temperatures to fluctuate at these periods with reduced amplitudes and phase delays at sub-bottom depths. Seawater entrainment into the mound has been previously suggested at the low heat flow zone. We quantitatively evaluate the seawater entrainment rate at both sites from a one-dimensional numerical model, combined with a heat conduction model for the semi-diurnal variations. The entrainment rate of seawater at the base of CBC is estimated as 1.3±0.5×10⁻⁵ m/s, at least from August 17 to 30, 1994. On the other hand, the seawater entrainment rate at the low heat flow zone was undetected by long-term temperature monitoring at shallow sub-bottom depth. Nevertheless an increase in heat flow observed at the low heat flow zone during ODP drilling can be interpreted as a decrease in the entrainment rate of seawater. Before ODP Leg 158, Daibutsu measured three sub-bottom temperature anomalies at the base of CBC not derived from bottom-water temperature variations and Hobo also detected a CBC fluid temperature anomaly, indicating some natural changes in fluid flow within the mound. Daibutsu and Hobo also measured temperature anomalies during and after drilling at the ODP TAG-1 area. The Hobo temperature anomalies are inferred to have occurred when the cold fluid entrained through the drill holes at TAG-1 site reached or cooled the main fluid path to CBC. The entrained seawater through the drill holes appears to have contributed to dissolution and precipitation of anhydrite within the mound and perhaps affected the local permeability structure inside the mound. The temperature anomalies measured with Daibutsu at the base of CBC may have been induced by the change in the fluid flow pattern as a result of such permeability changes within the mound.     

Faulting in the Mikawa earthquake of 1945

This paper discusses the fault parameters of the Mikawa earthquake of January 12, 1945 on the basis of a simple dislocation model. Basically, the model assumes a rectangular shape of the fault plane striking N-S, so that it may fit the observed surface fault trace. Several sets of the fault parameters are tested to interpret the vertical and horizontal ground movements as observed geodetically. The fault model which is finally accepted is as follows: total length: 12 km; width: 11 km; dip angle: 30°; reverse dip-slip: 2 m; right-lateral strike-slip: 1 m. Geometry and slip in the present model seem to harmonize with the other sorts of evidence such as the seismological, tsunami genetic and reconnaissance data. From the tectonic point of view, this earthquake may be attributed to the secondary fault activity associated with the right lateral movement of the Median Tectonic Line.