Properties of simulated cosmic matters after gamma-ray and neutron irradiation

Interstellar and circumstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. The effects of irradiation on simulated interstellar and circumstellar matter such as CaCO₃, MgCO₃, SiO₂ and Al₂O₃ are investigated. Especially, thermoluminescence (TL) spectra after γ-ray and neutron irradiation are compared carefully. It is shown that the thermoluminescence after neutron irradiation appears significantly in the wavelength of blue region. On the reflectance in infrared region, the irradiation effect appears scarcely.     

Blueschist blocks at Mochimaru in the Tari-Misaka ultramafic complex: Their petrologic characteristics and significance

Blueschist tectonic blocks occur in serpentinites at Mochimaru, Hiroshima Prefecture, Southwest Japan. They contain alkali amphibole coexisting with pumpellyite and chlorite, with or without calcic amphibole. Textural and chemical analyses reveal that the blueschists, together with other mafic schists, have similar metamorphic history. After their capture by serpentinites and before the emplacement of the serpentinites into the present geological position, the tectonic blocks were subjected to high P/T metamorphism around the boundary between the blueschist and pumpellyite–actinolite facies. The amphiboles formed by this metamorphism change from tremolite through glaucophane to ferroglaucophane with increasing FeO/MgO of whole rock compositions. The P–T conditions are estimated to be within 200–350°C and 5–7 kbar. These are higher P/T conditions than those of the regional metamorphism of Southwest Japan. The difference in the P–T conditions implies differences in tectonic situation and timing of metamorphism between the blocks and regional metamorphic rocks. In addition, the high P/T metamorphism of the tectonic blocks probably occurred in more reducing environments than the regional metamorphism. Because the ferric/ferrous iron ratios of the tectonic blocks are within a narrow range, it is stressed that oxygen fugacity was externally buffered during the high P/T metamorphism by the serpentinization process of the host ultramafic rocks. The reducing effect of serpentinization is common throughout the high P/T metamorphic terranes of Southwest Japan.     

藏北高原土壤温度的变化特征

通过GAME -Tibet野外工作前期所得到的土壤温度资料 ,初步分析了藏北高原不同地点不同深度土壤温度随时间的变化特征 ,并探讨了这种特征形成的原因。认为这可能与降雪、反照率、长波辐射、凝结潜热等的反馈过程及土壤湿度有关。由于土壤湿度等的影响 ,较潮湿的地方下层土壤从开始冻结到完全冻结需要一个较长的时间过程。     

Ventilation revealed by the observation of dissolved oxygen concentration south of the Kuroshio Extension during 2012–2013

From the moored buoy observation at \(33.9^{\circ }\)N, \(144.9^{\circ }\)E south of the Kuroshio Extension (KE), we obtained Eulerian time series of dissolved oxygen concentration (DO) at 200, 400, and 600 m depths from June 2012 to March 2013. We observed ventilation by meso- and submesoscale processes that transport water southward across the KE jet. First, the cyclonic mesoscale eddy in June 2012 substantially depressed DO at depths of 400 and 600 m but maintained DO at 200 m, suggesting near-surface lateral transport of high-DO water derived from the north of the KE. Second, subduction of high-DO (>230 \({\upmu }\)mol kg\(^{-1}\)) water to a depth of 600 m was observed from early February to March 2013, associated with a mesoscale/submesoscale meandering of the KE jet. In mid-March 2013, shipboard hydrographic data were collected where the water mass at the mooring site would be advected by the eastward current on the southern flank of the KE. Based on these data, the subduction event was identified as an intrusion of an anomalously thick water mass from approximately 400–900 dbar. Ventilation of the subtropical mode water at a depth of 200 m around a subsurface DO maximum layer was detected as a rapid rise in DO in January 2013. This occurred after a significant seasonal decrease in DO at a rate of \(-0.130 \pm 0.007\) \({\upmu }\)mol kg\(^{-1}\) day\(^{-1}\) from July to December 2012.     

Identifying spatial heterogeneity of coal resource quality in a multilayer coal deposit by multivariate geostatistics

This study presents a new geostatistical approach to characterization of the geometry and quality of a multilayer coal deposit using the data of seam thickness as a geometric property and the contents of ash, sodium, total sulphur, and the heating value as quality properties. A coal deposit in East Kalimantan (Borneo), Indonesia, which has a synclinal geological structure, was chosen as the study site. Semivariogram analysis clarified the strong dependence of heating value on ash content in the top and bottom parts of each seam and the existence of a strong correlation with sodium content over the sub-seams in the same location. The correlations between the geometry and quality of the seams were generally weak. A linear coregionalization model was used to derive the spatial correlation coefficients of two variables at each scale component from the single- and cross-semivariogram matrices. Because the data were correlated spatially in the same seam or over different seams, multivariate techniques (ordinary cokriging and factorial cokriging) were mainly used and the resultant spatial estimates were compared to those derived using a univariate technique (ordinary kriging). A factorial cokriging was effective to decompose the spatial correlation structures with different scales. Another important characteristic was that the sodium content shows distinct segregation: the low zones are concentrated near the boundary of the sedimentary basin, while the high zones are concentrated in the central part. The main component of sodium originates from the abundance of saline water. Therefore, it can be inferred that seawater had stronger effects on the coal depositional process in the central basin than in the border part. The geostatistical modeling results suggest that the thicknesses of all the major seams were controlled by the syncline structure, while the coal qualities chiefly were originated from the coal depositional and diagenetic processes.     

An earthquake swarm in the northern part of the Aso caldera and migration of their foci

A seismicity gap was observed in the early stage of the activity of the earthquake swarm which has been taken place in the northern part of the Aso caldera during January 1975. In the following stage, small earthquakes began to occur, until at last the largest earthquake occured within the seismicity gap. The b-value appreciably increased after the largest earthquake. The above-mentioned characteristics of this earthquake swarm may be a typical example of the fracturing phenomena in relatively heterogeneous rocks. From the estimation of the ultimate strain energy that can be stored up in the seismicity gap, it may be concluded that the above-mentioned largest earthquake took place by the release of ultimate strain energy stored within the seismicity gap.     

Comparison of upper ocean thermal conditions in the western North Pacific between two pentads: 1938–42 and 1978–82

In order to understand long-term changes in the temperature structure of the upper western North Pacific, we compared thermal conditions in two pentads, 1938–42 (P34) and 1978–82 (P78). The 1938–42 data were taken mostly by the Japanese Imperial Navy in a series of hydrographic surveys. The 1978–82 data were mostly XBT data taken as part of the TRANSPAC program. For each pentad, the data were interpolated to a set of standard depths, put through quality control procedures and averaged on a 1^o×1^o grid. A large area of the central subtropical gyre was warmer during P78, while the southern subtropical gyre, in the area of the North Equatorial Current was warmer during P34. This suggests that the transports of the Kuroshio and North Equatorial currents were larger during P78. Properties of North Pacific subtropical mode water (NPSTMW) were compared between pentads. It was found that NPSTMW was thicker, more uniform in temperature and more confined geographically during P34. A greater thickness is shown to result from stronger wintertime cooling during P34. Changes in the geographic extent of NPSTMW probably result from reduced advection by the Kuroshio current system during P34. The reason for the reduced advection maybe the Kuroshio was in a large meander state for a larger fraction of the earlier pentad, which can cut off advection west of the Izu Ridge.     

Four Decadal Ocean-Atmosphere Modes in the North Pacific Revealed by Various Analysis Methods

Various statistical methods (empirical orthogonal function (EOF), rotated EOF, singular value decomposition (SVD), principal oscillation pattern (POP), complex EOF (CEOF) and joint CEOF) were applied to low-pass filtered (>7 years) sea surface temperature (SST), subsurface temperature and 500 hPa geopotential height in order to reveal standing and propagating features of decadal variations in the North Pacific. Four decadal ocean-atmosphere covariant modes were found in this study. The first mode is the well-known ENSO-like mode associated with the “Pacific-North American” atmospheric pattern, showing SST variations reversed between the tropics and the extratropics. In the western tropical Pacific, subsurface temperature variations were found to be out of phase with the SST variations. The other three modes are related to the oceanic general circulation composed of the subtropical gyre, the Alaskan gyre and the subpolar gyre, respectively. The 1988/89 event in the northern North Pacific was found to be closely associated with the subtropical gyre mode, and the atmospheric pattern associated with this mode is the Arctic Oscillation. An upper ocean heat budget analysis suggests that the surface net heat flux and mean gyre advection are important to the Alaskan gyre mode. For the subpolar gyre mode, the mean gyre advection, local Ekman pumping and surface net heat flux play important roles. Possible air-sea interactions in the North Pacific are also discussed. The oceanic signals for these decadal modes occupy a thick layer in the North Pacific, so that accumulated heat content may in turn support long-term climate variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transformation from Cartesian to Geodetic Coordinates Accelerated by Halley’s Method

By using Halley’s third-order formula to find the root of a non-linear equation, we develop a new iterative procedure to solve an irrational form of the “latitude equation”, the equation to determine the geodetic latitude for given Cartesian coordinates. With a limit to one iteration, starting from zero height, and minimizing the number of divisions by means of the rational form representation of Halley’s formula, we obtain a new non-iterative method to transform Cartesian coordinates to geodetic ones. The new method is sufficiently precise in the sense that the maximum error of the latitude and the relative height is less than 6 micro-arcseconds for the range of height, −10 km ≤ h ≤ 30,000 km. The new method is around 50% faster than our previous method, roughly twice as fast as the well-known Bowring’s method, and much faster than the recently developed methods of Borkowski, Laskowski, Lin and Wang, Jones, Pollard, and Vermeille.     

Three-Dimensional Interpolation and Lithofacies Analysis of Granular Composition Data for Earthquake-Engineering Characterization of Shallow Soil

In Japan, many major cities are located on tectonic basins which are surrounded by faults and underlain by soft alluvial materials. Because these areas are subject to earthquake damages, it is important to determine their seismic engineering characteristics. Geotechnical databases which contain many borehole logs are useful information sources for this type of analysis. Each datum stored in the database has a value or an attribute, and its location is irregular in both horizontal and vertical directions. A new interpolation method based on the optimization principle is proposed here to deal with such three-dimensionally distributed data. Susceptibility of unconsolidated ground to liquefaction is known to be related to the content of loose and saturated sand. The mixture ratio of several soil types in a deposit, i.e., granular composition, is strongly influenced by the sedimentary environment. There are two numerical methods: the optimization principle method (OPM) used to determine three-dimensional distribution of granular composition and the model used to evaluate liquefaction. The application of the proposed methods to two locations in Japan indicated that the zones with high susceptibility to liquefaction were indeed those that had suffered from liquefaction during past earthquakes.