Spectral observations of impact dark spots

We carried out a spectral observation of traces of the comet impacts within the wavelength region between 440 and 830 nm. Three dark spots of fragments K, E, and G impact sites were investigated. The spectrum of these dark spots shows no special emission or absorption lines in this observation. The global spectral feature resembles that of Jovian zone cloud rather than that of the belt. While the continuum reflectivity of the dark spots of K and E sites is less than 0.42 at 600 nm, that of the G site is 0.33. These values should be interpreted as an upper limits because of the influence of atmospheric seeing. The equivalent width of the absorption lines at the K sites is also derived. Both the continuum reflectivity and the equivalent width of the dark spots are smaller than those of any Jovian zonal cloud. This indicates that the dark spots are low-albedo cloud formed at the upper atmosphere.     

Pi 3 magnetic pulsations associated with substorms

Using magnetic data from the North American IMS network at high latitudes, Pi 3 pulsations are analysed for a period of $\text{4}\text{1}\text{2}$ continuously-disturbed days. The data were obtained from 13 stations in the Alaska and Fort Churchill meridional chains and in the east-west chain along the auroral zone. In the past, Pi 3 pulsations associated with substorms have been classified into two sub-categories, Pi p and Ps 6. However, we find that Pi 3's which have longer periods than Pi p and which are different from Ps 6 are more commonly observed than these two special types. Power spectra, coherence and phase differences are compared among the stations. Results show that noticeable differences for latitudinal dependence of period and amplitude exist among midnight, morning and late-evening Pi 3 pulsations. Results for Pi 3 occurring near midnight indicate that the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the center of the westward auroral electrojet. On the other hand, for Pi 3 pulsations occurring in the morning, the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the poleward edge of the westward electrojet. Furthermore, for Pi 3 pulsations occurring in the late evening, their periods are longer and their amplitudes larger near both the Harang discontinuity and the poleward edge of the westward electrojet than near its center. Correlations between pairs of adjoining stations are better in the polar cap than at auroral latitudes. It is also found from hodograms that the sense of polarization often varies from one station to another for the same event, and that the time duration in which the same rotational sense is maintained is shorter near midnight than in the morning and late evening. It is suggested that the source regions of the morning and late-evening Pi 3's lie on the electrojet boundaries; that is at the Harang discontinuity (in the evening) and at the poleward edge of the westward electrojet (in the morning and evening). The generation of midnight Pi 3 pulsations, centered at a location within the westward auroral electrojet appears to be associated directly with the generation of that electrojet.     

Growth of Emerald Crystals by Evaporation of Na2O—MoO3 Flux

Well-formed crystals of emerald, Be3AI2Si6O18:Cr, were easily grown from an Na2O-MoO3 flux by an isothermal technique. The crystal growth was conducted by heating a mixture of solute and flux at 1 100 ℃ for 24 h. The evaporation loss of flux depended on the amount of Na2O added to MoO3. Emerald crystals of lengths up to 2.1 mm and widths of 1. 4 mm were grown. The crystal sizes were dependent on the evaporation loss of the flux. The obtained crystals were transparent and exhibited the typical emerald-green color. The form of the emerald crystals was a twelve-sided prism bounded by well-developed faces. The aspect ratios were in the region of 1. 4 to 2. 3. The density was (2. 64±0.02) g/cm3. The IR absorption bands were in good agreement with the literature data.     

The chemical Th-U-total Pb isochron ages of Jiaodong and Jiaonan metamorphic rocks in the Shandong Peninsula, eastern China

Abstract The chemical Th-U-total Pb isochron method (CHIME) was applied to determine the age of monazite and thorite in five gneisses and zircon in an ultra high-pressure (UHP) phengite schist from the Su-Lu region, eastern China. The CHIME ages and isotopic ages reported in the literature show that gneisses in the Su-Lu region are divided into middle Proterozoic (1500–1720 Ma) and Mesozoic (100–250 Ma) groups. The Proterozoic group includes paragneiss and orthogneiss of the amphibolite-granulite facies, and their protolith age is late Archean-early Proterozoic. The Mesozoic group is mainly composed of orthogneiss of the greenschist-epidote amphibolite facies, and the protolith age is Middle Paleozoic-Early Proterozoic. The Proterozoic and Mesozoic gneisses occupy northern and southern areas of the Su-Lu region, respectively, which are divided by a major Wulian-Qingdao-Yantai fault. Ultra high-pressure metamorphic rocks occur as blocks in the Mesozoic gneisses, and form a UHP complex.
The UHP phengite schist in the Mesozoic orthogneiss contains detrital zircons with late Proterozoic CHIME age ( ca 860 Ma). Age of the UHP metamorphism is late Proterozoic or younger, and protolith age of the UHP metamorphic rocks is probably different from that of the surrounding Mesozoic gneisses.     

High pressure transitions in the system KAlSi3O8-NaAlSi3O8

Phase relations in the system KAlSi₃O₈-NaAlSi ₃O₈ have been examined at pressures of 5–23 GPa and temperatures of 700–1200° C. KAlSi₃O₈ sanidine first dissociates into a mixture of wadeite-type K₂Si₄O₉, kyanite and coesite at 6–7 GPa, which further recombines into KAlSi₃O₈ hollandite at 9–10 GPa. In contrast, NaAlSi₃O₈ hollandite is not stable at 800–1200° C near 23 GPa, where the mixture of jadeite plus stishovite directly changes into the assemblage of calcium ferrite-type NaAlSiO₄ plus stishovite. Phase relations in the system KAlSi₃O₈-NaAlSi₃O₈ at 1000° C show that NaAlSi₃O₈ component gradually dissolves into hollandite with increasing pressure. The maximum solubility of NaAlSi₃O₈ in hollandite at 1000° C was about 40 mol% at 22.5 GPa, above which it decreases with pressure. Unit cell volume of the hollandite solid solution decreases with increasing NaAlSi₃O₈ component. The hollandite solid solution in this system may be an important candidate as a host mineral of K and Na in the uppermost lower mantle     

Measurement of elastic properties of single-crystal CaO up to 1200 K

The elastic moduli of a single-crystal calcium oxide, CaO, are measured in the temperature range from 300 to 1200 K (1.8 times of the Debye temperature) by the resonant sphere technique (RST). The lowest 18 modes are identified in the frequency range from 0.6 to 1.4 MHz for the vibrating spherical specimen, which is 5.6564 mm in diameter and 3.3493 g/cm³ in density at room temperature, and the resonant frequencies are traced as a function of temperature. The adiabatic elastic moduli are determined in the present temperature range from the observed frequencies by inversion calculations. Most of the elastic moduli, except forC ₁₂ modulus, decrease as temperature increases. The temperature curves ofC _s andC ₄₄ moduli cross at 372 K. This means that the CaO specimen has an isotropic elasticity at the temperature. The temperature derivatives (?C ₁₁/?T) _P and (?C _s/?T) _P become slightly less negative with temperature increase and (?C _s /?T) _P and (?C ₄₄/?T) _P are almost constant. Combining the present elastic data with thermal expansion and specimen heat capacity data of CaO, we present the temperature dependence of thermodynamic parameters important in the studies of earth's interior.     

Soil erosion and overland flow in Japanese cypress plantations: spatio-temporal variations and a sampling strategy

ABSTRACT

Many studies have focused on soil erosion in unmanaged Japanese cypress plantations because the sparse understory vegetation and litter covering the forest ground enhance soil erosion. In this study, soil erosion, litter, and overland flow measurements were conducted over 14 months to identify the spatio-temporal variation and examine the optimal sample size. Fifteen traps (each 0.25 m wide) were installed in line along the bottom of a 15-m-wide slope. Soil erosion and overland flow had large spatial variations as compared to litter. The temporal coefficient of variation of soil erosion and overland flow was highest during dry seasons, while smaller during wet seasons. The random sampling analysis showed that the rate of decrease in spatio-temporal variation became moderate as the sample size increased beyond six. This result indicated that the optimal sample size was five, the total width of which was equivalent to about 8% of the monitored slope width.     

Local equilibrium during the contact metamorphism of siliceous dolomites in Kasuga-mura,Gifu-ken,Japan

Metamorphism to intermediate-pressure granulite grade had a minimal effect on the geochemistry of layered gneisses in central Australia. The overall composition of the terrain is granodioritic and major element compositions have equivalents in igneous and sedimentary supracrustal rocks. K, Rb, Sr and probably Th concentrations, and K/Rb ratios are normal; the initial isotopic composition of Sr shows the usual range of crustal rocks. However, U is strongly depleted and was lost by a pervasive process, probably dehydration, rather than by anatexis. Comparison with other areas in which major chemical depletions and unusually low initial Sr isotopic ratios are postulated leads to alternative interpretations of these areas which do not involve large scale chemical migration. An intermediate composition for the lower crust may result from a high density of basic intrusions rather than chemical processes.     

Crustal structure in the Matsushiro Earthquake Swarm area

The crustal structure of the Matsushiro area, Central Japan, was studied in two profiles, A and B, with the explosion seismic method to obtain a better understanding of the physical processes of the Matsushiro Swarm Earthquakes. The layer with a velocity of 6.0 km/sec is extremely shallow and becomes deeper west of Chikuma River and around the southeastern end of profile B; there exists a faultlike structure in the most active area. The comparison of hypocenter distributions with the crustal structure shows that almost all swarm earthquakes have their hypocenters below the 6.0 km/sec layer and are confined to the region where this 6.0 km/sec layer is shallow. The velocity gradient in the 6.0 km/ sec layer is determined with certainty by the time-term analysis.

In the seismically most active region the anomalous structure is derived not only from the traveltime analysis but also from the amplitude studies; that is, the velocity and the Q-value are smaller than in other regions.     

Application of microtremor measurements to the estimation of earthquake ground motions in Kushiro city during the Kushiro-Oki earthquake of 15 january 1993

Microtremor measurements were conducted in Kushiro City, Hokkaido Island of Japan. The thickness of alluvial deposits in the central area of Kushiro City abruptly changes from 0 to 80 m. Predominant ground motion at a microtremor measuring site is represented by the spectral ratio, the ratio of Fourier amplitude spectrum of microtremor in the horizontal direction to that in the vertical direction. The peak frequency of the spectral ratio corresponds well to the predominant frequency estimated from the thickness of alluvial layer at each site. Based on a hypothesis that the spectral ratio can be regarded identical with a half of the amplification factor from diluvial bed rock to the ground surface, the strong ground motion due to the Kushiro-oki earthquake at each site is estimated. The method of estimation is verified by the comparison of the synthesized accelerogram with the recorded one at West Port of Kushiro. The results satisfactorily explain major damages and vibrations felt in Kushiro City during the earthquake.