New discoveries in dynamics of an M8 earthquake-phenomena and their implications from the 2003 Tokachi-oki earthquake using a long term monitoring cabled observatory

At the 2003 Tokachi-oki earthquake of M8, seafloor phenomena such as a generation process of tsunami, seafloor uplifts, turbidity current, etc., were observed using a cabled observatory installed on the seafloor. The turbidity current was observed as a benthic storm caused presumably by the mainshock. The seafloor uplifts were observed at the mainshock and continuously after the mainshock. The uplifts were 0.35, 0.37, and 0.12 m for epicentral distances of 25.5, 31.4, and 81.7 km, respectively. After the mainshock, a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock. In this paper, we first show what was observed using the cabled observatory installed right above the focal area of the earthquake, and then we discuss to summarize these phenomena associated with the earthquake, its possible causes, and future directions in long term monitoring of seismogenic processes.     

Hydrogen, Oxygen and Sulfur Isotope Studies of Seafloor Hydrothermal System at the Desmos Caldera, Manus Back-arc Basin, Papua New Guinea: An Analogue of Terrestrial Acid Hot Crater-lake

Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ³⁴S values of native sulfur range from -6.5 to -9.3 %o. δ³⁴S values of H₂S and SO₄ in the hydrothermal fluid are -4.3 to -9.9 %o and +18.6 to +20.0 %o, respectively. These δ³⁴S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ³⁴S values and the acidic nature of the vent fluids suggest that volcanic SO₂ gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ³⁴S values of S-bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO₂ gas. The predicted δ³⁴S values of SO₂ agree with the measured whole rock δ³⁴S values. δD and δ¹⁸O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.     

Deterioration of eelgrass,Zostera marina L., meadows by water pollution in Seto Inland Sea,Japan

Survival of transplanted Zostera marina L. (eelgrass) and environmental conditions (water quality, bottom sediments, sedimentation on leaves and flow regime) were studied concurrently in the center, edge, and at the outside of a eelgrass meadow located in a eutrophic coastal zone in northern Hiroshima Bay, Seto Inland Sea, Japan. Eelgrass transplants at the outside of the meadow declined significantly, whereas those at the center were consistently well established. Silt content in the bottom sediments at the outside was higher than that at the center. The sediment was oxic from the surface to 2 cm deep at the center, whereas those at the edge and the outside were reductive almost from the surface. The sediment characteristics typical in eutrophic water seemed to be a factor responsible for the deterioration of eelgrass meadows. Although suspended solid concentrations in the water columns were almost the same, the amount of sediments deposited on leaves of eelgrass at the outside was higher than that at the center of the meadow. The amount of the deposition at the outside seems to be enough to inhibit photosynthesis; i.e. photosynthetic photon flux density (PPFD) available for eelgrass was only 36% of that without any deposition. The deposition in the center, however, was small enough to allow 84% of the original PPFD. Flow rates, determined at 30 cm above the bottom, a half height of average eelgrass, suggested that the rate at the outside was not enough to remove deposited sediments from the surface of eelgrass leaves. Thus, the large amount of sediment deposition caused by water pollution and/or eutrophication seemed to be another factor to inhibit the survival of eelgrass at the outside edge of the meadow.     

非海相双壳类江西蛤（Jiangxiella）首次发现于日本

首次报道日本西南部发现的晚三叠世非海相双壳类江西蛤（Jiangxiella)，并讨论这一发现的意义。认为原产于湘、赣、粤地区的江西蛤是地理分布极有限的土著属，它在日本西南部的发现表明当时该区与华南东部的古地理关系极为密切，可能原属同一地块。     

Late Mesozoic low-P/high-T metamorphism preceding emplacement of Cretaceous granitic rocks in the Gosaisho-Takanuki district, Abukuma metamorphic belt

Abstract The central part of Abukuma metamorphic belt consists of two geologic units, the Gosaisho Group and the Takanuki Group. Although the deformation styles differ between the Gosaisho and the Takanuki Groups, their rock facies show a gradual transition. In both Groups early regional low-pressure (over 3 kb) metamorphism has been overprinted by contact metamorphism. Evidence for the P/T condition of the regional metamorphism is recorded in cores of armored minerals. Metamorphic zones have been defined on mineral rim assemblages of meta-mafite, meta-pelite and meta-calc-siliceous schist and on the degree of graphitization of meta-pelite. The mineral-core chemistry of plagioclase, Ca-amphibole and garnet changes with increasing metamorphic grade, and indicates that the regional metamorphism of the Gosaisho Group took place in a high pressure region of the andalusite stability field. The Takanuki metamorphic rocks are structurally overlain by the Gosaisho Group and have undergone regional metamorphism whose conditions have passed near the triple point of Al-silicates and kyanite has crystallized. The contact aureoles in both groups are developed around middle Cretaceous granitic intrusions. Rims of plagioclase, Ca-amphibole and garnet overgrew on the mineral-cores during the contact metamorphism. The regional metamorphism began after the sedimentation of Jurassic chert and was succeeded by the contact metamorphism in the middle Cretaceous.     

Underground storage of carbon dioxide in depleted natural gas reservoirs and in useless aquifers

Depleted reservoirs of natural gas and petroleum can provide excellent traps for carbon dioxide. Deep aquifers, which are not used due to high salinity, can host larger amount of the carbon dioxide under their high formation pressure than natural gas and oir reservoirs. Small fraction of aquifers in sedimentary basins in the world are enough to host about 87 gigaton-C of carbon dioxide.

A preliminary technical and economical survey on the carbon dioxide injection system suggests that the energy requirement for carbon dioxide injection into subterranean aquifers is about 269 kWh/ton-C and that the investment and operation costs for system are 79 $/ton-C. By our preliminary cost estimation in Japan, the CO₂-emission-free electricity generation may become possible with a cost increase of 35% for natural-gas-fired power station, and of 60% for coal-fired-power station.     

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.     

Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano,Hawaii

Eighteen basalts and some volcanic gases from the submarine and subaerial parts of Kilauea volcano were analyzed for the concentration and isotope ratios of sulfur. By means of a newly developed technique, sulfide and sulfate sulfur in the basalts were separately but simultaneously determined. The submarine basalt has 700 ± 100 ppm total sulfur with δ³⁴S_Σs of $\text{0.7 ± 0.1 ‰}$. The sulfate/sulfide molar ratio ranges from 0.15 to 0.56 and the fractionation factor between sulfate and sulfide is $\text{+7.5 ± 1.5‰}$. On the other hand, the concentration and δ³⁴S_Σs values of the total sulfur in the subaerial basalt are reduced to 150 ± 50 ppm and $\text{?0.8 ± 0.2‰}$, respectively. The sulfate to sulfide ratio and the fractionation factor between them are also smaller, 0.01 to 0.25 and +3.0‰, respectively. Chemical and isotopic evidence strongly suggests that sulfate and sulfide in the submarine basalt are in chemical and isotopic equilibria with each other at magmatic conditions. Their relative abundance and the isotope fractionation factors may be used to estimate the $\text{?o}{}_2$ and temperature of these basalts at the time of their extrusion onto the sea floor. The observed change in sulfur chemistry and isotopic ratios from the submarine to subaerial basalts can be interpreted as degassing of the SO₂ from basalt thereby depleting sulfate and ³⁴S in basalt.The volcanic sulfur gases, predominantly SO₂, from the 1971 and 1974 fissures in Kilauea Crater have δ³⁴S values of 0.8 to 0.9%., slightly heavier than the total sulfur in the submarine basalts and definitely heavier than the subaerial basalts, in accord with the above model. However, the δ³⁴S value of sulfur gases (largely SO₂) from Sulfur Bank is 8.0%., implying a secondary origin of the sulfur. The δ³⁴S values of native sulfur deposits at various sites of Kilauea and Mauna Loa volcanos, sulfate ions of four deep wells and hydrogen sulfide from a geothermal well along the east rift zone are also reported. The high δ³⁴S values (+5 to +6%._o) found for the hydrogen sulfide might be an indication of hot basaltseawater reaction beneath the east rift zone.     

Meteoric hydrothermal origin of calcites in “Green Tuff” formations,Miocene age,Japan

Oxygen and carbon isotope compositions were determined for calcites from the Green Tuff formations of Miocene age in Japan. Values of ¹⁸O from 24 calcites in altered rocks from 5 districts range from –2 to +16_SMOW, in most cases from 0 to +8_SMOW. The low ¹⁸O values rule out the possibility of their low-temperature origin or any significant contribution of magmatic fluid in the calcite precipitation. These values, coupled with their mineral assemblages, suggest that the calcites formed from meteoric hydrothermal solutions which caused propylitic alteration after the submarine strata became emergent.Values of ¹³C from the calcites show a wide variation from –17 to 0_PDB. Calcites from different districts have different ranges of ¹³C values, indicating that there was no homogeneous reservoir of carbon at the time the calcite formed, and that the carbon had local sources. Carbon isotopic compositions of calcite within ore deposits in the Green Tuff formations range from –19 to 0_PDB, similar to those of calcite in the altered rocks in the same district, suggesting that the carbon in ore calcites was likely supplied from the surrounding rocks through activity of meteoric hydrothermal solutions.     

Oxygen isotope study of metamorphic and granitic rocks of the Yanai district in the Ryoke belt,Japan

¹⁸O/¹⁶O ratios have been obtained for 134 whole-rocks and minerals from metamorphic and granitic rocks of the Yanai district in the Ryoke belt, Southwest Japan. The ¹⁸O/¹⁶O ratios of pelitic rocks of the marginal metamorphic zone decrease progressively with increasing metamorphic grade. In the gneiss-granite complex (zone of migmatite [1]), the most characteristic feature of the rocks is that oxygen isotopic homogenization proceeds on both local and regional scales in parallel with “granitization” or chemical homogenization. Granitic rocks of various origin are fairly uniform in isotopic composition with δ ¹⁸O of quartz of 12 to 14‰ (SMOW) and δ ¹⁸O of biotite of 7 to 9‰ and are about 3 to 4‰ enriched in ¹⁸O compared to other Cretaceous granites of non-metamorphic terranes in Japan. The high ¹⁸O/¹⁶O ratios of granitic rocks of this district were discussed in relation to the ¹⁸O-depletion in metasediments. Oxygen isotopic fractionations among coexisting minerals from various rock-types of the gneiss-granite complex indicate that these minerals were formed under near isotopic equilibrium at a temperature of about 600 to 700° C. Some abnormal fractionations of quartz-biotite pairs also were obtained for rocks which had undergone a progressive ¹⁸O-depletion or ¹⁸O-enrichment. This is due to high resistivity of quartz and contrastive susceptibility of biotite to isotopic exchange during metamorphism and “granitization”.