Double seismic zones and stresses of intermediate depth earthquakes

Summary. Data from Japanese local seismograph networks suggest that the stresses in double seismic zones are in-plate compression for the upper zone and in-plate tension for the lower zone; the stresses do not necessarily appear to be down-dip. It may therefore be possible to identify other double seismic zones on the basis of data which indicate that events with differing orientations of in-plate stresses occur in a given segment of slab.
A global survey of published focal mechanisms for intermediate depth earthquakes suggests that the stress in the slab is controlled, at least in part, by the age of the slab and the rate of convergence. Old and slow slabs are under in-plate tensile stresses and the amount of in-plate compression in the slab increases with increasing convergence rate or decreasing slab age. Young and fast slabs are an exception to this trend; all such slabs are down-dip tensile. Since these slabs all subduct under continents, they may be bent by continental loading. Double seismic zones are not a feature common to all subduction zones and are only observed in slabs which are not dominated by tensile or compressive stresses.
Unbending of the lithosphere and upper mantle phase changes are unlikely to be the causes of the major features of double zones, although they may contribute to producing some of their characteristics. Sagging or thermal effects, possibly aided by asthenospheric relative motion, may produce the local deviatoric stresses that cause double zones.     

Organic models of interstellar grains

A number of experimental studies have been carried out to verify the claim that interstellar grains largely consist of organic material, including biological cells. Our spectroscopic studies on biological cells and organic extracts from carbonaceous compounds have failed to identify the well-known 2200 Å interstellar extinction peak with the organic material.     

The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism

Carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the Hida metamorphic terrain, central Japan, display typical metamorphic fluid-enhanced isotopic zonations. Isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion-enhanced isotopic exchange may control these profiles. Carbon and oxygen isotopic behaviour in grain boundaries is remarkably different. Oxygen isotopic troughs (¹⁸O depleted rims) around the calcite-grain boundaries are widely observed in this contact aureole, demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite. In contrast, no difference is observed in carbon isotopic profiles obtained from grain cores and rims. There is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation. Carbon chemical species such as CO₂ and CO₃ ions in metamorphic fluid migrate mainly through lattice diffusion. The carbon and oxygen isotope profiles may be modelled by diffusion into a semi-infinite medium. Empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes, and oxygen grain-boundary diffusion is ten times faster than oxygen lattice diffusion. Oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer. From the stability of wollastonite and the attainment of oxygen isotopic equilibrium, we suggest that diffusion of oxygen occurred through an aqueous fluid phase. The timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0.76 × 10⁶ years using the experimentally determined diffusion constant. Received: 14 January 1997 / Accepted: 23 April 1998     

Organic model of interstellar grains

Extinction efficiency of grains is calculated from the Mie formula on the premise that the grains are of organic composition. The optical constants adopted for the calculations are those ofE. coli, polystyrene and bovine albumin. The grain radiusa is assumed to obey a distribution of the formN(a) a ^– and the value of is chosen so as to make the calculated extinction curve match the observed interstellar extinction curve. Although the calculated curve gives a reasonably good fit to the observed extinction curve for wavelength less than 2100 Å, at longer wavelength region agreement is poor. It is concluded that another component is required for the organic model to be viable.     

Researches on the stability of porphyra-334 solution and its influence factors

1　Introduction　Ultravioletradiationisahighlyactivecomponentofsolarspectrum .Ultravioletradiationhasdetrimentaleffectsonlivingthingsexposedtosunlight ,includingthedestructionofDNA ,proteinsandothermolecules(Harm ,1980 ) ,inhibitionofphotosynthesisandgrow…     

Primary productivity in the fast ice area near syowa station,Antarctica, during spring and summer 1983/84

In situ measurements of the primary productivity of ice algae and phytoplankton were carried out in the fast ice area near Syowa Station (69°00S, 39°35E) during the austral spring and summer of 1983/84. Standing stock of ice algae reached a maximum of 45.1 mg chla m^–2 in late October. Phytoplankton standing stock attained a value of 3.57 mg chla m^–2 in mid-January. Primary production of ice algae in late October (7.64 mgC m^–2 hr^–1) was 14 times greater than that in mid-January (0.54 mgC m^–2 hr^–1). Production in the water column in mid-January (3.46 mgC m^–2 hr^–1) was 50 times greater than that in late October (0.07 mgC m^–2 hr^–1). These results indicate a substantial production by ice algae in the spring and by phytoplankton in the summer period.     

Graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms,Japan

This study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Graphitization can be parameterized using crystal structure and chemical and isotopic compositions. The extent of graphitization could be characterized mainly by temperature, duration of metamorphism and rock composition. We compared the graphitization trends for two metamorphic terrains, a contact aureole of the Kasuga area and a regional metamorphic terrain of high-temperature/low pressure type of the Ryoke metamorphic terrain in Northern Kiso area, Central Japan, and for two different lithologies (carbonate and pelite), using X-ray diffractogram, DTA-TG analysis, and chemical and stable isotope analyses. During contact metamorphism, graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks. The decreases in basal spacing d(002) of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400° C. Furthermore, carbon isotopic ratios of graphite in carbonate rocks also change to ¹³C-enriched values implying exchange with carbonates. The beginning of this enrichment of ¹³C in the carbonaceous matter coincides with an abrupt increase of the graphitization processes. Carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400° C. Carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well-crystallized graphite detritus. DTA-TG analysis is an effective tool for the distinction of detrital graphitic material. Two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the Kasuga contact aureole can be distinguished, about-28 and-24 regardless of the presence of detrital graphite, and were mainly controlled by depositional environment of the sediments. Graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole. In the low-temperature range, the differences in extent of graphitization between the two metamorphic regions is large. However, at temperatures higher than 600° C, the extent of graphitization in both regions is indistinguishable. The degree of graphitization is different in limestones and pelitic rocks from the Ryoke metamorphic terrain. We demonstrate that the graphitization involves a progressive re-construction process of the crystal structure. The sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three-dimensional structured graphite.     

Biological community and sediment fatty acids associated with the deep-sea whale skeleton at the Torishima Seamount

A whale skeleton was discovered on the flat-topped summit of the Torishima Seamount, 4037 m deep, northwest Pacific Ocean, during a dive by the submersibleShinkai 6500 in 1992. The skeleton was encrusted with mytilid mussels and harbored benthic animals such as galatheid crabs, echinoderms, sea anemones, and unidentifiable tube worms. The whale skeleton was revisited in 1993. Sediment samples were collected to outline the chemical-microbial distribution in the sediment associated with the skeleton. In the sediment, there was a gradient of sulfide concentration with the peak of 20 n moles per gram sediment just beneath a bone. Corresponding gradients were observed in thiosulfate-oxidizing enzyme activity, bacterial colony counts and fatty acid amounts. Direct analysis of the sediment fatty acid composition suggested the occurrence of methane-oxidizing bacteria and sulfur-reducing bacteria in close association with the whale skeleton. These observations imply that the methane and sulfides were formed during the saprogenic process and utilized for the chemosynthetic bacterial production to feed the whale skeleton-animal community.     

A neutron activation analysis of iridium concentration in Yamato carbonaceous chondrite

Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57 ± 0.06) g per gramme for the chondrite.