Horizontal layered structure with heterogeneity beneath continents and island arcs from particle orbits of long-period P waves

We investigate the particle orbits of long-period (about 20 s) P waves observed with the global seismic network. By analysing 84 three-component seismograms recorded at 25 stations from 60 earthquakes occurring beneath 300 km, we quantitatively evaluate the orbits by three sets of eigenvalues and eigenvectors, using a covariance matrix method. The eigenvalues for P waves recorded at stations located on continents are explained by the standard horizontal layered structure model (iasp91). On the other hand, the orbits observed at stations close to island arcs are affected not only by the horizontal layered structure but also by heterogeneity due to subducting plates, mantle diapirs and so on. On the basis of a single-scattering model for a plane P wave, we quantify the heterogeneities by an isotropic scattering coefficient g0. Fitting the theoretical eigenvalues to the observed ones, we estimate g0 for the crust and upper mantle beneath continents to be less than 0.0005 km^-1, and the mean g₀ for the structure beneath island arcs to be about 0.0015 to 0.003 km^-1.     

The Ediacaran radiogenic Sr isotope excursion in the Doushantuo Formation in the Three Gorges area,South China

The Ediacaran period was one of the most important times for the evolution of life. However, the scarcity of well-preserved outcrops of Ediacaran rocks still leaves ambiguity in decoding ambient surface environmental changes and biological evolution.The Ediacaran strata in South China are almost continuously exposed, comprise mainly carbonate rocks with subordinate black shales and sandstones, and they contain many fossils, suitable for study of environmental and biological changes in the Ediacaran. We conducted drilling through the Doushantuo Fm at four sites in the Three Gorges area to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed ⁸⁷Sr/⁸⁶Sr and ⁸⁸Sr/⁸⁶Sr ratios of the fresh carbonate rocks, selected on the basis of microscopic observations and the geochemical signatures of Sr contents, Mn/Sr and Rb/Sr ratios, and δ¹⁸O values, with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS).The chemostratigraphy of the ⁸⁷Sr/⁸⁶Sr ratios of the drilled samples displays a smooth curve and two large positive shifts during Ediacaran time. The combination of the detailed chemostratigraphies of δ¹³C, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values and Mn and Fe contents enables us to decode the surface environmental changes and their causes in the Ediacaran. The first large positive excursion of ⁸⁷Sr/⁸⁶Sr occurred together with negative δ¹³C and positive δ¹⁸O excursions. The higher ⁸⁷Sr/⁸⁶Sr values indicate an enhancement of continental weathering, whereas the positive δ¹⁸O excursion suggests global cooling. Global regression due to global cooling enhanced the oxidative decay of exposed marine organic sediments and continental weathering. Accelerated influx of nutrients promoted primary productivity, resulting in oxidation of dissolved organic carbon (DOC), whereas active sulfate reduction due to a higher sulfate influx from the continents caused remineralization of the large DOC, both of which caused a negative δ¹³C anomaly. The 580 Ma Gaskiers glaciation accounts for the close correlation among the positive ⁸⁷Sr/⁸⁶Sr, negative δ¹³C and positive δ¹⁸O excursions.The second large positive shift of ⁸⁷Sr/⁸⁶Sr firstly accompanied a positive δ¹³C excursion, and continued through the Shuram δ¹³C negative excursion. The positive correlation of δ¹³C and ⁸⁷Sr/⁸⁶Sr values is consistent with an enhanced continental weathering rate due to continental collisions that built Trans-Gondwana mountain chains, and with a higher primary activity due to the enhancement of continental weathering and consequent higher nutrient contents in seawater. The accompanied increase in Mn and Fe contents implies a gradual decline of the seawater oxygen content due to more active aerobic respiration and oxidation of reductive materials flowing in the oceans. In the Shuram excursion, higher ⁸⁷Sr/⁸⁶Sr values and a transition from increase to decrease in Mn and Fe contents were accompanied by the large negative δ¹³C excursion. The higher ⁸⁷Sr/⁸⁶Sr values are the first compelling evidence for enhanced continental weathering, which was responsible for the large δ¹³C anomaly through the remineralization of the DOC by more active sulfate reduction due to a higher sulfate influx. Higher Mn and Fe contents in the early and middle stages of the excursion suggest a decline in the oxygen content of seawater due to oxidative decay of the DOC, whereas in the late stages the decrease in Mn and Fe contents is consistent with oceanic oxygenation.The emergence of Ediacara biota after the Gaskiers glaciation and the prosperity of the latest Ediacaran is concomitant with the formation of more radiogenic seawater with high ⁸⁷Sr/⁸⁶Sr values, suggesting that enhanced continental weathering, and the consequent higher influx of nutrients, played an important role in biological evolution.     

Oceanic crust and Moho of the Pacific Plate in the eastern Ogasawara Plateau region

Abstract   To show the structure of oceanic crust and Moho around the eastern Ogasawara Plateau, we have analyzed industry-standard two-dimensional multichannel seismic reflection data. To obtain improved velocity models, phase information of seismic signals was used for velocity analysis and velocity models for oceanic crust above Moho were determined. We apply this velocity analysis technique to seismic reflection data around the eastern Ogasawara Plateau, with the result of clear images of structures within oceanic crust and Moho. South of the Ogasawara Plateau, Moho deepens proximal to the Plateau. Moho distal to the Plateau is ca 7 km below sea floor (bsf), whereas it is ca 10 km bsf near the Plateau. The characters of oceanic crust and Moho differ significantly north and south of the Plateau. To the north, the structure of oceanic crust is ambiguous, the sea floor is shallower and less smooth, and Moho is discontinuous. To the south, structures within oceanic crust and Moho are imaged clearly, and the sea floor is deeper. A strong Moho reflection south of the Plateau might represent a sharp boundary between layered gabbro and peridotite. However, discontinuous Moho reflections north of the Plateau might represent rough topography because of intensive magmatism or a gradual downward increase in velocity within a thick Moho transition zone. A fracture zone north of the Plateau also appears to separate oceanic crust and Moho of different characters, suggesting vigorous magmatism between the Plateau and the fracture zone, and that the Ogasawara Plateau and the fracture zone influenced the genesis of oceanic crust and upper mantle. Differences in acoustic characteristics to the north and south of the Plateau are apparent in profiles illuminated by seismic attributes.     

CCD Photometry of KZ Hya using the 45-CM Telescope in Paraguay

A SX Phe-type pulsating variable KZ Hya (HD94033) was observed with CCD set attached to the 45-cm reflector at Asuncion Astronomical Observatory in Paraguay. In the present work, 12 maximum phases were covered. A new ephemeris has been obtained, and the result suggests a probable change of the pulsation period of KZ Hya.     

New automated maritime telephone system

As one of the most valuable services in telecommunication service, NTT has developed a new automated maritime telephone system for public use. Calls between ship and land subscribers, or between one ship and another can be connected automatically by subscribers' dialing in the nationwide system. The new system adopts a lot of technical features such as automatic location registration, new signaling methods, etc. An outline of system performance and function is described herein.     

Time variations of hard X-rays from Sco X-1

Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation.     

Hydrogen isotopic substitution of solid methylamine through atomic surface reactions at low temperatures: A potential contribution to the D/H ratio of methylamine in molecular clouds

We experimentally studied hydrogen (H)–deuterium (D) substitution reactions of solid methylamine (CH₃NH₂) under astrophysically relevant conditions. We also calculated the potential energy surface for the H–D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18 kJ mol^?1, CH₃NH₂ reacted with D atoms to yield deuterated methylamines at 10 K, suggesting that the H–D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.     

Motion of iron sulfide inclusions inside a shock‐melted chondrule

Abstract— We calculated the trajectories of molten spheres of iron sulfide inclusions inside a melted chondrule during the nebular shock wave heating. Our calculations included the effects of high‐velocity internal flow in the melted chondrule and apparent gravitational force caused by the drag force of nebular gas flow. The calculated results show that large iron sulfide inclusions, which have radii 0.23 times larger than those of the parent chondrules, must reach the surface of the melted chondrule within a short period of time (<<1 s). This effect will provide us with very important information about chondrule formation by nebular shock wave heating.