Isotopic compositions of potassium and calcium in magnetic spherules from marine sediments

Isotopic compositions of potassium and calcium in individual magnetic spherules were determined. No significant anomaly was observed for potassium within twice the statistical error (2σ), although for calcium isotopes enrichments of⁴⁶Ca,⁴⁴Ca and⁴²Ca were observed in one spherule. The relative excess of⁴⁶Ca,⁴⁴Ca and⁴²Ca in the spherule agrees with the relative yield of spallogenic calcium isotopes observed in iron meteorites. This fact indicates that the enrichment in the calcium isotopes was caused by cosmic ray irradiation of the spherule in outer space.     

Statistical discrimination of foreshocks from other earthquake clusters

When earthquake activity begins, it may be a foreshock sequence to a larger earthquake, a swarm, or a simple main-shock-aftershock sequence. This paper is concerned with the conditional probability that it will be foreshock activity of a later larger earthquake, depending on the occurrence pattern of some early events in the sequence. The earthquake catalogue of the Japan Meteorological Agency (1926-1993, M_J≥4) is decomposed into a large number of clusters in time and space in order to compare statistical features of foreshocks with those of swarms and aftershocks. Using such a data set, Ogata, Utsu & Katsura (1995) revealed some discriminating features of foreshocks relative to the other types of clusters, for example the events' closer proximity in time and space, and a tendency towards chronologically increasing magnitudes, which encouraged us to construct models which forecast the probability of the earthquakes being foreshocks. Specifically, the probability is a function of the history of magnitude differences, spans between origin times and distances between epicentres within a cluster. For purposes of illustration, the models were fitted to the early part of the data (1926-1975) and the validity of the forecasting procedure was checked on data from the later period (1976-1993). Two procedures for evaluating the performance of the probability forecast are suggested. Furthermore, for the case where only a single event is available (i.e. either it is the first event in a cluster or an isolated event), we also forecast the probability of the event being a foreshock as a function of its geographic location. Then, the validity of the forecast is demonstrated in a similar manner. Finally, making use of the multi-element prediction formula, we show that the forecasting performance is enhanced by the joint use of the information in the location of the first event, and that in the subsequent interevent history in the cluster.     

The Global Stratotype Section and Point （GSSP） for the base of the Holocene Series/Epoch （Quaternary System/Period） in the NGRIP ice core

The Greenland ice core from NorthGRIP （NGRIP） contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision.     

Measurements of atmospheric hydroperoxides at a rural site in central Japan

Measurements of hydroperoxides (H₂O₂ and MHP) at ground level were made from 2012 to 2015 in Imizu City, Toyama Prefecture in central Japan. H₂O₂ and MHP concentrations ranged from 0.01 to 3.5 ppb and from below the level of detection (< 0.01 ppb) to 1.4 ppb, respectively. The concentrations of H₂O₂ and MHP were high in the summer and low in the winter. The H₂O₂ concentration was at its maximum in July and August, whereas the concentration of O₃ in the daytime was highest in May and June. The ratio of [H₂O₂]/[SO₂] presented clear seasonal variations. Many cases showed the condition of [H₂O₂] < [SO₂], called oxidant limitation especially in the cold months. Hydroperoxide concentrations in the rainwater were also high in the summer. The concentrations of MHP were much lower than those of H₂O₂ in the rain water. High concentrations of H₂O₂ (> 2.5 ppb) were detected in the summer during the inflow of air pollution. The concentrations of H₂O₂ were significantly high in July and August of 2013. The H₂O₂ was well correlated with the O₃ in July and August whereas there was no correlation between O₃ and H₂O₂ in May and June. There was a negative correlation between NO_X and H₂O₂.     

Growth and sedimentation of dust grains in the primordial solar nebula

Of the formation processes in the solar system, the process of growth and sedimentation of dust grains in the primordial solar nebula is investigated for a region near the Earth's orbit. The growth equation for dust grains, which are sinking as well as being in thermal motion, is solved numerically in the wide mass range between 10^?12 and 10⁶ g. Any turbulent motions in the nebula are assumed to have already decayed when the sedimentation begins. The numerical simulation shows that the growth and sedimentation proceed faster than was found by Kusaka et al. (1970) but in accordance with the estimate of Safronov (1969) owing to a cooperative interaction of the growth and the sedimentation; that is, at about 3 × 10³ years after the beginning of the growth and sedimentation a dust layer, composed of centimeter-sized grains, is formed at the equator of the solar nebula. Furthermore, the mass density of dust grains floating in the outer layers of the nebula is found to be of the order of 10^?5 after 10⁵ years compared with that before the sedimentation. From these results, it can be estimated that at about 5 × 10³ years after the beginning of sedimentation the dust layer breaks up owing to the onset of gravitational instability.     

High-resolution shallow seismic and ground penetrating radar investigations revealing the evolution of the Uemachi Fault system, Osaka, Japan

Abstract Ground penetrating radar (GPR) and high‐resolution shallow reflection seismic surveying were carried out to investigate the subsurface geology in and around the Uemachi Fault zone in the Yamato River area, Osaka, Japan. Shallow drilling in the area showed a major displacement event during the middle Pleistocene. The main Uemachi Fault plane could be clearly imaged on the seismic section, except for the most shallow 200 m. Several shallow normal fault planes with less displacement could be detected on both sides of the fault plane. GPR profiles confirmed the presence of several shallow normal faults within the area near the fault zone. These shallow faults could be followed in all of the GPR profiles crossing the fault zone. The integration of seismic section, GPR profiles and drilling data led to a conceptual model that explains the evolution of the Uemachi Fault system. The proposed model suggests the occurrence of several cycles of small vertical displacement along the deep part of the fault plane caused by the regional east–west compressional stress. The ductile nature of the shallow sedimentary cover and the absence of confining pressure in the shallow part allow for a considerable amount of plastic bending before failing in the shallow sedimentary layers. This bending generates stretching force within the shallow sedimentary cover, which in time, along with gravitational force, gives rise to the formation of the swarm of normal faults within the shallow layers near the fault zone. Some of the detected faults extend to a depth of less than 3 m below the ground surface, suggesting that the last tectonic activity along the fault plane may have occurred recently.     

Giant planet formation

The accumulation of giant planets involves processes typical for terrestrial planet formation as well as gasdynamic processes that were previously known only in stars. The condensible element cores of the gas-giants grow by solid body accretion while envelope formation is governed by stellar-like equilibria and the dynamic departures thereof. Two hypotheses for forming Uranus/Neptune-type planets — at sufficiently large heliocentric distances while allowing accretion of massive gaseous envelopes, i.e. Jupiter-type planets at intermediate distances — have been worked out in detailed numerical calculations: (1) Hydrostatic gas-accretion models with time-dependent solid body accretion-rates show a slow-down of core-accretion at the appropriate masses of Uranus and Neptune. As a consequence, gas-accretion also stagnates and a window is opened for removing the solar nebula during a time of roughly constant envelope mass. (2) Gasdynamic calculations of envelope accretion for constant planetesimal accretion-rates show a dynamic transition to new envelope equilibria at the so called critical mass. For a wide range of solar nebula conditions the new envelopes have respective masses similar to those of Uranus and Neptune and are more tightly bound to the cores. The transitions occur under lower density conditions typical for the outer parts of the solar nebula, whereas for higher densities, i.e. closer to the Sun, gasdynamic envelope accretion sets in and is able to proceed to Jupiter-masses.