Seasonal variation of atmospheric 210Pb and Al in the western North Pacific region

The atmospheric concentration of ²¹⁰Pb was determined for two years at six stations in the western North Pacific region. The following results were obtained and discussed by comparing them with those of Al. The atmospheric concentration of ²¹⁰Pb varied widely from week to week, but the degree of variation was about a half that of Al. Contrary to Al, the year-to-year variation of ²¹⁰Pb was not pronounced and its seasonal variation was well expressed by a sine curve. The ²¹⁰Pb concentration did not show a marked latitudinal variation and its base-line concentration was high in the surface air over the North Pacific. These suggest that atmospheric ²¹⁰Pb has a longer residence time, due to its transportation through higher altitudes and deposits much more evenly onto the Earth's surface and the ocean, as compared with Al in mineral dust which is larger in size in the source region.     

Estimation of maximum temperature of mudstone by two kinetic parameters; epimerization of sterane and hopane

A geochemical method for estimation of the maximum temperature of mudstones is proposed. The extents of epimerization of the sterane and the hopane are used. The temperature function is:

$\text{T}{}_{\mathrm{max.}}\text{(°C) =}\text{6060}\text{15.0?In(dU}\text{dU}\text{dV)}\text{?273}$

where U = ln (1 ? α/0.54), V = ln(1 ? β/0.61), α = 20S-/20S- + 20R-24-ethyl-5α(H), 14α(H), 17α(H)-cholestane(C₂₉-sterane) and β = 22S-/22S- + 22R-17α(H), 21β(H)-bishomohopane(C₃₂-hopane). The value of dU/dV can be obtained from the tangent to the evolution curve in the UversusV. This temperature function is applicable to the temperature analysis in the range of 50°C–150°C.     

Elastic properties of a single-crystal forsterite Mg2SiO4, up to 1,200 K

Elastic moduli of forsterite were measured between 300 and 1,200 K (? 1.6 times the Debye temperature) by the Rectangular Parallelepiped Resonance method. All the moduli decrease regularly with temperature. A summary of the results is as follows:

Factors governing the flow lineation of a large-scale pyroclastic flow — An example in the ata pyroclastic flow deposit,Japan

Schmincke andSwanson (1967) explained laminar flowage structures as indicators for flow direction of pyroclastic flows that show a radial flow pattern away from the source. Several other authors have reported similar examples, but the influence of pre-flow topographic relief has not been analyzed. Flow lineations were measured for the Ata pyroclastic flow deposit, southwestern Japan. This deposit has covered an undulating basement topography. Preferred orientation of crystals and lithic fragments were measured on thin sections cut parallel to sedimentary layering. The following three factors which control the flow lineation have been recognized. 1) Flow lineations oriented radially away from the source, as described by previous authors, were obtained only for samples collected from the surface of the pyroclastic flow plateau where the basement valleys were nearly filled by earlier flow units. 2) Lineations near the floor of narrow valleys were parallel to the strike of the valley. 3) Flow lineations near the wall of valleys tend to be parallel to the dip of the valley walls. These data suggest that the initial radial movement of pyroclastic flows from the source gradually changes direction to parallel the strike of deep valleys due to confining effect of valley wall. Flows which are trapped within a valley, tends to move towards the bottom of the valley just prior to the final settlement. After the basement topographic relief has been filled up with earlier flow units, the later flows maintain their original radial movement until final settlement.     

3-D velocity structure of the 2003 Bam earthquake area (SE Iran): Existence of a low-Poisson's ratio layer and its relation to heavy damage

To understand the generation mechanism of the Bam earthquake (Mw 6.6), we studied three-dimensional V_P, V_S and Poisson's ratio (σ) structures in the Bam area by using the seismic tomography method. We inverted accurate arrival times of 19490 P waves and 19015 S waves from 2396 aftershocks recorded by a temporal high-sensitivity seismic network. The 3-D velocity structure of the seismogenic region was well resolved to a depth of 14 km with significant velocity variations of up to 5%. The general pattern of aftershock distribution was relocated by using the 3-D structure to delineate a source fault for a length of approximately 20 km along a line 4.5 km west of the known geological Bam fault; this source fault dips steeply westward and strikes a nearly north–south line. The main shallow cluster of aftershocks south of the city of Bam is distributed just under the minor surface ruptures in the desert. The 3-D velocity structure shows a thick layer of high V_S and low σ (minimum: 0.20) at a depth range of 2–6 km. The deeper layer, with a thickness of about 2 km, appears to have a low V_S and high σ (maximum: 0.28) from 6 km depth beneath Bam to a depth of 9 km south of the city. The inferred increase of Poisson's ratio from 2 to 10 km in depth may be associated with a change from rigid and SiO₂-rich rock to more mafic rock, including the probable existence of fluids. The main seismic gap of aftershock distribution at the depth range of 2 to 7 km coincides well with the large slip zone in the shallow thick layer of high V_S and low σ. The large slip propagating mainly in the shallow rigid layer may be one of the main reasons why the Bam area suffered heavy damage.     

Os, Nd, and Sr isotopic and chemical compositions of ultramafic xenoliths from Kurose, SW Japan: Implications for contribution of slab-derived material to wedge mantle

We examined seven ultramafic xenoliths from 1~3 Ma alkali olivine basalt reefs near the Eurasian continent and one sample of the host alkali basalt to identify the mantle wedge material and to constrain the origin and evolution of mantle beneath SW Japan. Six xenoliths are from Kurose and one xenolith is from Takashima, northern part of the Kyushu islands, SW Japan. The Sr and Nd isotopic ratios vary from 0.70416 to 0.70773 and from 0.51228 to 0.51283, respectively. The Kurose and Takashima xenoliths have higher Sr isotopic ratios and lower Nd isotopic ratios than those of the peridotite xenoliths from the other arc settings such as Simcoe and NE Japan.

The Kurose xenoliths have less radiogenic Os isotopic ratios (¹⁸⁷Os/¹⁸⁸Os = 0.123–0.129) than the primitive upper mantle (PUM) estimate and limited variation compared to the other arc xenoliths. Their Os isotope compositions are rather similar to the ultramafic xenoliths from NE and east China. In addition, the samples of the Kurose and Takashima xenoliths plot along a mixing line between ultramafic xenoliths from SE and NE China and a slab component in Sr–Nd–Os isotopic space. Our results suggest that fragments of continental lithospheric mantle from the China craton may exist beneath Kurose and Takashima after the Sea of Japan expansion when the Japanese islands were rifted away from the Eurasian continent during Miocene. Later magmatism due to subduction of the Philippine Sea Plate beneath the SW Japan arc around 15 Ma ago may have introduced fluids or melts derived from slab component, interpreted to be oceanic sediments rather than altered oceanic crust, that possibly modified the original composition of the lithospheric mantle sampled by the peridotite xenoliths from Kurose and Takashima.     

Topographic characterization of seismic networks using topographic position index and Voronoi tiles: a case of the Hokuriku region,Japan

Usually, seismic record stations are established in various topographic slope positions, from valleys to ridges. In most previous studies, topographic amplification factor (TAF) is proposed as one of the indicators of earthquake wave amplification which can lead to overestimation of earthquake magnitudes in seismic networks. This paper uses an indicator called the “Topographic Position Index” for topographic characterization of seismic stations in the Hokuriku region, Japan, and deals with a seismic individuation method through Voronoi tessellation, which is a spatial approach, to propose suitable sites for topographically unbiased or less-biased seismic stations.     

Potential Influence of Ocean Acidification on Deep-Sea Fe–Mn Nodules and Pelagic Clays: An Improved Assessment by Using Artificial Seawater

In order to assess the potential risk of metal release from deep-sea sediments in response to pH decrease in seawater, the mobility of elements from ferromanganese (Fe–Mn) nodules and pelagic clays was examined. Two geochemical reference samples (JMn-1 and JMS-2) were reacted with the pH-controlled artificial seawater (ASW) using a CO₂-induced pH regulation system. Our experiments demonstrated that deep-sea sediments have weak buffer capacities by acid–base dissociation of surface hydroxyl groups on metal oxides/oxyhydroxides and silicate minerals. Element concentrations in the ASW were mainly controlled by elemental speciation in the solid phase and sorption–desorption reaction between the charged solid surface and ion species in the ASW. These results indicated that the release of heavy metals such as Mn, Cu, Zn and Cd should be taken into consideration when assessing the influence of ocean acidification on deep-sea environment.     

Neutron diffraction study of aluminous hydroxide δ-AlOOD

We have determined the position of deuterium atoms in δ-AlOOD by neutron powder diffraction at ambient pressure. As previously reported by theoretical and experimental studies, the deuterium atoms are located in the tunnel formed by the chains of AlO₆ octahedra. The data are best fit with the P2₁ nm structure, producing bond lengths of D–O1 of 1.552(2) Å, O2–D of 1.020(2) Å and O1–O2 of 2.571(2). This study confirms that the hydrogen bond is asymmetric at ambient conditions in agreement with recent single-crystal synchrotron study for δ-AlOOH.