Diffusion and sorption of Cs, I and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Clay-based modeling approach

Diffusion and sorption behaviors of cationic Cs⁺, anionic I⁻ and neutral HTO in samples of the Wakkanai Formation from the Horonobe underground research laboratory (URL), Japan, were investigated as a function of ionic strength (I) of synthetic groundwater by through-diffusion and batch sorption experiments and mechanistic modeling. The effective diffusivities (D_e) measured by through-diffusion experiments showed cation excess and anion exclusion effects, which were strongly dependent on I; D_e for Cs⁺ decreased as I increased, D_e for I⁻ showed the opposite dependency and D_e for HTO showed no dependence. The sorption of Cs⁺ measured by through-diffusion and batch sorption experiments were described by Freundlich isotherms with consistent parameters and decreased with I as a result of competitive ion exchange.Diffusion and sorption behaviors were interpreted by assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The component additive (CA) sorption model, which includes illite and smectite contents and their ion exchange constants, provided a reasonable account of the Cs⁺ sorption trends measured as functions of I and Cs concentration. The diffusion model was developed by coupling the electrical double layer (EDL) model, describing the change of ionic concentrations (cation excess and anion deficit) and viscoelectric effects caused by electrostatic interaction at negatively charged clay surfaces, and a simplified pore model assuming one type of pore shape and includes their size distribution. When averaging the electrostatic effects by using the pore surface area distribution, the model could predict the cation excess and anion exclusion effects, and its dependence on I reasonably well. This result implies the nanoscale pores dominating the pore surface area can strongly impact on ionic diffusion in argillaceous rocks. The clay-based modeling approach described here provides a useful tool to predict ionic diffusion and sorption in argillaceous rocks.     

http://www.sciencedirect.com/science/article/pii/S167498711200148X

The Earth was born from a giant impact at 4.56 Ga. It is generally thought that the Earth subsequently cooled, and hence shrunk, over geologic time. However, if the Earth's convection was double-layered, there must have been a peak of expansion during uni-directional cooling. We computed the expansion-contraction effect using first principles mineral physics data. The result shows a radius about 120 km larger than that of the present Earth immediately after the consolidation of the magma-ocean on the surface, and subsequent shrinkage of about 110 km in radius within about 10 m.y., followed by gradual expansion of 11 km in radius due to radiogenic heating in the lower mantle in spite of cooling in the upper mantle in the Archean. This was due to double-layered convection in the Archean with final collapse of overturn with contraction of about 8 km in radius, presumably by the end of the Archean. Since then, the Earth has gradually cooled down to reduce its radius by around 12 km. Geologic evidence supports the late Archean mantle overturn ca. 2.6 Ga, such as the global distribution of super-liquidus flood basalts on nearly all cratonic fragments (>35 examples). If our inference is correct, the surface environment of the Earth must have undergone extensive volcanism and emergence of local landmasses, because of the thin ocean cover (3–5 km thickness). Global unconformity appeared in cratonic fragments with stromatolite back to 2.9 Ga with a peak at 2.6 Ga. The global magmatism brought extensive crustal melting to yield explosive felsic volcanism to transport volcanic ash into the stratosphere during the catastrophic mantle overturn. This event seems to be recorded by sulfur mass-independent fractionation (SMIF) at 2.6 Ga. During the mantle overturn, a number of mantle plumes penetrated into the upper mantle and caused local upward doming of by ca. 2–3 km which raised local landmasses above sea-level. The consequent increase of atmospheric oxygen enabled life evolution from prokaryotes to eukaryotes by 2.1 Ga, or even earlier in the Earth history.     

Soil H<Subscript>2</Subscript> and CO<Subscript>2</Subscript> Surveys at Several Active Faults in Japan

Soil H₂ and CO₂ surveys were carried out along seven active faults and around the aftershock region of the 2000 Tottori-ken Seibu earthquake in Japan. Diffuse CO₂ effluxes were also measured along one fault and around the 2000 aftershock region. The results show highly variable H₂ concentration in space and time and it seems that the maximum H₂ concentration at each active fault correlates with fault activity as exemplified by the time of the latest big earthquakes. Even though observed H₂ concentrations in four faults were markedly lower than those collected previously in the latter half of the 1970s, it is evident that the higher H₂ concentrations in this study are due to the addition of the fault gases. Comparing the chemical composition of trapped gases (H₂: 5–20% and CO₂/H₂: 0.5–12) in fractured rocks of drill cores bored at the Nojima fault, a soil gas sample with the highest H₂ concentration showed large amounts of the trapped fault gas, diluted with atmospheric component. The profile experiment across a fracture zone at the Yamasaki fault showed higher H₂ concentrations and lower CO₂/H₂ ratios as was observed in soil gas from the fracture zone. A few days after the 2000 Tottori-kei Seibu earthquake, no CO₂ effluxes related to the occurrence of earthquakes were observed at the aftershock region. However, only above the epicenter zone, relatively high H₂ concentrations in soil gases were observed.     

Field experiments on remediation of coastal sediments using granulated coal ash

Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L⁻¹ in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment.     

Limestone of the Daiichi Kashima Seamount and the fate of a subducting guyot: fact and speculation from the Kaiko “Nautile” dives

The Daiichi-Kashima Seamount subducting in the Japan Trench has two reef-capped flat tops with different depths, which are bounded by a nearly straight scarp. The western (inboard) crest is 5300–5450 m deep, and the eastern (outboard) one is 3880–4000 m deep.

A variety of shallow-water reefoid limestones studied by the Kaiko “Nautile” dives not only confirms the similarity in thickness and lithologies, but also establishes an approximate biostratigraphic correlation between the two reefoid caps, based for the first time on the orbitolinid foraminifers (Orbitolina (Mesorbitolina) parva from the western block and O. (M.) texana from the eastern block).

This conclusion supports the interpretation that the present topography of the seamount has resulted from a subduction-induced faulting of a once single reef-capped guyot. A plausible scenario of the fate of a subducting Early Cretaceous guyot in the Western Pacific is outlined as exemplified by the Daiichi-Kashima Seamount.     

Inter‐annual variations and factors controlling evapotranspiration in a temperate Japanese cypress forest

This study was undertaken to evaluate the effects of climatic variability on inter‐annual variations in each component of evapotranspiration (ET) and the total ET in a temperate coniferous forest in Japan. We conducted eddy covariance flux and meteorological measurements for 7 years and parameterized a one‐dimensional multi‐layer biosphere‐atmosphere model (Kosugi et al., 2006 ) that partitions ET to transpiration (Tr), wet‐canopy evaporation (E_wet), and soil evaporation (E_soil). The model was validated with the observed flux data. Using the model, the components of ET were estimated for the 7 years. Annual precipitation, ET, Tr, E_wet, and E_soil over the 7 years were 1536 ± 334 mm, 752 ± 29 mm, 425 ± 37 mm, 219 ± 34 mm, and 108 ± 10 mm, respectively. The maximum inter‐annual fluctuation of observed ET was 64 mm with a coefficient of variance (CV) of 2.7%, in contrast to relatively large year‐to‐year variations in annual rainfall (CV = 20.1%). Tr was related to the vapour pressure deficit, incoming radiation, and air temperature with relatively small inter‐annual variations (CV = 8.2%). E_soil (CV = 8.6%) was related mainly to the vapour pressure deficit. E_wet was related to precipitation with large inter‐annual variations (CV = 14.3%) because of the variability in precipitation. The variations in E_wet were counterbalanced by the variations in Tr and E_soil, producing the small inter‐annual variations in total ET. Copyright © 2016 John Wiley & Sons, Ltd.     

Space—time correlations between inland earthquakes in central Japan and great offshore earthquakes along the Nankai trough: Implication for destructive earthquake prediction

Based on the tectonic framework of central Japan, including the surrounding submarine areas, the space-time relationship between destructive inland earthquakes of magnitudesM 6.4 or greater and great offshore earthquakes along the Nankai trough was examined. From east to west, four tectonic lines are defined as lines linking active faults: the Itoigawa-Shizuoka tectonic line (ISTL), the Tsurugawan-Isewan tectonic line (TITL), the Hanaore-Kongo fault line (HKFL), and the Arima-Takatsuki tectonic line (ATTL). The TITL divides central Japan into the Chubu and Kinki districts, and probably extends southward to the Nankai trough. The Chubu district is subdivided into four blocks by boundary lines linking NW-SE trending active faults having left-lateral strike slip. In the Kinki district, N-S trending, active reverse, steep-dip faults are dominant in the triangular region north of the Median Tectonic line, between the TITL and HKFL, forming a basin-and-range province.

Starting from 1586 A.D., a seismic space-time sequence of high seismic activity in the Chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central Japan was identified. The sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the Nankai trough. It was also found that a destructive earthquake tends to occur on the HKFL within 30 years after the occurrence on the TITL, and that the western Nankai trough generated great earthquakes ofM≥7.0 at intervals ranging from 8 to 49 years after the HKFL earthquakes. If the eastern Nankai trough is coupled with the western Nankai trough, a forthcoming greater earthquake measuringM 8.5 may be expected. Since such great earthquakes are always accompanied by large tsunamis, much attention should be focussed on possible tsunami disasters along the Pacific coast of central Japan.

Based on its tectonic structure, a tectonic model of central Japan is proposed. The seismic space-time sequence, which attempts to explain the cause of the sequential earthquake generation, is also discussed.