Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region

A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes.     

Experimental study on the collisional disruption of porous gypsum spheres

Abstract— In order to study the catastrophic disruption of porous bodies such as asteroids and planetesimals, we conducted several impact experiments using porous gypsum spheres (porosity: 50%). We investigated the fragment mass and velocity of disrupted gypsum spheres over a wide range of specific energies from 3 times 10³ J/kg to 5 times 10⁴ J/kg. We compared the largest fragment mass (m₁/M_t) and the antipodal velocity (V_a) of gypsum with those of non‐porous materials such as basalt and ice. The results showed that the impact strength of gypsum was notably higher than that of the non‐porous bodies; however, the fragment velocity of gypsum was slower than that of the non‐porous bodies. This was because the micro‐pores dispersed in the gypsum spheres caused a rapid attenuation of shock pressure in them. From these results, we expect that the collisional disruption of porous bodies could be significantly different from that of non‐porous bodies.     

Temporal variability in physicochemical properties,phytoplankton standing crop and primary production for 7 years (2002–2008) in the neritic area of Sagami Bay,Japan

Seasonal and interannual variations in physicochemical properties (i.e., temperature, salinity, dissolved oxygen and dissolved inorganic nutrients), chlorophyll a (Chl-a), particulate carbon and nitrogen (PC and PN, respectively), and primary production were investigated in the neritic area of Sagami Bay, Kanagawa, Japan, from January 2002 to December 2008. These abiotic/biotic variables, except for NH₄ ⁺–N, repeated similar seasonal variations for all 7 years. On the basis of the analysis of data obtained on 167 sampling dates, depth-integrated primary production in this water can be easily estimated from Chl-a at the surface using the regression equations obtained in the present study. Intermittently high values of dissolved inorganic nutrients, Chl-a, PC, PN and primary productivity at the surface during the summer stratified period were induced by high freshwater discharge from the rivers after rainfalls and by the expansion of nutrient-rich Tokyo Bay Water. Temperature, salinity and dissolved inorganic nutrients showed drastic variations within a scale of a few days and/or weeks, and these variations were related to sea levels that represent the intrusion of the Kuroshio Water, Intermediate Oyashio Water or deep water from the continental slope. However, there was no consistent trend in the variations in Chl-a, PC, PN and primary production due to the complex effects of these waters.     

Measurements in a heated turbulent wall jet on a concave wall

The paper contains the results of extensive single-point hot-wire and resistance-thermometer measurements in a wall jet on a heated concave wall with an external free stream. It is found that the turbulence in the inner (wall) and outer layers is sensitive to the distortion produced by the curved wall, broadly confirming current views of these effects. The effect on the turbulence of streamline curvature is stabilising in the outer layer, destabilising in the inner. Consequently the point of zero shear stress is closer to the point of maximum mean velocity than in flat and convex wall jets with which these new results are compared. The rate of growth is about 80% of that of the equivalent flat wall flow, and about half that of the convex wall flow. Changes in the wall shear stress and heat flux, which are increased relative to the flat wall flow, are significant but less than the changes in the corresponding convex wall flow. The greatest changes occur in the triple products.List of Symbols c _f skin friction coefficient, 2 _w / U _M ² - q ² u ² +v ²+w ² - R radius of curvature of wall - r radius of curvature - St Stanton number,-q _w /c _p U _M (T –T _w ) - T mean temperature - U streamwise mean velocity - U _J initial wall-jet velocity - U ₁ initial free-stream velocity - U ₀ U _M –U _PW - u, v, w fluctuating velocity components - x, y distances measured along and normal to the wall - y _0.5,y _M wall-jet thicknesses defined in the text - y _S ,y _T wall-jet thicknesses defined in the text - T T _W –T - shear-layer thickness - ₂ momentum thickness - temperature fluctuation - M point of maximum velocity - P potential flow - s point of zero shear stress - W wall value - free stream value     

Fossil fluid reservoir beneath a duplex fault structure within the Central Range of Taiwan: implications for fluid leakage and lubrication during earthquake rupturing process

In order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake, we examined exposed rocks in the Taiwan Slate belt, where the pressure and temperature conditions most resembled the hypocentre of the Chi-Chi earthquake, i.e. sub-greenschist facies. Field observations and composition analyses of the silicified vein-rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep-seated fluids. These fluids most likely come from the Taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions (or partial melting). In addition, the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting. It is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures.     

Spatial and Temporal Changes of Floating Population in China Between 1990 and 2000

By studying the county-level census data of 1990 and 2000, we analyzed the spatial and temporal changes in the floating population in China between 1990 and 2000. The results of the analysis revealed the following characteris- tics. First, the spatial distribution of the migrants (referred to as 'floaters' in this paper) became increasingly concentrated in the cities during the 1990s. Second, the number of floaters increased rapidly during this period, and the area in which the floaters settled expanded quickly into four population explosion belts: the coast, the Changjiang River Delta, the Beijing-Guangzhou Railway and national border belts. Third, the number of inter-province floaters increased rapidly and exceeded that of intra-province floaters in the 1990s. In addition, to obtain a quantitative relationship between the number of floaters and 10 socio-economic variables by using statistical methods and also to find the chiefly important pulling factors of the migration destination, the authors selected approximately 100 cities with the largest population of floaters. Consequently, we found that four factors-GDP, passenger trips per 10,000 persons, per capita GDP and foreign direct investment-could provide an explanation for 83.7% of the number of floaters in 2000. The GDP showed the highest correlation with the number of floaters, suggesting that a highly developed economy is the most important factor that attracts floaters. Furthermore, a fairly close relationship between the number of floaters and the GDP was also found in 2000 for all the counties.     

Petrogenesis of the EET 92023 achondrite and implications for early impact events

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low‐Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.     

Three‐dimensional texture of natural pseudotachylyte: Pseudotachylyte formation mechanism in hydrous accretionary complex

Melt‐origin pseudotachylyte is the most reliable seismogenic fault rock. It is commonly believed that pseudotachylyte generation is rare in the plate subduction zone where interstitial fluids are abundant and can trigger dynamic fault‐weakening mechanisms such as thermal pressurization. Some recent studies, however, have discovered pseudotachylyte‐bearing faults in exhumed ancient accretionary complexes, indicating that frictional melting also occurrs during earthquakes in subduction zones. To clarify the pseudotachylyte generation mechanism and the variation of slip behavior in the plate subduction zone, a pseudotachylyte found in the exhumed fossil accretionary complex (the Shimanto Belt, Nobeoka, Japan) was re‐focused and microscopic and three‐dimensional observations of the pseudotachylyte‐bearing fault were performed based on optical, electron, and X‐ray microscope images. Based on the patterns contained in the fragment, the pseudotachylyte is divided into four domains, although no clear domain boundaries or layering structures are not found. Three‐dimensional observation also suggests that the pseudotachylyte were fragmented or isolated by cataclasite or carbonate breccia. The pseudotachylyte was rather injected into the surrounding carbonate breccia, which is composed of angular fragments of the host rock and a matrix of tiny crystalline carbonate. The pseudotachylyte volume was extracted from the X‐ray microscope image and the heat abundance consumed by the pseudotachylyte generation was estimated at 2.18 MJ/m², which can be supplied during a slip of approximately 0.5 m. These observations and calculations, together with the results of the previous investigations, suggest hydrofracturing and rapid carbonate precipitation that preceded or accompanied the frictional melting. Dynamic hydrofracturing during a slip can be caused by rapid fluid pressurization, and can induce abrupt decrease in fluid pressure while drastically enhancing the shear strength of the shear zone. Consequently, frictional heating would be reactivated and generate the pseudotachylyte. These deformation processes can explain pseudotachylyte generation in hydrous faults with the impermeable wall rock.     

Petrology of the diamond-grade eclogite in the Kokchetav Massif, northern Kazakhstan

Abstract The Kokchetav Massif of northern Kazakhstan is unique because of the abundant occurrence of microdiamond inclusions in garnet, zircon and clinopyroxene of metasediments. In order to determine precise pressure–temperature (P–T) conditions, we have systematically investigated mineral inclusions and the compositions of major silicates in Ti–clinohumite–garnet peridotite and diamond-grade eclogite from Kumdy–Kol. It was found that garnet peridotites from Kumdy–Kol contain assemblages of garnet, olivine, Ti–clinohumite and ilmenite. The garnet contains inclusions that are indicative of both ultrahigh pressure (UHP) and retrograde conditions. Inclusions of hydrous phases such as chlorite, amphibole and zoisite were formed at the post-UHP stage. The study also found that eclogite from Kumdy–Kol contains albite–augite symplectites after omphacitic pyroxene. The core of pyroxene (sodic augite) contains high K₂O (up to 1wt%; average 0.24wt%). Phengite is included in the core. Applying the K₂O-in-augite geobarometry, which is based on recent experiments, and the garnet–clinopyroxene (Grt–Cpx) geothermometer for peak metamorphism, the eclogites yield P–T estimates of > 6 GPa and > 1000 °C, and the diamond-grade eclogites yield lower temperature estimates at 900–1000 °C and 5 GPa.