Characteristics of isolated hybrid tremor (HBT) during a calm activity period at Aso Volcano

Isolated-type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed during the fumarolic activity stage at Aso Volcano. These isolated tremors are called hybrid tremors (HBT) and comprise two parts: an initial part named the “HF-part” with a dominant frequency in the high-frequency region (approximately 10 Hz) and the following part named the “LF-part” with a dominant frequency in the low-frequency region (approximately 2 Hz). The LF-part is observed after the HF-part, and the HBT is accompanied by a long-period tremor (LPT). Hypocenters and source parameters are estimated using seismograms recorded at 64 stations around Nakadake crater. The amplitude distributions of all HF-parts have almost similar trends. Similarly, the amplitude distributions of all LF-parts have almost similar trends. However, the amplitude distributions of HF- and LF-parts are not similar. From these results, we proposed that the hypocenters and source parameters of HF- and LF-parts are not common, but each of them have common hypocenters and source parameters. The hypocenter region of HF-parts was estimated to be just beneath the fumarole region south of the 1st crater: the volume fluctuation is the major source factor. The hypocenter region of LF-parts is estimated to be at a depth of approximately 300 m beneath the first crater: the strike–slip component is the major source parameter. The hypocentral depth of LF-parts is located at the upper end of the crack estimated to be the source of the LPTs. The LPTs and HBTs are observed almost simultaneously. We consider that volcanic fluid is involved in the source mechanisms of both HBT and LPT.     

Morphology,structure and flow phases in soil pipes developing in forested hillslopes underlain by a Quaternary sand–gravel formation,Hokkaido, northern main island in Japan

Preferential flow pathways, such as soil pipes, are usually present in the soil of slopes. Subsurface flow through the soil pipes affects the subsurface drainage system and is responsible for sediment removal from slopes. However, a record of the inner structure of soil pipes has rarely been reported for slopes. A fibrescope examination of the morphology and flow phases in soil pipes in hillslopes underlain by a Quaternary sand–gravel formation provided the following information: the main pores of the soil pipes ran mostly parallel with the slope gradient; the cross‐sections of the soil pipes were approximately circular; and occurred on a few occasions; with some triple junctions being present. In addition, both full flow and partly full‐depth conditions occurred simultaneously in the soil pipe. The full flow condition has long been used in hydrological studies to model the pipe flow mechanism. Both the full flow condition and the partly full‐depth condition, however, must be examined closely in order to evaluate the subsurface hydrology in heterogeneous soil and the hydrogeomorphological processes of subsurface hydraulic erosion. Copyright © 2000 John Wiley & Sons, Ltd.     

Energy balance above a boreal coniferous forest: a difference in turbulent fluxes between snow‐covered and snow‐free canopies

To evaluate the interactive effects of snow and forest on turbulent fluxes between the forest surface and the atmosphere, the surface energy balance above a forest was measured by the eddy correlation method during the winter of 1995–1996. The forest was a young coniferous plantation comprised of spruce and fir. The study site, in Sapporo, northern Japan, had heavy and frequent snowfalls and the canopy was frequently covered with snow during the study period. A comparison of the observed energy balance above the forest for periods with and without a snow‐covered canopy and an analysis using a single‐source model gave the following results: during daytime when the canopy was covered with snow, the upward latent heat flux was large, about 80% of the net radiation, and the sensible heat flux was positive but small. On the other hand, during daytime when the canopy was dry and free from snow, the sensible heat flux was dominant and the latent heat flux was minor, about 10% of the net radiation. To explain this difference of energy partition between snow‐covered and snow‐free conditions, not only differences in temperature but also differences in the bulk transfer coefficients for latent heat flux were necessary in the model. Therefore, the high evaporation rate from the snow‐covered canopy can be attributed largely to the high moisture availability of the canopy surface. Evaporation from the forest during a 60‐day period in midwinter was estimated on a daily basis as net radiation minus sensible heat flux. The overall average evaporation during the 60‐day period was 0·6 mm day⁻¹, which is larger than that from open snow fields. Copyright © 1999 John Wiley & Sons, Ltd.     

Visualising Crime Clusters in a Space‐time Cube: An Exploratory Data‐analysis Approach Using Space‐time Kernel Density Estimation and Scan Statistics

For an effective interpretation of spatio‐temporal patterns of crime clusters/hotspots, we explore the possibility of three‐dimensional mapping of crime events in a space‐time cube with the aid of space‐time variants of kernel density estimation and scan statistics. Using the crime occurrence dataset of snatch‐and‐run offences in Kyoto City from 2003 to 2004, we confirm that the proposed methodology enables simultaneous visualisation of the geographical extent and duration of crime clusters, by which stable and transient space‐time crime clusters can be intuitively differentiated. Also, the combined use of the two statistical techniques revealed temporal inter‐cluster associations showing that transient clusters alternatively appeared in a pair of hotspot regions, suggesting a new type of “displacement” phenomenon of crime. Highlighting the complementary aspects of the two space‐time statistical approaches, we conclude that combining these approaches in a space‐time cube display is particularly valuable for a spatio‐temporal exploratory data analysis of clusters to extract new knowledge of crime epidemiology from a data set of space‐time crime events.     

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed,northern Japan

Surface flow and suspended sediment discharge from the head hollow of the Jozankei Experimental Watershed in Hokkaido, northern Japan, were measured to clarify the implications of subsurface hydrology for soil movement. Subsurface discharges during the extremely large storms of 1993 to 1994 were measured in a V-notch weir installed at a natural spring near the bottom of the head hollow, and shallow groundwater levels were observed in the wells excavated in the hollow. Sediment samples whose particle size range from 0·001 to 0·1 mm were manually and automatically collected at 15 to 60 min intervals, by use of 1 or 21 polyethylene bottles. Maximum concentration and flux of suspended sediment during the storms preceded the peak discharge of subsurface flow by several hours. Neither the changes in concentration (mg l⁻¹) nor flux (mg s⁻¹) of suspended sediment coincided with those in subsurface discharge (l s⁻¹). Furthermore, sediment concentration was poorly correlated with the rate of change in subsurface discharge (l s⁻²) during the rising limb of the hydrograph. Suspended sediment flux during the acceleratory limb, however, was closely correlated with the rate of change in subsurface discharge. The relationship between suspended sediment flux and rate of change in subsurface discharge were in inverse proportion to initial subsurface discharge before the storm runoff and they represented rare seasonal variation. Subsurface hydraulic erosion and transport of suspended sediment resulting from changes in rate of change in subsurface discharge actively occur during the acceleratory rising limb of the hydrograph. Accordingly, subsurface hydraulic erosion during the acceleratory rising limb of the hydrograph can be physically understood by analysing suspended sediment flux associated with rate of change in subsurface discharge and initial subsurface discharge. © 1997 John Wiley & Sons, Ltd.     

Simple DEM-Based Methods to Delineate Channel Networks for Hydrogeomorphological Mapping

To delineate channel networks from DEMs regardless of landform type, this article proposes a new method using slope-weighted flow accumulation. To validate the method, SRTM-3, a global DEM dataset with a resolution of approximately 90 m, was used for analysis of the Loess Plateau, China. Channel networks delineated with and without slope-weighted flow accumulation were derived in both uplands and hilly lands for comparison. In the weighted flow accumulation method, the thresholds for delineating the channels were defined by detecting a turning point in the frequency distribution of the weighted flow accumulation function or by visual similarity with drainage channels extracted from topographic maps. The channel networks delineated with weighting showed closer correlation with a topographic map than the channel networks without weighting, despite the differences in thresholds. Moreover, the channel networks delineated with weighting represented the differences between landform types, while the channel networks without weighting did not. Weighting on the basis of the slope angle shows promise as a general channel delineation method which reflects the actual topography due to its hydrogeomorphological functions.     

Heating experiments of the Tagish Lake meteorite: Investigation of the effects of short‐term heating on chondritic organics

We present in this study the effects of short‐term heating on organics in the Tagish Lake meteorite and how the difference in the heating conditions can modify the organic matter (OM) in a way that complicates the interpretation of a parent body's heating extent with common cosmothermometers. The kinetics of short‐term heating and its influence on the organic structure are not well understood, and any study of OM is further complicated by the complex alteration processes of the thermally metamorphosed carbonaceous chondrites—potential analogues of the target asteroid Ryugu of the Hayabusa2 mission—which had experienced posthydration, short‐duration local heating. In an attempt to understand the effects of short‐term heating on chondritic OM, we investigated the change in the OM contents of the experimentally heated Tagish Lake meteorite samples using Raman spectroscopy, scanning transmission X‐ray microscopy utilizing X‐ray absorption near edge structure spectroscopy, and ultraperformance liquid chromatography fluorescence detection and quadrupole time of flight hybrid mass spectrometry. Our experiment suggests that graphitization of OM did not take place despite the samples being heated to 900 °C for 96 h, as the OM maturity trend was influenced by the heating conditions, kinetics, and the nature of the OM precursor, such as the presence of abundant oxygenated moieties. Although both the intensity of the 1s?σ* exciton cannot be used to accurately interpret the peak metamorphic temperature of the experimentally heated Tagish Lake sample, the Raman graphite band widths of the heated products significantly differ from that of chondritic OM modified by long‐term internal heating.     

Recognizing cryptic environmental changes by using paleoecology and taphonomy of Pleistocene bivalve assemblages in the Oga Peninsula,northern Japan

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.     

Transit time evaluation using a chloride concentration input step shift after forest cutting in a Japanese headwater catchment

Mean transit times were estimated for a small headwater catchment in Japan (the Fukuroyamasawa Experimental Watershed) using the step shift in input chloride (Cl^?) concentrations that occurred immediately after an episode of forest clear‐cutting. Measured Cl^? concentrations in stream water began to decrease immediately after clear‐cutting, and this trend continued for 6 years. Before clear‐cutting, the input Cl^? concentrations were controlled by wet and dry deposition processes, and most of the dry Cl^? deposition was collected by the forest canopy and reached the ground as throughfall and stemflow. After clear‐cutting, dry deposition was no longer collected by the canopy in this way, thus causing a sharp decrease in input Cl^? concentrations. By comparing measured Cl^? concentrations in stream water with estimates based on the input and evaporative Cl^? concentrations, it was shown that the decrease in stream water Cl^? concentrations was caused mainly by this step shift in the Cl^? input. It was proposed that the change in Cl^? concentrations after forest cutting could be used to represent the replacement of ‘old’ water that existed before cutting by ‘new’ water that was supplied after cutting. The breakthrough curve for the new water fraction gave an approximately exponential distribution of transit times in flow‐corrected time. The mean flow‐corrected transit time was estimated as 1068 days (runoff: 3497 mm). It was therefore concluded that the step change in input Cl^? concentrations immediately following forest clear‐cutting could be successfully used to estimate transit times for the entire catchment. Copyright © 2009 John Wiley & Sons, Ltd.     

Yamato 86029: Aqueously altered and thermally metamorphosed CI‐like chondrite with unusual textures

Abstract— We describe the petrologic and trace element characteristics of the Yamato 86029 (Y‐86029) meteorite. Y‐86029 is a breccia consisting of a variety of clasts, and abundant secondary minerals including coarse‐ and fine‐grained phyllosilicates, Fe‐Ni sulfides, carbonates, and magnetite. There are no chondrules, but a few anhydrous olivine‐rich grains are present within a very fine‐grained phyllosilicate‐rich matrix. Analyses of 14 thermally mobile trace elements suggest that Y‐86029 experienced moderate, open‐system thermal metamorphism. Comparison with data for other heated carbonaceous chondrites suggests metamorphic temperatures of 500–600°C for Y‐86029. This is apparent petrographically, in partial dehydration of phyllosilicates to incompletely re‐crystallized olivine. This transformation appears to proceed through ‘intermediate’ highly‐disordered ‘poorly crystalline’ phases consisting of newly formed olivine and residual desiccated phyllosilicate and their mixtures. Periclase is also present as a possible heating product of Mg‐rich carbonate precursors. Y‐86029 shows unusual textures rarely encountered in carbonaceous chondrites. The periclase occurs as unusually large Fe‐rich clasts (300–500 μm). Fine‐grained carbonates with uniform texture are also present as small (10–15 μm in diameter), rounded to sub‐rounded ‘shells’ of ankerite/siderite enclosing magnetite. These carbonates appear to have formed by low temperature aqueous alteration at specific thermal decomposition temperatures consistent with thermodynamic models of carbonate formation. The fine and uniform texture suggests crystallization from a fluid circulating in interconnected spaces throughout entire growth. One isolated aggregate in Y‐86029 also consists of a mosaic of polycrystalline olivine aggregates and sulfide blebs typical of shock‐induced melt re‐crystallization. Except for these unusual textures, the isotopic, petrologic and chemical characteristics of Y‐86029 are quite similar to those of Y‐82162, the only other heated CI‐like chondrite known. They were probably derived from similar asteroids rather than one asteroid, and hence may not necessarily be paired.