Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region,Japan

The duration of the soil‐depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near‐surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing–thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near‐surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil‐depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. Copyright © 2014 John Wiley & Sons, Ltd.     

Meteor Orbit Determinations with Multistatic Receivers Using the MU Radar

The MU radar of RISH (Research Institute for Sustainable Humanosphere, Kyoto University), which is a MST radar (46.5 MHz, 1 MW peak power), has been successfully applied to meteor studies by using its very high versatility. The system has recently renewed with 25 channel digital receivers which significantly improved the sensitivity and precision of interferometer used in meteor observation. The transmission is now synchronized to GPS signals, and two external receiving sites with a ranging capability has additionally been operated in order to determine the trajectories and speeds of meteoroids.     

Variations in stress and driving pore fluid pressure ratio using vein orientations along megasplay faults : Example from the Nobeoka Thrust,Southwest Japan

The Nobeoka Thrust of Southwest Japan is an on‐land example of an ancient megasplay fault that provides an excellent record of deformation and fluid flow at seismogenic depths. The present study reports: (i) temporal stress changes for the seismogenic period of the Nobeoka Thrust; and (ii) spatial heterogeneities in driving pressure ratios P* obtained from mineral veins around the Nobeoka Thrust fault zone. Many quartz veins that filled mode I cracks can be observed in the hanging wall and footwall of the thrust. Inversion for stress orientation suggests that normal faulting dominated in both the hanging wall and footwall, with similar stress axis orientations in both. The orientation of σ₃ for the estimated stress regime is parallel to the slip direction of the Nobeoka Thrust. The detected normal‐faulting‐type stress regimes likely resulted from post‐seismic stress buildup after megathrust earthquakes. The hanging wall of the Nobeoka Thrust has smaller P* values than the footwall. Two possible explanations are proposed for the observed spatial variations in the driving pore fluid pressure ratio, P*: spatial variations in pore fluid pressure P_f are directly responsible for P* variations, or P* variations are controlled by differences in mechanical properties between the hanging wall and footwall.     

Groundwater dynamics of Fongafale Islet, Funafuti Atoll, Tuvalu

Geoelectric and hydrologic surveys during spring tides revealed the spatiotemporal distribution of groundwater quality produced by tidal forcing in Fongafale Islet, Funafuti Atoll, Tuvalu. The observed low resistivity showed that saline water largely immersed the surficial Holocene aquifer, indicating that there is no thick freshwater lens in Fongafale Islet, unlike in other atoll islands of comparable size. Half of the islet was constructed by reclaiming the original swamp with porous, highly permeable coral blocks; this reclaimed area should not be considered as part of the islet width for calculation of the expected thickness of the freshwater lens. The degree of aquifer salinization depends on the topographic characteristics and the hydrologic controls on the inland propagation of the tidal forcing. Large changes in bulk resistivity and the electrical conductivity of groundwater from wells indicate that periodic salinization in phase with the semidiurnal tides was occurring widely, especially in areas at lower elevation than the high-tide level and in reclaimed areas with high permeability. Thin sheets of nearly fresh and brackish water were observed in the surficial aquifer in areas above the high-tide level and in taro swamps, respectively. The thinness of the brackish and freshwater sheets suggests that the taro swamps and the fresh groundwater resources of the islet are highly vulnerable to salinization from anticipated sea-level rise. An understanding of the inherent geologic and topographic features of an atoll is necessary to evaluate the groundwater resources of the atoll and assess the vulnerability of its water resources to climate change.     

Tectonics of an Early Carboniferous forearc inferred from a high-P/T schist-bearing conglomerate in the Nedamo Terrane, Northeast Japan

The Nedamo Terrane, an Early Carboniferous accretionary complex, is the oldest biostratigraphically dated accretionary complex in Japan. The purpose of this study is to describe and interpret a conglomerate from the Nedamo Terrane that contains clasts of high-pressure/low-temperature (high- P/T ) schist (mainly garnet-bearing phengite schist) and ultramafic rock, and to infer the tectonics of an Early Carboniferous arc–trench system at the eastern margin of the paleo-Asian continent. Clasts of high- P/T schist and ultramafic rock within the conglomerate make up 8.4 and 6.7% of the total clasts, respectively, based on modal counts. These clasts are subangular to subrounded, whereas volcanic clasts are well rounded. The source of the schist clasts, which yield a radiometric age of 347–317 Ma, is considered to be the Renge Metamorphic Rocks of Southwest Japan or equivalent rocks. Based on the chemical composition of chromian spinel, the source of ultramafic clasts is inferred to be the island-arc-type Ordovician Miyamori and Hayachine ultramafic complexes in the Kitakami Massif. The conglomerate records multiple provenance regions, including an island arc (South Kitakami Terrane) and a forearc ridge; the high P/T schist and ultramafic rocks were exhumed in the forearc region. The duration of the interval from the early stages of exhumation of the schist to its deposition in the trench as clasts is estimated to have been less than 30 my.     

A survey of emission-line stars in the CMa star formation region

A survey of emission-line stars was carried out in the CMa star formation region, based on spectral observations with the Kiso Schmidt telescope. In total, 128 emission-line stars were detected, ranging fromV=6 to 15, and the majority are found withV between 11 and 14. A comparison with the existing catalogues shows that some emission-line stars are common with ours, while some exhibit no detectable emission line on our plates, suggesting the variability of emission-line strength. The two-colour (U–B, B–V) diagram is also shown for the detected stars.Paper presented at the IAU Third-Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.On leave from the Bosscha Observatory, Institute of Technology Bandung, Indonesia.     

Laboratory measurement of P-wave velocity in crustal and upper mantle xenoliths from Ichino-megata, NE Japan: ultrabasic hydrous lower crust beneath the NE Honshu arc

Ultrasonic laboratory measurements of P-wave velocity (Vp) were carried out up to 1.0 GPa in a temperature range of 25–400 °C for crustal and mantle xenoliths of Ichino-megata, northeast Japan. The rocks used in the present study cover a nearly entire range of lithological variation of the Ichino-megata xenoliths and are considered as representative rock samples of the lower crust and upper mantle of the back arc side of the northeast (NE) Honshu arc. The Vp values measured at 25 °C and 1.0 GPa are 6.7–7.2 km/s for the hornblende gabbros (38.6–46.9 wt.% SiO₂), 7.2 km/s for the hornblende-pyroxene gabbro (43.8 wt.% SiO₂), 6.9–7.3 km/s for the amphibolites (36.1–44.3 wt.% SiO₂), 8.0–8.1 km/s for the spinel lherzolites (46.2–47.2 wt.% SiO₂) and 6.30 km/s for the biotite granite (72.1 wt.% SiO₂). Combining the present data with the Vp profile of the NE Honshu arc [Iwasaki, T., Kato, W., Moriya, T., Hasemi, A., Umino, N., Okada, T., Miyashita, K., Mizogami, T., Takeda, T., Sekine, S., Matsushima, T., Tashiro, K., Miyamachi, H. 2001. Extensional structure in northern Honshu Arc as inferred from seismic refraction/wide-angle reflection profiling. Geophys. Res. Lett. 28 (12), 2329–2332], we infer that the 15 km thick lower crust of the NE Honshu arc is composed of amphibolite and/or hornblende (±pyroxene) gabbro with ultrabasic composition. The present study suggests that the Vp range of the lower crustal layer (6.6–7.0 km/s) in the NE Honshu arc, which is significantly lower than that obtained from various seismic measurements (e.g. the northern Izu-Bonin-Mariana arc: 7.1–7.3 km/s), is due to the thick hydrous lower crustal layer where hornblende, plagioclase and magnetite are dominant.     

Evaluations of subsurface flow for reconstructions of climate change using borehole temperature and isotope data in Kamchatka

Subsurface temperature is affected by heat advection due to groundwater flow and surface temperature changes. To evaluate their effects, it was implemented the measurements of temperature-depth profile (T-D profile) and the continuous monitoring of soil temperature in the southern part of Kamchatka which has not affected by human activity. Additionally, stable isotopic compositions of surface water and groundwater were analyzed. T-D profile and stable isotopic compositions show groundwater flow system is differ from the shallow aquifer to the deep aquifer. In the shallow aquifer, T-D profile suggests the existence of upward groundwater flux. On the other hand, the annual variation of soil temperature is divided into the large variation period (VP) and the stable period (SP) by the magnitude of daily and seasonal variation. VP and SP correspond to the summer and the winter season, respectively, and it considers that the difference between VP and SP is caused by the effect of snow cover. Therefore, the T-D profile is affected by not only upward groundwater flux but also the surface warming particularly in the summer season (VP).     

Extending Multivariate Space-Time Geostatistics for Environmental Data Analysis

Environmental studies require multivariate data such as chemical concentrations with space-time coordinates. There are two general conditions related to such data: the existence of correlations among the coregionalized variables and the differences in numbers of data which occur because of insufficient data caused by measurement error or bad weather conditions. This study proposes geostatistical techniques for space-time multivariate modeling that take into consideration these correlations and data absences. These techniques consist of suitable modeling of semivariograms and cross-semivariograms for quantifying correlation structures among multivariables and of extending standardized ordinary cokriging. The tensor product cubic smoothing surface method is used for space-time semivariogram modeling. These methods are applied to the chemical component data of the Ariake Sea, a typical closed sea in southwest Japan. In order to clarify environmental changes in the Ariake Sea, the concentration data of four nutritive salts (NO₂–N, NO₃–N, NH₄–N, and PO₄–P) at 38 stations over 25 years are used as environmental indicators. For each of the kinds of data, there are spaces and times for which there is no data available. The effectiveness of the modeling of space-time semivariograms and the high estimation capability of the extended cokriging are demonstrated by cross-validation. Compared with ordinary kriging for a single variable, multivariate space-time standardized ordinary cokriging can provide a more detailed concentration map of nutritive salts and while elucidating their temporal changes over sparsely spaced data areas. In the space-time models by ordinary kriging, on the other hand, smooth trends are obvious.