Evidence of a hidden landslide slip surface beneath a mountain hamlet

Earthquake-triggered landslides are some of the most destructive natural disasters. Although remote detection of landslides is economic and efficient, it may miss the more subtle signs of hidden landslides. The Kizawa Tunnel and facilities in its vicinity were severely damaged in the 2004 mid-Niigata Prefecture earthquake. After investigation of the most prominent cracks, the damage was attributed to the slip along a hidden weakness plane. Evidence supporting this argument is summarized in this paper. However, the extent of the shear plane is not limited to the interior of the northern part of the tunnel. The dislocation observed in the two wells to the south of the Kizawa Tunnel together with other findings from previous studies indicates that Kizawa hamlet lies on the southern extension of the same shear plane. Taking account of the presence of flat sedimentary structures, the shear plane may extend in all directions. The authors also surveyed other signs of damage along the perimeter where the shear plane intersects the ground surface. The geological and geomorphological features of the hidden landslide are discussed. Reactivation of interlayer sliding is a threat to the local residents, and thus more attention should be paid to monitoring the movement of the slope to avoid devastating damages.     

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay

Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300 %) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied.

     

Incessant excitation of the Earth's free oscillations: global comparison of superconducting gravimeter records

Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsähovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band.     

Unique Origin of Skarn at the Ohori Base Metal Deposit,Yamagata Prefecture,NE Japan: C,O and S Isotopic Study

The Ohori ore deposit is one of the Cu–Pb–Zn deposits in the Green Tuff region, NE Japan, and consists of skarn‐type (Kaninomata) and vein‐type (Nakanomata) orebodies. The former has a unique origin because its original calcareous rocks were made by hydrothermal precipitation during Miocene submarine volcanism. Carbon and oxygen isotope ratios of skarn calcite and sulfur isotope ratios of sulfides were measured in and around the deposit. Carbon and oxygen isotope ratios of the skarn calcite are δ¹³C = ?15.51 to ?5.1‰, δ¹⁸O = +3.6 to +22.5‰. δ¹³C values are slightly lower than those of the Cretaceous skarn deposits in Japan. These isotope ratios of the Kaninomata skarn show that the original calcareous rocks resemble the present submarine hydrothermal carbonates at the CLAM Site, Okinawa Trough, than Cenozoic limestones, even though some isotopic shifts had occurred during later skarnization. δ³⁴S ratios of the sulfide minerals from the Kaninomata and Nakanomata orebodies are mostly in a narrow range of +4.0 to +7.0‰ and they resemble each other, suggesting the same sulfur origin for the both deposits. The magnetite‐series Tertiary Kaninomatasawa granite is distributed just beneath the skarn layer and has δ³⁴S ratios of +7.5 to 8.1‰. The heavy sulfur isotope ratio of the skarn sulfides may have been affected by the Kaninomatasawa granite.     

Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery

Abstract

Human activities have created high nutrient surpluses in agricultural lands due to the increasing rate of chemical fertilizer application and the increase in livestock production. To analyse the nutrient characteristics and estimate the nutrient load in streams, we conducted extensive field survey and water quality experiments from 2007 to 2008 in Koise River, a major river of the Lake Kasumigaura watershed, Japan. Water quality indicators of total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) were investigated. The nutrient loads of TN, TP and TOC, as well as dissolved total nitrogen, dissolved inorganic nitrogen, dissolved organic nitrogen, particle organic nitrogen, dissolved total phosphorus, dissolved organic carbon and particle organic carbon were also estimated for the Koise River. Seasonal variation of the nutrient concentration from 2007 to 2008 was analysed considering the river discharge variation and agricultural activities. The results showed that the irrigation water from Lake Kasumigaura has the potential ability to decrease the TN concentration and increase the TOC concentration in the Koise River. Significant correlation coefficients between nutrient load and river discharge were found. The monthly pollution loads from different sources were then evaluated based on land cover classification generated from high-resolution Quick Bird remote sensing imagery. This study presents a useful interpretation of water quality data sets with a view to obtaining better information about water quality for more effective management of water resources in river basins.

Editor Z.W. Kundzewicz

Citation He, B., Oki, K., Wang, Y., Oki, T., Yamashiki, Y., Takara, K., Miura, S., Imai, A., Komatsu, K. and Kawasaki, N., 2012. Analysis of stream water quality and estimation of nutrient load with the aid of Quick Bird remote sensing imagery. Hydrological Sciences Journal, 57 (5), 850–860.     

Unsteady flows in Io’s atmosphere caused by condensation and sublimation during and after eclipse: Numerical study based on a model Boltzmann equation

The behavior of Io’s atmosphere during and after eclipse is investigated on the basis of kinetic theory. The atmosphere is mainly composed of sulfur dioxide (SO₂) gas, which condenses to or sublimates from the frost of SO₂ on the surface depending on the variation of surface temperature (～90–114 K). The atmosphere may also contain a noncondensable gas, such as sulfur monoxide (SO) or oxygen (O₂), as a minor component. In the present study, an accurate numerical analysis for a model Boltzmann equation by a finite-difference method is performed for a one-dimensional atmosphere, and the detailed structure of unsteady gas flows caused by the phase transition of SO₂ is clarified. For instance, the following scenario is obtained. The condensation of SO₂ on the surface, starting when eclipse begins, gives rise to a downward flow of the atmosphere. The falling atmosphere then bounces upward when colliding with the lower atmosphere but soon falls again. This process of falling and bounce back of the atmosphere repeats during the eclipse, resulting in a temporal oscillation of the macroscopic quantities, such as the velocity and temperature, at a fixed altitude. For a pure SO₂ atmosphere, the amplitude of the oscillation is large because of a fast downward flow, but the oscillation decays rapidly. In contrast, for a mixture, the downward flow is slow because the noncondensable gas adjacent to the surface hinders the condensation of SO₂. The oscillation in this case is weak but lasts much longer than in the case of pure SO₂. The present paper is complementary to the work by Moore et al. (Moore, C.H., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Stewart, B. [2009]. Icarus 201, 585–597) using the direct simulation Monte Carlo (DSMC) method.     

Long-term variability of the low-luminosity active galactic nucleus of M81

Long-term X-ray variability of the low-luminosity active galactic nucleus of M81 was studied, using 16 ASCA observations spanning 5.5 yr. The object exhibits a factor of 3 variation over the 5.5 yr. The source intensity was relatively constant within each observation which lasted typically for one day, but intra-day variability by 30 per cent was detected on the 15th observation. The power-spectral density (PSD) was estimated in a 'forward' manner, over a frequency range of 10^−8.2–10^−4.3 Hz (period range of 0.25 d–5.5 yr), by utilizing the structure function and extensive Monte Carlo simulations in order to overcome the very sparse and uneven data samplings. When the PSD is assumed to be white below a 'break frequency' f _b and falls off as ∝  f ^{− α} above f _b, where f is frequency and α is a positive parameter, the M81 light curve is well described with 1/ f _b≥800 d and α =1.4±0.2.