Occurrence of Free-Gas Associated with Methane-Hydrate-Bearing Formations in the MITI Nankai Trough Wells, Offshore Tokai, Japan

Abstract. The MITI Nankai Trough wells were drilled for exploration of methane-hydrate-bearing sediments in association with seismic inferred bottom simulating reflectors (BSRs). In this project, log data showed low velocity compressional-wave (P-wave) layers below methane-hydrate-bearing formations. Dipole shear sonic acoustic tools (DSI) could not acquire accurate compres-sional velocity in this zone, thus it was not possible to accurately correlate between logging, VSP and surface seismic profiles.
Small amount of gas was presumed to cause the problem in obtaining the low velocity P-wave data. VSP interval velocity data was used to assess the DSI inferred low-velocity layer, which showed lower values than the velocity of the drilling muds. Synthetic seismogram was created by VSP-compensated velocity to compare against corridor stack of VSP. As a result, the depths above and below the methane-hydrate-bearing interval were correlated with synthetic seismograms and reflectivity events on the VSP profiles. By using this correlation technique, distribution of methane-hydrate-bearing formations and free-gas-bearing formations can be determined.     

Formation of Polycrystalline Graphite Aggregates in High-Pressure Metamorphic Rocks from the Kokchetav Massif,Northern Kazkhstan

Doklady Earth Sciences - An inclusion of graphite in zircon from the diamond- and tourmaline-bearing rocks of the Kokchetav massif (Northern Kazakhstan) has been studied. The inclusion, associated...     

Diel Vertical Migration of the Marine Cladoceran Podon Leuckarti: Variations with Reproductive Stage

Diel vertical migration (DVM) of the marine cladoceran Podon leuckarti was investigated with reference to their reproductive stages and size. Males and females, except for gamogenic females with an advanced resting egg (GA), aggregated at the near-bottom layer or at the surface during the day and dispersed into the water column at night. Both the near-bottom aggregation and the surface aggregation during daytime are suggested to be behavior that reduces the predation risk from visual predators. However, GA aggregated in the near-bottom layer during daytime and avoided the surface layer. The near-bottom aggregation might be more effective behavior for GAs to reduce risk of visual predation than the surface aggregation because of the conspicuous resting egg they carried. These results show that carrying an advanced resting egg influenced the DVM of P. leuckarti.     

Rainwater and reclaimed wastewater for sustainable urban water use

Concern about the sustainability of urban water use is the strong motivation to understand the potential of rainwater use and water recycling in urbanized cities. The history of water supply in Tokyo and its experience may provide useful information to develop sustainable urban water use and find future possible tasks in rapidly growing cities. Besides, various innovative strategies to meet the current and future water demand in Tokyo may help us to consider new approaches adjusting to the developing mega cities in Asia. In this paper, the past and current practices on utilization of latent water resources such as rainwater and reclaimed wastewater in Tokyo are summarized from the viewpoint of sustainable water use.The storage of rainwater is a useful measure for water demand in emergency cases. In addition, the rainwater use can work as a kind of environmental education to make citizens aware of sustainable urban water use. There are 850 facilities for rainwater use in Tokyo. Since reclaimed wastewater use has several benefits, a huge water volume has been utilized for various purposes such as washing, water-cooling, toilet flushing, waterway restoration and creation of recreational waterfront. From the viewpoint of human health risk, new micropollutants such as estrogens, endocrine disrupters and surfactants should be considered as quality guideline parameter besides the conventional ones. Importance of infiltration facilities should be also highlighted to secure the sound water cycle. Groundwater recharge through the infiltration facilities provide a potential storage of water resource which can be withdrawn in the future if necessary.     

Influence of Seasonal Pumping on Groundwater Sources and Flow System,Nagaoka Plain,Japan

Intensive groundwater development in the urban area of the Nagaoka Plain, Japan, has induced changes in the pH and saturation index of calcite in groundwater. To account for these chemical changes, it is important to determine seasonal variations of recharge and the groundwater flow system in the aquifer. This study identified the sources and flow system of groundwater in this urban area by a comprehensive method using stable isotope data and a numerical groundwater model of the Nagaoka Plain. Stable isotope evidence shows that the groundwater is recharged by meteoric water originating from low‐elevation areas rather than the mountains surrounding the plain. The water table in the study area is drawn down during the winter and recovers in the other seasons. Numerical modeling shows that discharge occurs primarily along the Shinano River during the recovery period, whereas discharge is centered in urbanized areas during the drawdown period, when a conical depression of the water table stimulates recharge from the immediate area. These results are indications of a local groundwater flow system, with its recharge area between the Shinano River and the urban areas, which is governed by intensive seasonal groundwater extraction.     

Exploration of S-wave velocity profiles at strong motion stations in Eskisehir,Turkey, using microtremor phase velocity and S-wave amplification

We have explored 1D S-wave velocity profiles of shallow and deep soil layers over a basement at strong motion stations in Eskisehir Province, Turkey. Microtremor array explorations were conducted at eight strong motion stations in the area to know shallow 1D S-wave velocity models. Rayleigh wave phase velocity at a frequency range from 3 to 30 Hz was estimated with the spatial autocorrelation analysis of array records of vertical microtremors at each station. Individual phase velocity was inverted to a shallow S-wave velocity profile. Low-velocity layers were identified at the stations in the basin. Site amplification factors from S-wave parts of earthquake records that had been estimated at the strong motion stations by Yamanaka et al. (2017) were inverted to the S-wave velocities and Q-values of the sedimentary layers. The depths to the basement with an S-wave velocity of 2.2 km/s are about 1 km in the central part of the basin, while the basement becomes shallow as 0.3 km in the marginal part of the basin. We finally discussed the effects of the shallow and deep sedimentary layers on the 1D S-wave amplification characteristics using the revealed profiles. It is found that the shallow soil layers have no significant effects in the amplification at a frequency range lower than 3 Hz in the area.     

Broadband ground-motion simulation of the 24 May 2014 Gokceada (North Aegean Sea) earthquake (Mw 6.9) in NW Turkey considering local soil effects

On 24 May 2014, a Mw 6.9 earthquake occurred in the west of Gokceada Island, northern Aegean Sea. The earthquake was close to Canakkale, Enez, Tekirdag cities, and damaged 300 buildings in the Marmara Region, NW Turkey. We simulated its broadband (0.1–10 Hz) ground motions including 1D deep and shallow structures soil amplification effects at the 12 strong ground motion stations in the western Marmara Region. The 1D deep velocity structures from the focal layer to the engineering bedrock with an S-wave velocity of 0.78 km/s in different azimuthal directions were tuned by comparing the observed group-velocity dispersion curves of Rayleigh and Love waves from the mainshock with theoretical ones. We also added the shallow parts from previous surveys into the 1D models. Synthetic seismograms on the engineering bedrock were generated using the discrete wave number method with a source model and the 1D deep velocity structures. Then the surface motion was generated considering shallow soil amplification. The synthetic seismograms are generally in good agreement with the observed low and high-frequency parts at most of the stations indicating an appropriateness of the source model and the 1D structural model.     

DO-increasing effects of a microscopic bubble generating system in a fish farm

We have developed a "microscopic bubble generating system for the fish farm" and evaluated its ability to improve the quality of seawater and costs of it in marine cages of red sea bream (Pagrus major) in Kusuura Bay, Japan. Our results revealed that DO concentration of bubbling net pens increased and became significantly higher than the level outside the net pen (between 0.52 and 0.87 mg/L), and the whole water column was nearly saturated. Temperatures of the bubbling net pens decreased slightly between 0.08 and 0.12 degrees C in all the layers. Furthermore, micro-bubbles seemed to reach the deeper water due to the downward flow and diffusion. This study demonstrated that the microscopic bubble generating system developed in our research project could increase efficiently the dissolved oxygen concentration throughout all water layers of the fish farm. A capital and operation costs of the system is recoverable within a year.     

Stable isotope-guided analysis of congener-specific PCB concentrations in a Japanese coastal food web

Organisms collected from a coastal ecosystem in Japan were analyzed for concentrations of 205 polychlorinated biphenyls (PCBs) congeners; analyses were guided by δ¹³C and δ¹⁵N measurements. The regression slopes of log PCB concentration on δ¹⁵N value are regarded as indices of biomagnification in food webs. The slope (wet weight basis) of ΣPCBs was +0.104; the slope (lipid weight basis) was close to zero. Lipid content increased from 0.06% in a primary producer to 8.32% in the highest trophic level consumer. Hence, biomagnification of ΣPCBs (wet weight basis) can be attributed to increase of lipid content through the food web. For most of the congeners, the slopes (wet weight basis) exceeded those (lipid weight basis) by ca. 0.10. Slopes increased with increasing PCB chlorination levels between chlorine numbers 1–6; slopes decreased at higher chlorination levels. This decrease is likely caused by a decrease in membrane permeability with increasing molecular weight.     

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.