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141.
Geological evidence of severe tsunami inundation has been discovered in northern Japan. In the dune fields of Shimokita, in northernmost Tohoku, we have found two distinctive sand layers that are tsunami deposits. The run-up height of >20 m and inland inundation of at least 1.4 km are notably larger than any known historical case in Japan. The tsunami-genic earthquake that resulted in these deposits is thought to have taken place in the Kuril Forearc-Trench system nearly 700 years ago. The recurrence interval of major tsunamis originating in the Kuril subduction zone is about 400 years. Given that the most recent unusually large earthquake took place in AD 1611 (corresponding to the Keicho earthquake tsunami), the findings presented here increase the potential and hazard for an outsized tsunami striking the Pacific coast of northern Japan. 相似文献
142.
Fundamental scientific questions concerning the internal structure and dynamics of the Moon, and their implications on the Earth-Moon System, are driving the deployment of a new broadband seismological network on the surface of the Moon. Informations about lunar seismicity and seismic subsurface models from the Apollo missions are used as a priori information in this study to optimise the geometry of future lunar seismic networks in order to best resolve the seismic interior structure of the Moon. Deep moonquake events and simulated meteoroid impacts are the assumed seismic sources. Synthetic P and S wave arrivals computed in a radial seismic model of the Moon are the assumed seismic data. The linearised estimates of resolution and covariance of radial seismic velocity perturbations can be computed for a particular seismic network geometry. The non-linear inverse problem relating the seismic station positions to the linearised estimates of covariance and resolution of radial seismic velocity perturbations is written and solved by the Neighbourhood Algorithm. This optimisation study favours near side seismic station positions at southern latitudes in order to constrain the deep mantle structure from deep moonquake data at large epicentral distances. The addition of a far side station allows to divide by two the size of the error bar on the seismic velocity model. The monitoring of lunar impact flashes from the Earth allows to improve the radial seismic model in the top of the mantle by adding much more meteor impact data at short epicentral distances due to the high accuracy of the space/time location of these seismic sources. Such meteor impact detections may be necessary to investigate the 3D structure of the lunar crust. 相似文献
143.
Masanao Shinohara Toshihiko Kanazawa Tomoaki Yamada Yuya Machida Takashi Shinbo Shin’ichi Sakai 《Marine Geophysical Researches》2014,35(3):231-242
The Japanese islands are positioned near the subduction zones, and large earthquakes have repeatedly occurred in marine areas around Japan. However, the number of permanent earthquake observatories in the oceans is quite limited. It is important for understanding generation of large earthquakes to observe seismic activities on the seafloor just above these seismogenic zones. An ocean bottom cabled seismometer (OBCS) is the best solution because data can be collected in real-time. We have developed a new compact OBCS system. A developed system is controlled by a microprocessor, and signals from accelerometers are 24-bit digitized. Clock is delivered from the global positioning system receiver on a landing station using a simple dedicated line. Data collected at each cabled seismometer (CS) are transmitted using standard Internet Protocol to landing stations. The network configuration of the system adopts two dual methods. We installed the first practical OBCS system in the Japan Sea, where large earthquakes occurred in past. The first OBCS system has a total length of 25 km and 4 stations with 5 km interval. Installation was carried out in August 2010. The CSs and single armored optical submarine cable were buried 1 m below the seafloor to avoid a conflict with fishing activity. The data are stored on a landing station and sent to Earthquake Research Institute, University of Tokyo by using the Internet. After the installation, data are being collected continuously. According to burial of the CSs, seismic ambient noises are smaller than those observed on seafloor. 相似文献
144.
13–8 Ma (middle to late Miocene) is a key period for understanding how the unique vegetation was established in Japan. Palynostratigraphy is useful for estimating the ages of plant-bearing strata deposited in shallow-marine and non-marine environments, but has low temporal resolution for this key period in Japan. We compiled Neogene and early Quaternary palynological records for the Hokuriku district of Central Japan to clarify palynostratigraphic events that may improve the temporal resolution. Our results showed that palynoassemblages changed considerably during 10–6.4 Ma in the Hokuriku district, following a relatively stable period during 13–10 Ma. We found that evergreen Quercus abundance increased at 11.5–10 Ma. We used these palynostratigraphic signatures, along with other biostratigraphic markers, to infer the ages of the Miocene plant-bearing Saikawa and Koderayama Formations in the southern Kanazawa area of Ishikawa Prefecture in the Hokuriku district. The ages of the Saikawa and Koderayama Formations were inferred as ~13 and 10–6.4 Ma, respectively. The palynoflora of the Koderayama Formation shows floristic similarity to that of present south China, implying that the unique flora of Japan established after the age of the Koderayama Formation. 相似文献
145.
146.
Estimation of methane emission from whole waste landfill site using correlation between flux and ground temperature 总被引:1,自引:0,他引:1
Tomonori Ishigaki Masato Yamada Masanao Nagamori Yusaku Ono Yuzo Inoue 《Environmental Geology》2005,48(7):845-853
A methodology to estimate a methane emission in a waste landfill site was developed. The methane flux at a waste landfill
site in summer, autumn, and winter was within the following ranges: from −1.3×10−2 to 16, from −6.4×10−2 to 7.5, and from −1.6×10−3 to 1.5×10−2 g-CH4 m−2 h−1, respectively. In those seasons, the mean methane emission rate and coefficient of variation were 1.1 g-CH4 m−2 h−1 ±290%, 0.57 g-CH4 m−2 h−1 ±347%, and 5.4×10−2 g-CH4 m−2 h−1 ±370%, respectively. These results simultaneously showed that fluctuations of methane emission from the landfill surface
were both of spatial and temporal variability. In each season, an exponential relationship was observed between the methane
flux density and the ground temperature. Total methane emissions were estimated to be 5.7×10−2, 7.1×10−3, and 1.7×10−3 g-CH4 m−2 h−1 in the summer, autumn, and winter surveys, respectively, using a temperature surrogated-kriging method. The results of this
study would improve upon the labor-intensive closed-chamber method, and could be a more practical way to estimate methane
emissions from waste landfills. 相似文献
147.
The spectrum of the S-component of solar radio emission has been investigated at 4 GHz, 17 GHz, 35 GHz, 70 GHz, and 94 GHz. The spectrum for a spot group which appeared late in March 1966 (McMath plage No. 8223), seems to be flat at the frequencies above about 35 GHz. This implies that the emission is due to pure free-free emission at the frequencies above 35 GHz. 相似文献
148.
A semi-analytical method has been developed for calculating oil recovery in two and three dimensions, and for calculating effective relative permeabilities for coarse grids. The calculations are based on the assumption that the effects of a changing mobility field can be accounted for by using fixed streamtube geometries with flowrates updated to account for the changing mobility distribution. The single-phase pressure distribution from a numerical solution of Laplace's equation is used to calculate the pressure distribution for a two-phase flow based on a mapping of the solution of the Buckley-Leverett equation onto the streamtubes derived from the single-phase solution. The displacement calculations for oil recovery are based on theory previously developed by Dykstra and Parsons, extended to include the effects of spatially varying permeability and continuously changing mobilities, as occurs in solutions of the Buckley-Leverett equation for typical values of the mobility ratio. This idea has also been extended to the calculation of effective relative permeabilities for coarse-grid simulation and finally establishes the proper rules for averaging the results of fine-grid numerical simulations of two-phase flow for the definition of effective two-phase flow properties on coarse grids. These calculations have been generalized to three-dimensional flows by the simple device of conceptually inserting a gridded plane across the flow and defining each streamtube at that location as those streamlines which pass through any one of the grid cells. When combined with time-of-flight calculations from the gridded plane to both the producer and injector, the distribution of pore volume along each streamtube can be calculated. This information, combined with a tabulation of the single-phase, steady-state pressure distribution along each streamtube, provides all of the information needed for the semi-analytical calculation of oil recovery and effective flow properties in three-dimensional flows. © 1997 Elsevier Science Ltd. All rights reserved 相似文献
149.
We present a numerical evaluation of the potential improvements in seismic disturbance rejection to be obtained by using active variable damping control in a structure. Using the responses to seismic excitation of an optimally controlled variable structure and of a minimax-optimal designed fixed structure, we obtain an upper bound on the achievable performance and a lower bound on the acceptable performance of a control system for a variable-damping structure. Both of these bounds are relative to an energy-function criterion. Our numerical experiments lead to the following conclusions:
- (i) The gap between the upper and lower bounds is rather small, which makes designing a feedback law, that results in performance superior to that of a minimax-optimal designed structure, very difficult. The best choice for a feedback law appears to be continuous moving horizon control, whose implementation requires ground motion prediction up to 0.2 sec ahead, possibly using sensors located a small distance away from the site.
- (ii) A minimax-optimal designed structure gives very good seismic disturbance suppression, not only for the earthquakes used in its design, but also for other earthquakes of similar intensity. Controlled variable structures are likely to offer advantages when earthquakes are moderate to severe, particularly at sites, such as landfills and dry lake beds, where resonances can be expected, but the resonance frequency cannot be estimated in advance.
150.
By using Acoustic Doppler Current Profiler (ADCP) measurements with the four round-trips method to remove diurnal/semidiurnal
tidal currents, the detailed current structure and volume transport of the Tsushima Warm Current (TWC) along the northwestern
Japanese coast in the northeastern Japan Sea were examined in the period September–October 2000. The volume transport of the
First Branch of the TWC (FBTWC) east of the Noto Peninsula was estimated as approximately 1.0 Sv (106 m3/s), and the FBTWC continued to flow along the Honshu Island to the south of the Oga Peninsula. To the north of the Oga Peninsula,
the Second Branch of Tsushima Warm Current and the eastward current established by the subarctic front were recombined with
the FBTWC and the total volume transport increased to 1.9 Sv. The water properties at each ADCP line strongly suggested that
most of the upper portion of the TWC with high temperature and low salinity flowed out to the North Pacific as the Tsugaru
Warm Current. In the north of the Tsugaru Strait, the volume transport of the northward current was observed to be as almost
1 Sv. However, the component of the TWC water was small (approximately 0.3 Sv). 相似文献