A Study on Confined Flow of Ground Water Through a Tunnel

Confined flow of ground water through a tunnel, which might be encountered in tunneling under the bottom of a sea or river, is numerically analyzed by a reductive finite element method formulated in our research. That is, the rate and potential distribution of the confined flow of ground water through an opening are obtained in connection with the permeability of rock masses, the thickness of covered ground, the location of impermeable bedrock, and other variables. In addition, flow through an opening in the ground with highly permeable masses and discharge of ground water through a tunnel in grouted masses are illustrated, and some useful results for the practical application of tunneling work are obtained.     

Deep seismic reflection profiling across the Ou Backbone range, northern Honshu Island, Japan

Knowledge of the crustal structure, especially the geometry of seismogenic faults, is key to understanding active tectonic processes and assessing the size and frequency of future earthquakes. To reveal the relationship between crustal structure and earthquake activity in northern Honshu Island, common midpoint (CMP) deep reflection profiling and earthquake observations by densely deployed seismic stations were carried out across the active reverse faults that bound the Ou Backbone range. The 40-km-long CMP profiles portray a relatively simple fault geometry within the seismogenic layer. The reverse faults merge at a midcrustal detachment just below the base of the seismogenic layer, producing a pop-up structure that forms the Ou Backbone range. The top of the reflective middle to lower crust (4.5 s in travel time (TWT)) nearly coincides with the bottom of seismogenic layer. The P-wave velocity structure and surface geology suggest that the bounding faults are Miocene normal faults that have been reactivated as reverse faults.     

Structural design of buried pipelines for severe earthquakes

In order to realistically assess the seismic risk of a pipeline system, the accurate estimate of the pipe strains which depend upon structural details, pipe material, properties of the surrounding soil, the nature of the propagating wave, etc. is critical. Emphasis in this study, therefore has been placed on the analysis of a structural strain for several types of piping elements unique to the buried pipeline and also the provision of a simplified design formula which can be used practically. The purpose of this study is (a) to define the slippage factor in order to estimate the decrease in pipe strain resulting from the slippage effect, (b) to propose a simplified method to evaluate the plastic deformation of the pipeline for severe earthquakes, and (c) to derive a practical design formula for the structural strains of bent pipes.     

Grain size dependence of far-infrared extinction spectra of amorphous fine grains

The far-infrared extinction spectra of fused silica grains with the size range from 1.8 m to 60 Å were measured. The spectra depend clearly on the grain size. For large grain sizes (from 1.8 m to 400 Å) the spectra show almost the ^–2 dependence ( is the wavelength), which resembles that of the bulk material. For fine grains (70 and 60 Å) the spectra are less steep, the wavelength dependence being ^–1. This grain size dependence of extinction spectra agrees essentially with the prediction of Seki and Yamamoto.     

Validation of a decadal OGCM simulation for the tropical Pacific

An ocean general circulation model is forced with NCEP reanalysis over the 1948–1999 period. The simulated dynamic height and sea level are compared respectively to the dynamic height computed from hydrological data and to the sea level measured by tide gauges in the tropical Pacific. The model is shown to capture important features of the temporal structure of variability in the tide gauge data over the last several decades. However, the comparison reveals a largely artificial trend in the simulation, which consists of a decreasing dynamic height and sea level in the southwest and northwest of the tropical Pacific. Model sensitivity experiments show this trend is controlled by the NCEP surface wind stresses and more precisely by a weakening in the trade winds and a trend in the off-equatorial wind curl, with this trend existing mainly before the mid 1970s. For studies of decadal variability, the simple removal of a linear trend is an inadequate way to solve the problem, due to the inhomogeneities in the data used in reanalysis products and the non-linearity of models.     

Modeling of spring bloom in the western subarctic Pacific (off Japan) with observed vertical density structure

Effects of vertical stability on spring blooms of phytoplankton were investigated for the western subarctic Pacific ocean using a one-dimensional (depth) ecosystem model. In the model, vertical stability was expressed by diffusion constants calculated from observed density distribution. Dynamics of phytoplankton in blooms was calculated by the model using the vertical diffusion. Then, the calculated results were compared with the Coastal Zone Color Scanner (CZCS) data. The comparison shows that the shallow surface mixed layer causes early start days of spring blooms at inshore (northern) stations. In addition, spring blooms continue long at inshore (northern) stations since a water column has weak stability. This is because weak stability of a water column causes large nutrient supply from a deep layer and large diffusive transport of phytoplankton biomass from the subsurface maximum.     

Propagation of semi-diurnal internal tides observed off fukushima,along the east coast of Japan

Analysis of current velocity and temperature records obtained from moored buoy systems deployed off the east coast of Japan reveals the intermittent occurrence of semi-diurnal internal tides and their manner of propagation. The internal tidal waves clearly propagate toward the shore, which is confirmed by cross-correlation of the onshore current velocity and temperature between neighboring stations. The propagation speed of the internal tide increases with water depth except in the area furthest offshore. In this area, motions near the second mode seem to occur occasionally, while in the nearshore area the motions for the most part consist of the first mode. Through harmonic analysis, it is shown that theM ₁ internal motions were not vertically homogeneous. That is, the internal motions are greater at the lower level in the nearshore area while they are greater at the upper level in the offshore area. Pathways along which the energy of the internal tide should propagate are estimated in such a way that the characteristic curves pass through the area over which relatively large onshore/offshoreM ₂ velocity is distributed. The movement of the characteristic ray of a certain phase explains the observed phase velocity estimated from the cross-correlation diagrams. Internal motions around the characteristic ray were pronounced in a rather wide area. Thus, it is suggested that the generation region of the internal tide in the present study area might be relatively wide.