Inflow and outflow in a rotating circular container—A laboratory model for the Loop Current of the Gulf of Mexico

The Loop Current of the Gulf of Mexico is simulated in the laboratory. A circular tank is filled with water and is placed off-center on a rotating table and the flow field is generated by injecting and withdrawing water at two openings on the wall. The free surface becomes parabolic due to balance of gravitational and centrifugal forces, simulating the latitudinal change of the Coriolis parameter (-effect) in the ocean. The flow characteristics depend on the influx and the rate of rotation and can be classified according to non-dimensional parameters (Rossby, Ekman and Froude numbers denoted byR ₀,E andF, respectively). When the influx is small and the rotation rate is large (smallR ₀,E andF) the flow will be almost linear, and the fluid flows along the side-wall boundary layer under constraint of the -effect. For a very large influx (largeR ₀ andE) inertial forces become very large compared to the Coriolis force and the flow behaves like a potential flow. The flow studied had characteristics between these two extreme cases and hasR ₀ andF similar to the Gulf circulation, though similarity inE is ambiguous. Photographs of the flow indicate that the inflow penetrates further into the interior when the rotation rate is increased while the influx is kept constant. The numerical analysis of the non-linear vorticity equation confirms this for the parameters corresponding to the experiment. In addition, the photographs reveal eddies embedded on both sides of the main stream, particularly near the inflow region. These eddies are intensified and become uniform in size as the influx increases. It is pointed out that such eddies were actually observed near the Loop Current north of the Yucatan Straits.     

Upper limit of heaving pressure derived by pore-water pressure measurements of partially frozen soil

Experiments were conducted to estimate heaving pressures of saturated soil partially frozen in a closed system. Temperatures at both ends of a specimen were kept constant, i.e., positive at the top and negative at the bottom. When the overburden pressure P was maintained at a constant value, the pore-water pressure P_w, which showed a certain value before freezing, decreased gradually as freezing progressed, finally attaining a specific value, whereafter the specimen ceased taking water into it. The pressure difference between P and P_w, at this stage was defined as the upper limit of heaving pressure σ_u, which evidently depended on the temperature θ_c of the cooling end, in accordance with the relation: σ_u = −11.4 θ_c (kg/cm²)

It corresponds to the modified Clausius-Clapeyron's formula, which gives the freezingpoint depression of an ice—water system, where the pressure acting on the ice differs from that on the water. This is the same as the value obtained by Radd and Oertle (1973). It is considered, however, that, when θ_c lowers, the value of θ_u reaches finally a constant value smaller than the one obtained by the above equation. Denoted by σ_{u max}, it was defined as a maximum heaving pressure. The value of σ_{u max} depended on soil type.     

Application of aerial photography to the study of small scale upper ocean phenomena

The industrial waste dumped 180 n. miles south of Galveston was monitored in July 1977 by water sampling, hydrographic measurements, acoustic tracking on board two vessels, and by aerial photography. The plume of the waste diffused vertically and horizontally. Photodensitometry of aerial photos of the plume showed lateral dispersion of the plume in agreement with two other methods: acoustic tracking of the waste suspensoid and transmissometer sampling. In addition, the method showed small scale features like the lateral and longitudinal variations in the photodensity, indicating the waste concentration. This waste concentration showed periodic changes in its axial distance, with the spectral peak at about 160 m wave length. It shows a sharp increase at the windward edge of the plume as do the acoustic records. This phenomenon is explained in terms of the shearing current near the surface together with vertical diffusion. The periodic change along the axis is explained in terms of the Langmuir circulation and in terms of internal ship waves.     

Seismotectonics at the Trench-Trench-Trench triple junction off central Honshu

We study earthquakes in and near the TTT type triple junction off Boso peninsula, central Honshu, to elucidate the plate interaction in this area. The Pacific, North America (northeast Japan) and Philippine Sea plates meet at the junction of the Japan and Izu-Bonin Trenches, and the Sagami Trough. We determine focal mechanisms using WWSSN data. We also determine accurate focal depths by modeling body-waves. There is no serious trade-off between focal depth and source time function for the events treated in this study.The earthquake mechanisms and their focal depths show two major modes of deformation of the Pacific slab at the junction. One mode is represented by nearly vertical normal faults with strikes perpendicular to the Bonin Trench. This mode of faulting is dominant in regions south of the junction and characteristically the southwest block is downthrown. The other mode is represented by nearly vertical normal faults that strike parallel to the Japan Trench and indicate the northwest block is downthrown. This latter mode is dominant in regions north of the junction. The former mode may represent the accommodation of the slab geometry to the change in dip angle between the northeast Japan and Izu-Bonin arcs; the Izu-Bonin slab has a larger dip than that of the northeast Japan slab. The latter mode shows that normal faults parallel to the trench strike, usually seen in trench axis-outer rise regions, continue to occur further landward of the trench axis in the area just north of the junction. This might be caused by the loading of the Philippine Sea slab which penetrates between northeast Japan and the Pacific slab north of the Sagami Trough.Further north of these normal faults north of the junction, we find earthquakes which represent the relative motion between the Pacific and North American plates. This means that the Philippine Sea slab does not exist there. With the aid of earthquakes which represent the Philippine Sea-Pacific and Philippine Sea-North America motions located northwest of the normal faults, we can depict a possible area where the Philippine Sea slab exists north of the Sagami Trough.     

Trends and short-term prospects for copper demand

In recent years, the rate of consumption of minerals and energy has been increasing. Herein, a few fundamental components of mineral consumption including population growth, rising standard of living, advances in technology, and economic growth are analyzed. Copper is one of the best resources for illustrating the growth of metal consumption and components of that growth because statistical data for copper are quite comprehensive. Among the various factors examined, an index of rising standards of living is the most significant factors explaining growth of copper consumption.     

Monitoring degradation of the 1995 Nojima earthquake fault scarps at Awaji Island, southwestern Japan

The Nojima fault on the northwestern coast of Awaji Island, south of Kobe, was reactivated during the January 17, 1995 Hyogoken-nanbu earthquake. This fault rupture was dominated by right-lateral offset (max. 1.7 m) along a high-angle reverse fault which has a maximum vertical displacement of 1.3 m on the southeastern side. We repeatedly measured seven profiles across the fault scarp in two areas (Hirabayashi to the northeast and Ogura to the southwest) for approximately 1 year following the earthquake. The original profile of the fault scarp was an overhanging scarp at Hirabayashi and Ogura, corresponding to the 70–80 ° dip of the fault plane. The fault scarp at Hirabayashi displaces Plio-Pleistocene siltstones of the Osaka Group and is overlain by a thin bed of unconsolidated gravel. The Ogura area is entirely underlain by the Osaka Group. Scarp degradation at Hirabayashi occurred by collapse of the gravel bed and proceeded more quickly than at Ogura, where fault scarp degradation proceeded mainly by exfoliation of the Osaka Group siltstones. The degradation occurred at a very fast rate until March at Hirabayashi, and until June or July at Ogura. Since then, the degradation has been very slow. Our data strongly indicate that the scarp profile was initially controlled mainly by the dip of the fault plane, and scarp degradation has been primarily controlled by lithological factors. The degradation of the Nojima earthquake fault scarp proceeded much more quickly than that of normal fault scarps in the western U.S.A., where many observations of the initial stages of scarp degradation have been carried out. The extremely rapid degradation of the Nojima fault scarp in weak late Neogene siltstones might, in combination with rapid cultural modification of the landscape, explain the paucity of geomorphic scarps along the numerous active faults in Japan. This observation may also have implications for tectonic geomorphology and paleoseismicity studies in other countries characterised by weak bedrock and moderate to high rainfall regimes.     

Determination of Zirconium in Carbonate Rock Reference Materials with Xylenol Orange Spectrophotometric Method

The zirconium content of six carbonate rock reference samples has been determined by a spectrophotometric method using xylenol orange after sample decomposition by acid digestion or alkali fusion. The interference of calcium was eliminated by adding the same concentration of calcium to the blank solution.     

Development of an apparatus to measure groundwater qualities in situ and to sample groundwater using boreholes

 To accurately measure the pH, Eh, EC and temperature of groundwater retrieved from boreholes, a deep groundwater sampling apparatus was developed which provided sensory measurements both in situ and in a flow-through cell at ground level. Under a pressure of 1×10⁶ Pa the in situ accuracy of the apparatus sensor was within the following limits: pH ±0.2, temperature ±0.1°C, Eh ±10 mV, and EC ±2.4%. The measuring and sampling of deep groundwater from a borehole of more than 1000 m in depth was performed continuously for 30 days. Values of pH were the same for the in situ sensor, the flow-through cell sensor and the laboratory measurements of the sampled water. At the beginning of the sampling period, Eh values of the in situ sensor indicated deep groundwater conditions. The apparatus is particularly useful for Eh measurement. Chemical composition and stable isotope ratios indicated that the groundwater sampled from more than 1000 m depth was a connate water with a chemical composition slightly different from seawater of the present time, and the groundwater retrieved from 800 m depth was a meteoric water. Natural radioactive elements are thought to be the origin of the tritium in the groundwater retrieved from the 1000 m depth. Received: 6 August 1996 / Accepted: 22 October 1996