Hyperpycnal flow is one type of turbidity current, which is generated at a river mouth when the suspended sediment concentration of river discharge is so high that the density of the effluent exceeds the water of the receiving basin. Generations of this type of flow have become a common phenomenon recently. A lot of hyperpycnal flow deposits are expected to be preserved naturally in stratigraphic records. Hyperpycnal flow deposits (hyperpycnites) might become an innovative factor for turbidite paradigm considering the particularity of the flow, and bring facies analysis towards the next step. In this review paper, the criteria for identifying hyperpycnal flow deposits from strata are proposed by summarizing studies on hyperpycnal flow and its deposits. Typical characteristics of hyperpycnal flow include : (1) vertical succession composed of 2 parts, inversely-graded lower part and normally-graded upper part, (2) internal scour surface, (3) repetitive alternation of fine-grained and coarse-grained layers, or laminated and massive layers, (4) abrupt pinch-out of beds, and (5) inclusion of terrestrial materials such as leaves. Hyperpycnal flow gradually waxes and then wanes to terminate in response to flood conditions, resulting in (1). The internal scour surface (2) developed in accordance with the degree of waxing. Fluctuations of flow velocity and sediment concentration due to changes of river discharge and/or internal waves can occur during the flow event, and lead to repetitive alternation of (3). Because of the fresh interstitial water, the marine hyperpycnal flow might start to lift off after losing suspended sediments to the degree that the density of the flow is exceeded by ambient saline water. This results in (4) at the lifting point. Terrestrial materials referred to in (5) are the result of the fact that the hyperpycnal flow originated from terrestrial floods. A much wider variety of deposits, which form in one history of a turbidity current, than that expected from the Bouma sequence model, is shown. Exploration of the variety has just started.
The relationship between temperature changes and the expansion of Tokyo Metropolitan Area was studied using multi-temporal Landsat Thematic Mapper (TM) satellite images. The correlation between the ratio of green covering and brightness temperature was assumed to be an index of urbanization, thus, the relation between the ratio of green covering and air temperature in different seasons was verified around the Automated Meteorological Data Acquisition System (AMeDAS) observation point in Tokyo Metropolitan Area. The area located in NDVI >0.1 was assumed to be a vegetation region, on the other hand, the vegetation in the concentric circle of 0.6 km from the point where AMeDAS was observed, had been extracted from multitemporal TM data. The interrelationships between vegetated area and air temperature in Tokyo metropolis were established by comparing the daily average maximum temperature (Tmax), the daily average minimum temperature (Tmin) the average temperature at 9 p.m. (T21), during winter, summer and autumn using TM images and AMeDAS data. As a result, the strong correlation between a green covering and the daily minimum temperature was revealed at each season. In contrast, such a relation was not observed between the ratio of green covering and the maximum temperature. The variation of brightness temperature of the Tokyo area was estimated using thermal infrared data of TM band 6. Because the DN value changes with the state of performance degradation of the sensor or the atmosphere interface, the absolute value of derived temperature can not be compared to the heat island phenomena. Therefore, the relative change of DN value of thermal infrared data was ideal for studying the heat island phenomena. DN values were extracted from 2 Landsat TM night images acquired on August 1984 and August 1994, which had been used to estimate the expansion of the heat island phenomena. Relative Warming Index (RWI) of the AMeDAS observation point was also evaluated from the rate of change (19841994) of the daily minimum temperature of Tokyo (Otemachi). The rate of change of RWI corresponded to the distribution of differences in brightness temperature around Tokyo. The spatial analysis of relative warming index (RWI) for the 10 years of observations suggests that the warming rate of suburban area was much more pronounced than that of central Tokyo, and the rural side of the suburban area recorded a relatively low RWI than that of the same facing towards central Tokyo. The results from satellite images show of consistency with meteorological records.
Excavating a pit across a small up-hill facing fault scarp on a mountain slope could be a paleoseismological tool for intramontane active faults, which usually lack suitable sites for traditional trenching. We tested this method on the Daguchi fault, north of Lake Biwa, southwest Japan, a typical short strike-slip fault in a mountainous region. Our test excavation at the Kurokoyama site on the southern subsegment of the fault, together with a re-interpretation of our previous excavation at the Daguchi site on the northern subsegment, allow us to obtain some constraints on the surface-faulting history of the fault. The timing of the most recent event is estimated to be 450-1050 cal. y.B.P. (900-1500 A.D.), whereas that of the penultimate event is poorly constrained : 1500-7300 cal. y.B.P. or prior to 5000-7300 cal. y.B.P., depending on different interpretations of the infilled fissure exposed on the pit wall. For either interpretation, our result is consistent with estimates from a previous paleoseismic study by Sugiyama and Yoshioka (1999), but the presence of other stratigraphically unidentifiable events cannot be ruled out, given the lack of piecing layers across the main fault in our pits, as well as their trench. The principal reason for the poor age control is an unexpected lack of peaty sediments at the Kurokoyama site, which is probably related to a high sedimentation rate and an unusual sedimentation process due to rapid soil creep on the mountain slope. Although application of this method might be limited on a mountain slope with rapid soil creep, which is commonly implied by the downslope bending of tree trunks as it is at the Kurokoyama site, our test excavations suggest that pit excavation on a mountain slope basically works as a paleoseismological tool in mountainous regions.
The rate, mode and time of soil creep were observed by depths using the combination of a strain probe method and a white-sand marker method. The latter method has an advantage to know the total dislocation by depths while the former indicates the time of movement at each depth. Application of the combined method associated with temporal measurement of soil moisture to valley-head slopes covered by natural forest in Sendai, northeastern Japan, in humid temperate climate which was not expected to induce effective freeze-thaw action, revealed the following characteristics of soil creep. The rate of soil creep, which differs considerably from place to place, ranges from almost zero to several centimeters per year, which contains rates several times higher than previously reported ones. The dislocation often occurs synchronously at different positions in the slope in every season. The movement in B and BC horizons, which show almost the same dislocation within the same horizon and abrupt change of displacement at the boundaries of soil horizons, indicates a slide-type movement characterized by micro-slip planes at the boundaries of soil horizons. In contrast, the flow-type movement, in which dislocation is accumulating upward, is dominant in A horizon. This shows the significance of soil horizons in the occurrence of soil creep and suggests the importance of soil creep in soil-horizon differentiation on hillslopes.
This study examines the interaction between the politics in Fussa City and the Yokota Air Force Base, that is “the politics of place, ” from a range of political, economic, and cultural processes which maintain the existence of the base. Military bases are generally established for global geopolitical purposes. However, the establishment of a military base has cultural implications for the local communities where the base is located, i.e., increased concerns about crimes committed by seavicepersons and noise by aircrafts. Although these military bases have some serious impacts, especially in Japan, geographers have not yet examined the issues regarding a particular military base and the resultant politics in the city. On the contrary, since the 1980s, Anglo-American political geographers have paid more attention to “the politics of place” This refers to the local politics that occur due to the interaction between a structural constraint and the individuality of a particular place. Therefore, this study examines “the politics of place” on the Yokota Air Base in Fussa City, Tokyo, by using resources from the local newspapers, novels, magazine articles, and council proceedings. The results are as follows : (1) Owing to the independence between the U.S. Air Force and local political and economic actors, an urban structure and local economy that depended on the Yokota Air Force Base were constructed in Fussa Town after the establishment of the base in 1945; (2) because of this structure, the local economy became to depend on Air Force personnel as consumers; (3) however, due to a shift to the floating exchanging rate and a reduction in the population of the base in the first half of the 1970s, there was a decrease in the influence that Air Force personnel had on the local economy; (4) since the 1980s, an economic agent utilized the “atmosphere” and “image” adjacent to the base to revitalize the local economy; (5) furthermore, the mass media represented Fussa City as a “base town” and conducted a review of the city in the 1960s, thus contributing to its revitalization; (6) during the economic slump in the 1970s, some local political agents were against the existence of the base. However, successive mayors of Fussa City have accepted the existence of the base, and utilized the subsidies it receives from the national government in order to construct the urban infrastructure.
The Noto Peninsula district is known as a N-S trending uplift zone in the Neogene Tertiary to Quaternary. A geological survey mainly composed of sonic prospecting was conducted in the west sea area of the Noto Peninsula. 8 units of stratum, in particular, 5 units in the Quaternary, were found clearly as acoustic stratigraphy. This made it possible to describe the geological development of the Neogene Tertiary to Quaternary of the district in more detail than has ever been reported. The study area can be divided into 2 areas. In the southern part, 2 bilaterally asymmetric folds that are relatively newly developed with a N-S trend have been formed probably by block movement. In the northern part, which is just the southwestern extension of Okunoto Hill, one of the typical tilted block mountains on Noto Peninsula, there are distributed 2 NE-SW trending tilted blocks accompanied by faulting. These tilted blocks have been uplifted by block movement. A relatively new uplift can be found in the block located in the extended part of the N-S trending fold. Consideration based on the facts above and reported show that the newly developed N-S trending geological structure of the Noto Peninsula district has been formed by block movement at least since the late Pliocene.
This study aims to reconstruct paleo-environments since 30 ka from the viewpoint of the characteristics of eolian dust and fluvial materials at Hosoike moor in the Chugoku Mountains, western Japan. We collected 2 boring cores 3 meters deep from the moor, which is located at 960 meters asl., on the Chugoku mountain ridge. The moor deposits, which have accumulated for 30 ka, consist of peat, silt, silt with organic matter, sand and gravel, and 4 tephras K-Ah, SUk, DHg, and AT. These deposits can be classified as fluvial material and eolian dust on the basis of the characteristics of ESR oxygen vacancy and grain size distribution. The fluvial material consists of coarse grain of more than 30 μm, while eolian dust consists of a finer material of less than 20μm. Peaks of lithogenic matter density, which consists of fluvial material, may be correlated with Interstadials 1 to 4, as indicated by the GRIP climate record. Fluvial materials were deposited during warmer, wetter periods such as the interstadial periods, whereas eolian dust was deposited during the drier colder periods of MIS 2 and 3. As Hosoike moor was located north of the polar front during MIS 2 and 3, eolian dust was transported from the pre-Cambrian rock areas of north Asia by northwesterly winds. During MIS 1, eolian dust is transported from the Chinese inland deserts by westerly winds.
On Oct. 8, 2005, a large earthquake occurred near the Main Boundary Thrust in the northwestern region of Pakistan. The earthquake showed a shallow rupture with a reverse fault-type focal mechanism, which probably represents the relative plate consumption between the Indian and Eurasian plates. The history of the Himalayan collision and features of earthquakes in the collision zone are reviewed.