A gravelly spit-offshore gravel bar model convincingly explains the depositional process of gravel beds in a transgressive systems tract. According to this model, large-scale gravelly foreset beds are deposited on the slope of a spit platform, which is the subaqueous portion of a gravelly spit. Massive, horizontally stratified, or planar cross-stratified subhorizontal sets (topset beds) overlie the foreset beds, and exhibit a foreset and topset structure. The topset beds include nearshore deposits on the spit platform and offshore gravel bar deposits, which are reworked sediments from the pre-existing spit-beach gravels that had formed during a transgression. Large-scale foreset beds of gravelly spits have a high preservation potential, because gravelly spits are likely to form in fluvially incised valleys, in which gravelly spit deposits are preserved from truncation by shoreface erosion during shoreface retreat. The gravelly spit provides a new example of large-scale foreset beds. The foreset beds of the gravelly spit are easily differentiated from those of fluvial gravel bars and tidally influenced dunes in a marine environment, but are similar to those of Gilbert-type deltas. Sequencestratigraphic interpretations differ depending on the depositional model that is applied to the foreset beds : a delta during a highstand, lowstand, or shelf-margin systems tracts; a gravelly spit in a transgressive systems tract. At this point we need to find a criterion to differentiate the foreset beds of gravelly spits from those of deltas.
The use of humic acid green fraction (Pg) as a paleoenvironmental indicator still requires integrated case studies applied to tephra and loess soil sequences (Watanabe and Kado, 2000; Watanabe et al., 2001a), as well as biochemical studies on humic acid Pg (Watanabe et al., 2001b). The stability and the chemical transformation of humic acid Pg should be elucidated by investigating paleosols and terrestrial deposits. This study aims to clarify the properties of humic acid green fraction Pg in the Shimosueyoshi buried layer (SB layer), the buried humic soil originating from tephra supplies of Hakone Caldera, corresponding to Marine oxygen isotope stage 5e. Pg absorption strength (Pg abs), total carbon content (TC), carbon content of extracted humic acid (CHA), pH (NaF) value, major element compositions, and phytolith analyses, together with selective dissolution of Fe compounds, and color measurement according to CIE color system were conducted. The obtained results were : 1) Clear Pg absorption bands at around 450, 570, and 615 nm were detected from all the humic acid of paleosols, corresponding to > 100 ka, located at Oiso Hill, central Japan. The fluctuation of Pg abs of humic acid in the investigated profile showed a significant increase in the SB layer (ca. 130 ka), equivalent to the early stage of MIOS 5e. 2) According to the measurement error of Pg abs determined through the profile, the significant level of Pg abs in this study is confirmed to be much lower than that of Pg abs in previous studies carried on younger tephra soil sequences. It is considered that humic acid Pg is transformed in paleosols over 100 ka. 3) Although the relations among amorphous and crystalline iron hydroxides and Pg absorption strength were not clear in this profile, unlike the previous reports (Kawahigashi et al., 1999, Watanabe and Kobayashi, 2001), the SB layer was characterized by the existence of geothite-like iron hydroxides, suggesting a humid environment.
The Ca-zoning of garnet in Sanbagawa pelitic schist shows its maxima at the intermediate region. The compositional trend of the grossular component, which is controlled by a dehydration-decarbonation reaction of 2Clinozoisite + 5Calcite + 3Quartz = 3Grossular + 5CO2 + H2O, is examined thermodynamically in the system of CaO-TiO2-Al2O3-SiO2-C-H2-O2 in the presence of calcite, clinozoisite, quartz, graphite, and fluid phase to estimate changes in pressure, temperature, and fluid composition during Sanbagawa metamorphism. At the onset of garnet formation, the chemical composition of a metamorphic fluid was low in XCO2 because titanite was stable in pelitic schists from the chlorite zone. With the formation of garnet, XCO2> increases. XCO2 released by the garnet formation at XCa = 0.35 is 0.240 and led the pelitic system to the XCO2-buffered system defined by the reaction of Titanite + CO2 = Calcite + Rutile + Quartz. In the XCO2-buffered system, the grossular content of garnet is determined as a function of pressure and temperature. The isopleth of the grossular content of garnet on the pressure-temperature diagram depends slightly on pressure and distinctly on temperature. In carbonate-bearing metamorphic rocks, mixed volatile reactions take place at much lower temperatures than dehydration reactions for major mineral formations.
The Median Tectonic Line (MTL) active fault system is one of the most active intraplate faults in Japan. The fault system, which is more than 300 km long, is a right-lateral strikeslip fault with an average slip rate of 5-10 mm/y in east Shikoku. The 13.5-km-long Mino fault of the MTL active fault system is located at the western part of Tokushima Prefecture in east Shikoku. We carried out trench excavation surveys of the Mino fault at Ueno in Mino Town and Ikenoura in Mima Town. Both sites are situated at fault depressions formed on the middle and lower terrace surfaces by the activity of the Mino fault. Fault depression deposits consist of younger and finer grained layers with abundant 14C dating samples. We inferred the dates of faulting events from upward fault terminations on the trench walls. At Ueno, it is recognized that the latest rupture event occurred between 1, 295-1, 390 cal A.D. and 1, 660-1, 950 cal A.D. (190 ± 50 years B.P.). Multiple faulting events are also suggested after K-Ah ash fall (about 5, 200 B.C.), because the ash layer steepens to near vertical. At Ikenoura, the latest rupture event is estimated to have occurred after 1, 525-1, 660 cal A.D. Taking account of the previous reports on the eastern extension at Chichio and Zunden faults, we conclude that the MTL active fault system in east Shikoku ruptured in the 16th century A.D. or later. The liquefactions, which occurred between the latter half of the 16th century A.D. and the beginning of the 17th century A.D., are recognized at archaeological sites at Maruyama and Ogaki in the western part of Tokushima Prefecture. These sites are located immediately south of the Mino fault and the Ikeda fault to the west. This fact suggests that the liquefactions were caused by faulting of the MTL active fault system in east Shikoku.
The Middle to Upper Permian shallow-water limestone in the Kamura area in central Kyushu was originally derived from an mid-superoceanic paleo-atoll on a seamount, although it occurs at present as an allochthonous block in the Jurassic accretionary complex of the Chichibu belt. A secular change in stable carbon isotopic composition (δ 13Ccarb) is revealed from 64 samples of the limestone at Kamura; the Middle Permian (Guadalupian) black limestone of the Iwato Formation (with 19 m thickness) and the overlying Late Permian (Lopingian) light gray limestone of the Mitai Formation (with 17 m thickness). The δ 13Ccarb values of the study section range from + 1.87 to + 6.21‰. The profile of δ 13Ccarb in the study section is divided into five stratigraphic intervals, i.e., 1) 11 m interval of + 5‰, 2) 2 m interval of sharp decline from + 5.29 to + 2.93‰, 3) 4 m interval of 2‰ increase, 4) 4 m interval of 2‰ decline, and 5) 9 minterval of 1.5‰ increase, in ascending order. The intervals 1) and 2) correspond to the Middle Permian black limestone (Iwato Formation), while the intervals 3), 4), and 5) correspond to the Upper Permian light gray limestone (Mitai Formation). It is remarkable that δ13Ccarb values drop sharply for about 2‰ at the top of the Middle Permian. The sharp change both inδ13Ccarbvalues and in lithofacies across the boundary between the Iwato/Mitai Formations mayhave been linked to the Guadalupian-Lopingian boundary evevnt and related global environmental change.
Urban heat island (UHI) phenomenon, as an important environmental issue affecting cities, has received much attentions in the past decades. The spatial structure of UHI, however, is not easy to verify in detail because of the complexity of its mechanism and cost of observations. Many researchers have studied this issue with satellite sensed thermal images, based on the assumption that the remotely sensed surface temperature and the ground air temperature are correlative to a large extent. This study, focusing on Tokyo Metropolitan Area, examined the statistical and spatial correlation between remotely observed brightness temperature and ground air temperature observation. Five scenes of thermal images of Landsat TM, including two daytime ones and three nighttime ones, and about 100 stationary meteorological observations have been used as data sources. The ground air temperature extracted from the meteorological records is compared separately to the satellite-estimated surface temperature for each data set and each radius from 100 m to 1000 m around meteorological stations. As a result, the following factors are concluded. The correlation coefficient between ground-observed air temperature and satellite derived surface temperature could reach 0.9 under good observation conditions. However, the magnitude of the coefficients is affected by weather conditions, time and date of data acquisitions as well as spatial scale of data aggregation. Wind speed not only affects the intensity of UHI but also the correlation coefficients of surface temperature and air temperature. The weaker the wind is, the stronger the UHI is, and the larger the coefficient is between the two measurements. The correlation coefficients between the two are weak on daytime images but strong on nocturnal images. This suggests that nocturnal thermal images prefer to capture the same structure of a surface heat island with air heat island at night. Emissivity correction of surface temperature can enhance the correlation, but the intensity of improvement is uncertain. The gap of correlations between nocturnal images and daytime images could not be closed up sufficiently with an emissivity correction. The surface temperature from the radiative power is mainly influenced by the urban canopy layer composed by micro land features. However, the ground air temperature is also affected by the local or mesoscale urban boundary layer. This essential difference causes the correlation of surface temperature and air temperature spatial-dependently. The maximal correlation is within 600 m around a meteorological station. Therefore, the range of 400-600 m may be a reasonable distance for planners to discuss mitigation policy. This could also be a reference to decide the spatial resolution in a simulation model. The simple linear regressive equation in this paper could not be applied to other data and other cities. However, this study successfully verified the possibility of transferring satellite derived surface temperature to air temperature. This is meaningful for researchers and planners to explore the structure of heat islands or to discuss mitigation policies in microscale. Further research is in progress to identify the correlations between air temperature and surface temperature with urban landforms and environmental factors.
Although the climatic environment has not been quantified, it is commonly believed that subtropical dry scrub is distributed in the dryer areas of Chichijima Island in the Ogasawara (Bonin) Islands, the northwestern Pacific. To clarify the hydroclimatic conditions of subtropical dry scrub, year-round atmospheric and soil moisture observations were carried out in an area of subtropical dry scrub at Hatsune-yama Point in the eastern part of Chichijima Island. In the summer of 2001, the forest height and cover ratios of all scrub and forest species, and soil moisture, were measured at twelve sites on the island, including Hatsuneyama Point, along an east-west transect across the ecotone between subtropical dry scrub and secondary mesic forest. The subtropical dry scrub was not distinguished from the mesic forests by year-round dry atmospheric conditions; annual precipitation was larger and potential evaporation weaker at Hatsune-yama Point than at Chichijima Observatory on the western side of the island. At the former, however, the lack of precipitation and the very high potential evaporation extremely depleted soil moisture, to less than 20 volumetric %, during the summer, just after the rainy season. This severe depletion of soil moisture occurred only in the areas of subtropical dry scrub, and, consequently, formed a dry-wet gradient of soil moisture across the ecotone between the subtropical dry scrub and the secondary mesic forest. Since forest height was significantly correlated with this dry-wet gradient of soil moisture, the degree of depletion of soil moisture during summer just after the rainy season presumably affects forest structure on Chichijima Island. Based on these results, we conclude that subtropical dry scrub is distributed only in areas with seasonally dry edaphic conditions. This demonstration of hydroclimatic conditions using observational data implies that edaphic heterogeneity determines the vegetation pattern on Chichijima Island.
Yaku-shima is a mountainous island, with area of approximately 500 km2 and peak of 1, 935 m, located in the western North Pacific around 30° N, 131° E (Fig. 1). This island is known as one of the highest precipitation areas in Japan where annual mean precipitation in the mountainous region exceeds 7, 000 mm. In the present study, distribution of monthly and annual mean precipitation is presented, and that of heavy rainfall days when daily precipitation exceeding 100 mm is observed at least one station in the island is investigated by using station data in so far as possible. For the mean distribution, data of 16 stations are available, while for heavy rainfall distribution data of 23 stations are utilized (Table 1). First, distribution of monthly and annual mean precipitation is presented. Monthly mean precipitation at some stations is over 1, 000 mm in June or September (Fig. 2). Annual mean precipitation exceeds 5, 000 mm in the inland area, with the highest value of 7, 373 mm in the southeastern part (Fig. 3). Next, precipitation distribution of heavy rainfall days from 1996 to 1998 is analyzed as follows : for each heavy rainfall day when rainfall amount over 100 mm/day is observed at anystations in the island, “relative precipitation (RP)” is calculated as a ratio of daily precipitation at each station to the maximum daily precipitation observed in the island on the same day. The cause of rainfall on each heavy rainfall day is identified as typhoon (Ty), extratropical cyclone (Ec), stationary front (Sf), or cold front (Cf), by inspecting daily surface weather charts analyzed by the Japan Meteorological Agency. Then, “averaged relative precipitation of heavy rainfall days (ARP)” is computed by averaging RP at each station classified by each synoptic system (Fig. 4). For ARP distribution due to Ty, ARP is very high in the inland area but in contrast it is very low in the coastal area. For ARP distributions due to Ec, Sf, and Cf, the highest ARP (over 0.6) area is located in the southeastern part of the inland area. However, the moderate ARP (0.3-0.5) area is expanding more westward in case of Cf, but it is located in only eastern part in case of Ec. Applying a cluster analysis to monthly mean precipitation and ARP, Yaku-shima Island is divided into 5 regions (Fig. 7). In region A, located in the coastal area except for the eastern coast, precipitation is relatively low in each month and ARP is also low in all cases. In region B of the southeastern coastal area, precipitation is high in March and April, and ARP is high in case of Ec, Sf, and Cf. In region C of the southeastern inland area, precipitation is high in each month and ARP is high in all cases. In region D of the northern inland area and the northeastern coastal area, precipitation is high in August and September, and ARP is high in case of Ty. In region E of the central inland area, ARP is high in case of Ty, Sf, and Cf.
Trench excavation is a less effective paleoseismic investigation for intramontane active faults because there are fewer good trench sites along them. We propose a new method called “pit excavation on a mountain slope” to determine the timing of the latest events of such faults. This method is carried out across a small uphill-facing fault scarp preserved on a mountain slope. Sediment trapped by the scarp should provide good information concerning the timing of the latest event. We applied the method to the northern segment of the Daguchi fault, one of the short rightlateral active faults in the Nosaka Mountains, north of Lake Biwa, southwest Japan. The rupture history of the segment has remained unknown because no good trench site exists along the fault trace. However, our precise geomorphological mapping revealed the presence of a 1 m-high uphill-facing fault scarp preserved on a mountain slope, and therefore we carried out a pit excavation across the scarp using man power. A very clear fault and 75 cm-thick trapped sediments were observed on the pit wall. Since these sediments showed neither displacement nor deformation associated with surface faulting, we interpret that they were all deposited after the latest event. For more accurate age control, we identified species and portion for wood fragments from the sediments. Unfortunately, all samples except those that could not be identified were parts of Cryptomeria japonica, Chamaecyparis obtusa Endl. or Cupressaceae, which can live for hundreds or even thousands of years : this means a possible large offset between deposition and radiocarbon age for these samples, leading to less accurate age control. However, some of them were from the outermost trunk, for which we can regard radiocarbon age as the deposition age in consideration of the very small catchment area of the pit site (several hundreds of m2). Based on the radiocarbon ages of the outermost trunk samples, the initiation of sediment trapping or equivalently the timing of the latest event is estimated to be about 1500 years ago (5th to 7th century AD). Our investigation on the Daguchi fault successfully revealed the accurate timing of the latest event, supporting the effectiveness of our new method. However, some problems remain unsolved, including application of the method to other faults, especially those with long dormancy, and necessity of a crosschecking excavation on a historically ruptured fault.
The purpose of this paper is to discuss the digitization of CORONA Satellite Photographs Positive Film (CSPPF) and its availability based on actual data of constructions and field survey, focusing on the active faults and the historical ruins of the Turpan Basin, North West of China. The following results were obtained : 1) The direct stereo-optical interpretation of the CSPPF with two zoom lupes, providing more detailed information than a single image, targets with a diameter of 4 m and lineament, such as active faults, with 5 m relative height can be recognized. 2) Two kinds of the digitized CSPPF image, namely Direct Digitized Image (DDI) and Expanded Digitized Image (EDI), were used for the detailed interpretation results. Digitization of the CSPPF makes it easy to exhibit the interpretation results and the stereooptical images through image processing. 3) Both the target with a diameter of 7 m on the EDI and those of 10 m on the DDI can be recognized. The low linear object with a relative height of 5 m such as fault scarps and walls of ruins are also recognized on both images. Concluding from the above, DDI has sufficient resolution to interpret and display low fault scarps and cliffs of terraces. 4) Both positive and negative films can be digitized, but with the former it is easier to obtain the actual image than the latter. It is efficient to select positive films to interpret small targets such as watch-towers.