Structure of the subsurface counter current beneath the Tsushima warm current simulated by an ocean general circulation model     

You-Ichiro Sasajima  Satoshi Nakada  Naoki Hirose  Jong-Hwan Yoon 《Journal of Oceanography》2007,63(6):913-926

The subsurface counter current beneath the Tsushima Warm Current is simulated using a three-dimensional circulation model. The model well reproduces the counter current beneath the Tsushima Warm Current on the shelf break. The counter current appears as nearshore parts of the subsurface clockwise circulations from spring to early winter. The clockwise circulations are separated by developed shelves such as the Oki Spur and the Noto Peninsula, thus the counter current is not a continuous flow along the Japanese coast in this model. The vertical structure of the counter current can be explained by a density structure with the thermal wind relationship. The permanent and seasonal pycnoclines form mutually opposite horizontal density gradients near the Japanese coast in summer. Such a density structure results in a speed maximum of the counter current away from the bottom. It is remarkable that the second baroclinic mode is dominant in nearshore parts of the subsurface clockwise circulations in summer, which are attributed to the density structure. Similar density structures are also found in some coastal regions of the world oceans where subsurface counter currents are expected.  相似文献   

Seasonal Variations of Water Properties and the Baroclinic Flow Pattern in Toyama Bay under the Influence of the Tsushima Warm Current     

Satoshi Nakada  Yutaka Isoda  Isamu Uchiyama 《Journal of Oceanography》2005,61(5):943-952

The seasonal variations of water properties and the baroclinic flow pattern in the upper layer of Toyama Bay, where the shelf breaks in the passway of the eastward coastal branch of the Tsushima Warm Current, have been examined using temperature and salinity data from 26 local stations collected in the 32 years from 1963 through 1994. The results show that the flow pattern around the bay, as inferred from the distributions of the geopotential anomaly at 300 dbar and saline core water, changes remarkably from summer to autumn. There are two obvious inflows into Toyama Bay in a year. One is the surface inflow of less saline water from east of the Noto Peninsula as the coastal-trapped density-driven flow of the coastal branch during the transition from May to July. In September, this inflow is abruptly weakened by a transient northwestward reversal flow in the intermediate layer around 100 m depth. This reversal flow is accompanied by the temporary shallowness of the pycnoclines inside the bay. At that time, another inflow with more saline water of the year occurs in the intermediate layer. From November until January, this reversal flow disappears and a southeastward passing through-flow gradually intensifies across the bay mouth, accompanied by deepening of the pycnoclines inside the bay. According to our interannual analysis over the 32-year study period, this reversal flow has been a stable seasonal phenomenon, except for only 4 years, in which a local warm region or warm eddy developed just north of the Noto Peninsula.  相似文献   

Interpretation of landslide distribution triggered by the 2005 Northern Pakistan earthquake using SPOT 5 imagery   总被引：7，自引：4，他引：7  

Hiroshi P. Sato  Hiroyuki Hasegawa  Satoshi Fujiwara  Mikio Tobita  Mamoru Koarai  Hiroshi Une  Junko Iwahashi 《Landslides》2007,4(2):113-122

The 2005 northern Pakistan earthquake (magnitude 7.6) of 8 October 2005 occurred in the northwestern part of the Himalayas. We interpreted landslides triggered by the earthquake using black-and-white 2.5-m-resolution System Pour l’Observation de la Terre 5 (SPOT 5) stereo images. As a result, the counts of 2,424 landslides were identified in the study area of 55 by 51 km. About 79% or 1,925 of the landslides were small (less than 0.5 ha in area), whereas 207 of the landslides (about 9%) were large (1 ha and more in area). Judging from our field survey, most of the small landslides are shallow rock falls and slides. However, the resolution and whitish image in the photos prevented interpreting the movement type and geomorphologic features of the landslide sites in detail. It is known that this earthquake took place along preexisting active reverse faults. The landslide distribution was mapped and superimposed on the crustal deformation detected by the environmental satellite/synthetic aperture radar (SAR) data, active faults map, geological map, and shuttle radar topography mission data. The landslide distribution showed the following characteristics: (1) Most of the landslides occurred on the hanging-wall side of the Balakot–Garhi fault; (2) greater than one third of the landslides occurred within 1 km from the active fault; (3) the greatest number of landslides (1,147 counts), landslide density (3.2 counts/km²), and landslide area ratio (2.3 ha/km²) was found within Miocene sandstone and siltstone, Precambrian schist and quartzite, and Eocene and Paleocene limestone and shale, respectively; (4) there was a slight trend that large landslides occurred on vertically convex slopes rather than on concave slopes; furthermore, large landslides occurred on steeper (30° and more) slopes than on gentler slopes; (5) many large landslides occurred on slopes facing S and SW directions, which is consistent with SAR-detected horizontal dominant direction of crustal deformation on the hanging wall.  相似文献   

Earthquake-related Changes in Groundwater Levels at the Dogo Hot Spring,Japan   总被引：1，自引：0，他引：1  

Satoshi Itaba  Naoji Koizumi 《Pure and Applied Geophysics》2007,164(12):2397-2410

The Dogo hot spring, situated in Matsuyama City, Ehime Prefecture, Japan, is one of the oldest and most famous hot springs in Japan. The groundwater level or discharge at the spring decreased four times during the past eight or nine Nankai earthquakes. These are large interplate earthquakes that have occurred repeatedly in the western part of the Nankai Trough at intervals of 100–200 years since A.D. 684. To clarify the mechanism of these earthquake-related changes in the water level at the spring, we analyzed groundwater-level data recorded at the spring immediately after the 1946 Nankai earthquake and over the period from 1985 to 2006. We detected the other nine postseismic increases in groundwater level and no decreases, except for a large decrease of 11.4 m related to the 1946 Nankai earthquake. The increases were probably caused by ground-shaking, while the decrease was caused by a change in coseismic volumetric strain. These results lead to the following explanation of the recorded earthquake-related changes in the groundwater level at the Dogo hot spring. Both coseismic changes in volumetric strain and ground-shaking can lead to postseismic changes in groundwater pressure. The increase in groundwater pressure arising from ground-shaking is generally greater than the change in pressure associated with changes in coseismic volumetric strain; however, at the time of the Nankai earthquakes, the spring experiences a large increase in coseismic volumetric strain, leading to a considerably larger decrease in the groundwater level than the increase associated with ground-shaking. Therefore, the groundwater level at the Dogo hot spring usually increases at times of relatively large earthquakes, although the groundwater level or discharge decreases in the case of the Nankai earthquakes.  相似文献   

Microtopographic analysis of plant distribution in polar desert     

Masaki Okuda  Satoshi Imura  Masaharu Tanemura   《Polar Science》2007,1(2-4):113-120

We suggest methods for the analysis of the spatial distribution of plant species in a research area divided into a quadrat lattice. In particular, information about the topography and the spaces without plants is used for the analysis. At sites with a homogeneous substratum, we classify the topography by whether a target grid is concave or convex with respect to a standard surface of altitude. At other sites, we classify the topography according to whether the grid is located at the edge of rock and/or at a water pool. Information about the topography and the plant existence is used for constructing 2 × 2 contingency tables. In order to determine the strength of dependence between the topography and plant existence, the Akaike information criterion (AIC) is used. The methods are applied to data of the microtopography and distribution of mosses in continental Antarctica.  相似文献   

Detection of Aseismic Slip on an Inland Fault by Crustal Movement and Groundwater Observations: A Case Study on the Yamasaki Fault, Japan     

Yuichi Kitagawa  Naoji Koizumi  Ryu Ohtani  Kunihiko Watanabe  Satoshi Itaba 《Pure and Applied Geophysics》2006,163(4):657-673

To understand the detailed process of fault activity, aseismic slip may play a crucial role. Aseismic slip of inland faults in Japan is not well known, except for that related to the Atotsugawa fault. To know whether aseismic slip does not occur, or is merely not detected, is an important question. The National Institute of Advanced Industrial Science and Technology constructed an observation site near Yasutomi fault, a part of the Yamasaki fault system, and has collected data on the crustal strain field, groundwater pressures, and crustal movement using GPS. In a departure from the long-term trend, a transient change of the crustal strain field lasting a few months was recorded. It indicated the possibility of an aseismic slip event. Furthermore, analyses of data from the extensometers at Yasutomi and Osawa observation vaults of Kyoto University, as well as GPS data from the Geographical Survey Institute (GEONET), revealed unsteady crustal strain changes. All data could be explained by local, left-lateral, aseismic slip of the order of 1 mm in the shallow part of the Yasutomi fault.  相似文献   

Concentrations of 222 Rn, Its Short-Lived Daughters And 212 Pb And Their Ratios Under Complex Atmospheric Conditions And Topography     

Toshio Kataoka  Eiji Yunoki  Mitsuo Shimizu  Tadashige Mori  Osamu Tsukamoto  Satoshi Takahashi  Hironori Fudeyasu  Yukitaka Ohashi  Ken Sahashi  Toshihiko Maitani  Koh'ichi Miyashita  Toru Iwata  Takayuki Sasaki  Yoko Fujikawa  Akira Kudo  Roger H. Shaw 《Boundary-Layer Meteorology》2003,107(1):219-249

Atmospheric activity concentrations of ²¹²Pb and short-lived ²²²Rndaughters, together with meteorological elements, have been observed continuously atthree sites at Kamisaibara Village in Japan. In addition, atmospheric activity concentrationof ²²²Rn, equilibrium-equivalent concentration of ²²²Rn and conditionsof the lower atmosphere were observed for three intensive observation periods at Akawase,one of the three sites in Kamisaibara Village. The equilibrium-equivalent concentration of²²²Rn is almost the same as the atmospheric activity concentration of short-lived²²²Rn daughters.The activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughtersand their ratio were low in the daytime owing to convective mixing, and high at nightowing to the surface-based inversion during periods of no precipitation. Their variationshave several patterns corresponding to the scale of the drainage wind or weak mixing.Mechanical mixing due to strong winds through both day and night during the first andsecond observation periods made the atmospheric activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughters continuously low. However, their ratios werecontinuously high during the first period yet continuously low during the second period.This difference can be explained by the effect ofextraction of ²²⁰Rn and ²²²Rndue to strong winds and snow cover. There were also cases in which the ratio of theatmospheric activity concentration of ²¹²Pb to that of the short-lived ²²²Rndaughters at night was equal to or less than the ratio in the daytime. Thisinverse trend, asin the periods of no precipitation mentioned above, is considered to be due to near-neutralconditions on these nights.We find a difference in the ratio of the equilibrium-equivalent concentration of²²²Rn (the activity concentration of short-lived ²²²Rn daughters) tothe activity concentration of ²²²Rn during the first observation period and thatduring the second. The difference can be explained by snow cover on the ground. Wealso find differences among the ratios of the activity concentration of the short-lived²²²Rn daughters to that of ²²²Rn during the three observation periods.These differences can be explained by the submergence of paddy fields.  相似文献   

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake     

Tatsuo Matsuda  Kentaro Omura  Ryuji Ikeda  Takashi Arai  Kenta Kobayashi  Koji Shimada  Hidemi Tanaka  Tomoaki Tomita  Satoshi Hirano   《Tectonophysics》2004,378(3-4):143

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.  相似文献   

Changing distribution of gender in the Extended Bangkok Region under globalization     

Satoshi Nakagawa 《GeoJournal》2004,61(3):255-262

This study examines recent changes in the structure of migration and population by gender in the Extended Bangkok Region (EBR) taking the influences of economic globalization into consideration. The EBR is understood here to consist of three concentric zones, namely the Bangkok Metropolis (BM), the Vicinity and the Extended Urban Region (EUR). The spatial policy of the Thai government has encouraged investors to build manufacturing factories outside the BM. Consequently the industrial structure of the BM has turned strongly into service-dominated while the Vicinity and the EUR have attracted factories mainly owned by foreign capitals. Light industries and electronics industries, both of which set up relatively earlier, concentrated on the Vicinity, the adjacent provinces to the BM, while heavy and petrochemical industries are recently have developed in the outer regions, the EUR. Service sectors and light industries as well as electronics industries prefer females to males to employ as workers. As a consequence the population structures of the BM and the Vicinity became female-dominant while male workers were likely to gather in the EUR attracted by heavy and petrochemical industries. The gender imbalance in the population in the areas in concern may have been one of the consequences of the economic globalization of Thailand. The Thai government supported the economic globalization through its investment promotion policy, but it seems that the government did not assume the policy resulted in such gender imbalance. It can be suggested that in the future this gender imbalance may cause changes in family formation behaviors of the Thai population. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993     

Srivastava  Nandita  Gonzalez  Walter D.  Gonzalez  Alicia L.C.  Masuda  Satoshi 《Solar physics》1998,183(2):419-434

Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.  相似文献