著者

Mitsuhisa WATANABE

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:0022135X)

巻号頁・発行日

vol.116, no.3-4, pp.387-393, 2007-08-25 (Released:2009-11-12)

参考文献数

20

被引用文献数

3 6

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The cabinet office of the Japanese government demonstrated the prospects of future seismic hazards associated with a working model for possible earthquakes in the capital area of Japan. If this assumption is not unrealistic, it is reasonable to use this working model. However, it has already been reported that several active faults may exist in this area. This discrepancy can lead the assessment into unreal issue.I reveal the nature of the Ayasegawa fault located close to the capital area on the basis of geomorphic features. The fault extends in the NWSE direction for at least over 30 km, and the fault trace is linear, which is indicative of lateral movement. There is a graben structure delineated by the fault in the Minuma ward, Saitama City. The vertical component of the Ayasegawa fault is upthrown to the southwest and the average vertical slip rate is 0.05 to 0.1 m/ky. The netslip rate should be much larger than the vertical one, taking lateral movement into account. Although the single vertical offset is assumed to be 0.8 to 4 m, the rupture history of the fault remains unknown.The Ayasegawa fault is an southeastern extension of the Fukaya fault, and is composed of an active fault extending more than 120km through the Kanto Plain across the capital area of Japan. To prepare for a real seismic hazard and to try to reduce damage, we should check the properties and clarify the rupture history of these active faults as an urgent task. Precise local information on these active faults is necessary for motivating people to develop an awareness of disaster mitigation.

著者

Isamu KAYANE

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:0022135X)

巻号頁・発行日

vol.98, no.2, pp.128-138, 1989-04-25 (Released:2009-11-12)

参考文献数

22

被引用文献数

1

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Both river and groundwater are mode of occurrence of water in the hydrologic cycle. Relation between river water and groundwater are discussed on the basis of groundwater flow system, whose water table configuration is controlled by the topography and the distribution of specific flux within the system by the geology. Examples of the relation are shown for sand dunes, mountains composed of permeable rocks, volcanoes, hills, uplands, alluvial fans and lowlands.

著者

Kayori MAENO Hiroo OHMORI Jun MATSUMOTO Taiichi HAYASHI

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:0022135X)

巻号頁・発行日

vol.113, no.4, pp.512-523, 2004-08-25 (Released:2009-11-12)

参考文献数

23

被引用文献数

2 1

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This paper analyzes the characteristics of daily precipitation during the monsoon season from June to September for 21 years from 1976 to 1996 in Nepal, which is situated in the southern Himalaya. The average monsoon precipitation, and the number of rainy days in Nepal are 1, 410 mm, and 73 days, respectively. On the basis of the total monsoon precipitationand the number of rainy days, 1978, 1984, and 1985 are classified as wet years, and 1977, 1979, and 1992 are classified as dry years. Nepal is divided into six regions on the basis of the statistical characteristics of total monsoon precipitation and number of rainy days.On the other hand, the distribution pattern of 5-year probable rainfall in Nepal, is considerably different from that of average monsoon precipitation. Five-year probable rainfall is small in northern Nepal, and becomes large toward the south. On the basis of 5-year probable rainfall, which is regarded to be the threshold value of heavy rainfall in Nepal, heavy rainfall occurred more frequently in 1981 and 1987. These years did not agree with the wet years based on total precipitation and number of rainy days, indicating that the occurrence of heavy rainfall that causes water hazards in Nepal does not synchronize with wet years.

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:18840884)

巻号頁・発行日

vol.90, no.1, pp.25-37, 1981-02-25 (Released:2010-10-13)

被引用文献数

2

著者

Shigeko HARUYAMA Masahiko OYA Yoshio MIZUHARA

出版者

Tokyo Geographical Society

雑誌

Journal of Geography (Chigaku Zasshi) (ISSN:0022135X)

巻号頁・発行日

vol.101, no.2, pp.89-106, 1992-04-25 (Released:2010-10-13)

参考文献数

7

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We have conducted our research on the influence of the eruption of the Kelud Volcano on the Kali Brantas, conservation of the river basin, mitigation of the resulting volcanic and flooding hazards, and development process of the basin.For this purposes, we have made geomorphic land classification maps in the Kali Brantas Basin, utilizing the aerial photographs (scale is around 1/40, 000) and LANDSAT Images which were taken in 1972.The Kali Brantas is located in the eastern part of Java, i. e. easternmost part of the Himalaya-Alps Orogenic Zone. The Kali Brantas originates in Mt. Arjuno and round the foot of the Butac and Kelud Volcanos which are active volcanos, and then pours into the Madura Strait.The southern part of the Kelud Volcano consists of the following geomorphic elements: piedmont gentle slope of the volcano, a slightly hilly area on the gently sloping terrace, valley floor plain, marsh, abandoned river course, steep slope, etc.The Kali Brantas plain consists of the following geomorphic elements: natural levees, back-swamps, a delta, lagoon, sand-spits, etc. Natural levees are developed well around the city of Kediri and the river bed is higher than that of the adjacent plain.The Kelud Volcano has erupted approximately once every 15 years. We have a record of its eruption since 1, 000 years A. D. The eruption in 1919 was especially severe, and about 3, 800×104m3 of “Lahar” flowed down to have killed 5, 100 persons. Due to the eruption in the year 1586, about 10, 000 persons were killed.In order to mitigate the damage by “Lahar” a tunnel for decreasing water in the crater was constructed during the Dutch Colonial period. This drainage tunnel reduced the volume of the water from 4, 000×104m3 to 2, 000×104m3 in 1966. After the construction of the tunnel, the lahar damages decreased. However, aggradation as a result of this eruption reduced the depth of the crater about 50m to destroy the tunnel. Then the tunnel was repaired again.After 1970, thre lowering of the river bed has occured partly because of the construction of dams, particularly the construction of “Sabo” dam for “Lahar” and partly the because of the volcanic eruption. Although the lowering of the river bed decreased the possibility of the flooding, it becomes difficult to take the water for irrigation.In February 1990, the Kelud Volcano erupted again. And a lot of volcanic ash was deposited on the southern slopes of the volcano. The tunnel disappered again. So we must look again for the tunnel. Directly after the eruption, torrential rainfall occurred at the upper reaches of the Brantas River. The erosion in the upper reaches was remarkable and a lot of sand and gravel flowed down to the middle reaches and several reservoirs were burned immediately.In conclusion, we would like to indicate that it is very important to predict the geomorphological changes of the river basin in the case of making development plain of the river basin.