著者
田口 雄作 吉川 清志
出版者
The Association of Japanese Geographers
雑誌
地理学評論 (ISSN:00167444)
巻号頁・発行日
vol.56, no.11, pp.769-779, 1983-11-01 (Released:2008-12-24)
参考文献数
11
被引用文献数
1 2

1981年8月24日午前2時12分頃,利根川支流小貝川の左岸堤防が,台風8115号のもたらした降水による増水のため,茨城県竜ヶ崎市内で決壊した.冠水域は竜ヶ崎市を中心に,約3,300haに及んだ. 筆者らは,冠水域内の165地点の標高点において,洪水痕跡から浸水流の最高水面標高の測定を行なった.また,氾濫時に撮影された空中写真の判読等によって検討を加えた結果,浸水流の挙動に関し,次のような知見を得た. (1) 浸水流は北上流,直進流,南下流の3つの主要な流下方向を有していた.このうち,最も水勢が強く,浸水流の主流となったのは南下流であった. (2) 浸水流は水勢の強い時には,地表面の起伏にあまり支配されずに直進するが,流心から離れるに従って,あるいは水勢が弱まるに従って,地表の低まりに追従する. (3) 論所排水は,洪水排水総量は多かったかもしれないが,浸水流の主要な流路ではなかった. (4) 江戸時代に築かれた内堤防の存在の有無が,今回の冠水域の拡大に,大きな影響を及ぼした. (5) 古文書など諸資料から,経験的な土地利用,防災対策を読み取り,活用することは,現代社会にとっても大いに重要である.
著者
吉川 清志
出版者
公益社団法人 東京地学協会
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.99, no.7, pp.743-758, 1990-12-25 (Released:2009-11-12)
参考文献数
32
被引用文献数
9 18

Inductively coupled plasma emission spectrometry (ICP) is applied for the chemical analyses of volcanic glasses to improve the efficiency of identification of widespread tephra.The differences of specific gravity and magnetic property among glass and minerals are effective for purification.The ICP method is very useful for routine analyses. The values of chemical analysis by the ICP are close to the EPMA data. The reproducibility is exellent, while fluctuation coefficients of most elements of tephra are about 5 %. Good correlations are found between the sum of major elements except of SiO2 and the refractivity of glass, and between the Fe/Mg ratio and the refractivity of orthopyroxene.Unique tephra in middle Pleistocene can be classified into two different groups of tephra by their minor elements Y and MnO. Tephra in north eastern Hokkaido are mainly came from two sources, which can not be distinguished in the field. The contents of incompatible elements of two types of tephra are clearly different. The source regions of Pliocene to Pleistocene tephra in Tokai and Kinki area can be estimated by the regional characteristics of their chemical compositions. The ICP method is also successfully applied for identification of submarine tephra in eastern Japan Sea, and correlation of sediments of Kanto to Kyushu areas and discovery of source of some widespread tephra in early to middle Pleistocene.
著者
加藤 完 高橋 誠 吉川 清志
出版者
公益社団法人 日本地震学会
雑誌
地震 第2輯 (ISSN:00371114)
巻号頁・発行日
vol.39, no.1, pp.47-55, 1986-03-25 (Released:2010-11-17)
参考文献数
16
被引用文献数
2

Weekly monitoring of radon concentration in soil gas in some active fault areas has been carried out using cellulose nitrate film as a part of earthquake prediction research. As the results of observation, we found increase of track density (tracks/cm2day) along the Median Tectonic Line (distance 100km) and the Matsushiro fault (_??_100km) since summer of 1982 and along the Ateta fault (_??_25km) since summer of 1983. We considered it as a precursor of the Western Nagano Prefecture Earthquake, 1984, by the reason that this increase just fit with the empirical formulas which relate the distance and apperance time of the precursory anomaly against the magnitude of an earthquake.At the same time, we found an annual variation of track density higher in summer and lower in winter. Supposing this annual variation being due to the seasonal variation of soil temperature, using uranium ore as source of random. As the result of experiment, it was clarified that track density increased with increased exposure temperature.