著者

石橋 克彦

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.31, no.3, pp.342-345, 1978-10-31 (Released:2010-03-11)

参考文献数

12

著者

佐伯 龍男 梅田 康弘

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.41, no.2, pp.163-171, 1988-06-25 (Released:2010-03-11)

参考文献数

13

被引用文献数

2

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The high accelerations exceeding the earth's gravity were observed on the small area near the main shock of the 1984 Western Nagano Prefecture Earthquake (M=6.8). Few aftershocks occurred in this small high acceleration spot of main fault. It is inferred that great destruction producing the high accelerations occurred within this small spot. For detecting the evidence of great destruction, we tried to investigate the crack orientation and density by using Shear-wave polarization method.We have identified that directions of polarization in and out of the high acceleration spot are N40-70°W. These directions are consistent with the axis of maximum compression obtained from earthquake fault mechanisms and geodetic surveys. There are no difference in polarizations between in- and out of the high acceleration spot. It suggests that open-cracks had been made before the main shock. Great destructions of the main shock seems to have little influences on S-wave polarization. The average time-lag between arrival of leading and slower shear-wave is 0.02S. It indicates that present open-cracks are distributed in a shallow depth.

著者

梅田 康弘 黒磯 章夫 伊藤 潔 飯尾 能久 佐伯 龍男

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.2, pp.217-228, 1986-06-25 (Released:2010-03-11)

参考文献数

27

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Many boulders were thrown off out of their former sockets by the Western Nagano Prefecture Earthquake of September 14, 1984. Anomalous high accelerations of 5-30g, in the frequency range of 5-10Hz, are estimated from the displacement of these thrown out boulders.Almost all of the thrown out boulders were found on the tops, ridges and suddles of the mountains covered with the volcanic ash. The amplification effects by topography and soil sediment of the surface are estimated from the observation of the aftershocks recorded on the mountain-top, -foot and rock. The spectral ratios of seismic waves with the frequencies of 5-10Hz, namely mountain-top/-foot and soil/rock, are 2-7 and 2-10, respectively.The accelerations on the basement rock are obtained dividing the accelerations estimated on the mountain-tops. The high accelerations exceeding 1g distribute within a small area with a length of 3km and a width of 1km. This small area corresponds to the large dislocation portion of the assumed fault and the low active region of aftershocks.

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

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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.

著者

杉崎 隆一 杉浦 孜

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.99-109, 1986-03-25 (Released:2010-11-17)

参考文献数

31

被引用文献数

1

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Remarkable anomalies in gas compositions were observed at a fumarole and three mineral springs before the Western Nagano Prefecture Earthquake, 1984. The epicentral distance are 9 km for the fumarole and 50 km, 71 km and 95 km for the springs, respectively. Deep seated gas emission induced by the compressive stress of the earth tide had been observed previously at the two mineral springs as the monitoring stations and at a lava lake in Hawaii. It is analogically inferred that the gas anomaly before the earthquake can be attributed to the variation in the emission rate of deep seated gas resulting from changes in pore pressure and magma-reservior volume, which are subjected to the tectonic stress that caused the earthquake. Another aspect is emissions of H2 gas at three mineral springs and gases from different sources at one spring. These indicate the formation of new cracks near monitoring stations and the permeation of groundwater into the cracks. The mechanical processes inferred from the present geochemical observation are compatible with those described by geophysical models based on fracturing experiments.