Anomalous change in atmospheric radon concentration sourced from broad crustal deformation: A case study of the 1995 Kobe earthquake |
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| Authors: | Yumi Yasuoka Yusuke Kawada Yasutaka Omori Hiroyuki Nagahama Tetsuo Ishikawa Shinji Tokonami Masahiro Hosoda Tetsuo Hashimoto Masaki Shinogi |
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| Institution: | 1. Institute of Radioisotope Research, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada-ku, Kobe 658-8558, Japan;2. Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan;3. National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan;4. Department of Geoenvironmental Sciences, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai 980-8578, Japan;5. Department of Radiation Physics, Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Hon-cho, Hirosaki, Aomori 036-8564, Japan;6. Department of Radiological Life Sciences, Graduate School of Health Sciences, Hirosaki University, 66-1 Hon-cho, Hirosaki, Aomori 036-8564, Japan;g NRI-Institute, 2-2-10 Teraomae-dori, Nishi-ku, Niigata 950-2053, Japan |
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| Abstract: | Before the Kobe earthquake, an anomalous increase in atmospheric Rn concentration was observed. By separating the measured concentration of atmospheric Rn into three components according to the distance from the monitoring station, the variation of Rn exhalation rate can be estimated for the respective area using the daily minimum and maximum concentrations. The mean rate of Rn exhalation gradually increased in an area of 20 km around the monitoring station, becoming five times higher than normal in the period between October 1994 and the date of the earthquake. This area had a large co-seismic displacement of up to 30 cm, which roughly corresponds to the crustal strain of 10−6-order, and it is considered the main source for the atmospheric Rn prior to the Kobe earthquake. Analyses revealed that the pre-seismic change in the atmospheric Rn concentration exhibited an anomalous pattern which would yield information on the spatial distribution of the mechanical response of the ground. |
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