Possible underlying mechanism responsible for the earthquake lighting that appeared immediately before and after the 1995 M7.3 Kobe earthquake

Abstract

Immediately before and after the 1995 Kobe earthquake that occurred at 5:46 local time on January 17, 1995, the sky, which is normally dark at that time in mid-winter, displayed a mysterious illumination such that it became brighter like daytime, changed color, and after a while, returned to its normal dark appearance. This long-lived earthquake lightning (EQL) consisted of several luminous cloud masses floating in the lower atmosphere, from which mottled streak clouds, colored pale bluish, whitish, and reddish extended into the sky. This EQL did not occur above the Rokko-Awajisima fault zone, which was violently active during the Kobe earthquake, but above the Uemachi fault zone, which is located across Osaka Bay. The cause of this mysterious EQL has long remained unresolved. In this article, we propose a radioluminescence model due to radon emanating from the Uemachi fault shear zone, which has a peculiar geological structure, as a reasonable hypothesis for the mysterious EQL, and discuss the validity of the hypothesis while referring to various physicochemical anomalies observed in the Kobe earthquake as well as numerical simulation of radon and/or radon/methane bearing water vapor migration in the air.