Sizes and Some Features of Luminous Sources Associated with the 1995 Hyogo-ken Nanbu Earthquake

Abstract

Sources of luminescence and their buildup processes accompanying the 1995 Hyogo-ken Nanbu earthquake of M 7.2 are studied based on pieces of information obtained mainly by interviewing eyewitnesses. Gross forms of relatively large-scale luminous sources are roughly classified into four types: lightning with zigzag lines, a swelling shield-shaped source, an upward-extending fan-shaped source, and a belt of lights. The last one includes an arc-like source. Each source is predominantly in tones of either colorless-white, blue or orange-color. This paper presents 23 spottings, distributed as wide as 50 km from the epicenter of the mainshock near Kobe City. Along with these spottings, some local flashing events were reported. The upper limit of the height of several sources was able to be estimated as less than 200 m above the ground. The linear dimension of the horizontal extent ranged from about 1 to 8 km. The luminance was estimated to be more than an order of 103 cd/m2 for an arc-like orange colored source at the eastern part of the aftershock area. Not a few sources were glittering more intensely than this case. According to most of the yewitnesses, the luminosity started from ground level on land, suggesting that discharge processes of the polarized electricity in near-surface rocks may be the primary driving force of the luminescence. However, electricity charged in the air should be also responsible to some luminous phenomena, especially a kind of lightning above the sea. Fog or dust was observed in the air in the region around Nishinomiya City, east of Kobe, preceding the quake, which might have played the role of an effective electrical conductor in glow discharge.