Earthquake light, emerging from the ground as flashes at night (neglecting other more minor forms), usually has a white hemispherical center and blue outer part. The blue resembles daytime blue sky. Its existence is increasingly verified, with about 80 videos on the web to mid-2017. However, the light must be differentiated from power-grid faults, so sound/color/form/length criteria were developed in this paper through examination of many videos. Light should be coseismic (i.e. when the S-waves arrive), hemispherical, not during a storm, less than 1 s long, without fire or smoke, and without many rapid color changes. Warnings about camera artifacts are included. This light accompanied two recent earthquakes: M7.8 November 14, 2016, New Zealand, and M8.1 September 8, 2017, Mexico. Definite green flash earthquake light has only been caught once on video and it is shown that others are sometimes electrical overload of mercury vapor lamps, or difficulty with classifying pale turquoise flashes that are only slightly more green than blue. Three separate frames from videos (NZ, Turkey, and Ecuador) have views actually within the blue light. These data exemplify the Freund principle of positive charge production from quartz by high stress-rate, then charge separation and expulsion to the ground surface and creation of light, but the hypotheses of quartz piezoelectricity or voltages from fracture mechanisms are not accepted.
WHITEHEAD, NEIL and ULUSOY, ÜLKÜ
"Blue sky at midnight - earthquake lightning,"
Turkish Journal of Earth Sciences: Vol. 28:
1, Article 8.
Available at: https://journals.tubitak.gov.tr/earth/vol28/iss1/8