Q: What are earthquake lights? Are they real?A: Observations of earthquake lights (EQL), mostly white to bluish flashes or glows lasting several seconds associated with moderate to large earthquakes, have been reported infrequently by observers since ancient times. It wasn't until the phenomenon was captured in photographs, taken during the Matsushiro earthquake swarm in Japan between 1965 and 1967, that the seismological community acknowledged their occurrence. A satisfactory theory to explain EQL, however, has been elusive and is still not agreed upon. Proposed mechanisms include piezoelectricity, frictional heating, exoelectron emissions, sonoluminescence, phosphine gas emissions, and fluid injection (electrokinetics), but the most recent theory suggests that EQL are caused by separation of positive hole charge carriers that turn rocks momentarily into p-type semiconductors (first and second references below).
The most extensive modern study of EQL observations comes from the Saguenay, Quebec, earthquakes of 1988-1989 (third reference below). At least 46 well-documented reports span the time from three weeks before the main shock to two months after. The general categories of observations include: (1) seismic lightning, (2) atmospheric luminous bands, (3) globular incandescent masses, (4) fire tongues, (5) seismic flames, and a newly-recognized category, (6) coronal or point discharges. The latter observations, resulting from one observer being in the right place at the time of the main shock, strongly support the positive hole theory.
Observations of earthquake lights during the 1995 M6.9 Kobe, Japan earthquake were documented in the fourth of the references below. There were 23 sightings within 50 km of the epicenter of a white, blue, or orange light all with an upper height of 200 meters and a linear dimension of 1 to 8 km. The types of phosphorescent phenomena were classified as: lightening with zig-zag lines, swelling shield-shaped sources, upward-extending fan-shaped sources, or a belt of lights (including arc-shaped sources).
While EQL sightings are often given more exotic labels, they are a recognized geophysical phenomenon that may one day contribute to the possibility of forecasting earthquakes in the few locations where they occur.
The following links and references provide additional information about earthquake lights:
* Freund, Friedemann T., Rocks that Crackle and Sparkle and Glow:Strange Pre-Earthquake Phenomena. Journal of Scientific Exploration, 17, no. 1, p. 37-71,2003.
* St-Laurent, France, and Freund, Friedemann T, Earthquake Lights andthe Stress Activation of Positive Hole Charge Carriers in Rocks. International Workshop on Seismo Electromagnetics (IWSE), 2005 (in press).
* St-Laurent, France, The Saguenay, Quebec, Earthquake Lights of November 1988 - January 1989. Seismological Research Letters, 71, no. 2, p. 160-174, 2000.
* Tsukuda, Tameshinge, Sizes and some features of luminous sources associated with the 1995 Hyogo-ken Nanbu earthquake, Journal of Physicsof the Earth, 45, no.2, p. 73-82, 1997.
* Hough, Susan E.,
A volcano in North Carolina? A closer look at a tall tale, Seismological Research Letters, 71, no. 6, p. 704-708, 2000.
* Derr, John S., Earthquake lights: A review of observations and present theories. Bulletin of the Seismological Society of America, 63, no. 2, p. 2177-2187, 1973.
* Derr, John S., Luminous phenomena and their relationship to rock fracture. Nature 321, no. 6069, p. 470-471, 1986.
* Tilling, Robert I. et al.,
November 29, 1975 Kalapana Earthquake
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