They are also observed at great distances from the epicenter of high energy earthquakes and can sometimes anticipate the tremors by several months. But little is still known about these strange luminescent phenomena.

The huge spread of smartphones on a planetary scale and the possibility of being able to use them as immediately available tools to document everything around us is now a fact. Georefenced and synchronized, amateur video can provide valuable information to those who try to understand a phenomenon as elusive and certainly not intentionally reproducible as that of seismic lights. To be honest, although ephemeral, the phenomenon has been known for centuries: Pliny the Elder, two thousand years ago, certainly did not miss the wonderful opportunity to tell in his work “Historia Naturalis” a luminous event, which occurred during the earthquake in near Modena in 91 BC The Middle Ages, then, is full of written evidence on the subject. But their consistency is often between legends and enigmatic tales.

At the end of the 1700s even the German philosopher Immanuel Kant became interested in the subject, conducting research on the phenomena that precede and accompany earthquakes, also with reference to luminous phenomena. Coming to the times closest to ours, for Italy it is necessary to point out the valid effort made by the priest and professor of natural sciences Ignazio Galli for having drawn up in 1910 a first “classification of the luminous phenomena observed in earthquakes”, as the title of the his work still widely cited in scientific articles.
In recent times, the literature of the sector has been enriched by the many reviews and reports on these phenomena, observed in the various parts of the world where earthquakes of magnitude greater than 5 occur most frequently, such as Canada, Mexico, Greece, Peru. , Japan, New Zealand and Italy (with the earthquakes of Irpinia in 1930, of Friuli in 1976, of L’Aquila in 2006 and of the last sequence Amatrice, Visso, Norcia in 2016-2017).

On 8 September in Mexico City, many people declared that they had observed (and in some cases even recorded with video, already present on social networks) seismic lights in conjunction with the 8.2 magnitude earthquake, despite having occurred at a distance of over 700 km from the epicenter, near Pijijiapan, in the Chiapas region.
The different forms of luminous phenomena contemplate luminous globes of various shapes, colors and sizes. Mostly white or bluish flashes, light beams of varying thickness with very intense light, diffuse clouds similar to auroras with horizontal development and similar to flames. According to the testimonies, all these phenomena occur from the bottom up.

Any serious approach to the study of this phenomenon must also pass through the analysis of the reliability of the sources and the direct credibility of the witnesses and the total number of the same phenomenon observed by several places and by several people simultaneously. Another important check is to exclude any concomitance with phenomena related to local meteorology, such as lightning (although their duration of 10-50 microseconds is five orders less than the average duration of seismic lights of about 0.5 seconds). A check on possible short circuits from electrical distribution plants and connected equipment or other high-tech systems scattered throughout the territory could eliminate cases not attributable to the earthquake.

The road still seems long and winding. Besides the historical hypothesis that recalls the generation of intense electric fields, created by piezoelectric and piezomagnetic mechanisms following the tectonic movements of rocks containing quartz, some recent models suggest that the generation of seismic lights may involve the ionization of the oxygen contained in some types of rocks (dolomite, rhyolite, etc.) as a result of stress before and during an earthquake. The ions would be able to cross layers of rock, preferring a path through the cracks inside the rock itself, and once they reach the soil-atmosphere interface, they could even ionize small volumes of air, transforming them into light-emitting plasma packets. Some laboratory experiments have confirmed that specific rock samples trigger this internal ionization mechanism when subjected to high pressures. Other researches, however, have shown that the probability of generating seismic lights may depend on the angle of the fault with an increase in the case of sub-vertical or almost vertical faults.

With regard, then, to the local alteration of the earth’s magnetic field and of the ionosphere in the region subjected to tectonic stress, this phenomenon does not seem to be a verified effect for all seismic events and, therefore, requires more in-depth investigations and reflections.

Source: ingv

Read also: earthquakes linked to earths rotation

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