An earthquake with a magnitude of 8.2 has struck the coast of Mexico early this morning. It was felt more than 966 km (600 mi) from the epicenter. According to the latest reports, 6 people were killed. The earthquake triggered a tsunami and warnings for countries across Central America.
Witnesses published videos on social media showing mysterious blue and green flashes light up the sky above Mexico City. It is not clear whether these flashes of light happened before or after the earthquake struck the region.
What do we know about them?
These unusual flashes of light are called “earthquake lights” or “earthquake lightning”. They appear in the sky near areas that have experienced a stress in the tectonic plates. Although they resemble regular lightning strikes, they originate out of the ground instead of the sky and can stretch up to 200 m (650 m). This phenomenon generally happens while an earthquake is occurring, but it can also happen before or after earthquakes occur.
How do they form?
Over the past few years, various theories have been proposed for how earthquake lights form, including the disruption of the Earth’s magnetic field by tectonic stress and the so-called piezoelectric effect, in which quartz-bearing rocks produce voltages when compressed in a certain way. ~ National Geographic
According to a study published in 2014, these lights can be caused by a certain type of rocks (namely basalts and gabbros) that can unleash electric charges when stressed. In some regions these rocks can be present in vertical structures called dikes and they can be as deep as 97 km (60 mi) underground.
The stress in the tectonic plates causes these rocks to “form a kind of plasma-like state, which can travel at very high velocities and burst out at the surface to make electric discharges in the air. Those discharges are what make the colorful light shows.” study coauthor Friedemann Freund told National Geographic.