Earthquake luminosities

Mysterious natural electric lights (perhaps some are glow mode plasma discharges?) have been observed before, during and after earthquakes since man could record such things.

Earthquake electric lights Earthquake lights are a phenomenon so unusual that they border on myth. The first known reports of them are from 89 BC, with spotty descriptions over the centuries.

... Earthquake lights are electric discharges that come out of the ground and can rise up to more than 200 yards in the air, Freund says. Lights are sometimes observed in the days and hours leading up to an earthquake; in other cases, they are visible during or after a quake. How they work is a mystery.

Part of the challenge in learning more is that earthquake lights have been described in many ways: as glowing globes, flickering flames from the ground, or even branches of lightning originating from the surface instead of the sky.
What caused the mysterious lights in the night sky after Mexico’s earthquake? | Washington Post

The article goes on to describe the various natural electromagnetic processes that could possibly explain what natural electromagnetic circuits might be happening.

Old earthquake lights (EQL)

With the beginning of seismology as a science in the 19th century, many scholars devoted time to reporting luminosities associated with earthquake activity. To name a few, the Irish engineer Robert Mallet, the 'founder of seismology', published a five part catalog entitled 'On the Facts of Earthquake Phenomenal, in which numerous reports on earthquake luminosities can be found. His catalog, first presented to the British Association of Science, covers the years 1606 BC to 1842 AD.

Ignazio Galli, an Italian priest who graduated in Natural Sciences, published in the early 1900s a catalog of 148 seismic events associated with different types of luminosities. His catalog covers the years 89 BC to 1910 AD and focuses mainly, but not exclusively, on European events
Prevalence of Earthquake Lights Associated with Rift Environments | GeoScienceWorld

Ebingen electromagnetic earthquake

Earthquake lights  eqlOriginally, a total of 110 light sightings were reported for the Ebingen earthquake. Of those, 43 observations were described by von Schmidt and Mack. EQL were observed as far as 110 km from the epicenter, and appear to have had a tendency to occur along the eastern margin of the Upper Rhine Graben and in the vicinity of the Hohenzollern Graben. Several light sightings were also reported from the margins of the Tertiary volcanic fields.

One of the most detailed EQL observations was made near Ebingen, in which two people, after hearing a distant noise accompanied by a faint vibration, saw a bright flash emitted from the ground, which then, at a considerable height, turned into a ball of light and eventually divided itself like lightning in the direction of Ebingen. The tremors began with the appearance of the ball of light. After the seismic waves had rolled past, toward the town, the two witnesses observed a second sphere of light, while the entire surroundings were brightly illuminated.
Prevalence of Earthquake Lights Associated with Rift Environments | GeoScienceWorld

Electric geology earthquakes and electrical discharges

Freund conducted experiments several years ago that led him to develop these ideas. In 2003, he and his assistants monitored red granite blocks placed under a 1,500 ton press. As the pressure on the granite increased, sensitive detectors registered infrared emissions, as well as a voltage build-up on the surface.

Most rocks act like insulators, preventing the flow of electric charge. However, when placed under extreme pressure, they change state and can act like semiconductors. Freund’s conclusion was that before an earthquake, positive charges (so-called “defect electrons” in the crystalline matrix due to fracturing) relocate to the surface of stressed rocks where they recombine, releasing infrared radiation. It is why the voltage increases on his granite blocks, as well.

... Electric Universe theory also considers electric discharges through stressed strata in Earth’s crust. The build-up of charge across compressed rocks can cause sudden electrical breakdown. So, earthquakes could be considered a form of underground lightning. If earthquakes are underground lightning bolts, then perhaps seismic waves are the thunderclaps. In that case, it seems likely that the majority of energy released during an earthquake may not be from the fracturing and movement of strata, but the result of electrical energy released within the rock matrix.

Earth lights are the precursors and earthquakes the result of electricity flowing through our planet.
Earth Lights | Thunderbolts

Electric Universe lights

The missing link between the sunspots and earthquakes is the fact that the electric discharges to the Sun that cause sunspots can also affect the Earth’s ionosphere. The ionosphere forms one “plate” of a capacitor, while the Earth forms the other. Changes of voltage on one plate will induce movement of charge on the other. But unlike a capacitor, the Earth also has charge distributed in rock beneath the surface. And if the subsurface rock has become semi-conducting because of stress, there is an opportunity for sudden electrical breakdown to occur through that rock.

We should expect similar processes to occur underground as is found in atmospheric lightning. There will be precursor electromagnetic effects due to the small-scale travelling of charge – rather like 'stepped leaders' between cloud and ground. That may be the limit of activity in small tremors. But in a large earthquake, the entire circuit may be involved, from below the Earth, through the atmosphere to the ionosphere. This would explain the massive disturbance of the ionosphere over a large area accompanying a major earthquake.

The mystery of the source of the current is solved – it comes from a charged Earth.
Electric Earthquakes | Holoscience

There is also a long discussion and investigation about Electric Earthquakes on the forum