What causes "earthquake lights?"

Video uploaded onto YouTube depicting the "Earthquake Lights"in Mapastepec, Chiapas, Mexico

On September 7, a major earthquake struck off the southern coast of Mexico. Videos and images of the so-called "earthquake lights" quickly went viral. An article by Mike McKinnon reposted by the Washington post (originally from newscientist.com) examines the question "What caused the mysterious lights in the night sky after Mexico's earthquake?" (original article linked HERE).

Reports of this phenomena may date back to a s early as 89 BC, with descriptions that describe "glowing globes, flickering flames from the ground, or even branching lightning that sparks from Earth instead of the sky." With modern technology able to record images of this phenomena, scientists now have more of a chance to analyze possible causes.

One such suggestion is that "triboluminescence" is the cause of this phenomena. This postulation asserts that the breaking of chemical bonds through "rubbing, crushing, or scratching" can release light. This can be observed on a much smaller scale when quartz is squeezed, which pushes ions out of their original position and generates a small electric current. Troy Shinbrot from Rutgers University is skeptical about the ability of triboluminescence, which has only been observed small-scale in lab, to result in such a large and widely observed phenomena. 

Example of Triboluminescence in a Lifesaver Candy (if you're curious as to why this happens with Lifesavers, you can check out an article on it HERE)

Another suggestion is that the molecular bonds of igneous or metamorphic rock in the ground break under the stress caused by the earthquake's movement. The breaking of these bonds then allows ionized oxygen to travel through the rocks. Freidemann Freund from NASA's Ames Research Center states, "The faster we stretch the rocks, the more these positive-charge carriers are released." This could cause areas of localized electric fields, possible resulting in "coronal discharges-brief bursts of visible light."

While these explanations are all possible, the absolute cause still remains a mystery.