One theory suggests ionisation of Oxygen as cause

Another theory suggests electric field generation during earthquake as cause

Another theory likens the phenomenon to Auroras

The 6.8 Magnitude Earthquake that rocked Morocco was also accompanied by the manifestation of a light. This is not the first time this has happened. Accounts of such occurrences have been recorded from the 18th century. However it has remained to be one of the unanswered questions of science. 

“People have wondered about them forever. It’s one of those persistent mysteries that hang around and never quite get nailed.” Karen Daniels, a physicist at North Carolina State University said in an interaction with the New York Times. 

Earthquake lights appear around the region of tectonic stress occasionally. 

There are various explanations posited for this phenomenon. One model suggests that ionisation of Oxygen during tectonic stress is responsible for this. The ions that are released from the surface of the earth ionise air particles, hence causing illumination. This links the angle of the fault to whether or not the phenomenon would materialise. 

Another model suggests that it is due to the electric fields that get generated when rocks that possess Quartz undergo rapid tectonic movement.  

Another theory likens the phenomenon to Auroras that are observed in regions of high altitude due to disturbance of the magnetosphere caused by solar winds.