The book Earthlights by Paul Devereux explains how tectonic activity, which is particularly considerable near fault lines, can produce EM fields in the surrounding environment. These are typically created by rock/minerals under tremendous stress, and in fact, certain minerals such as quartz have even been found to produce luminous phenomena under such conditions. Similar lights have been reported far back into antiquity. Strange balls of light, referred to in folklore as ghost lights, fairy l...