A South Carolina ghost story could have a very earthly explanation.Starting in the 1950s, folks in the Summerville, S.C., area began reporting sightings of strange balls of light floating down a remote road near some former railroad tracks. Local lore has it that the eerie illuminations, known as the Summerville Light, are the glow of a lantern carried by a forlorn ghost.But perhaps earthquakes are the source of this phantom light, and of some other ghostly legends too, geologist Susan Hough proposes January 22 in Seismological Research Letters. Radon, methane or other gases that rise from the ground during quakes could have been ignited by static electricity or sparks from shifting rocks or passing trains, causing the vapors to luminesce, suggests Hough, of the United States Geological Survey in Pasadena, Calif.Located far from any tectonic plate boundaries, Summerville might seem an unlikely spot for quakes. But in 1886, a temblor of around magnitude 7 devastated the nearby city of Charleston, killing 60 people. That event and hundreds of aftershocks over the following decades revealed the areas pronounced seismic hazard.The region is rich in ghost tales too, the most famous of which may be the Legend of the Summerville Light. The story generally goes that one night, a railroad workers wife was waiting for him by some tracks when she learned that he was decapitated in an accident. From then on, and even after her death, the woman returns to the tracks each night, carrying a lantern as she searches for her husbands head.Curious if the light could be explained by a physical mechanism, Hough reviewed books, magazines and online sources for recorded sightings of the mysterious orbs and other supernatural claims from the area. She also studied the areas earthquake history, focusing on 1890 to 1960 the period leading up to the start of the sightings.These earthquake lights were photographed just before dawn on March 23, 1977, near Brasov, Romania. A magnitude 7.2 earthquake rocked the region on March 4 and aftershocks occurred in the following weeks.Mihai Danciu, F. St-Laurent/Seismological Research Letters 2000Only a few quakes were documented during that time span, she found. There was a magnitude 3.9 in 1907, and then in 1959 around when the sightings began a magnitude 4.4, followed shortly thereafter by a couple of smaller quakes in 1960. These earthquakes would have most likely been accompanied by additional, even smaller quakes that went undetected, Hough says. Despite their small size, she says, its possible that such temblors could have generated earthquake lights without anyone suspecting a quake had occurred.Other instances of supernatural activity reported in the area, such as cars shaking violently, objects and doors moving spontaneously and footsteps heard in upstairs rooms could also be explained by inconspicuous earthquakes. Many of the reports seem to fit with shaking known to occur at a II on the Modified Mercalli Intensity scale, which scientists use to rate quakes based on afflicted damage, Hough says. Shaking is generally considered to be at Mercalli intensity II if it is weak and felt only by a few persons at rest, especially on upper floors of building.Houghs proposal is reasonable, says earthquake scientist Yuji Enomoto of Shinshu University in Matsumoto, Japan, but more geologic data is needed to clarify which natural mechanism could be behind the Summerville Light. Specifically, data on the presence of an anaerobic environment containing organic matter capable of generating methane, and the existence of granitic bedrock containing radium, which can produce radon would be most helpful, Enomoto says.For Hough, one of the more intriguing implications of the work is the possibility that similar ghost stories elsewhere could be associated with subtle seismic activity. Theres a bunch of ghosts wandering the rails in different places in the United States carrying lanterns looking for severed heads, Hough says. Maybe they are illuminating shallow active faults.