Scientists may have solved the mystery of ‘ghostly’ lights and whispers that occur over train tracks in the US.

The lights over the rail line in Summerville, South Carolina, have become a local phenomenon, said to be carried by the ghost of a woman who is waiting for her husband to return.

But scientists believe they have got to the bottom of the mystery. A new study in Seismological Research Letters suggests they could be attributed to tremors in the earth too small to be felt.

The ‘earthquake lights’ have been spotted across the globe in the form of glowing spheres, sparks, pillars and other shapes. But there has been no one theory explaining them until now.

Some theories suggest the lights could be caused by the ignition of released underground gases like methane or radon, or by an electric discharge from during tremors.

Seismologist Susan E Hough from the US Geological Survey suggests in the study that Summerville's ‘ghostly’ phenomenon could result from the area’s mix of shallow faults and railroad tracks.

Dr Hough assessed historical accounts of the strange light orbs found in newspapers and local books, and compared them with data on earthquakes in the region.

Sightings date back to the 1950s and 60s, with residents seeing orbs slamming doors and making spooky sounds. Three magnitude 3.5 to 4.4 earthquakes were recorded in the area in 1959 and 1960.

The seismologist suggested that shallow earthquakes in the area could release a water-soluble gas like radon or methane, which then got ignited by a spark of static electricity or rock movement.

This would explain why the lights are often seen at night. And the ‘whispers’ heard would be gas escaping from the earth or the ignition potentially produced by the steel rails of an abandoned railway line and nearby scrap heaps.

“From working in Charleston I know that when old tracks were replaced or repaired, the old tracks weren't always hauled away. You find piles of old metal along the tracks,” Dr Hough told the Independent.

She said the theory can be easily tested by using gas detectors to look for escaping gases or by conducting experiments to look for shallow faults.

“Maybe here we have an example of the recipe for the environments that might generate earthquake lights. And maybe the friendly ghosts are illuminating fault zones in the east,” Dr Hough said.