For many years witnesses have reported seeing eerie lights appearing before or around the time of an earthquake. Now scientists have a theory to explain the phenomenon in the January-February issue of Seismological Research Letters.

People have always been intrigued by the illuminated balls of light that ominously float through the air appearing before or during an earthquake. These lights are rarely seen after an earthquake. Earthquake lights can also take up different forms.

In 2009 L’Aquila, Italy witnesses saw 10 centimeter tall flames flickering on the paving stones of Francesco Crispi Avenue.

In 1988 Quebec, Canada witnesses watched a bright purple and pink globe of light moving along the St. Lawrence River. The Quebec region would have a powerful earthquake 11 days later.

In 1906 San Francisco, California a couple of witnesses saw streams of light running across the ground on two consecutive nights leading up to an earthquake in the region.

To help explain the eerie earthquake lights, scientists studied a total of 65 cases since 1600 A.D. which reported the phenomenon. A total of 97 percent of the earthquakes were adjacent to sub-vertical faults and 85 percent were on or near rifts. These rifts or sub-vertical faults are also called graben, strike-slip, or transform faults. Intraplate faults such as these only accounts for five percent of all seismic activity. However, those five percent are responsible for generating 97 percent of the reports of earthquake lights.

A geologist with the Ministère des Ressources of Québec, Robert Thériault, and his colleagues studied the best cases of earthquake lights in our recorded history and found the numbers were striking and unexpected. Only two events were associated with subduction zones, but Thériault suggests that this may be because the areas may also have unknown sub-vertical faults. The faults in these two areas may also have some sedimentary layers or ground water obscuring their unknown fault structure.

The 65 earthquakes studies ranged from magnitude 3.6 to 9.2 but 80 percent of them were of M 5.0 or greater. The most common kind of earthquake lights were brightly lit globes of light that were sometimes stationary and sometimes moving. Other common types were flame-like lights near the ground or atmospheric lights.

In the majority of cases studied, the timing and the distance to the quake’s epicenter wildly varied. The lights were always seen prior an earthquake or during, which led the scientists to believe that the phenomenon was in relation to the rapid build-up of stress before a fault ruptures. The lights are said to be caused by mobile electrical charge carriers that get activated by stress, then they flow electricity swiftly along the stress gradients until they reach the earth’s surface. When the charges reach the surface, they ionize with the air molecules and give off the energy as the earthquake light phenomenon.

With the popularity of cameras and technology being so widely available, more and more of these earthquake lights have been documented since the 1960’s. The 2007 earthquake in Pisco, Peru was a M 8.0 earthquake that allowed many security cameras to record these eerie lights. When the camera footage was matched up with seismic records of the earthquake it helped investigators to identify and explain them as being earthquake’s eerie lights. The lights may be a sure-fire way of predicting an upcoming earthquake.

By Brent Matsalla

Sources:

io9

Stuff

Phys.org

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