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    Once dismissed as the hallucinations of those who had supped one too many cups of the local hooch, earthquake lights, although rare, are now a well recorded phenomenon, thanks to the almost ubiquitous presence of recording devices.

    Lights are associated with rift environments

    A team of Canadian geologists studying earthquake lights (EQL) have a new hypothesis about the rainbow-coloured flickering flames pillars, or orbs of floating lights that can appear before or during certain earthquakes but rarely after. They say the lights are likely associated with rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface.

    The research, led by Dr Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, examined 65 of the best documented EQL cases in the Americas and Europe since 1600 AD. The researchers found that 85% of the recorded lights appeared spatially on or near rifts, and 97% appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults (in the interior of a tectonic plate, rather than on a plate boundary) are associated with just 5% of Earth’s seismic activity but 97% of documented cases of earthquake lights.

    The earthquakes ranged in magnitude from M 3.6 to 9.2 – 80% were greater than M 5.0.

    “The numbers are striking and unexpected,” said Dr Thériault in a press release from Seismological Research Letters. “We don’t know quite yet why more earthquake light events are related to rift environments than other types of faults, but unlike other faults that may dip at a 30–35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases.”

    Two of the 65 EQL events are associated with subduction zones, but Dr Thériault suggests there may be an unknown subvertical fault present. “We may not know the fault distribution beneath the ground. We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure.”

    Examples from Canada and Italy

    On 12 November 1988, a bright purple-pink globe of light was recorded moving through the sky along the St Lawrence River near the city of Quebec, 11 days before a powerful quake.

    Seconds before the 6 April 2009 L’Aquila, Italy, earthquake, people reported seeing 10 cm high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town’s historical city centre.

    Does the new theory add up for New Zealand quakes?

    New Zealand has a long history of EQL sightings. Many people recorded unusual blue, white and/or rainbow lights above Christchurch on 4 September 2010. There are a number of eye-witness accounts and photos on the New Zealand Herald website in an article by weatherman Philip Duncan who witnessed the phenomenon. But does the new hypothesis fit the Darfield quake? New Zealand is astride a plate boundary, and in the North Canterbury region, there is a southward transition from a subduction zone to continental collision.

    However, GNS seismologist Dr John Ristau says that, at a local level, it does work. “Darfield fits with their model. The [research] says that 97% of the earthquakes where EQL were observed fall into three categories: 1) intraplate rifts or grabens, 2) back-arc or pull-apart rifts or grabens, 3) strike-slip or transform faults, irrespective of the tectonic setting. Darfield would fall into category 3.

    “One of the main criteria is for the earthquake to be intraplate, which Darfield is considered to be even though it’s close to the subduction zone. Another is for the earthquake to occur in a region of highly stressed igneous or metamorphic rocks, which the crustal structure of Canterbury falls into. The combination of a high stress environment coupled with a strong fault seems to be very important. It might also be important to keep in mind that the Canterbury region includes Banks Peninsula which is an old volcano; therefore, it may retain some of the characteristics of a rift environment.”

    A possible predictor

    Dr Thériault concluded that

    Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake.

    Dr Thériault

    On an unrelated but interesting aside, perhaps some UFO sightings of floating orbs of light could possibly have been EQL.

    Useful link

    Read about weather analyst Philip Duncan’s experience with earthquake lights during the Darfield September 2010 earthquakes.

    This news story includes some video of earthquake lights.

    References

    Thériault, R., Freund, F.T. & Derr, J.S. (2014). Prevalence of earthquake lights associated with rift environments. Seismological Research Letters volume 85-1, Jan–Feb issue, 2014.

     

      Published 24 March 2014 Referencing Hub articles