Radar appears to show birds taking off 15 minutes before Oklahoma quake
Radar images that appear to show birds taking to the air about 15 minutes before an earthquake in the US have added to debate over whether animals can tell quakes are coming.
The 5.6-magnitude quake struck in Oklahoma around 7.03am on September 3 (local time) at a shallow depth of just 4.5km.
Shortly afterwards, Mike Eilts, who is involved with the RadarScope weather radar app, posted radar images on Facebook showing the hours leading up to the quake.
The images show an explosion of activity from 6.47am - about 15 minutes before the quake.
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"The large growth in echoes is birds taking off," Eilts posted. "What is interesting to me is that it appears that birds starting flying about 6:47, yet the 5.6 earthquake occurred at 7:03, what do they know that we do not know?"
In a new development, Eilts posted a blog Wednesday (NZT) in which he looked at whether the bird activity might just have been natural and nothing to do with the earthquake.
"This blog is a follow-up to that post to show a bit more scientifically whether the rapid increase of the radar echoes was a normal morning event (many birds typically fly from their overnight roost just before sunrise) or not. Note that sunrise was at 7:04 a.m. that morning," he said.
Eilts compared radar images from the minutes leading up to and after the quake, and for the same times 24 hours later. The weather was nearly the same both mornings.
"Evidence does point to more radar echoes, which are likely birds, to increase significantly ~15 minutes before the earthquake. The day after, there was also an increase about the same time (maybe a bit delayed), which is consistent with birds flying from their nightly roosting spot.
"However, on the day of the earthquake the echo size was much larger and stronger intensity, suggesting more birds took flight earlier," Eilts concluded.
Matt Mahler, meteorologist at News9.com in Oklahoma, said he had been receiving comments related to Eilts' Facebook post, noting that birds did take off just before sunrise every morning.
"However, with the earthquake happening so close to sunrise, it's hard to tell if it wasn't a combination of both. Still a cool thing to see for sure," Mahler said on his Facebook page.
The USGS said it was easy to explain unusual animal behaviour seconds before humans felt an earthquake.
"Very few humans notice the smaller P wave that travels the fastest from the earthquake source and arrives before the larger S wave. But many animals with more keen senses are able to feel the P wave seconds before the S wave arrives," USGS said.
"As for sensing an impending earthquake days or weeks before it occurs, that's a different story," it said.
"Anecdotal evidence abounds of animals, fish, birds, reptiles, and insects exhibiting strange behaviour anywhere from weeks to seconds before an earthquake. However, consistent and reliable behaviour prior to seismic events, and a mechanism explaining how it could work, still eludes us. Most, but not all, scientists pursuing this mystery are in China or Japan."
In the Chinese city of Nanjing, seven places that keep animals, such as farms and ecological parks, double as seismic stations. They update the city's seismological bureau on the behaviour of their animals twice a day.
Support for the animal prediction theory came from researchers in Peru who were using motion-activated cameras to record animal sightings.
They recorded five or fewer animal sightings a day in the 23-days leading up to a magnitude-7.0 quake in 2011, compared with five to 15 sightings before that. For five of the seven days immediately before the quake, no movements were recorded.
One of the better known examples of earthquake prediction was in the Chinese city of Haicheng when an evacuation was in full swing hours before a magnitude-7.3 earthquake struck in February 1975.
Strange animal behaviour in the weeks before the quake included geese flying into trees, and pigs biting at each other or digging beneath fences, but there was also a rash of small quakes.