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Skyquakes
What Are Skyquakes?
BY PATRICK
J. KIGER
At approximately 1:45 p.m. on Nov. 14, 2017, residents of 15 Alabama counties reportedly
were shocked by a startlingly loud boom that caused some to call 911 operators
in alarm.
As the National Weather Service's Birmingham
station tweeted not quite a couple of hours later, there wasn't any
clear explanation for the noise.
Radar scans and satellite imagery of the region
didn't show any large fires or smoke from an explosion, and the U.S. Geological
Survey didn't spot any signs of an earthquake on its seismic
monitoring system.
"We don't have an answer, and we can only
hypothesize with you," tweeted the NWS,
which speculated that the sound may have been caused by an aircraft or a meteor.
But a NASA scientist soon knocked down those
possible explanations.
Bill Cooke, head of the space
agency's Meteroid Environment Office at the Marshall Space Flight
Center in Huntsville, told Al.com that he was skeptical that the
sound could have been caused by a meteor, because there were no reports of
anyone seeing a fireball.
Cooke also discounted the possibility that the
boom had been created by an aircraft, noting that the seismic signature "is
not characteristic of that produced by a supersonic jet's boom."
The Elginfield
Infrasound Array, 600 miles (966 kilometers) to the north in Ontario,
Canada, picked up an infrasound wave that
apparently was linked to the boom.
It usually takes something pretty big, such as a
severe storm, an avalanche or a rocket launch to trigger such a wave.
To add to the weirdness, less than two weeks later on Nov.
26, another, similarly unexplained boom was heard in the Birmingham
area at 7:24 a.m.
James Coker, director of the Jefferson County,
Alabama, Emergency Management Agency, says in an email that he heard
a double boom, "although the sound I heard may have included an
echo caused by the mountains."
Worldwide
Phenomenon
But Alabama isn't the only place where things have been
booming lately.
Skyquakes, as they're commonly called, recently
have been heard across the U.S., in states ranging from New
Jersey to Idaho, as well as in places as far away as India, where the
seaside resort towns of Digha and Mandarmani were jolted in August by a boom so
loud that it shattered hotel windows, according to the Dhaka Tribune.
Indeed, as USGS scientist emeritus David Hill detailed in a 2011
article on the subject, mysterious booms have been heard for many years in
places across the world.
In Belgium, they're known as
"mistpouffers," while the Italians call them "brontidi."
In the vicinity of Lake Seneca in the Catskill
Mountains of New York, residents have long heard the "Seneca
Guns," a phenomenon that was described by author James
Fenimore Cooper back in 1851 as "a sound resembling the explosion
of a heavy piece of artillery, that can be accounted for by none of the known
laws of nature."
As Hill noted in his article, numerous explanations for
skyquakes have been proposed over the years, including shallow earthquakes that
could produce audible sounds without noticeable shaking, massive tsunami waves
breaking far from shore, explosions of methane gas released from methane
hydrate beds, sand dunes sheared by avalanches and, of course,
meteors.
As Hill wrote, meteors penetrating the upper
atmosphere could create sonic waves that wouldn't reach Earth's surface until
after the meteor had vanished, so that the connection between the two wouldn't
be apparent.
People also have raised the possibility that the
booms (or at least some of them) might be caused by tests of secret U.S.
military aircraft, such as the long-rumored spy plane that aircraft buffs have
dubbed "Aurora."
"I would imagine many of them are related to
classified missions involving military aircraft," television meteorologist James Spann,
whose Facebook and Twitter accounts became a clearinghouse
for information about the Alabama booms, writes in an email.
In fact, there may not be one single explanation
for all the booms.
"It is indeed the case that there may be several
plausible explanations for any given incidence of a mysterious booming sound,
and that the environment where the sound is heard will determine which of the
possible explanations are most reasonable," Hill explains.
"A sound heard in the middle of the desert,
for example, is not likely due to breaking surf."
Hill says that most booming sounds are heard over a limited
range, so reports of clusters of booming sounds separated by large distances
are mostly likely coming from multiple sources.
The exceptions "may include the
sound from a meteorite exploding in the atmosphere high above the Earth, a
massive volcanic eruption or an aircraft flying at supersonic speeds for an
extended distance."
NOW THAT'S INTERESTING
Back in 2012, the small city of Clintonville,
Wisconsin, was shaken by a mysterious series of booms and vibrations that kept residents awake for three nights.
Eventually, as CNN reported, USGS
scientists determined that the sounds were caused by a swarm of small
earthquakes.
Patrick Kiger @patrickjkiger
Patrick J. Kiger has written for
HowStuffWorks since 2008 covering a wide array of topics, from history and
politics to pop culture and technology. He worked as a newspaper reporter for
the Pittsburgh Press, and the Orange County Register in California, where he
covered one of the biggest serial murder cases in U.S. history, and also as a
staff writer at Baltimore Magazine. As a freelancer, Patrick has written for
print publications such as GQ, Mother Jones and the Los Angeles Times, and on
the web for National Geographic Channel, Discovery News, Science Channel and
Fast Company, among others. In recent years, he's become increasingly
interested in how technological advances are altering urban life and the design
of cities, and has written extensively on that subject for Urban Land magazine.
In his spare time, Patrick is a longtime martial arts student and a fan of
crime fiction, punk rock and classic Hollywood films.
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