WEBVTT - What on Earth Are Skyquakes?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works. Hi brain Stuff,

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<v Speaker 1>Lauren boblebam here. One November afternoon, in residents of fifteen

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<v Speaker 1>Alabama counties were reportedly startled by a loud boom that

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<v Speaker 1>caused some to call nine one one operators in alarm.

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<v Speaker 1>As the National Weather Services Birmingham station tweeted not quite

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<v Speaker 1>a couple hours later, there wasn't any clear explanation for

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<v Speaker 1>the noise. Radar scans and satellite imagery of the region

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<v Speaker 1>didn't show any large fires or smoke from an explosion,

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<v Speaker 1>and the U S Geological Survey didn't spot any signs

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<v Speaker 1>of an earthquake on its seizemic monitoring system. In their tweet,

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<v Speaker 1>the National Weather Service speculated that the sound may have

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<v Speaker 1>been caused by an aircraft or meteor, but said we

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<v Speaker 1>don't have an answer and we can only hypothesize with you.

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<v Speaker 1>A NASA scientist soon knocked down those possible explanations. Bill Cook,

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<v Speaker 1>head of these space agencies Meteoroid Environment office at the

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<v Speaker 1>Marshall Space Flight Center in Huntsville, Alabama, told al dot

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<v Speaker 1>com that he was skeptical that sound could have been

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<v Speaker 1>caused by meteor because there were no reports of anyone

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<v Speaker 1>seeing a fireball. Cook also discounted the possibility that the

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<v Speaker 1>boom had been created by an aircraft, noting that the

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<v Speaker 1>seismic signature is not characteristic of that produced by supersonic jets.

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<v Speaker 1>Boom about six hundred miles or nine and seven kilometers

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<v Speaker 1>to the north in Ontario, Canada, the Elgin Field infrasound

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<v Speaker 1>array picked up an infrasound wave that apparently was linked

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<v Speaker 1>to the boom. It usually takes something pretty big, such

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<v Speaker 1>as a severe storm and avalanche or a rocket launch

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<v Speaker 1>to trigger such a wave. To add to the weirdness,

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<v Speaker 1>less than two weeks later, another similarly unexplained boom was

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<v Speaker 1>heard one morning in the Birmingham area. We spoke with

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<v Speaker 1>James Cooker, director of the Jefferson County, Alabama Emergency Management Agency,

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<v Speaker 1>via email. He said that he heard a double boom,

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<v Speaker 1>although the sound I heard may have included an echo

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<v Speaker 1>caused by the mountains, he said, and Alabama isn't the

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<v Speaker 1>only place where things have been booming lately. Skyquakes as

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<v Speaker 1>they're commonly called, recently have been heard across the US

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<v Speaker 1>in stay ranging from New Jersey to Idaho, as well

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<v Speaker 1>as in places as far away as India, where two

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<v Speaker 1>seaside resort towns were jolted in August by a boom

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<v Speaker 1>so loud that it shattered hotel windows, according to the

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<v Speaker 1>Dacca Tribune. Indeed, as u S Geological Survey scientist emeritus

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<v Speaker 1>David Hill detailed in a article on the subject, mysterious

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<v Speaker 1>booms have been heard for many years in places across

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<v Speaker 1>the world. In Belgium, they're known as MIAs poofer's, while

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<v Speaker 1>the Italians call them bron titi. In the vicinity of

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<v Speaker 1>Lake Seneca and the Catskill Mountains of New York, residents

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<v Speaker 1>have long heard the Seneca guns, a phenomenon that was

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<v Speaker 1>described by author James Fenimore Cooper back in eighteen fifty

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<v Speaker 1>one as a sound resembling the explosion of a heavy

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<v Speaker 1>piece of artillery that can be accounted for by none

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<v Speaker 1>of the known laws of nature. As Hill noted in

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<v Speaker 1>his article, numerous explanations for skyquakes have been proposed over

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<v Speaker 1>the years, including shallow earthquakes that could produce audible sounds

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<v Speaker 1>without noticeable shaking, massive tsunami waves breaking far from shore,

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<v Speaker 1>explosions of methane gas released from the methyl hydrate beds

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<v Speaker 1>sand dunes, shared by avalanches and of course meteors. As

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<v Speaker 1>Hill wrote, meteors penetrating the upper atmosphere could create sonic

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<v Speaker 1>waves that wouldn't reach Earth's surface until after the meteor

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<v Speaker 1>had vanished, so the connection between the two wouldn't be apparent.

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<v Speaker 1>People have also raised the possibility that the booms, or

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<v Speaker 1>at least some of them, might be caused by tests

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<v Speaker 1>a secret U S military aircraft, such as the long

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<v Speaker 1>rumored spy plane that aircraft buffs have dubbed Aurora. However,

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<v Speaker 1>there may not be one single explanation for all the booms.

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<v Speaker 1>Hill explains it is indeed the case that there may

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<v Speaker 1>be several plausible explanations for any given incidents of a

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<v Speaker 1>mysterious booming sound, and that the environment where the sound

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<v Speaker 1>is heard will determine which of the possible explanations are

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<v Speaker 1>the most reasonable. A sound heard in the middle of

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<v Speaker 1>the desert, for example, is not likely due to breaking surf.

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<v Speaker 1>Hill says that most booming sounds are heard over a

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<v Speaker 1>limited range, so reports of clusters of booming sounds separated

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<v Speaker 1>by large distances are most likely coming from multiple sources.

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<v Speaker 1>The exceptions, he says, a main clue the sound from

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<v Speaker 1>a meteorite exploding in the atmosphere high above the Earth,

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<v Speaker 1>a massive volcanic eruption, or an aircraft flying it's supersonic

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<v Speaker 1>speeds for an extended distance. Today's episode was written by

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<v Speaker 1>Patrick Jake Haiger and produced by Tristan McNeil. For more

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<v Speaker 1>on this and lots of other mysterious topics, visit our

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<v Speaker 1>home planet, how stuff Works dot com.