The meteor that lit up the night sky over southeast Michigan and shook the ground Tuesday night did not actually cause an earthquake, researchers say.

In fact, meteors do not cause earthquakes to rupture along a fault, according to William Yeck, a research geophysicist at the United States Geological Survey's National Earthquake Information Center in Golden, Colorado.

The seismic observations associated with the meteor were assigned a magnitude 2.0 by the United States Geological Survey, which said the event was centered about 5 miles west-southwest of New Haven, Michigan, some 40 miles northeast of Detroit. The National Weather Service sent out a tweet that said, "USGS confirms meteor occurred around 810 pm, causing a magnitude 2.0 earthquake."

But Yeck said the magnitude cannot be directly used to compare the meteor's size to an earthquake because the source of the seismic signals are different.

"While the event was reported as a magnitude 2, the magnitude scale is used to estimate the size of earthquakes and therefore is not an accurate representation of the observations from a meteor," Yeck told ABC News.

Researchers are still investigating this specific incident, Yeck said. The seismic waves observed from these events are typically not from an impact but instead are sound waves generated in the atmosphere.




PHOTO: Image taken from video, Jan. 16, 2018, showing the meteor that the National Weather Service tweeted USGS confirms meteor occurred around 810 pm, causing a magnitude 2.0 earthquake.@topherlaine/Twitter
Image taken from video, Jan. 16, 2018, showing the meteor that the National Weather Service tweeted "USGS confirms meteor occurred around 810 pm, causing a magnitude 2.0 earthquake."more +


Bill Cooke, the lead of NASA's Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Alabama, said Tuesday night's phenomenon occurred when a meteor, measuring about 2 yards in diameter and traveling at about 28,000 mph, entered the Earth's atmosphere over Michigan.

The pressure difference between the air in front of the meteor and the air behind it caused the rock to break apart and explode in the sky with the force of less than 100 tonnes of TNT, Cooke said. That explosion generated shock waves that traveled down to the ground northeast of Detroit, where residents heard a loud boom and felt the ground beneath them tremble.

The meteor would not have landed intact, Cooke said, but rather tiny pieces weighing only a few ounces would have scattered over the area.



And it's not a rare event.

"It's common with fireballs that produce meteorites on the ground," Cooke said. "When the shock waves hit the ground, it will shake the ground a bit."



Still, the explosive flash, the sonic boom and the ensuing vibrations on the ground both dazzled and startled residents.

"That's probably a little bit disconcerting," Cooke said.

Although meteorites have damaged cars and the roofs of homes, Cooke said no one has been killed by a meteorite in recorded history.

"I would say most folks are pretty safe," he said.

Quelle: abcNews


Update: 20.01.2018


Hunters Recover Meteorites From Michigan Fireball

A spectacular fireball seen by hundreds of people from Iowa to Ontario delivered precious samples from the asteroid belt to the lake country of southern Michigan Tuesday night.


A beautiful, fusion-crusted meteorite fragment from the Michigan fall finds itself on the snowy Earth after traveling millions of miles.
Mike Hankey / American Meteor Society


On January 16th around 8:10 p.m. EST, a brilliant, green fireball crackled across southern Michigan skies. Eyewitnesses described it as brighter than the full Moon with sparks and an orange tail. At least 77 observers reported hearing explosive sounds as the meteoroid broke apart overhead.

The American Meteor Society(AMS), a clearinghouse for meteor sightings, has received 657 reports of the fireball with some as far away as Iowa and southern Ontario.

The fireball traveled relatively slowly at around 45,000 km (28,000 miles) per hour. That sounds fast, but it's more than 4½ times slower than a typical summertime Perseid.  Its slow speed and great brilliance suggests a fairly large space rock that penetrated deep into the atmosphere, according to Mike Hankey of the AMS.


Professional meteorite hunter Robert Ward holds one of the first-discovered meteorites from the Michigan fireball that blazed across the sky on January 16th. Ward and at least one other person have recovered several rocks from the fall. The black crust is a thin skin of rock that melted as the meteoroid was heated by the atmosphere during its fall.
American Meteor Society (AMS)


While fireballs are relatively common, ones that drop meteorites are rare, and it's rarer still for someone to find those black treasures. But by using Doppler weather radar data and seismic traces (more on that in a moment), meteorite hunters were able to pinpoint the strewn field, the name for the ground footprint where the space rocks might have fallen. Lately of the asteroid belt, these interplanetary fragments now call the Township of Hamburg, Michigan, home.


The figures represent folks who spotted the fireball Tuesday night.
Google / AMS

The strewn field extends about 5 miles, oriented east-southeast to west-northwest, from about Highway 23 up to Bass Lake, some 20 miles northwest of Ann Arbor. Since the area has many lakes, make sure the ice is sound before venturing out.

Anyone living in that area should be on the lookout for black rocks poking out of the snow similar to what Ward is holding in the photograph above. The black coating, called fusion crust, forms when the outside of the meteoroid is heated and melted by friction from the air during its flight through the atmosphere. Fusion crust is typically only 1-2 mm thick.


This is a trace of the pressure wave recorded at Ann Arbor.
Rob Matson

The Michigan fireball not only put on a light show, it "knocked down the door," announcing its arrival with a 2.0-magnitude seismic event recorded by the U.S. Geological Survey. The blast was not from the impact itself but from the air pressure wave created during the explosive breakup of the meteoroid in the atmosphere.

A preliminary analysis indicates it's possibly an L6 chondrite, a common stony meteorite type.  The "L" stands for low iron and "6" (on a scale from 3 to 7, from least to most altered by heat) indicates that the meteorite was strongly heated, so it likely originated from a larger asteroid. Samples are on their way now to the Chicago Field Museum for more detailed analysis.

Quelle: Sky&Telescope