By ANDREW E. KRAMER
Copyright 2013 The New York Times
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Copyright 2013 The New York Times
CHELYABINSKY, Russia —
The shock wave from a meteor that exploded above in Siberia last week somehow sheared the roof off a brick and steel factory building while leaving a nearby glass facade unscathed.
In some high-rises in this city, the first modern urban community to have felt the breath of a cosmic close encounter, every window blew out on the top floor; elsewhere, the ground floors suffered.
More ominously, reports came in to local news media over the weekend of stranger phenomena: Behind unshattered apartment windows, glass jugs were said to explode into shards, dishes to crack, electronics to die. Balconies rattled. One man said a bottle broke right in his hand.
Anna V. Popova was at home with her daughter when she saw the flash, then heard explosions, then found the windows of her enclosed balcony blown in; her neighbour, with identical windows, escaped without property damage.
"A lot of people suffered, not us alone," Popova said, but added that there seemed to be randomness in whose property was damaged. "Who are we supposed to blame for all this? Nobody, of course."
Scientists believe that the space rock that tore through the atmosphere on Friday morning and blew apart here was the largest to have entered the atmosphere since 1908 and that it was unusual as well for the scale of its effects: more than 1,200 people injured and broad property damage. (Read: Russian meteor damage estimated at over $30 million)
Indeed, the event is providing a first indication of the type of structural and infrastructural costs meteors can exact from a highly industrialized society. NASA scientists say a meteor of this size strikes the Earth about once every hundred years.
Shattered glass caused most of the damage and injuries here in Chelyabinsk, a sprawling industrial city of about 1 million people.
What shattered the glass, scientists say, was both the explosion as the meteor fragmented and the waves of pressure created as it decelerated. Such low-frequency waves - called infrasound - are sometimes detected by Cold War-era nuclear blast sensors in remote parts of the Pacific Ocean or Alaska, according to meteor experts.
The waves can bounce off buildings and be stronger in some places than others; they can also resonate with glass, explaining why bottles and dishes might have shattered inside undamaged kitchens, as if crushed by the airy hand of the meteor itself.
"A shock wave is like a ball," Alexander Y. Dudorov, director of the theoretical physics department at Chelyabinsk State University, said in an interview. "Throw a ball into a room and it will bounce from one wall to another."
Russia has mobilized 24,000 emergency officials to inspect roads, railroads, hospitals, factories and military facilities. Most are undamaged, including 122 sites identified as particularly critical, including nuclear power plants, dams and chemical factories, and a space launching site called Strela.
Also Sunday, Russia's consumer safety inspection agency, Rospotrebnadzor, released a statement saying the water in Lake Chebarkul, where a hole in the ice appeared on Friday, was not radioactive.
It was unclear why the agency released this finding only Sunday, or whether the tests were conducted to assuage popular concerns or out of any real official uncertainty over what happened on Friday. In any case, the agency said a mobile laboratory quietly dispatched to the lake tested for but did not discover cesium 137 and strontium 90, isotopes created in nuclear explosions.
Infrasound waves have not previously been studied in a cityscape, Richard P. Binzel, a professor of planetary science at the Massachusetts Institute of Technology and an author of a textbook on asteroids and meteorites, said in a telephone interview. But he noted that the apparent randomness of the damage was consistent with the way such waves function.
"A shock wave can be coming from a particular direction, and if you face that direction you are more susceptible," Binzel said.
"One building might shadow another, or you may have a street that is optimally aligned to channel the wave, either in a fortunate or unfortunate way."
Peter Brown, a professor of physics at the University of Western Ontario, wrote in an email that an infrasound wave "is very efficient at traveling long distances," and that "windows, structures or even glass jars susceptible to resonate at this frequency could be a factor to seemingly random damage at widely disparate locations."
Brown studied a similar, though smaller, explosion of a meteor over the Pacific Ocean on Oct. 8, 2009, which also sent out low-frequency waves, though too remote to affect homes or industry.
They were, though, registered by a network of infrasound sensors established to monitor compliance with the international ban on nuclear tests, according to Brown.
Alekdander V. Anusiyev, the spokesman for the governor of Chelyabinsk region, characterized the damage here as without a discernible pattern. "It is impossible to say more glass broke in one part of the city or another," he said. "Glass broke everywhere."
The roof of the zinc factory that collapsed was reinforced with a lattice of steel beams and supported by concrete joists that are now broken, jutting upward with mangled re-bar protruding. Windows on a neighbouring house blew in with such force that the frames went with them.
Yet a few yards away on Sverdlovsky Street, the cosmos spared a seemingly vulnerable Hundai dealership, a three-story cube sheathed in glass, with glistening display models inside. Not a window broke.
"People can consider Feb. 15 their second birthday," the governor of Chelyabinsk, Mikhail Yurevich, told reporters, referring to the day of the meteor strike. "God directed danger away."
© 2013, The New York Times News Service
Viktor Grokhovsky, a member of the Russian Academy of Science's committee on meteorites, said scientists have examined 53 fragments they collected around the hole in the lake, all less than a centimeter in size.
“The fragments we have found are traces of the outer layer of the meteorite – there is a melted crust and so forth – which means that the basic mass lies there, in the lake,” Mr. Grokhovsky told the Interfax news service on Monday. He said he believed the meteorite was probably no larger than two feet in diameter.
Since the meteorite illuminated the sky on Friday morning, a parade of journalists and curiosity-seekers have trekked across the ice of Lake Chebarkul, about 50 miles from the city of Chelyabinsk, one of four sites that the government believes felt a significant impact. A witness who was on the lake shore on Friday said she saw a star growing brighter until it resembled the sun, and instinctively closed her eyes.
Mr. Grokhovsky, of Urals State University, said a group of local scientists visited the lake and gathered the fragments around the hole in the ice, which is about 20 feet in diameter.
He said preliminary examination suggested the fragments were stone, composed of around 10 percent iron. In comments to RIA-Novosti, he said emergency officials had not allowed the scientists to approach the edge of the hole, but they retrieved 53 fragments and delivered them to a university laboratory for analysis.
On Saturday, a spokeswoman for the Emergency Services Ministry said a dive expedition had been completed and “found no traces of the meteorite,” Interfax reported. Igor Murog, the deputy governor of the Chelyabinsk district, told the news service that he believed the hole in Lake Chebarkul had not been caused by a meteorite.
NASA has said the meteor weighed upward of 7,000 tons when it entered the earth's atmosphere and exploded over the Ural Mountains region around 9:20 a.m. local time on Friday with the force of 500 kilotons of TNT. Small fragments likely reached the earth, NASA said.