The blast on 15 February over the Urals Mountains of a fireball that had entered the Earth’s atmosphere over the Kazakh-Russian border was the largest explosion ever recorded by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), according to the first detailed analysis of the event. The result is consistent with rougher, early estimates first reported by Nature (see ‘Russian meteor largest in a century’).

Twenty infrasound monitoring stations around the world registered the explosion, scientists report in a paper accepted for publication in Geophysical Research Letters (abstract here). A meteor explosion on 8 October 2009 over Indonesia had been recorded by 17 stations.

Some 460 kilotonnes of trinitrotoluene (TNT) equivalent — almost ten times the energy of the 2009 Indonesia event — were released when the 9,000-tonne object exploded over the Urals city of Chelyabinsk, injuring more than 1,000 people. It was the most energetic confirmed airburst since the explosion in 1908 of the Tunguska meteor over Siberia, which is estimated to have packed between 3 and 5 megatonnes of TNT equivalent. Fireball events in the order of 500 kilotonnes of explosive energy occur, on average, every 75 years.

The team reports that infrasound signals of the Chelyabinsk explosion circled twice around the globe and were recorded until almost 3 days after the event. The data on infrasound propagation can be used for calibrating the performance of the international monitoring network designed to detect violations of the nuclear-test-ban treaty that came into force last year.