Infrasound Station in Qaanaaq, Greenland (IMAGE) Terry Collins Assoc Caption The CTBTO monitors infrasound -- sound waves at frequencies too low to be detected by the human ear -- with 48 stations. Four more are under construction and another eight are planned. Twenty of the CTBTO's infrasound monitoring stations detected signals made by a meteor that had entered the atmosphere and disintegrated in the skies over Chelyabinsk, Russia on February 15, 2013. A station in Antarctica, some 15,000 kilometres away, detected the meteor's sub-audible sound. The station detected sound waves generated by the blast twice, travelling in opposite directions, as they circumnavigated the Earth. A station in Alaska, some 6,500 kilometres away, clocked it circling the Earth three times. Credit Courtesy of CTBTO Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.