Putting nuclear-test monitoring to the test

On the 22 August 1998, 0.1 kilotonnes of conventional explosives was fired underground at the nuclear test site of the former Soviet Union at Degelen Mountain in eastern Kazakhstan. This explosion, which we refer to as K980822, was carried out by the Republic of Kazakhstan, in cooperation with the United States, to seal tunnels at the site. It provided an opportunity to assess the network of seismological stations being set up as part of the International Monitoring System (IMS) to verify the Comprehensive Test Ban by detecting and identifying low-magnitude disturbances. Despite its low yield, short-period signals from the explosion were recorded up to 88° away. The seismograms recorded are sufficient to identify the disturbance as suspicious and, if the test-ban treaty were in force, could have led to a demand for an on-site inspection to determine whether a nuclear test had taken place.