Homing in on the event

The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) today updated its Member States on the progress in the analysis of its findings on the nuclear test declared by the Democratic People’s Republic of Korea (DPRK) on Monday, 25 May.

Seismic findings fine-tuned

The final location estimate for the 2009 announced test (red) is more precise than for the 2006 test (green). The other two ellipses (blue and yellow) show two preliminary automatic location estimates for the event in 2009.

CTBTO experts further elaborated on the seismic signals from the event, which clearly displayed explosion-like characteristics while also featuring certain earthquake-like traits, see May 27 press release. Less than 48 hours after the event, Member States had already received the so-called Reviewed Event Bulletin (REB), a “data product” in which the seismic analysis has undergone careful review by CTBTO experts. With the help of this analysis, the error ellipse could now be decreased to establish the event’s location with a certainty of about +/- 10 km (see red circle).

 

Meeting the Treaty’s requirements
The nascent CTBTO’s verification regime has thereby proven its ability to meet two important benchmarks required of it when the Comprehensive Nuclear-Test-Ban Treaty (CTBT) enters into force. Firstly, it issued the Reviewed Event Bulletin within the required timeline of 48 hours. And secondly, had the Treaty been in force, it would have cleared the way for an eventual on-site inspection  by homing in on the event precisely enough to stay within the 1,000 km² to which on-site inspections are limited. In fact, the CTBTO’s initial findings have already fulfilled this requirement.

Sixty-one stations registered the May 25 event

61 stations registered the event.

CTBTO experts could base their thorough analysis on seismic data from no less than 61 stations (31 primary seismic stations and 30 auxiliary seismic stations). The study therefore profited from almost three times as much seismic data as the first DPRK nuclear test in October 2006, which was registered by 22 stations.

“Waiting for the right winds to blow”

Click for ATM animation.

With these words CTBTO Executive Secretary Tibor Tóth described the status of the second phase in monitoring nuclear test explosions, which involves monitoring the atmosphere for radioactive particles or noble gases. On the basis of the assumption that the event involved a noble gas release, the CTBTO used a technique called Atmospheric Transport Modelling (ATM) to predict that the first readings of noble gases could occur seven to nine days after the event, i.e. from 1 to 3 June. The first noble gas stations that the cloud of the radioactive noble gas xenon133 would reach are located in Japan, Russia and the Philippines.

The CTBTO will provide an update if and when noble gas has been detected and analyzed.