Abstract

The International Data Centre (IDC) of the Comprehensive Nuclear‐Test‐Ban Treaty Organization (CTBTO) has been issuing the Reviewed Event Bulletin (REB) routinely, on a daily basis, since 21 February 2000, except for some 30 days between 2000 and 2005. Quality assurance work for the REB has accompanied the bulletin production at the IDC and been carried out for the years from 2000 to 2007. This involved comparing the REB with the final global bulletin, the Published Bulletin, of the International Seismological Centre (ISC). The quality assessments focus on evaluating the consistency of event locations for common events that originate from the REB and that were relocated by the ISC. The following are also taken into consideration: the extent and the geospatial location of the events that were only produced in the REB and verified as valid events; and ISC relocated events not contained in the REB and that were missed during IDC analysis.

For the eight years that were evaluated, location differences were observed of <1° (0.5°) on average for about 94% (85%) of the common events, reaching nearly 97% (90%) for the most recent years. On the other hand, <1% were located as being more than 2° apart by the IDC and the ISC. We found a level of error‐ellipse intersection that was almost constant for 2002–2007, whereas the percentage of events with non‐intersecting ellipses decreased over that period. Also, the percentage of events with the ISC ellipse completely inside the IDC ellipse rose slightly during this time. The increase in common locations occurred during a time of smaller formal location errors. The smaller formal location errors are in response to the number of contributing stations and suggest an improved accuracy, in terms of reliability relative to the ISC, for 2007 when compared to 2002.

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