Development of calibration techniques for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) international monitoring system

A prototype International Data Centre (pIDC) is developing and testing concepts for the International Monitoring System that will be put into place to monitor compliance with the recently-signed Comprehensive Test Ban Treaty (CTBT). The testing includes the routine production of a daily bulletin of global seismic activity, several days after real time, since the beginning of 1995. A wider variety of seismic phases are used for location than is the practice of existing agencies producing global bulletins at greater delays, and another difference is that observed slowness vectors are used in addition to arrival time. Comparisons of pIDC bulletins with those provided by national agencies that operate denser networks have demonstrated both random and systematic errors in location that often exceed the formal error estimates. The pIDC is developing and testing techniques to reduce systematic biases through region- and path-dependent corrections to travel-time and slowness, and to better account for random errors. Initial results from this very long-term project are encouraging. (C) 1999 Elsevier Science B.V. All rights reserved.