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GSETT-3: Evaluation of the Detection and Location Capabilities of an Experimental Global Seismic Monitoring System

Angewandte Wissenschaft Software und Technologie GmbH
Mariahilfer Str. 47/3
A-1060 Wien, Austria
(J. W.)

CEA/DAM/DRIF/DASE
BP 12
F-91680 Bruyères le Chatel, France
(F. R., J. L. P., B. M., Y. C.)

CEA/DAM/DRIF/DCRE
BP 12
F-91680 Bruyères le Chatel, France
(R. C.)

This article presents the results of the seismological evaluation of the first 18 months (January 1995 to June 1996) of the Group of Scientific Experts third Technical Test (GSETT-3). Performance measures such as completeness, estimates of detection thresholds, and equivalent circle areas as an estimate of location accuracies are obtained by comparing the REB (Reviewed Event Bulletin) of GSETT-3 to global and regional reference bulletins, and also by intrinsic methods.

Incremental detection thresholds are stated on the PDE (Preliminary Determination of Epicenter) m_b scale: magnitude conversion formulae are derived to convert REB m_b and other reference bulletin magnitudes to this scale. At the 90% confidence level, an incremental detection threshold of about m_b (PDE) 3.5 or better is attained in northwest Europe and parts of North America, Central Asia, and Australia. Apart from these areas, the threshold is generally around 4.0 in the Northern Hemisphere. In the Southern Hemisphere it is 4.2 or better in most of South America and northern and equatorial Africa, and between 4.2 and 4.6 in other regions with the highest values being attained in some remote parts of the southern oceans. Still at the 90% confidence level, equivalent circle areas for the m_b (PDE) 4–4.5 magnitude range come close to 1,000 km² in northern Europe. The global average is about 8,000 km². At the 50% level (the median of all detected events), most northern hemisphere regions have equivalent circle areas at or below 1,000 km², and even in the southern hemisphere 5,000 km² are not exceeded.

Observed performance is used to calibrate network simulation codes, which allow to interpolate system capabilities over aseismic regions and to extrapolate for the capabilities of the future International Monitoring System (IMS) seismic network. It is concluded that at the 90% confidence level, except in remote ocean areas, a global incremental detection threshold of m_b (PDE) 4 and a location accuracy of the order of 1,000 km² are attainable with the IMS seismic network. However this will require a full calibration of the network and an optimized usage of the auxiliary station network. New computational methods as well as calibration will help to improve the depth determination.

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