Analysis of the operational capabilities for detection and location of seismic events at NORSAR

Abstract

Based on 1 year of data, April 1972-March 1973, the routine event detectability of the NORSAR array in Norway has been investigated in terms of 50 and 90 per cent cumulative detectability thresholds which were derived from frequency-magnitude distributions. The best performance was observed for events in central Asia and adjacent regions where the 90 per cent cumulative detectability values are in the range 3.6-3.8 NORSAR m_b values. For teleseismic events, the value is 3.8. For all regions, NOAA reports on the average a larger m_b value than NORSAR, and this relationship is magnitude-dependent. The accuracy of NORSAR-estimated epicenter solutions as compared to those of NOAA was also investigated. The best results were found for Japan and central Asia, where the median location difference is 95 and 105 km, respectively. For teleseismic events, the value is 145 km. The biased errors in the location estimates are demonstrated to have been eliminated for most of the regions considered. Finally, improvements of the present NORSAR event detectability performance are discussed in view of recently developed array data processing techniques.