Re-evaluation of the NORSAR Detection and Location Capabilities
Technical rept. 1 Jul 1975-30 Sep 1976
ROYAL NORWEGIAN COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH KJELLER
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Analysis on a regional basis of the NORSAR seismic bulletin data for the three years from April 1972 to March 1975 shows that there has been no significant temporal change in the detectability during this time period. The detectability has been examined using the least squares cumulative method, the least squares incremental method and the Lacoss-Kelly incremental method. The results are fairly consistent, although the incremental methods as expected give higher thresholds for example, for the Japan-Kuriles-Kamchatka region the three methods give, for the 90 detectability, values at NORSAR magnitudes 3.8, 3.9 and 4.0, respectively. The b- values have also been estimated using a weighted least squares method and the Utsu method, and the median of the b- values from the five techniques are for all regions in the range 0.7 to 1.1, with some regional variations. An extensive comparison with PDE solutions from USGS shows that norsar generally reports somewhat smaller magnitudes. The event locations as published by NORSAR since the beginning of 1973 are generally better than before. For the best regions the median location defference between NORSAR and USGS estimates is about 100 km, and very few regions show any significant differnece between the average distances and azimuths as reported by the two institutions.
- Seismic Detection and Detectors