Comparison between LDG-network and GERESS-array with respect to regional detection and location results

Abstract

The design of a global seismic system to monitor compliance with a ban on underground nuclear testing considerably deviates from previous concepts of international seismic data exchange. The new concept relies on centralized processing of continuous data from a fixed station network (“alpha” stations) which provides the primary detection and location capability. This alpha station network is augmented by additional stations (“beta” stations) which send data on request to refine the hypocentres of events which were detected by the alpha network. To test this concept we have used the GERESS array in Germany as a prototype alpha station and investigated its regional detection and location capability for events in France and surrounding areas. For this region, data from the national French network operated by LDG provide an excellent reference data base. Within a 5 degree distance, GERESS showed an excellent performance in terms of detection and location down to magnitude M(LDG) = 3. Between a 5 degree and 10 degree distance, the detection capability is still high but very often it is not sufficient to locate events below M(LDG) = 4. Generalizing these results, we can conclude that either the maximum distance between alpha stations should be 10 degrees or the contribution of beta stations has to play a significant role in a future monitoring system.