Detection Capability of the Seismic Network of the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty

We have investigated the Reviewed Event Bulletin (REB) of the International Data Center (IDC) for the time period 1 January 2001 to 31 December 2011 in order to quantify the event detection capability of individual seismic stations of the International Monitoring System (IMS). In order to obtain regionalized detection thresholds, we divide the events into a binned global grid system and investigate three estimation algorithms applied to each specific target area. Our preferred algorithm is to consider the ensemble of REB reported events in the area, and downscale each event magnitude with the observed signal-to-noise ratio (SNR) at the station. In this process, it is necessary to take into account events not detected by the station, in order to avoid a bias in the threshold estimate. We address this problem by using a maximum-likelihood estimation procedure whenever information on nondetections is available in the REB and correct for an estimated bias in other cases. A major result of this study is quantification and ranking of the IMS primary and auxiliary seismic stations based on their capability to detect events within regional and teleseismic distance ranges. We note that for each station, source regions with noticeable signal amplitude focusing effects (bright spots) and defocusing effects can be identified and quantified. We apply the results of this study to calculate updated global detection capability maps for the IMS primary seismic network.