Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part I: Grand master events

We propose to use waveform cross correlation techniques for seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) by proving the ability to build the Global Grid (GG) of master events using high-quality waveform templates at stations of the International Monitoring System. In seismically active regions, the choice of the highest quality and most representative signals from earthquakes as templates for master events is straightforward and one can reduce the current amplitude detection threshold at the International Data Centre (IDC) by a factor of 2 to 3. This gain practically doubles the number of built events, and thus, is crucial for seismic monitoring under the CTBT. However, the coverage by real masters is confined to areas with natural seismicity. Here, we investigate the possibility to populate the GG with real and synthetic master events as a two part study. In Part I, we estimate the effectiveness of cross correlation based on a regular grid filled with grand-master events with replicated high-quality waveform templates.In Part II, we develop and estimate efficiency of synthetic waveform templates for aseismic zones. Both approaches are quantitatively tested using the aftershock sequence of the April 11, 2012 Sumatera earthquake. The cross correlation bulletin previously built using sixteen real master events is a natural benchmark to evaluate the performance of the replicated masters and synthetic waveforms. In Part I, we prove that the replicated grand masters demonstrate the performance at the level of real masters. The Primary IMS Seismic Network includes many array stations, which provide a higher resolution monitoring based on cross correlation.