1 Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part II: Synthetic master events. Dmitry Bobrov 1 , Paul Friberg 2 , Ivan Kitov 1 , Mikhail Rozhkov 1 , and Lassina Zerbo 1 1 Comprehensive Nuclear-Test-Ban Treaty Organization 2 Instrumental Software Technologies, Inc. Corresponding author Mikhail Rozhkov: Mikhail.Rozhkov@ctbto.org, +43-1-26030-6450, VIC P.O. Box 1200, Vienna 1400, Austria Abstract Waveform cross correlation is an efficient tool for detection and characterization of seismic signals. However, the technique critically depends on the availability of master events. For the purposes of the Comprehensive Nuclear-Test-Ban Treaty, cross correlation can globally reduce the threshold of detection by 0.3 to 0.4 magnitude units. In seismically active regions, the optimal choice of master events is straightforward. There are two approaches to populate the global grid in aseismic areas: the replication of real masters and synthetic seismograms calculated for seismic arrays of the International Monitoring System. Synthetic templates depend on the accuracy of shape and amplitude predictions controlled by focal depth and mechanism, source function, velocity structure and attenuation along the master/station path. Here we test three focal mechanisms (explosion, thrust fault, and actual Harvard CMT solution for one of the April 11, 2012 Sumatra aftershocks) and two velocity structures (ak135 and CRUST 2.0). Sixteen synthetic master events were distributed over a 1 o x1 o grid. We built five cross correlation standard event lists (XSEL) and compared detections and events with those built using the real and grand master events as well as with the Reviewed Event Bulletin of the International Data Centre. The XSELs built using the source of explosion and ak135 and the