The importance of regional seismic networks in monitoring nuclear test-ban treaties

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) prohibits the testing of all nuclear weapons, no matter how small. Although the CTBT is not yet in force, its verification is supported by the International Monitoring System (IMS), which is about 90% complete. Using IMS data, seismologists are able to detect well-coupled underground nuclear explosions with yields larger than approximately 0.5-1 kt anywhere in the world with high confidence. Lowering the detection threshold significantly, say to yields of 10-4-10-1 kt fully coupled, will require augmenting IMS data with records from thousands of seismometers that are deployed in various regional, national, and global networks. It will also require routine analysis (detection, location, and characterization) of small seismic events (M 0-3) that are well recorded only at local distances (<150-200 km). This is the same problem faced by operators of regional seismic networks, who are tasked with developing earthquake catalogs as complete as possible without contamination from explosions and other nonearthquake sources. In the future, verification seismology is likely to become increasingly intertwined with the data, methods, and expertise of regional seismic network operators. Here, I highlight some of the important contributions to verification seismology that have recently been made using data recorded by regional seismic networks in North America, with a focus on small events recorded at local distances.