Comprehensive (nuclear) Test Ban Treaty Research

Seismic moment tensors hold potential for event discrimination. At issue is the use of regional to far regional distance methodologies with sparse network geometries as will be the case for the monitoring of low yield explosions using the International Monitoring System (IMS). Dreger and Woods ( 1998 preprint here!) have demonstrated that the anomalous radiation of Nevada Test Site (NTS) nuclear explosions may be discerned using as few as two regional distance broadband stations. Nuclear explosions are often accompanied by "tectonic release", possibly triggered earthquakes or other secondary source processes. It is the presence of tectonic release that poses the greatest challenge in the quest to discriminate an explosion from and earthquake using long-period waves and a regional distance seismic moment tensor methodology.

If seismic moment tensors do in fact provide discrimination capability the automated application of the methodology to the low frequency wavefield data stream may be tried. The Berkeley Seismological Laboratory has recently completed the first phase in the development, implementation and application of automated seismic moment tensor codes at the Prototype International Data Center (PIDC).

Event location is of critical importance in the monitoring of the CTBT. The objectives of CTBT monitoring using the IMS involve the location of events to magnitude 4.0 on a global scale with absolute mislocation error of less than 18 km. This is a tall order. We have investigated regional and far-regional event location using sparse networks of broadband stations in a controlled experiment in which southern California earthquakes are taken as ground truth and locations using regional broadband stations are compared. This research is also to improve the Berkeley Seismological Laboratories own capability of earthquake monitoring in central and northern California. Follow this link to see a paper describing our location study.