VFM Discrimination Results from a Ten Station Network

This report describes results of a discrimination experiment performed on a large number of Eurasian events. The objective was to identify each of these events as either an earthquake or an underground explosion based on an analysis of short-period P waves recorded at a global network of seismograph stations. Ten seismograph stations were involved in the experiment. Discrimination results obtained support the theoretical predictions of Archambeau, et al., (1964) and demonstrate that the variable frequency magnitude (VFM) approach provides very effective discrimination between Eurasian earthquakes and explosions recorded at both teleseismic and regional distances. One of the study's principal findings is that the effectiveness of m sub b(f) type discrimination at each of the stations included in this experiment is largely controlled by the attenuation properties of the upper mantle beneath a particular station. For instance, m sub b(f) estimates from data recorded at a station overlying high Q upper mantle (as evidenced either from the location of a station in a shield region and/or a region characterized by large negative P- wave travel-time residuals) consistently yield a greater degree of separation of earthquakes and explosions than do m sub b(f) estimates from a station located over low Q upper mantle.