Event Location and Source Characterisation

Abstract

The location of seismic events in space and time is an important part of seismological practice but has particularly significance in the context of monitoring a comprehensive test-ban treaty. A primary discriminant between man-made events and the majority of natural earthquakes is provided by the depth of the source. Drilling techniques for the emplacement of devices preclude a source depth of more than a few kilometres. If the depth of an event can be established to be deeper than 15 km then it is very unlikely to be man-made, even allowing for location errors. A major role of location procedures in a monitoring environment is therefore to act as a winnowing device for the very large number of intermediate and deep-focus events occurring in subduction zones, especially around the Pacific Rim. For shallower events there is a need to obtain the best possible location by combining data from regional and more distant stations, and then to try to characterise the source through its focal mechanism and spectral behaviour.