Improved Focal Depth Determination for Use in Seismic Monitoring of the Underground Nuclear Explosions
Final rept. 25 Sep 2001-28 Nov 2003
SCIENCE APPLICATIONS INTERNATIONAL CORPSAN DIEGO CA
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Seismic event location remains as one of the most important discriminants for separating natural tectonic and explosive events. For example, it has been estimated that approximately 8Oof known global earthquakes have focal depths greater than 50 km or are located more than 25 km at sea. Since underwater nuclear explosions can be confidently identified to very low yields using hydroacoustic data, it follows that the vast majority of earthquakes can potentially be identified on the basis of location alone. This is an important observation since global monitoring of underground nuclear testing may require the screening of tens of thousands of seismic events per year and, in order to perform this function efficiently, it will be necessary to have simple and robust discriminants available which can be used to eliminate the vast majority of these events from more detailed consideration. However, in order to be useful for such discrimination purposes, the uncertainties associated with seismic locations must be well defined and reliable and this has proved to be difficult to accomplish.