Improved Focal Depth Determination for Use in CTBT Monitoring
MAXWELL TECHNOLOGIES INC SAN DIEGO CA
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Seismic event location remains as one of the most important discriminants for separating natural tectonic and explosive events. However, in order to be useful for discrimination purposes, the uncertainties associated with seismic locations must be well defined and reliable, and this has proven to be difficult to accomplish to the required degree of accuracy. In particular, high-confidence estimation of focal depths remains as an outstanding monitoring problem. During the past year, we have continued to pursue a research program which is directed toward the development of improved detection and identification procedures for the depth phases pP and sP, as well as with formulation of a new algorithm for computing more reliable confidence intervals on focal depth estimates determined from P-wave first arrival times. With regard to depth phase identification , we have continued to investigate the utility of the fully automatic network stacking algorithm which maps the IDC post-P detection times at a station into candidate depth phases using the pP - P and sP - P delay times predicted by the IASPEI travel-time tables for that epicentral distance and then combines the individual station results as a function of candidate source depth. This automatic algorithm has now been applied to data from about 150 REB events in the Hindu Kush and in the Hokkaido and central Honshu regions of Japan. Prominent candidate pP and sP peaks have been identified in the resulting network detections stacks for a majority of these events, including some with mb values as low as 3.7 and depths as shallow as 50km. Current effort on this phase of the project centers on the incorporation of the Pearce algorithm Pearce, 1977 1980 into the depth phase identification procedure.
- Seismic Detection and Detectors