abstract

Schemes to automatically identify later phases using LASA and using LASA together with NORSAR were designed and tested. With a single array, phase identification was accomplished by searching for a P or PKP phase that could be associated with a particular later phase such as PP, PcP, etc. On the basis of the time interval between the signals, their slowness, and relative amplitudes, the best phase interpretation was chosen by means of the Neyman-Person likelihood ratio test. With two arrays, detections from one array were checked against detections from the other array for signals originating from the same event.

Testing the schemes on the LASA and NORSAR detection logs, 9 later phases per day were detected and 11 events per day were found common to the LASA and NORSAR detection logs. Confusion of later phases was very minor. The most serious problem was the identification of fictitious phases and events that occurred due to various coincidences.

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