Automatic Detection, Timing and Preliminary Discrimination of Seismic Signals with the Instantaneous Amplitude, Phase and Frequency
Technical rept no. 4
TEXAS INSTRUMENTS INC DALLAS EQUIPMENT GROUP
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The feasibility is evaluated of applying instantaneous amplitude, phase and frequency measurements to automatically detect, time and identify seismic events. Detection based on phase measurements is shown to be in principle 6 dB more sensitive than detection based on amplitude measurements. A phase detection and timing algorithm, using a priori known dispersion characteristics, is demonstrated to time the onset of simulated teleseismic long-period surface waves within 30 seconds accuracy in 70 of the tested cases, for waveforms down to 0 dB signal-to-noise ratio. By phase measurement, rather than by amplitude measurement, this algorithm also provides a measure of the surface wave signal-to-noise ratio. These results can be applied in the extraction of weak surface waves. Phase detection of teleseismic short-period bodywaves was not found to be feasible, due to the interference of early- arriving secondary signals. Therefore, short-period P-wave detection and timing are performed essentially by envelope peak detection instantaneous frequency measurements are also used in the timing process. Measurements of the instantaneous frequency permit analysis of the delay times of secondary signals partially overlapping with earlier primary signals, down to the primary signal detection level.