Abstract
An automatic detection algorithm has been developed which is capable
of time P-phase arrivals of both local and teleseismic earthquakes,
but rejects noise bursts and transient events. For each signal trace,
the envelope function is calculated and passed through a nonlinear
amplifier. The resulting signal is then subjected to a statistical
analysis to yield arrival time, first motion, and a measure of reliability
to be placed on the P-arrival pick. An incorporated dynamic threshold
lets the algorithm become very sensitive; thus, even weak signals
are timed precisely. During an extended performance evaluation on
a data set comprising 789 P phases of local events and 1857 P phases
of teleseismic events picked by an analyst, the automatic picker
selected 66 per cent of the local phases and 90 per cent of the teleseismic
phases. The accuracy of the automatic picks was "ideal" (i.e., could
not be improved by the analyst) for 60 per cent of the local events
and 63 per cent of the teleseismic events.
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