UBC Theses and Dissertations
Evaluation of a rectilinear motion detector Fuchs, Jens Peter
One criterion for distinguishing underground nuclear explosions from earthquakes is that most earthquakes occur at considerably larger depths. Focal depth can he determined with seismograms if both the P and the pP arrival are clearly distinguishable. "REMODE 5A" (REctilinear Motion DEtector), a time-varying polarization filter for the detection of P-type motion, is applied to artificial inputs and earthquakes. It is investigated how variation of the filter parameters affects the output. The length of the time window within which the cross-correlation filter operator is calculated must not be small compared to the signal period, especially if the onset of a quake is to be enhanced. If the window is very short, the filter outputs will be erratic. It makes little difference whether the truncated filter operator is tapered at the ends or not. REMODE 5A removes background noise and much of the signal-generated noise, but its efficiency in picking pP from complicated P coda is not significantly different from more elementary versions of REMODE filters. Through choice of parameters, REMODE 5A can be made arbitrarily selective to the degree of rectilinearity and the incident angle of signal and noise. However, since the sought-for pP and P will often be contaminated by signal-generated noise, too highly selective a filter may easily reject signal.
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