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TIME DOMAIN STUDIES OF SHORT PERIOD TELESEISMIC P PHASES
ARCTIC INST OF NORTH AMERICA ARLINGTON VA
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Forty-one seismic events recorded on the plains of western Alberta are subjected to a detailed study in the time domain. A P-detection time- varying polarization filter is described and applied to the events to detect segments of strong P motion in the first 25 seconds of the P phase coda. On seismograms of 23 events, 12 of which have reported depths shallower than 40 km, pP phases have been identified sP phases have been identified on 9 of the events. Considering estimated accuracies of observed and calculated pP-P times, assigned focal depths are accurate to within plus or minus 15 km. A varying upper crustal structure is found to make a similar contribution to the vertical components of the P phase for stations at separations up to 160 km. The radial components at these stations are similar only during time segments of strong P motion. The dissimilarity in other time segments of the radial components is attributed to different amplitudes and time-delays for PS converted phases generated at crustal layer interfaces. The largest PS converted phase, with amplitude up to about 1.5 that of P, is generated at the base of the sediments. A small number of PS converted phases generated at the base of the crust have been identified.
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