Bulletin of the Seismological Society of America; March 2002; v. 92; no. 2;
p. 751-760; DOI: 10.1785/0120010169
© 2002 Seismological Society of America
Origins of High-Frequency Scattered Waves near PKKP from Large Aperture Seismic Array Data
Paul S. Earle
U.S. Geological Survey
National Earthquake Information Center
MS 966, Box 25046, DFC
Denver, Colorado 80225
This article identifies the likely origin of 1-Hz scattered waves in the
vicinity of PKKP by comparing measurements of slowness and onset time
to ray-theoretical predictions. The measurements are obtained from slant
stacks of Large Aperture Seismic Array (LASA) data from 36 earthquakes and six
explosions in the range 30°116°. Three types of scattered waves
explain the main features seen in the stacks, including: P scattered
to PKP near the Earth's surface (P.PKP), PKKP
scattered near its coremantleboundary (CMB) reflection point
(PK.KP), and SKKP scattered near its CMB reflection point
(SK.KP). The LASA stacks image the amplitude and slowness variations
of the scattered waves with time. They also show where these waves can be
detected and where they are free from contaminating arrivals. SK.KP
waves rise above the noise approximately 100 sec before the onset time of the
main SKKP arrival near 113°. Observations of PK.KP span
30°100°. However, at distances greater than 50° they suffer
from P.PKP contamination. At distances less than 40° the
PK.KP last for about 280 sec. This is approximately 130 sec longer
than the maximum ray-theoretical prediction for waves scattered at the CMB,
indicating a possible combination of near-surface scattering and contributions
from the overlying mantle.
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