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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy<br />

(S) - <strong>IASPEI</strong> - International Association of Seismology and Physics of the Earth's<br />

Interior<br />

JSS011 Oral Presentation 2111<br />

Locating scatterers in the mantle using array analysis of PKP precursors<br />

from an earthquake doublet<br />

Prof. Barbara Romanowicz<br />

Berkeley Seismological Laboratory University of California at Berkeley <strong>IASPEI</strong><br />

Aimin Cao<br />

Well separated individual PKP precursors observed at the Yellowknife seismic array (YK) for a high<br />

quality doublet of earthquakes provide a good opportunity to study the corresponding scatterer<br />

locations and examine the stability of our adopted method of array analysis. Based on the comparison<br />

of the waveforms of non-linearly stacked individual precursors and those of PKIKP phases, for the first<br />

time, we are able to determine that most of these precursors originate from scattering of the PKPbc<br />

(rather than the PKPab) branch above the B caustic on the receiver side. This allows a reliable location<br />

of the scatterers in the lower mantle. The depths of the scatterers range from 2890km (the CMB) to<br />

2270km, and their surface projections range from southern Ontario to northern Saskatchewan in .<br />

These locations are associated with transitions from slow to fast velocities in mantle tomographic<br />

models and follow the expected general dip direction of fossil slabs under north America. This suggests<br />

that the subducted slab remnants under north America have retained their compositional signature.<br />

Average uncertainties in precursor slowness and back-azimuth are as small as 0.08s/deg and 1.4deg,<br />

respectively, indicating that it may be possible to locate such scatterers in the future using single<br />

earthquakes.<br />

Keywords: scatterers, lower mantle, structure

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