Seismic Velocity Structures of a HighVelocity Area Near the CoreMantle Boundary Beneath Eastern Eurasia
Abstract
The shear and compressional velocity structures of a highvelocity area near the coremantle boundary (CMB) beneath the eastern Eurasia are studied based on waveform modeling and differential travel time analysis of ScSHSH and PcPP phases. Our seismic data are obtained from the Fnet in Japan, the Global Seismographic Network and several PASSCAL arrays. The observed ScSHSH and PcPP differential travel time residuals show similar patterns, but also a change of P/S velocity ratio across the region. The seismic data suggest that the average shear and compressional velocity increases reach 3% and 2% in the lowermost 300 km of the mantle, respectively. The waveform data from the shear and compressional waves sampling the region can be explained by a model with a D" discontinuity with a large variability of its structure. The data sampling southwest and southeast of the highvelocity area can be explained by simplified onedimensional models with a D" discontinuity that are characterized by a shear velocity jump of 5% to 3.4% and a compressional velocity jump of 2.6% at about 220 km to 260 km above the CMB followed by a negative gradient toward the CMB. But, the shear wave data sampling the region between would exclude a D" discontinuity with a shear velocity jump greater than 1%. We will discuss effects of twodimensional wave propagation on the inferred seismic structures and the D" discontinuity, and implication to the origins of the inferred seismic structures in the region.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.U41B0407H
 Keywords:

 1213 Earth's interior: dynamics (1507;
 7207;
 7208;
 8115;
 8120);
 7203 Body waves;
 7208 Mantle (1212;
 1213;
 8124)