Wysession ME, Langenhorst A, Fouch MJ, Fischer KM, Al-Eqabi GI, Shore PJ, Clarke TJ. Lateral variations in Compressional/Shear velocities at the base of the mantle.
Science 1999;
284:120-5. [PMID:
10102807 DOI:
10.1126/science.284.5411.120]
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Abstract
Observations of core-diffracted P (Pdiff) and SH (SHdiff) waves recorded by the Missouri-to-Massachusetts (MOMA) seismic array show that the ratio of compressional (P) seismic velocities to horizontal shear (SH) velocities at the base of the mantle changes abruptly from beneath the mid-Pacific (VP/VS = 1.88, also the value predicted by reference Earth models) to beneath Alaska (VP/VS = 1.83). This change signifies a sudden lateral variation in material properties that may have a mineralogical or textural origin. A textural change could be a result of shear stresses induced during the arrival at the core of ancient lithosphere from the northern Pacific paleotrench.
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