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Lateral Variations in Compressional/Shear Velocities at the Base of the Mantle
Ist Teil von
Science (American Association for the Advancement of Science), 1999-04, Vol.284 (5411), p.120-125
Ort / Verlag
Washington, DC: American Society for the Advancement of Science
Erscheinungsjahr
1999
Quelle
Science Online_科学在线
Beschreibungen/Notizen
Observations of core-diffracted P (P$_{diff}$) and SH (SH$_{diff}$) 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 (V$_P$/V$_S$ = 1.88, also the value predicted by reference Earth models) to beneath Alaska (V$_P$/V$_S$ = 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.