Investigation of laterally heterogeneous shear velocity structure in D″ beneath Eurasia

Analyzes long-period, horizontally polarized (SH) shear waveforms from earthquakes in the northwest Pacific recorded in Europe and the Middle East for evidence of proposed laterally varying shear velocity stratification in D″ beneath Eurasia. Both the relative amplitude and differential travel time variations of the wave forms indicate that D″ beneath Eurasia is characterized by 1) broad regions in which the structure has large-scale stratification giving coherent long-period reflections, with superimposed velocity variations that scatter shorter-wavelength waves; and 2) smaller regions which are sufficiently heterogeneous to scatter even the long-period energy. These observations are consistent with a model of the lower mantle in which distributed heterogeneity is concentrated in D″, generating a locally stratified layer in some regions. -from Authors