Effects of subducting lithosphere on p-wave amplitudes and residuals

In studying the structure of the lithosphere and asthenosphere using the kinematic and dynamic parameters of seismic waves, in any area, the tectonics of focal regions should also be considered. Subduction zones represent large-scale inhomogeneities which affect the propagation of seismic waves both at small and teleseismic epicentral distances.A study on the magnitude corrections of seismic stations in Central Europe and Scandinavia revealed that even in the case of close seismic stations the observed differences of the amplitudes of teleseismic P waves depend on the strike and dip of the sinking plates in the Northwestern Pacific. The smaller the angle between a seismic ray and the bottom of the lithospheric plate, the larger the numerical decrease of the magnitude corrections. A similar dependence was found for the P-wave residuals; the rays propagating more along the slab are accelerated more. Besides that, we have observed systematic differences in the P-wave residuals of about 2 s for foci with different positions within the subducting lithosphere of the Kurile arc in investigating the dependence of the residuals on the epicentral distance in the direction of subduction. The differences in the residuals disappear in this region at an epicentral distance of about 52°.