Question

Why seismic wave velocity decreases at outer and inner core boundary?

Answer 1

Earth's Core. Seismic waves decrease in velocity at core/mantle discontinuity at 2900 km depth (fig. 10.6); decrease in velocity causes waves to be refracted inward at this boundary; creates a P-wave shadow zone between 103˚ and 143˚ from earthquake focus (figs. 10-7).