The boundary between this region and the one above it can be home to trapped spheroidal modes known as Stoneley modes. The existence of PKJKP waves traversing this region has not been observed, but high-frequency PKiKP waves 
The boundary between this region and the one above it can be home to trapped spheroidal modes known as Stoneley modes. The existence of PKJKP waves traversing this region has not been observed, but high-frequency PKiKP waves refracted through this region can be used to constrain the properties of its boundary. The boundary of this region sees a sharp increase in P-wave velocity over a distance of about 5 kilometers, and this region has a high Poisson ratio of about 0.45. The area between this region and the region directly above it is known as the "mushy zone", and the presence of this region was inferred from the presence of a "shadow" by Inge Lehman. This region of the earth has a radius of about 1215 kilometers, which is growing as the Earth cools and more material accretes in this region. For 10 points, identify this solid region of iron and nickel in the center of the earth.
The boundary between this region and the one above it can be home to trapped spheroidal modes known as Stoneley modes.
inner core [prompt on core; accept outer core before "PKiKP"]