Chapter 17 Earth’s Interior

Asthenosphere
A region of Earth’s outer shell beneath the lithosphere. The astenosphere is of indeterminate thickness and behaves plastically.

Convection
A very slow circulation of a substance driven by differences in temperature and density within that substance.

Core
The central zone of Earth.

Crust
The outer layer of rock, forming a thin skin over Earth’s surface.

Crustal Rebound
The rise of Earth’s crust after the removal of glacial ice.

Heat Flow
Gradual loss of heat (per unit of surface area) from Earth’s interior out into space.

Isostasy
The balance or equilibrium between adjacent blocks of crust resting on a plastic mantle.

Isostatic Adjustment
Concept of vertical movement of sections of Earth’s crust to achieve balance or equilibrium.

Lithosphere
The rigid outer shell of Earth, 70 to 125 or more kilometers thick.

Low velocity zone
Mantle zone at a depth of about 100 kilometers where seismic waves travel more slowly than in shallower layers of rock.

Mantle
A thick shell of rock that separates Earth’s crust above from the core below.

Mantle Transition Zone
The transition zone is part of the Earth’s mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 km (250 to 400 miles). The Earth’s mantle, including the transition zone, consists primarily of peridotite, an ultramafic igneous rock.

Moho
(Mohorovicic discontinuity) The boundary separating the crust from the mantle beneath it.

P-wave Shadow Zone
The region on Earth’s surface, 103 degrees to 142 degrees away from an earthquake epicenter, in which P-waves from the earthquake are absent.

S-Wave Shadow Zone
The region on Earth’s surface (at any distance more than 103 degrees from an earthquake epicenter) in which S waves from the earthquake are absent.

Seismic Reflection
The return of part of the energy of seismic waves to Earth’s surface after the waves bounce off a rock boundary.

Seismic Refraction
The bending of seismic waves as they pass from one material to another.

Seismic Tomography
Uses earthquake waves and powerful computers to study planar cross sections of the mantle following large earthquakes.