Seeing inside the Earth Glossary

An interface 2,900km below the Earth's surface separating the mantle and core.

The inner section of the core 5,155km deep to the Earth's centre at 6,371km, and consisting of solid iron alloy.

The asthenosphere underlying oceanic lithosphere in which seismic waves travel more slowly, probably because rock has partially melted.

The deepest section of the mantle, stretching from 670km down to the core-mantle boundary.

The seismic-velocity discontinuity that defines the boundary between the Earth's crust and mantle.

The section of the core, between 2,900km and 5,150km deep, that consists of liquid iron alloy.

A band between 103 and 143 degrees from an earthquake epicentre, as measured along the circumference of the Earth, inside which P-waves do not arrive at seismograph stations.

The bouncing off of a ray as it hits a boundary between two different materials.

The bending of a ray as it passes through a boundary between two different materials.

A band between 103 and 180 degrees from the epicentre of an earthquake inside of which S-waves do not arrive at seismograph stations.

The changing position of an imaginary point on a wave front as the front moves through rock.

A cross-sectional view of the crust made by measuring the reflection of artificial seismic waves off boundaries between different layers of rock in the crust.

Analysis by sophisticated computers of global seismic data in order to create a three-dimensional image of variations in seismic-wave velocities within the Earth.

A boundary in the Earth at which seismic velocity changes abruptly.

The middle portion of the mantle, from 400 to 670km deep, in which there are several jumps in seismic velocity.

The uppermost section of the mantle, reaching down to a depth of 400km.

A graph that shows the variation in the velocity of seismic waves with increasing depth in the Earth.

The boundary between the region through which a wave has passed and the region through which it has not yet passed.