GLOSSARY OF TERMS

Asthenosphere: The layer or shell of the earth below the lithosphere, which is weak and in which isostatic adjustments take place, magmas may be generated and seismic waves are strongly attenuated. The asthenosphere begins about 100 km below the surface and extends to a depth of about 350 km.

 Epicentre: An area of the surface of the earth directly above the earthquake focus.

(Earthquake) Intensity: A measure of the effects of an earthquake at a particular place.

Lithosphere: The solid outer shell of the earth, including the crust and uppermost rigid mantle.

Lithospheric plate: A segment of the lithosphere that moves over the plastic asthenosphere below.

(Earthquake) Magnitude: A measure of the strength of an earthquake.

Mercalli scale: An arbitrary scale of earthquake intensity graduated from I to XII.

Richter scale: A numerical scale of earthquake magnitude, devised in 1935 by C.F. Richter. It runs from 1 to 10.

Seismicity: The likelihood of an area being subjected to earthquakes.

Seismic zone: A zone of the Earth where earthquakes occur.