Elastic wave:

A wave that is propagated by some kind of elastic deformation, that is, a change in shape that disappears when the stresses are removed. A seismic wave is a type of elastic wave.

Epicentre:

The point on the earth's surface directly above the focus (hypocentre) of an earthquake.

Fault:

A zone of fractures or breaks in rocks, where movements occur. Earthquakes often occur along faults because they are weak zones in the rock.

Fault plane:

The plane that most closely coincides with the rupture surface of a fault.

First arrival:

The first recorded signal attributed to seismic wave travel from a source.

Flower structure:

More-or-less symmetrical splays into sub-faults near the intersection of the main fault with the ground surface.

Focal zone:

See Rupture Zone.

Foreshock:

An earthquake that is smaller than, and precedes, a "mainshock". Foreshocks tend to occur in the same area as the mainshock. Foreshocks have not been observed before damaging earthquakes in British Columbia.

Frequency:

Number of oscillations per unit time; unit is Hertz (Hz),which equals 1 cycle per second.

Gouge:

In a fault zone, crushed, sheared, and powdered rock altered to clay.

Graben:

A crustal block of rock generally long and narrow, that has dropped down along boundary faults relative to the adjacent rocks.

Great Earthquake:

An earthquake having a magnitude of 8 or greater on the Richter scale.