Hypocentre:

The subsurface location (focus) at which the energy of an earthquake is released. Earthquakes generally occur at depths less than about 30 km, but may occur to a depth of 600 km or more in some areas.

Incompressibility:

An index of the resistance of an elastic body, such as a rock, to volume change.

Inner core:

Central solid region of the Earth's core, probably mostly iron; radius about 1221 kilometers, discovered by Inge Lehmann in 1936.

Intensity:

The Modified Mercalli Scale is a numerical scale used to catagorize earthquakes based on descriptions of how the earthquake was felt. These effects may range from I (not felt except by a very few under especially favourable conditions) and XII (total damage).

Interplate earthquake:

Earthquake with its focus on a plate boundary. Offshore earthquakes of western Canada are of this type.

Intraplate earthquake:

Earthquake with its focus within a tectonic plate. Eastern Canadian earthquakes are of this type.

Island arc:

Chain of islands above a subduction zone (e.g., Japan, Aleutians).

Isoseismal Line:

A line connecting points on the Earth's surface at which earthquake intensity is the same. It is usually a closed curve around the epicentre.

Isostasy:

The way in which the lithosphere 'floats' on the asthenosphere.

Landslide:

An abrupt movement of geological materials downhill in response to gravity. Landslides can be triggered by an earthquake or other natural causes. Undersea landslides can cause tsunamis, such as the one triggered by the 1929 Grand Banks earthquake.

Latitude:

The location of a point north or south of the equator. Latitude is shown on a map or globe as east-west lines parallel to the equator.

Left-lateral fault: (sinistral)

A strike-slip fault on which the displacement of the far block is to the left when viewed from either side.