Teleseism:

An earthquake that is distant (usually more than 20 degrees) from the recording station.

Thrust fault:

A reverse fault in which the upper rocks above the fault plane move up and over the lower rocks at an angle of 30 ° or less so that older strata are placed over younger.

Tidal wave:

See Tsunami.

Tomography:

Construction of the image of velocity variations inside the Earth from measurements of seismic waves at the surface.

Transform fault:

A strike-slip fault connecting the ends of an offset in a midoceanic ridge, an island arc, or an arc-ridge chain. Pairs of plates slide past each other along transform faults.

Travel time:

The time required for a wave train to travel from its source to the point of observation.

Travel-time curve:

A graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve.

Trench:

Long, narrow arcuate depression in the seabed which results from the bending of the lithospheric plate as it descends into the mantle at a subduction zone.

Triple junction:

The point where three plates meet.

Tsunami:

(Japanese for "Harbour Wave"). A series of huge ocean waves caused by a rapid, large-scale disturbance of the sea water, such as a major earthquake beneath the seabed that causes large vertical movements. In deep water, Tsunami waves are less than a metre high, but they can travel at speeds exceeding 800 kilometres per hour and can easily cross an entire ocean basin. When they reach shallow water or narrow inlets the waves slow down and the height can build into a wall of water which causes devastation on the shore.

Unconsolidated:

Loosely arranged, not cemented together, so particles separate easily.

UTC:

Coordinated Universal Time. The time scale based on the atomic second but corrected every now and again to keep it in approximate sync with the earth's rotation. The corrections show up as the leap seconds put into UTC - usually on New Year's Eve. In the most common usage, the terms GMT and UTC are identical.