Is a crack or fracture along the blocks of rocks that make up the crust.

Fault Plane

A plane or weakness within the lithosphere that ruptures during an earthquake.

Fault Trace

The line where a fault plane interests the surface of the Earth.


Elongated fractures or cracks on the slopes of a volcano.

Flank Eruption

An eruption from the side of the volcano.

Focal depth

Refers to the depth of an earthquake’s from the epicenter to the hypocenter/focus.


See hypocenter.

Forecast (volcanoes)

A comparatively imprecise statement of the time, place, and nature of expected volcanic activity. Forecasts can be further subdivided into long- and short-term forecasts. Long-term forecasts are those that pertain to the coming years, decades or longer


Relatively smaller earthquakes that may preceded the largest earthquake (main shock) in a series/sequence. Not all main shocks have foreshocks.


A body of rock that is mappable at the Earth’s surface or traceable in the subsurface which can be identified by lithic characteristics and stratigraphic position.


The number of times something happens in a certain period of time such as ground shaking e.g. up and down during an earthquake.


Fumaroles are cracks or openings in the ground through which volcanic gases from beneath the Earth’s surface escape.