Rift:

Region where the crust has split apart, usually marked by a rift valley (e.g., East African Rift, Rhine Graben).

Right-lateral fault: (dextral)

A strike-slip fault on which the displacement of the far block is to the right when viewed from either side. The Queen Charlotte fault is one of this type of fault.

Rigidity:

An index of the resistance of an elastic body to shear. The ratio of the shearing stress to the amount of angular rotation it produces in a rock sample.

Risk (seismic):

The probabilistic risk is the odds of an earthquake occurring and causing damage within a given time interval and region.

Rossi-Forel Intensity Scale:

The Rossi-Forel scale is a measure of intensity of shaking from an earthquake. This scale was replaced by the Mercalli intensity scale.

Runup height:

The elevation of the water level above the immediate tide level when a tsunami runs up onto the coastal land.

Rupture Zone:

The area of the Earth through which faulting occurred during an earthquake. For very small earthquakes, this zone could be a few millimetres long, but in the case of a great earthquake, the rupture zone may extend several hundred kilometres in length and tens of kilometres in width.

S wave:

Also called shear, secondary, rotational, tangential, equivoluminal, distortional, transverse, or shake wave. These waves carry energy through the Earth in very complex patterns of transverse (crosswise) waves. These waves move more slowly than P waves, but in an earthquake they are usually bigger. S waves cannot travel through the outer core because these waves cannot exist in fluids, such as air, water or molten rock.

Sag (fault):

A narrow geological depression found in strike-slip fault zones. Those that contain water are called sag ponds.

Scarp (fault):

A cliff or steep slope formed by displacement of the ground surface.

Seiche:

A free or standing wave oscillation of the surface of water in an enclosed basin, that is initiated by local atmospheric changes, tidal currents, or earthquakes. Similar to water sloshing in a bathtub.

Seismic:

Of or having to do with earthquakes.