The maximum displacement of a wave from a reference base.


See ocean basin.


Underwater topography.

continental crust

The part of Earth's crust that includes and underlies the continents and continental shelves. The continental crust averages about 40 km thick.

continental margin

The portion of the seafloor adjacent to a continent. It may include the continental shelf, continental slope, and continental rise.

continental plate

A tectonic plate that includes continental crust, which is less dense than oceanic crust.

continental rise

The gently sloping surface at the base of the continental slope.

continental shelf

The gently sloping submerged portion of the continental margin extending from the shoreline to the continental slope.

continental slope

The steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf.


The outermost and thinnest of the solid Earth's layers, which consists of rocky material that is less dense than the rocks of the mantle below.


Information, often in the form of measurements or observations, which can be analyzed.


The act of laying down rock-forming matter (sediment) by a natural process, such as wind, water, or ice.


A sudden motion or trembling of Earth's crust caused by the passage of seismic waves radiated from a fault along which sudden movement has occurred.


The height of an object above a particular reference level, usually sea level.


The capacity of a physical system to do work. Energy can be converted among its various forms (motion, light, mass, etc.) but the total amount of energy remains constant.


The point on the surface of Earth directly above the subsurface source of an earthquake.


A place where fresh (non-salty) water enters the sea, such as at a river mouth.


A rock fracture or fracture zone along which there has been movement.

geologic time

The period of time covering the physical formation and development of Earth, as recorded within the succession of rocks.


The study of Earth, its history, its composition, its structure, and the dynamic processes that shape it.


The force of attraction acting between any two masses.kilometer (abbreviated km)A unit of length equal to 1,000 meters, or 0.62 miles.


The outer layer of solid rock that includes the crust and uppermost mantle. This layer, up to 100 km thick, forms Earth's tectonic plates.

magnitude (earthquake)

A measure of the total amount of energy released by an earthquake.


A unit of length in the metric system equal to 3.28 feet.

mid-ocean ridge

A nearly continuous undersea mountain chain that marks the location where tectonic plates (pieces of the lithosphere) are moving apart. Mid-ocean ridges are the locations of creation of new ocean crust.


A theoretical system that represents scientific processes using a set of variables and the quantitative relationships between them.

ocean basin

The seafloor from the base of the continental margin (generally at the beginning of the continental rise) to the mid-ocean ridge.

Pacific Northwest

The northwest corner of the United States (including Washington, Oregon, and sometimes parts of Montana, Idaho, Nevada, and California) and southwestern British Columbia.

Pacific Rim

The countries and landmasses surrounding the Pacific Ocean.rockAny naturally formed aggregate of one or more minerals, such as granite, shale, or marble.

runup height

The maximum vertical height a tsunami inundation reaches onshore. Runup height is generally referenced to sea level, though other baselines are sometimes used.

salt marsh

A low coastal grassland frequently inundated by tides.


Unconsolidated particles, ranging from clay-size to boulders, produced by the breakdown of rocks that may be carried by natural agents (wind, water, and ice), and eventually deposited to form sedimentary deposits. Organisms and chemical precipitation can also produce sediment.


An instrument that detects and records the vibrations of Earth.


The study of earthquakes and other seismic waves.


A representation, often mathematical or visual, of the behavior of a system over time.


Small changes in length and volume associated with deformation of Earth by tectonic stresses or by the passage of seismic waves.

subduction zone

The zone of convergence of two tectonic plates, one of which usually overrides the other.


Relating to the forces and the movements of Earth and its lithosphere. Earthquakes, volcanoes, and mountain building are related to tectonic activity.

tectonic plate

One of several large, mobile pieces of Earth's lithosphere adjoining other plates along zones of seismic activity.


The periodic change in the elevation of the ocean surface.

tide gauge

A device that measures sea level, which is used to quantify tides and the size of tsunamis.

tree-ring dating

The measurement of time intervals by counting the annual rings of trees; applicable to the last 3,000 to 4,000 years.


A device that measures water pressure in order to detect a tsunami traveling through the ocean.


An enormous ocean wave produced by an underwater earthquake, landslide, or volcanic eruption. It is the Japanese word for "harbor wave."


A vent or fissure in the Earth's surface through which molten lava, ash, and gases are ejected. It is also the name for the structure, usually conical, formed by the materials ejected from the vent or fissure.


A disturbance traveling through a medium by which energy is transferred from one particle of the medium to another without causing any permanent displacement of the medium itself.

wave height

The vertical distance between the trough and crest of a wave. It is double the amplitude.


The distance between successive wave crests, or troughs. Light of different wavelengths has different properties, such as color.