Earth's Crust Vocab

Earthquake

·      Natural vibrations, sometimes destructive, that radiate from a sudden movement along a fault zone within the Earth or from sudden movements of magma (molten rock) under a volcano.

Fault

·      A break in the rock of the Earth’s crust along which there has been displacement (movement).

Tilted Strata

·      Beds of rock (usually sedimentary), thought to have been deposited flat and level that have been pushed into a different inclination (angle), usually by motions of the Earth’s crust.

Walking the Outcrop

·      A method of following rock layers to correlate layers within the same outcropping.

 Focus

·      An Earthquake’s point of origin within the Earth.

Epicenter

·      A location along the Earth’s surface that is directly above the focus of an earthquake. 

·      An earthquake is felt most strongly at its epicenter.

Intensity

·      Strength.

Seismograph

·      An instrument designed to measure and record the magnitude of an earthquake.

Seismometer

·      An instrument that detects vibrations of the ground.

Seismic Waves

·      Vibrational energy that radiates through the Earth from an earthquake.

Magnitude

·      The total energy released by an earthquake, measured by the Richter scale.

P-Waves

·      Compressional (longitudinal) waves that are the fastest form of seismic waves to radiate from an earthquake and can travel through solids and liquids.

·      Also known as primary waves.

S-Waves

·      Transverse earthquake waves that arrive after the P-waves and that cannot travel through a liquid such as the outer core of the Earth.

·      Also known as secondary or shear waves.

Transverse Wave

·      An energy wave that vibrates perpendicular to the direction of travel.

o  Like S-waves and electromagnetic energy.

Wavelength

·      The distance between corresponding points on two successive crests or two successive troughs of a wave.

Seismologist

·      A scientist who studies earthquakes.

Origin Time

·      The time when an earthquake occurs at its epicenter.

Bedrock

·      The solid layer of rock that extends into the Earth. 

·      Bedrock can always be found beneath the soil.

Crust

·      The thin, outermost layer of the solid Earth.

Continental Crust

·      Rocks within the continents, usually a thin layer of sedimentary rocks over granite rocks that are lighter than oceanic crust.

Granitic

·      Rocks composed mostly of light-colored, low density minerals like quartz and feldspar.

Oceanic Crust

·      The relatively thin, dense layer of basaltic rock that underlies the ocean sediments and lies on top of the mantle layer.

Basaltic

·      Igneous rock composed mostly of dark-colored, dense minerals containing compounds of iron and magnesium.

Mantle

·      The portion of the Earth below the crust and above the core.

Moho (Mohoroičić Discontinuity)

·      The interface between the Earth’s crust and mantle.

Meteorites

·      A natural object that has fallen to the Earth from space.

Core

·      The innermost layer of the Earth, thought to be composed mostly of iron and nickel.

Outer Core

·      The outside portion of the Earth’s core that is thought to consist mostly of iron and nickel in the liquid state because S-waves cannot go through it.

Inner Core

·      The central portion of the Earth’s core that is thought to be composed mostly of iron and nickel in the solid state.

 “Ring of Fire”

·      The zone of volcanoes, earthquakes and mountain building that surrounds the Pacific Ocean.

Magma

·      Molten rock with the Earth.

Volcanic Ash

·      Cinders that are blown into the air by a volcano and that are useful in correlating rock outcrops in different locations.

Tsunami

·      An ocean wave or a series of waves usually associated with undersea earthquakes.

Continental Drift

·      The idea that the continents move over the surface of the Earth like rafts on water.

Isostasy

·      The theory that the Earth’s crust floats on the denser rock beneath it in a state of equilibrium.

Plate Tectonics

·      A unified theory of crustal motions that incorporates continental drift and ocean-floor spreading.

·      The theory that the Earth’s surface is composed of about a dozen large, rigid plates that carry the continents with them as they diverge and converge.

Tectonics

·      The study of large-scale deformations of the Earth.

Tectonic Structures

·      Rock structures formed by faulting and folding.

Subsidence

·      The gradual sinking of a portion of the Earth’s crust.

Plate Boundaries

·      The lines along which crustal plates meet and interact.

Convergence

·      The coming together of tectonic plates.

Convergent Boundary

·      A boundary at which crustal plates collide.

Subduction Zone

·      The region in which the Earth’s crust is destroyed as it is pulled down into the mantle.

Ocean Trench

·      An ocean floor depression that marks the zone where crust is being subducted.

Transform Boundary

·      A plate boundary at which crustal plates slide past one another.

Divergent Boundary

·      A plate boundary at which the plates move apart.

·      An upwelling of material that forms new crust that moves away from the boundary.

Mid-ocean Ridges

·      A system of submerged mountain ranges that encircles the Earth and often connects with mountain ranges on the continents, new crust forms here.

Ocean-floor Spreading

·      The theory that the oceanic crust has been constructed by material from deep within the Earth that rises and spreads apart at the mid-ocean ridges.

Zone of Crustal Activity

·      An area around an ocean ridge or continental mountain range where volcanoes and earthquake epicenters are concentrated.

Abyssal Plaines

·      The flat regions of the ocean basins.

Seamount

·      An isolated volcanic island located on the bottom of the ocean.

Rift

·      A linear feature of the Earth where new crust is being created.

Radiation

·      The emission and transfer of heat energy by means of electromagnetic waves, and the only way that energy can travel through empty space.

Conduction

·      The way in which heat energy is transferred through matter by the direct contact of molecules.

Convection

·      The circulation of a heated fluid (a liquid or a gas) caused by density currents.

·      A form of heat flow in which the heated material moves.

Convection Cells

·      The circular path of convection flow.

Lithosphere

·      The solid portion of the Earth below the atmosphere and hydrosphere.

·      A solid layer that includes the crust and the upper portion of the Earth’s mantle.

Asthenosphere

·      The part of the Earth’s interior below the lithosphere that is plastic in response to stress.

\