U3S4 Earthquakes

VOCABULARY flashcards covering key terms and concepts from the Earthquakes lecture notes.

Earthquake

The shaking that results from movement of rocks beneath Earth's surface.

Focus (hypocenter)

The point inside Earth where rocks rupture and an earthquake originates.

Epicenter

The point on Earth's surface directly above the focus.

Magnitude

A number that characterizes the size or energy released by an earthquake.

Seismic wave

A wave produced by an earthquake that travels through Earth, carrying energy.

Seismograph

An instrument that measures and records the details of earthquakes.

Seismogram

The recorded trace produced by a seismograph.

P waves (Primary waves)

The fastest seismic waves; compress and expand the ground; travel through solids and liquids.

S waves (Secondary waves)

Waves that move the ground side to side and up and down; arrive after P waves; travel only through solids.

Surface waves

Seismic waves that travel along Earth's surface; arrive after P and S waves and can cause substantial damage.

Stress

Force per area in rocks that leads to deformation and faulting.

Tension

A type of stress that stretches rocks.

Compression

A type of stress that squeezes rocks together.

Shearing

A type of stress that causes rocks to slide past one another.

Fault

A fracture along which rocks break and move, producing earthquakes.

Crust

Earth's outer layer where earthquakes originate within the crust.

Focus depth

The depth beneath Earth's surface where an earthquake begins, typically about 100 km.

Triangulation

A method to locate an earthquake's epicenter using distances from three or more seismic stations.

Richter scale

An older magnitude scale based on the size of seismic waves; best for small, nearby earthquakes.

Mercalli scale

A scale that rates earthquake damage based on observed effects, I to XII.

Moment Magnitude Scale

A scale that measures the total energy released by an earthquake; accurate for all sizes and uses seismograph data.

Sumatra earthquake of 2004

A 9.1–9.3 magnitude earthquake—the strongest ever recorded on the moment magnitude scale; lasted about 9 minutes and triggered a massive tsunami.

Tsunami

A large ocean wave generated by the displacement of the sea floor during an earthquake.