Seismic Waves and Plate Boundaries

Vocabulary flashcards covering seismic waves, earthquake measurement, faults, and plate-boundary processes.

Primary (P) Wave

The first type of seismic wave to reach and be recorded at a seismic station.

Secondary (S) Wave

The second type of earthquake wave to arrive at a seismic station after the P-wave.

Long (L) Surface Wave

A surface seismic wave detectable by a seismograph that travels along Earth’s exterior.

Seismograph

The instrument used to detect and record seismic waves.

Seismogram

The written or digital record produced by a seismograph.

Fault

A break in rock along which movement has occurred.

Fracture

Any break in rock where no significant movement has taken place.

Epicenter

The point on Earth’s surface directly above an earthquake’s focus.

Epicenter Distance Formula

d = (Td / 8 s) × 100 km, where Td is the P–S arrival time difference and d is the distance to the epicenter.

Plate Boundary

A region where two tectonic plates meet and interact, causing geologic activity.

Divergent Plate Boundary

A boundary where plates move apart, creating tension and new oceanic crust.

Rift Valley

A down-faulted valley formed as the crust splits apart at a divergent boundary.

Oceanic Ridge

An underwater mountain range formed by rising magma along a divergent boundary.

Mid-Atlantic Ridge

A well-known example of a divergent plate boundary in the Atlantic Ocean.

Convergent Plate Boundary

A boundary where plates move toward each other; may produce subduction, mountains, or trenches.

Subduction

The process in which one tectonic plate dives beneath another at a convergent boundary.

Seafloor Trench

A deep, narrow depression in the ocean floor formed where a plate subducts.

Pacific Ring of Fire

A zone of frequent earthquakes and volcanoes encircling the Pacific Ocean, caused by convergent boundaries.

Magma

Molten rock that rises from the mantle to create new crust at divergent boundaries and feed volcanoes at convergent margins.