Earth's Lithosphere and Plate Tectonics (Weeks 1-3)

Vocabulary flashcards covering lithosphere, crust, plates, plate boundaries, major and secondary plates, Ring of Fire, plate tectonics, seismic terms, and related concepts from Weeks 1–3.

Rigid outer layer of the Earth, consisting of the crust and upper mantle, broken into tectonic plates that float on the semi-plastic asthenosphere.

Lithosphere

The outermost solid shell of the Earth; two types: continental crust and oceanic crust.

Crust

A large, rigid slab of the lithosphere that moves slowly over the Earth's surface.

Tectonic plate

The edge where two tectonic plates meet; sites of most earthquakes, volcanoes, and Mountain-building activity.

Plate boundary

Tectonic plate associated with oceanic crust; thinner and more dense than continental plates.

Oceanic plate

Tectonic plate associated with continents; thicker and less dense, with granitic composition.

Continental plate

Mass per unit volume; oceanic lithosphere is denser (~3.0 g/cm3) than continental lithosphere (~2.7 g/cm3).

Density

Oceanic lithosphere is relatively younger; continental lithosphere is older (oldest oceanic ~260 million years; oldest continental ~4 billion years).

Age

Igneous rocks that make up most of the oceanic crust.

Basaltic rocks

Igneous rocks that make up most of the continental crust.

Granitic rocks

Divergent boundary

Boundary where plates move apart, often creating new crust and ocean basins.

Convergent boundary

Boundary where plates move toward each other; causes subduction and mountain building.

Transform boundary

Boundary where plates slide past one another; causes earthquakes.

Earthquake epicenter

Point on the Earth's surface directly above the focus where energy release is strongest.

Focus

Point within the Earth where an earthquake originates.

Seismograph

Instrument that records ground motion during seismic events.

P-waves

Primary (compressional) seismic waves; arrive first at stations; can travel through solids and liquids.

S-waves

Secondary (shear) seismic waves; slower than P-waves and cannot travel through liquids.

Surface waves

Seismic waves that travel along the Earth's surface and often cause significant shaking.

Triangulation method

Locating an earthquake epicenter using at least three seismic stations and intersecting distance circles.

Distance to epicenter

Estimated distance from a station calculated as (P–S arrival time difference) × 8 km/s.

Volcano

A mountain or hill with a crater/vent through which lava, rock fragments, and gases erupt from the crust.

Active volcano

A volcano that has erupted recently or shows signs of future eruption.

Mountain belt

A group of mountain ranges formed by the same geologic process (orogeny).