Plate Tectonics and Earthquake Mechanics Review

A comprehensive set of vocabulary flashcards covering mantle convection, plate motions, fault types, seismic waves, plate boundaries, supporting evidence for plate tectonics, and examples of major and minor tectonic plates.

Convection Currents

Circular movements of heated, less-dense mantle material that rise and sink, driving the motion of tectonic plates.

Convection Cell

A single loop of flowing mantle material created by temperature-driven density differences within Earth’s interior.

Lithosphere

Earth’s rigid outer shell—crust plus uppermost mantle—broken into moving tectonic plates.

Asthenosphere

Weak, hot, and partly molten upper mantle layer on which the lithospheric plates slide.

Inner Core

Solid, iron-rich center of Earth where immense pressure keeps material solid despite high temperature.

Outer Core

Liquid iron-nickel layer surrounding the inner core; source of Earth’s magnetic field.

Plate Tectonics Theory

Unifying geological theory stating that the lithosphere is divided into plates that move due to mantle convection, ridge push, slab pull, and other forces.

Continental Drift Theory

Alfred Wegener’s 1912 idea that today’s continents were once joined in a supercontinent called Pangaea and have since drifted apart.

Seafloor Spreading Theory

Harry Hess and Robert Dietz’s 1960s proposal that new oceanic crust forms at mid-ocean ridges and moves outward, recycling at subduction zones.

Convergent Plate Boundary

Destructive margin where two plates collide, causing subduction or continental collision.

Divergent Plate Boundary

Constructive margin where plates move apart, allowing magma to rise and create new crust (ridges or rift valleys).

Transform Fault Boundary

Conservative margin where two plates slide horizontally past one another, producing strike-slip faults like the San Andreas Fault.

Normal Fault

Fault produced by tension at divergent boundaries; hanging wall moves downward relative to footwall.

Reverse Fault

Fault formed by compression at convergent boundaries; hanging wall moves upward over footwall.

Strike-Slip Fault

Fault produced by shear forces where blocks slide laterally past each other; also called lateral fault.

Ridge Push

Force generated by elevated, warm, less-dense rock at mid-ocean ridges that pushes plates away from the ridge crest.

Slab Pull

Downward force exerted by a cold, dense subducting plate that drags the rest of the plate into the mantle.

Slab Suction

Small-scale mantle convection in the wedge above a subducting slab that helps pull the plate back toward the trench.

Earthquake

Shaking of the ground caused by sudden release of stored strain energy along faults within Earth’s crust.

Earthquake Fault

Fracture or weak zone in Earth’s crust where accumulated stress is released as seismic activity.

Interplate Earthquake

Earthquake that occurs along plate boundaries or fault zones (the majority of events).

Intraplate Earthquake

Less common earthquake occurring within a tectonic plate, away from plate boundaries.

Body Waves

Seismic waves that travel through Earth’s interior; include P waves and S waves.

P Waves

Primary, compressional body waves that are fastest and travel through solids, liquids, and gases.

S Waves

Secondary, shear body waves that are slower and travel only through solids.

Surface Waves

Seismic waves that propagate along Earth’s surface, causing most earthquake damage.

Diastrophism

All large-scale movements and deformations of Earth’s lithosphere, such as folding, faulting, and mountain building.

Isostasy

State of gravitational equilibrium wherein Earth’s lithosphere ‘floats’ on the denser, deformable asthenosphere below.

Major Tectonic Plate

Lithospheric plate covering more than 20 million km², e.g., Pacific, African, Eurasian Plates.

Minor Tectonic Plate

Secondary plate with an area between 1 million and 20 million km², e.g., Philippine Sea Plate, Nazca Plate.

Pacific Plate

Largest tectonic plate, beneath the Pacific Ocean, exceeding 103 million km².

Eurasian Plate

Major plate covering most of Europe and Asia, approximately 67.8 million km².

Nazca Plate

Oceanic plate east of the Pacific Plate, subducting beneath South America and forming the Andes and Peru Trench.

Philippine Sea Plate

5.5 million km² oceanic plate east of the Philippines, involved in complex subduction zones.

Subduction Zone

Region where a denser oceanic plate sinks beneath a less dense plate, generating trenches, volcanoes, and earthquakes.

Volcanic Island Arc

Curved chain of volcanic islands that forms above a subducting oceanic plate at an ocean-ocean convergence.

Continental Volcanic Arc

Line of volcanoes on a continent formed above a subducting oceanic plate at an ocean-continent convergence.

Trench

Deep, narrow depression on the ocean floor formed at subduction zones.

Mid-Ocean Ridge

Undersea mountain range where new oceanic crust forms at divergent plate boundaries.

Rift Valley

Linear depression formed as continental crust pulls apart at a divergent boundary.

Mountain Range (Collision Zone)

High topographic belt created when two continental plates converge without subduction, e.g., Himalayas.

Pangaea

Supercontinent that existed about 250 million years ago before breaking into Laurasia and Gondwanaland.

Laurasia

Northern supercontinent resulting from the breakup of Pangaea, containing present-day North America and Eurasia.

Gondwanaland

Southern supercontinent formed from Pangaea’s breakup, including present-day South America, Africa, Antarctica, Australia, and India.

Glossopteris

Extinct seed fern whose widespread fossils provided evidence for continental drift.

Gondwana Sequence

Matching pattern of sedimentary rock layers found across southern-hemisphere continents, supporting continental drift.

Theatrum Orbis Terrarum

First modern world atlas (1596) by Abraham Ortelius; early source hinting at continental fit.

Raisin Theory

Obsolete idea describing Earth’s surface wrinkles (mountains) as the planet cooled and contracted like a drying raisin.

Radioactive Decay

Process by which unstable isotopes release heat, contributing to mantle convection.

Residual Heat

Trapped primordial heat from Earth’s formation that still warms the mantle and drives convection.

Oceanic Crust

Thin, basaltic portion of Earth’s crust under oceans; denser and younger than continental crust.

Continental Crust

Thick, granitic portion of Earth’s crust forming continents; less dense and older than oceanic crust.

Seafloor Spreading

Creation of new oceanic crust at mid-ocean ridges as magma rises, cools, and pushes older crust outward.