Tectonic Plate
Definition
A massive segment of Earth's lithosphere that moves, floats, and sometimes fractures. There are 7 major and about 8 minor plates, and their interactions cause most earthquakes.
Example
The Pacific Plate is the largest tectonic plate, covering 103 million km².
Related Terms
Related Guides
What Is an Earthquake? A Complete Introduction
Learn what causes earthquakes, how they occur along fault lines, and why some regions experience more seismic activity than others.
Are Some Countries Immune to Earthquakes?
No country is completely immune to earthquakes. Learn why even stable continental regions can experience unexpected seismic events.
Plate Tectonics: The Engine Behind Earthquakes
How tectonic plates move, collide, and generate earthquakes — the fundamental theory explaining Earth's seismic activity.
Subduction Zones: Earth's Most Powerful Earthquake Factories
Subduction zones produce the world's largest earthquakes including the M9.5 Chile 1960 event. Learn how they work and where they exist.
The Ring of Fire: Why the Pacific Rim Shakes
90% of earthquakes occur around the Ring of Fire. Explore this 40,000 km horseshoe of volcanic and seismic activity.
Mantle Convection: The Heat Engine Driving Plate Motion
Earth's mantle circulates like a slow-motion boiler, driving tectonic plates. Learn how heat from the core powers earthquakes.
Lithosphere and Asthenosphere: Earth's Moving Layers
The rigid lithosphere rides atop the flowing asthenosphere. Understand these layers and how they enable plate tectonics.
GPS and Earthquakes: Measuring Ground Deformation
GPS stations track millimeter-scale crustal movements revealing how strain builds on faults between earthquakes.
How GPS Stations Track Tectonic Plate Movement
GPS stations measure plate movements of millimeters per year. Learn how this technology reveals fault strain and earthquake hazard.
Related Case Studies
The 1964 Great Alaska Earthquake: The Second-Largest Earthquake Ever Recorded (M9.2)
The second-largest earthquake ever recorded and the event whose geological investigation by George Plafker provided critical field evidence for the then-controversial theory of plate tectonics.
The 1906 Ecuador-Colombia Earthquake: The M8.8 Megathrust That Defined the Northern Andes Hazard
The earthquake that established the segmented rupture model for subduction zones, as its 500 km rupture was partially re-ruptured in three subsequent earthquakes -- a textbook case of megathrust supercycles.
Frequently Asked Questions
The epicenter is the point on the Earth's surface directly above the hypocenter (focus) where the earthquake rupture begins. It is typically reported as latitude and longitude coordinates. The strongest shaking usually occurs near the epicenter, though local soil conditions and fault geometry can shift the zone of maximum damage.
A seismograph (or seismometer) is an instrument that detects and records ground motion caused by seismic waves. Modern broadband seismometers can detect movements smaller than the width of an atom. Networks of seismographs around the world enable scientists to locate earthquakes and determine their magnitude within minutes.
P-waves (primary waves) are compressional waves that travel fastest through rock, arriving first at seismic stations. S-waves (secondary waves) are shear waves that arrive later but cause more ground shaking. P-waves travel through solids, liquids, and gases; S-waves only travel through solids. The time difference between them helps determine earthquake distance.
The hypocenter (or focus) is the point within the Earth where an earthquake rupture initiates. It is described by latitude, longitude, and depth. The vertical distance between the hypocenter and the surface directly above is the earthquake's depth, which strongly influences how the earthquake is felt at the surface.
Seismology is the scientific study of earthquakes and the propagation of seismic waves through the Earth. It encompasses earthquake detection, location, and characterization; Earth's internal structure; seismic hazard assessment; and earthquake engineering. Seismologists use data from global seismograph networks to study these phenomena.