What is an earthquake?
An earthquake is the shaking caused when energy is released inside the Earth. Many begin when rocks held in place by friction suddenly slip along a fault. The released energy travels outward as seismic waves.
The hypocenter, or focus, is where the rupture begins underground. The epicenter is the point directly above it on the surface. A large rupture can extend far beyond that starting point, so an epicenter alone does not describe the whole earthquake.
Start with a question, follow a map, or try a comparison.
The Ring of Fire
Follow the Pacific’s arc of earthquakes, volcanoes, and plate boundaries.
Earth’s tectonic plates
Meet the moving pieces of our planet, then explore them on the globe.
Three ways plates meet
See how collision, separation, and sliding shape the Earth.
Magnitude vs. intensity
An earthquake has a size. The shaking you feel depends on where you are.
Aftershocks explained
Understand earthquake sequences, foreshocks, and swarms.
Compare two earthquakes
Compare magnitudes to see the difference in amplitude and estimated energy.
The largest earthquakes
Put five extraordinary earthquakes into perspective with a map and comparison.
California earthquakes
Browse recent regional activity and learn about the faults beneath California.
Japan earthquakes
Explore Japan’s plate boundaries, shindo shaking scale, and major earthquakes.
See the connections
Most earthquakes occur near tectonic plate boundaries. Those boundaries help explain the pattern around the Ring of Fire and much of California’s earthquake activity.
Follow the Pacific to Japan to learn about subduction, major earthquakes, and the shindo scale used in Japanese shaking reports.
To understand an individual event, begin with magnitude and intensity. To understand what follows a larger earthquake, read about aftershocks.
The guides link to their scientific sources. For an introduction from the data provider, read USGS: What is an earthquake and what causes them to happen?. For questions about the Android app, visit App help.