What Is an Earthquake?
An earthquake is a sudden shaking of the ground caused by a rapid release of energy deep inside the Earth. Most of that energy comes from rock breaking and slipping along a fracture called a fault. The slip sends out vibrations — seismic waves — that travel outward in all directions and make the surface tremble, sometimes thousands of kilometres away.
Why the ground shakes: tectonic plates
The Earth's rigid outer shell is broken into a dozen or so large tectonic plates that float on the hotter, slowly flowing rock beneath. These plates creep past, into, or away from each other at about the speed your fingernails grow — a few centimetres a year. Where two plates meet, their edges snag and lock together while the rest of the plate keeps moving, so stress builds up in the rock like tension in a bent stick.
Faults and elastic rebound
When the stored stress finally exceeds the strength of the rock, the fault gives way and the two sides lurch past each other in seconds. The rock springs back toward its original shape — a process called elastic rebound — and the energy that had been stored for years or centuries is released all at once. That release is the earthquake. The bigger the area of fault that slips, and the further it moves, the larger the magnitude.
The key terms
- Hypocentre (focus): the point underground where the rupture begins.
- Epicentre: the point on the surface directly above the hypocentre — the location you see plotted on the tracker map.
- Depth: how far down the hypocentre is. Shallow quakes (under ~70 km) usually shake the surface harder than deep ones of the same size.
- Magnitude: a number describing the energy released. Intensity is different — it describes how strongly a place actually shook.
Foreshocks, mainshock and aftershocks
Earthquakes often come in sequences. Smaller foreshocks may precede the largest event (the mainshock), and many aftershocks follow it as the crust settles into its new position. This is normal, and it's why a region can keep shaking for days or weeks after a big quake.
Where earthquakes happen
Because they're driven by plate motion, earthquakes cluster along plate boundaries — most famously the "Ring of Fire" around the Pacific. Open the live tracker and you'll see the dots trace those boundaries almost exactly. A few quakes also happen far from boundaries, along old faults or from human activity, which we cover in the types of earthquakes.
See where earthquakes are happening right now, worldwide and near you.
Open the Earthquake Tracker