Earthquakes happen when built‑up stress inside the Earth is suddenly released, usually along cracks in the crust called faults.

Quick Scoop

  • Most earthquakes are caused by the movement of tectonic plates along faults.
  • The ground shakes because stored “elastic” energy is released as seismic waves.Think of it like a stretched rubber band snapping.
  • Some quakes are linked to volcanoes or even human activities like mining and deep wastewater injection.

1. The main cause: tectonic plates

Earth’s outer shell is broken into large plates that slowly move, grind, and collide.

When these plates get stuck at their boundaries but keep pushing, stress builds up in the rocks until they suddenly slip along a fault, releasing energy as an earthquake.

Where this happens

  • Convergent boundaries (plates collide): One plate may dive under another (subduction), generating powerful, often deep earthquakes (e.g., Peru–Chile trench).
  • Divergent boundaries (plates pull apart): Plates move away from each other, creating rifts and mid‑ocean ridges with frequent but usually smaller quakes.
  • Transform boundaries (plates slide past): Plates grind horizontally (like the San Andreas–type faults), causing shallow, often damaging quakes.

Inside this process, stress slowly deforms rocks on both sides of a fault until the fault finally slips, much like two rough pieces of foam catching and then jerking past each other.

2. What is actually “shaking”?

When the fault breaks, energy radiates outward as seismic waves that travel through and along the surface of the Earth.

These waves make the ground move up‑and‑down and side‑to‑side, which is what we feel during an earthquake.

Scientists describe this as the release of stored elastic strain energy in the rocks, which is the only type that can build up enough to cause major quakes.

3. Other natural causes

Not all earthquakes are classic plate‑boundary events; some are triggered by other natural processes.

  • Volcanic activity: Rising magma cracks rock and shifts stress, producing swarms of small quakes around volcanoes, sometimes used to forecast eruptions.
  • Gravitational and other internal processes: Changes in density, chemical reactions, or mass movement inside the Earth can also release energy and cause quakes, though these are less common than tectonic ones.

These quakes are often smaller or more localized, but they can still affect nearby communities.

4. Human‑induced earthquakes

Some earthquakes are linked to human activity that alters stress in the crust.

  • Mining: Removing large volumes of rock at depth can trigger small to moderate seismic events as surrounding rock readjusts.
  • Hydraulic fracturing (fracking): The fracturing itself rarely causes felt earthquakes, but it can create or reactivate small faults.
  • Wastewater disposal wells: Injecting large volumes of fluid deep underground is more clearly associated with induced earthquakes because it changes pressure along faults.
  • Large dams and reservoirs: The weight of new water and changes in pore pressure can “nudge” stressed faults, causing what’s called reservoir‑induced seismicity.

These are usually smaller than major tectonic quakes but can still be noticeable and sometimes damaging near the source.

5. Putting it simply

If you want a one‑line picture: earthquakes are like nature’s way of “unsticking” jammed rocks along faults after too much stress has built up.

Tectonic plate motion provides the slow, constant push; when the rocks can’t hold the strain any longer, they snap, and the released energy is what shakes the ground.

Information gathered from public forums or data available on the internet and portrayed here.