How Tectonic Plates Cause Earthquakes
Earth's outer layer is made of large pieces called tectonic plates that constantly move very slowly. Where these plates meet, they can push against each other, slide past each other, or pull apart. As plates try to move, friction holds them in place, causing stress and pressure to build up in the rocks. When this pressure becomes too strong, the rocks suddenly snap and shift position, releasing all that stored energy at once.
Types of Plate Movements
There are three main ways plates move and cause earthquakes. Convergent boundaries happen when two plates push toward each other and collide. Divergent boundaries occur when plates pull apart from each other. Transform boundaries happen when plates slide sideways past each other. Each type of movement can create earthquakes, but transform and convergent boundaries typically produce the strongest ones.
Seismic Waves
When rocks suddenly break and shift, they release energy in the form of seismic waves that travel outward through the ground in all directions. These waves make the ground shake and vibrate. The closer you are to where the earthquake started, called the epicenter, the stronger the shaking usually is. Seismic waves are what we feel and measure when an earthquake happens.
Other Causes of Earthquakes
While tectonic plate movement causes most earthquakes, other events can trigger them too. Volcanic eruptions, underground explosions, and large landslides can create earthquakes. Humans can also cause small earthquakes through mining, dam construction, and hydraulic fracturing. However, these human-caused earthquakes are much smaller and less frequent than those from plate movements.
Earthquake Zones
Earthquakes happen most often along the boundaries where tectonic plates meet. The Pacific Ring of Fire, which surrounds the Pacific Ocean, is the most active earthquake zone on Earth. This area contains about 75 percent of the world's earthquakes. Other active zones include the Mid-Ocean Ridges and areas where continents are colliding. 
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