In the Earth's crust, small movements eventually trigger earthquakes

Earth’s crust is made from several vast, jagged slabs of rock called tectonic plates,each riding on a hot, partially molten layer of Earth’s mantle.This causes the plates to spread very slowly,at anywhere from 1 to 20 centimeters per year.But these tiny movements are powerful enough to cause deep cracks in the interacting plates.And in unstable zones,the intensifying pressure may ultimately trigger an earthquake.