By Andrea Aust, Lindsey Hoshaw and Jenny Oh
You may have felt a jolt in the middle of the night when the South Napa Earthquake struck at 3:20 a.m.
But what causes the earth to shake and how does it happen? Well, the earth is constantly shifting and the Earth’s crust is broken up into many rocky plates, like pieces of a puzzle.
These plates are constantly moving, albeit very slowly, over the softer red-hot rock of the mantle underneath. As the plates move past each other, along fault zones, they sometimes get caught and pressure builds up.
When the plates finally give and slip due to the increased pressure, energy is released as seismic waves, causing the ground to shake. This is an earthquake.