Basic Earthquake Geology
Crustal plates are gigantic slabs of the earth's crust whose movements are governed by currents in the mantle.
These crustal slabs have rocky boundaries. It requires but little imagination to conclude it's easy for these massive craggy slabs to become stuck as they grind past each other.
Rocks have an amazing 'elastic' property. They are able to 'stretch' when the force of the currents in the mantle transports the mass of the plates, while the boundaries remains locked. The rocks will stretch until, like a rubber band, they reach their breaking point.
When this literal second in time arrives, the rocks snap, suddenly releasing their pent-up energy. This explosion of energy propagates seismic waves. When these waves reach you, you will feel the ground shake, roll, twist, rock.