An earthquake is a release in pressure between tectonic plates. Without tectonic plates there would be no earthquakes. Plate techtonics started as just a theory in 1915.
In 1915 a man by the name of Alfred Wagener first proposed his wild theory that the earth's continents were on large "plates" that could move. His theory was thought to be preposterous and was not accepted by most because of his lack of evidence and information regarding his theory. After his death evidence was finally found to support his theory. H. H. Hess in 1962 found this information.
The theory states that the surface of the earth's crust is broken into several parts or pieces called "plates." These gigantic plates float on top of the asthenosphere. The asthenosphere is the very thin layer (124 miles thick) of the upper mantle. There are places where these massive plates meet and these are called fault lines or faults. Faults are found all over the world from the San Andres fault, to faults underwater and in Asia.