Answer:
An earthquake occurs when there is a Shake or a fault in the earth. Therefore, this makes the tectonic plates to move slowly and but they are stuck at the edges because of friction. When resistance exceeds stress, then it causes the earthquake. It then releases energy that travels to the earth through the crust and making it shake as we feel it.
California experiences different types of plates; the principal boundary between the plates the fault from San Andrea is that is about 650 miles long towards the depths with other smaller defects at San Jacinto.