Pulled and pushed by forces deep within the planet, the Pacific plate is sliding northwest past North America at an average of about 2 inches a year – roughly the same rate as fingernails grow.
But movement along the fault usually occurs in bursts. Along most of the fault, the colder, more rigid rocks near the earth‘s surface resist the plate motions. Eventually, enough strain develops along a segment of the fault to overcome the resistance. en, in geologic terms, that stretch of the fault “breaks,” “fails,” or “ruptures” and a segment of the crust riding the Pacific plate surges north, creating an earthquake.