Final answer:
Earthquake intervals seem scattered due to the varying movement of tectonic plates and the release of built-up stress. For example, the San Andreas Fault slips every 25 years, while major earthquakes in Los Angeles occur every 150 years.
Step-by-step explanation:
Earthquakes occur when the tectonic plates in the Earth's crust slip and release built-up stress. The intervals between earthquakes can seem scattered because the movement of the plates is not constant. The longer the interval between earthquakes, the greater the stress and energy released when the surface finally moves. For example, the San Andreas Fault in California experiences slipping every 25 years, while the average interval between major earthquakes in Los Angeles is about 150 years.