Hollywood spends millions making movies about massive earthquakes destroying California. Some believe a large earthquake is going to send California careening into the Pacific. But is any of this based on scientific fact? Earthquakes are caused by sudden slips along faults where two sections of the earth's crust move past each other. Friction keeps the crust from moving smoothly, stress builds up and rock slips suddenly, releasing energy in waves. These waves are the shaking we feel during earthquakes. California has several large faults including the San Andreas. They are strike slip faults that move horizontally against each other, or dip slip faults that slide vertically. These faults can create fairly large earthquakes, but if you're looking for “the big one,” of a magnitude ten or higher, you need to look elsewhere. Mega earthquakes typically occur in subduction zones where one continental plate moves under another in what are called thrust faults. These zones can store up energy for many centuries before releasing it as a devastating quake and tsunami.