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?
What Do Earthquakes Do?
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.
Most of California isn’t at risk of such a quake, but its neighbors to the north Oregon, Washington and British Columbia–most definitely are.
The Big One
Geological evidence shows that over a dozen large earthquakes have occurred along North America’s Cascadia thrust fault in the last four thousand years. One in 1700 became part of Native American lore.
They tell of shaking coming in the night, people running from a massive flood, landslides, beaches turning to quicksand, and total villages vanishing. Geologic evidence of the resulting tsunami can be found as far away as Japan.
Hollywood is right, it is only a matter of time before “the big one” rattles the Northwest American coast. But it’s not going to be California that’s doing the worst shaking.