Part of the show Geology of Natural Disasters, Volcanoes and Earthquakes
Sam in Santa Barbara, California asked:
I've been told that Santa Barbara is the third most dangerous place to live in the United States because it at great risk of being struck by a tsunami. I've been told that we're at great risk because there's fault line between the coastline and the Channel Islands west of the Pacific Ocean. Is this true?
Tsunamis occur after earthquakes when one tectonic plate subducts or goes below a continental plate. This is generally between an oceanic plate and a continental plate. The deformation that accumulates between the two surfaces causes the tsunami. If you have two pieces of sandpaper and push them against each other, you'll see that at a certain point they'll move apart. That's essentially what happens between two tectonic plates. In the case of a tsunami, it needs a vertical movement of the ground to initiate a disturbance to the surface of the water. There is a plate in that region and it is a subduction zone, so it's possible that there will be a tsunami. However, you can get movements of one plate relative to another without large earthquakes happening and without vertical displacements of the ground below.