Tsunami?

At about 7:50 pm (PDT) yesterday evening, there was a very large (magnitude 7.0) earthquake under the sea, offshore from Crescent City, California. This is along the northern coast of California, not very far south of the Oregon border. As some of you may remember, Crescent City has been hit by tsunamis before — see information here, here, and here.

The danger from tsunamis on the San Diego coastline is much lower, but still present. See information here.

The earthquake last night (pictured on a seismographic map at right) resulted in a tsunami alert; it was quickly lifted when seismologists realized that the earthquake was caused by a lateral slip and not subsidence. Slippages typically do not cause tsunamis (unless there is an associated collapse of some geological feature, like an undersea mountain). Tsunamis are usually caused by significant vertical movements over a large area. You can find more information about this quake here, here, and here.

Way down here in southern California, where we live, we never felt a thing. But...we were awakened by a friend and neighbor, just after 8pm, who was concerned about her parents. They live down by Mission Bay, only a couple of blocks from the ocean, and our friend had heard the tsunami alert being broadcast over the emergency radio network. Yikes!

As things turned out, the tsunami alert was quickly withdrawn, there was no tsunami, and nobody was injured. So far as I'm aware, there was also no property damage. That's about as good as things can get with a magnitude 7.0 quake, so I'll call that very good news.

I did sleep uneasily, though. It's a little disconcerting to know that some disaster truly could be visited on us at any time. For us, the biggest risk is probably that some (previously) unknown fault could suddenly make itself known through a powerful earthquake right near us...not a pleasant thought...