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Tsunami and earthquake explainer

What’s up with the whirlpool, the “supermoon,” the Indonesian tsunami … and is the Pacific really shrinking?

Coish: This is a coincidence, but it’s nothing unusual. For a tsunami, the epicenter of the earthquake has to be in the ocean, and the sea floor has to break, moving up or down or both. When the sea floor moves, it displaces a huge mass of water. As the water approaches the shoreline and the sea shallows, it can become a huge wave with devastating force.

Tsunamis have been going on forever. There were tsunamis in Hawaii in 1960 and 1944. The 1960 earthquake in Chile, the largest ever recorded, had a tsunami as well. The devastation in Indonesia in 2004 brought them to light. Yet there’s no immediate relationship between these events. If a fault breaks through the ocean floor, that creates the tsunami. You can also get tsunamis from giant landslides off the continental shelf, but that’s rare.

GlobalPost: Okay, is there a connection between this and the volcano in Hawaii that’s been erupting lately?

Coish: No, I don’t think so. The volcano in Hawaii has been erupting continuously since 1982. That’s a very stable situation. The magma is always moving upwards. Sometimes it’s quiet, but when it finds a fracture it comes to the surface.

GlobalPost: Are we getting any better at predicting earthquakes?

Coish: Unfortunately, we’re not getting any better at predicting earthquakes. In the 1970s and 1980s there was a lot of hope that we were making progress. We can now tell, for example, that California will probably have an earthquake of 6 or greater in magnitude in the next 20 years. Exactly when or where on the fault will be is still an open question. We can’t narrow it down to days or months or years. Magnitude is even harder to predict.

Incidentally, Japan has the world’s finest building code and labs for predicting earthquakes. That’s where the state of the art is.

GlobalPost: Could there be a tsunami from a California quake?

Coish: There’s very little chance of that, because at the San Andreas fault you have two plates sliding past one another, rather than one subducting below another. So it would be unlikely to break the seafloor.

Follow David Case on Twitter: @DavidCaseReport

Condensed and edited by GlobalPost.

http://www.globalpost.com/dispatch/news/regions/asia-pacific/japan/110311/japan-tsunami-earthquake