When it doesn’t send a tsunami racing across the entire Pacific basin, that’s when. An earthquake of 8.3 qualifies as a "great" quake (the San Francisco earthquake of 1906 was probably somewhere between 7.7 and 8.3), and tsunami watches extended all the way from Washington State to Vietnam.
My Blackberry was melting this morning. But a lot of things have to go wrong to cause a serious tsunami.
Most important, the sea floor has to be shaken up in a way that pushes a lot of water around. If part of it is thrust upward, water will be forced away in all directions–or if part of it collapses, water will rush in, and past, because of the void created.
Neither happened–but at 6:14 this morning, Eastern Time, there was no way to know that. So you can’t blame the agencies that watch these things for being anxious.
The 2004 disaster is still fresh in everyone’s mind, with its 30-foot walls of water, hitting the shores of the Indian Ocean without warning. But Japan, being a wealthier country in an earthquake zone, was prepared–and as of now, the largest wave we’ve heard about was 22 inches. NOAA has two Tsunami Warning Centers, one in Hawaii, the other in Palmer, Alaska; their sumary is HERE.
The people in the Kuril Islands, north of Hokkaido, probably had a bad night. But to the rest of the world, with the advantage of distance, 8.3 didn’t sound like much.