New data raises the quake to a 9.0:

newscientist.com

Which makes it the 4th strongest in recorded history.

For those who have been wondering how Japan could have been moved 8 feet, here’s a basic geologic overview of the facts. There are three kinds of faults.

There are tensional faults, where land moves away from each other. You find these at mid-oceanic rifts, where new ocean crust is created and pushes the old crust sideways and in continental features of the same kind, like the African rift zone. These are spreading features, where plates are moving apart. Lots of low level seismic activity and volcanoes.

There are rotational (strike slip) faults where plates are in relative stasis and are simply grinding against each other rotationally (like the North American plate and the Pacific plate from around central Mexico to around the northern border of California). These result in quakes that have a lot of horizontal movement, bout no volcanoes.

Then there are compressional faults, where ocean crust is sliding under continental crust or where continental crust is being compressed against other continental crust. The best example of the latter is the area around New Madrid, Missouri, which is the triple compression point of a peculiar feature. The bottom half of the North American plate is in relative stasis with the Pacific plate. The northern half of the American plate, however, is still torquing to the southwest relative to the Pacific plate. That strain has got to be released somewhere, and southern Missouri is the spot. Hence the very rare occurrence of a mid-continental pressure valve.

The third kind is a traditional compressional fault. Unlike the New Madrid, these are dead common. Oceanic crustal plates subduct underneath continental plates. They are thinner. They have much less mass. They melt in the upper mantle of the earth, They form plumes of much lighter rocks, which dig holes through the continental plate and bust through the surface as flow basalts or volcanoes. This is what happens all across the north and south areas of the east Pacific (Alaska to Oregon, and southern mexico to Tierra del Fuego), where North and South America are torquing southwest and northeast, respectively, and pretty much along the entire expanse of the Asian plate from Kamchatka to New Guinea. lots of volcanoes, lots of quakes.

The Ring of Fire.

Now in Japan, there are two basic vectors in regard to the Pacific and Asian plates. As mentioned before, the Pacific plate is rotating counter clockwise relative to the Continental plates. So there will always be a strike-slip component to their relative movements. The vast majority of the past damaging quakes in Japan (Kobe, Tokyo in 1923) were strike-slip quakes.

This one however was a compressional, dip-slip quake. As the Pacific plate moves west, the Asian plate (Japan) grinds over it. This pulls down the eastern edge of the Asian plate like a really big spring. It also forms what is known as the Japanese trench, where the water gets really deep because the Pacific plate is being forced under Japan. And it’s not local. This is occurring the entire east coast of Japan. The entire country is being prevented from moving to the east by this compression.

Forces build until the compressional fault ruptures. And when it does, the continental plate says “Aaah” and moves in the direction of the subducting plate. In this case, along a rupture zone of over 400 miles, according to the USGS (!!!) Japan, part of that portion of the Asian plate moved 8 feet east. In the meantime the Asian plate, lifted anywhere from 90 to 120 feet, almost instantly. It SNAPPED UP. Causing the tsunami.

Lessons learned:

If you build cities along coastal boundaries where active subduction is occurring offshore, that city will eventually be destroyed by a tsunami.

If you are running nuke plants in an earthquake zone, triple redundancy is insufficient. Deactivate all of your second generation reactors and upgrade them.