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What I've Learned
California will eventually have a massive earthquake, break off, and drop into the ocean.
I used to believe that.
Silly unthinking me.
The San Andreas Fault is where two giant tectonic plates, the Pacific Plate and North American Plate, are rubbing against each other.
The San Andreas Fault System crosses California from the Salton Sea in the south to Cape Mendocino in the north. The Pacific Plate is moving northwest at a couple of inches per year. But that rate is an average, not a steady motion.
As the Pacific Plate tries to move northwest, it is held back by rubbing against the North American Plate. Eventually the Pacific Plate, held back by friction, overcomes that friction and slips forward a couple of feet in its movement. This causes strike-slip earthquakes.
To demonstrate what happens, take two pieces of pizza, one with pepperoni and one with pineapple and mushrooms, and set them edge to edge on a table. Push them firmly together and slide one so that its edge rubs against the edge of the other. Along those edges, cheese will jiggle, pepperoni will tear off, mushrooms will break, and pineapple chunks will get knocked askew.
San Diego, Los Angeles and Big Sur are on the Pacific Plate. San Francisco, Sacramento and the Sierra Nevada are on the North American Plate. California will not break off and drop into the ocean. It can't. But eventually, in centuries to come, San Francisco and Los Angeles will be neighbors.
The earthquakes in Japan are caused by a different motion. Instead of two tectonic plates moving along each other at an angle so that their edges rub, one plate — the Pacific Plate — is pushing directly against another plate and dipping under it. We have two large-surface plates rubbing together on their horizontal surfaces. The Pacific Plate, as it moves under the other plate (I'll talk more about this other plate in a moment.), is prevented from moving by friction. Eventually the stress becomes too great and the Pacific Plate overcomes the friction and jerks a few feet.
The vibrations this causes are huge, resulting in earthquakes of 8 to 9 on the Richter Scale. The fact that the place where these plates are passing — one over and one under — is about 19 miles beneath the ocean, means that giant waves — tsunamis — are created when the plates slip.
Understanding of tectonic plates and their movements didn't catch on in the scientific world until the 1960s. (It should be noted that not all geologists today buy into the idea.) There are believed to be a dozen or so tectonic plates, some huge and some smaller. About 90 percent of all earthquakes occur near plate boundaries.
Japan is particularly earthquake prone because there are four plates that meet in and around this island nation, creating a sort of four corners of shake-a-tude.
The Pacific Plate is shaped much like the ocean it's named for. The western edge of this plate is off the east coast of Japan.
To the west is the Eurasian Plate, which edge runs diagonally across Japan.
Southeast of Japan is the small, but active Philippine Plate.
The fourth plate, believe it or not, is our good old North American Plate, which is enormous. It reaches from the middle of the Atlantic Ocean and includes the U.S., Canada, and the Arctic, plus half of Russia. A part of it juts southward and points at the Philippine Plate. The western edge of this jutting leg meets the Eurasian Plate diagonally across Japan.
It's this southward jutting leg of the North American Plate that the Pacific Plate is being forced under. This happens off the eastern coast of Japan. So the same plate that on one side interacts with the Pacific Plate and causes earthquakes in California, wraps around and reaches down to interact with the opposite side of the Pacific Plate so as to cause earthquakes in Japan as well.
So what about Maine?
We are closer to the middle of the North American Plate than to any of its edges. Yet we've had earthquakes here. Why is that?
If tectonic plates are moving slowly about, certainly in things so large, there will be stresses in places other than the edges. Scientists don't know the exact causes, but quakes happen in places like Maine and are referred to as intraplate earthquakes.
So will California drop off into the ocean?
That doesn't mean there can't be serious earthly rumblings, here or there or anywhere.
April, in addition to being National Poetry Month, is National Earthquake Preparedness Month. On April 28, a bunch of states, including Oklahoma, Louisiana, Missouri, Mississippi, Alabama, Georgia, North and South Carolina, Tennessee, Kentucky, and Illinois, are having a drill called The Great Central US Shakeout.
Kids in school, workers in offices, emergency personnel, people in their homes — everyone — will pretend there is a giant earthquake and practice what to do during and after.
Indiana is having a drill on April 19. Nevada and California have theirs planned for October 21. Utah is scheduling one for 2012.
Maine, I would hope, is as smart as any of the states I just named. We should get prepared as well. Better safe than you know what.