The surface, or “crust”, of the Earth is like the shell of a large blue egg that has been accidentally dropped on the floor. It is criss-crossed by jagged fractures that separate the surface into irregular pieces, often referred to as plates. These plates float on a layer of semi-molten rock that allow them to jostle and slide about. Upwelling heat from the interior of the planet keeps them in motion. Where they collide with one another, one plate is forced beneath the other resulting in towering mountain ranges and deep submarine trenches. In these places crust is consumed. Where the plates pull apart from each other, a void is created which fills with magma from below and becomes new crust. But despite this creation and destruction of crust, the size of the Earth remains the same.
As these plates jostle with one another like loose boats in a harbor during a storm, smashing into and pulling apart from each other, there is a third type of movement that takes place. In this instance, the plates grind and slide past one another like a bus sliding along a guard rail. Friction between the plates holds them in place until the forces become too great and the plates bolt and slide until the pressure is released.
Another way to visualize this is as follows: put your palms together in front of you as if you were praying. Push them together and then try to slide them. If the pressure is not great, the palms will slide fairly easily and no strain builds up. But if you push your palms together with more force, they become bound by friction until the strain is released – causing a herky-jerky motion. This is known as a “strike-slip” fault and is the type of fault upon which the Port-au-Prince area of Haiti sits.
The geologic configuration of the area around Haiti is like a mouthful of crowded teeth. It is an orthodontist’s dream. Haiti rests upon a small remnant plate known as the Caribbean Plate. It is being consumed on virtually all sides by larger plates (North American, South American, Cocos) and is actually being spun around by this motion. As the larger plates drag past the Caribbean Plate, they cause the edges to smear like a deck of cards – each card relieving some of the pressure.
In Haiti last week, one of those small strike-slip faults, the southern most of a matched set that run along the north and south sides of the island, could take it no more. It gave way and slid sideways until the pressure was relieved. As it dragged along, the ground was wrenched violently, pulling the foundationless buildings of Haiti from their moorings and dropping them upon the unsuspecting populace.
It will happen again, and again, and again until the plate is consumed and the pressure is relieved. It may happen tomorrow, it may happen next year, or it may not happen for a thousand years. But the slow process will continue and as long as people continue to build flimsy houses in geologically unstable places, they will continue to be plagued by disaster.
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jmac1949
Lisa Scroggins
jlsathre
toritto
Deborah Young
I am Stretch
Salon.com
Comments
Also we have an Austrian clown for governor who does not realize that this is the last place on the planet that needs a high speed train!
Having been in the 1957 (Octavia Street, San Francisco) and the Loma Prieta (Castro Valley), I can tell you that we have done a lot to put as much technology and lesson learning to work as possible. But I still get very nervous whenever I do go to the Bay Area.
But having watched the "Tornado Chasers" series, I think that everywhere has the potential for something awful.
r
This phenomenon is hardly confined to places where the world's poor and underserved live. The city of St. Louis MO sits on a nasty fault that lets loose regularly and violently, and the bill is coming due there. I knew about this when I visited once, and I was shocked to see so many brick buildings. HUGE brick buildings. Here in the SF Bay Area where I have always lived, we generally don't call them "brick buildings." We call then "unreinforced masonry buildings" and everyone knows they are deadly, such is the general awareness of risk.
Folks who visit California for the first time often marvel at the studly columns holding up our freeways and other structures. I go elsewhere and marvel at how spindly theirs look.
St. Louis is headed for disaster and nobody appears to be doing anything, or to care. My brother-in-law's house is there. I was in his basement, marveling at the rotting brick-and-mortar column dead center that the entire interior structure rested on. I told him "you've got to do something about this. One good shake, this thing will crumble and your entire house will fall in on itself like a souffle." But I was wrong. I discovered that the house wasn't even bolted to the basement walls - they don't require that in their building codes - so the whole thing would probably slide off and fall in before it could collapse. Amazing to this California boy.
My brother-in-law never did anything about it, of course. They never have earthquakes in Missouri.
Well done, rated.
And Memphis is much less than prepared. Much less. And now, thanks to Katrina, we know that our preparation for such disasters is sorely lacking. (And the New Madrid slip will probably result in what is not so technically known as a 'roll-y' where the ground turns to liquid in essence. Very bad.)
It can happen anywhere, of course. I had a friend comment on how Haiti had no buildings built for earthquakes. She had a hard time hearing that, well, Memphis is pretty much in the same boat.