Monday, June 05, 2006

EKG

On December 26, 2004, the Earth's crust slipped beneath the Indian Ocean, generating a mammoth tsunami that left more than 250,000 people dead. We know what's going on down there: one great crustal plate is pushing down beneath another, dragged along by roiling convection loops deep in the planet's mantle. All is aboil inside the Earth, albeit on a time scale long by human standards. The surface plates move an inch a year or so, slowly rearranging the map.

Plates don't slip one under the other easily. Friction binds them. Pressure builds up, and up, and up, then -- zap! -- the crust crashes forward. The whole planet rings like a bell.Here is an astonishing diagram (click to enlarge) from the journal Nature showing (the red stars) the great tsunami quake and the second less devastating quake that followed on March 28. The vertical axis is latitude; the horizontal axis time. The other circles are associated quakes and aftershocks. On the day of the Big One, the Earth chattered along a line northward for 800 miles, like a piece of cloth being ripped asunder. The second big quake racheted southward for a few hundred miles. Then, for more than a year, the planet shivered along the fault.

What we see in the diagram is a stunning visualization of a massive and complex event, a kind of planetary coronary, the Earth shuddering forward, manifesting its geological destiny, oblivious to the biosphere that rides on its restless shoulders.