December 26th; 2 years in a row!

On this day in 2003 Bam, Iran was largely destroyed by a strong magnitude 6.7 earthquake.

In 2004 it was off the coast of Sumatra in the Indian Ocean that the pent up stress along a plate boundary was released as a giant earthquake. The 2004 quake was hundreds of times more powerful and resulted in 5-6 times as many deaths - most associated with the massive tsunamis that radiated from the spots where the Earth's crust suddenly jumped tens of meters. This vertical motion of the crust instantaneously moved billions of tons of sea water up and down setting in motion the tsunami waves that spread across the ocean in all directions at speeds up to 800 kms/hour.

The image attempts to convey the complicated nature of the plate tectonic makeup of the eastern Indian Ocean and SE Asia. Blues and purples designate depths below sealevel. The India plate is basically moving NE while the Eurasian plate is moving WSW. Caught in the vice are the Sunda and Burma plates which are also being pushed from the SE by movement of the Australian plate. The result of these jostling bumper cars are complicated mixtures of strike slip (horizontal) motion, and compressional thrust faulting. The magnitude 9 quake resulted from the Burma plate "leaping" suddenly southwestward relative to the Indian and Australian plates as it released years of pent up stress.

The most remarkable aspect of this display of the power of the earth is not that it happened; similar although generally smaller quakes happen all the time around the world. What is most remarkable is that the initial quake set off a series of very large aftershocks that record the breakage of the earth's crust over a distance of 1000+ km largely to the north along the subduction zone. The image at the right is a snap shot of the earthquake activity in the Indian Ocean in the hours after the main quake. Each red circle represents a single quake and the size of the circle is proportional to the magnitude. The yellow circles represent quakes in the 2 weeks prior to the big quake. The purple dots represent quakes over the past 5 years and delineate the major plate boundaries in this part of the world.

Below is an image created one day later - the giant quake is now orange (a day old) but note that the red circles continue to bloom along this immense tear in the Earth's surface.

Some of you may have watched the much maligned miniseries that aired last spring called "10.5" about a giant earthquake that destroys much of the west coast of the US. One of the concepts in that TV show was that a fault line existed all the way from Mexico to Canada and that if the entire fault effectively broke at the same time, an earthquake with a magnitude of 10+ (never before seen) could be generated. What occurred last month in the Indian Ocean is about as close to this TV show's concept as has ever been experienced by man. Here are some links to sites discussing and debunking the reasonableness of a 10.5 quake anywhere let alone the US:

Megaquakes and the Movies

Earthquake Facts and Fantasy

Place your mouse over the Before picture of Banda Aceh below to see the same area After the tsunami hit the northern tip of Sumatra.