Today's shallow, thrust-type earthquake occurred off the west coast of northern Sumatra at the interface between the India and Burma plates. In this region, the Burma plate is characterized by significant strain partitioning due to oblique convergence of the India and Australia plates to the west and the Sunda and Eurasian plates to the east. Off the west coast of northern Sumatra, the India plate is moving in a northeastward direction at about 5 cm per year relative to the Burma plate. Preliminary locations of larger aftershocks following today's earthquake show that approximately 1000 km of the plate boundary slipped as a result of the earthquake. Aftershocks are distributed along much of the shallow plate boundary between northern Sumatra (approximately 3 degrees north) to near Andaman Island (at about 14 degrees north).
I'm a bit confused over the "Burma Plate;" I think most sources call it the Andaman Plate.
1,000 km along the boundary . . . WOW.
Thanks much for the updated info.
There is a USGS graphic now posted at Drudge (titled M9.0 Andaman - Nicobar Islands Earthquake of 26 December 2004).
It is a map of the general vicinity and shows some of the main geological features. I believe Burma Plate is synonymous with Andaman Plate.
The area is an extremely complex quadruple junction of the Indian and Australian Plates, with the Burma (Andaman) and suda Plates.
There has been historic, major strike-slip activity (like that of the San Andreas Fault of California) through the center of the island of Sumatra; compressional subduction in the Sunda Trench and projected beneath the island arcs to the northeast; and rifting in the Andaman Sea. What a mess!
Another interesting thing I notice is that al most all of the aftershock activity is located to the north-northwest of the main shock. It looks like several hundred miles of the subduction zone are lit up with seismic activity.