Sunday, December 24, 2006 8:33:18 AM
On Friday 22 December 2006 the Andaman Islands were hit by a strong earthquake (6.1) at a depth of 45 km. There were no reports of damage or casualties following the quake, but understandably there was a lot of panic. The Islands lie on the Burma plate. The USGS map to the left shows the location of the earthquake. The part between the purple line (subduction zone) and the red line (spreading ridge) is on the Burma Microplate. The indian plate is to the left (west) of the purple line. To the right (east) of the red line (ridge) is the Sunda plate. The sea to the east of the Andaman Islands (and west of Thailand) is called the Andaman sea.
Running in a rough north-south line on the seabed of the Andaman Sea is the boundary between two tectonic plates, the Burma plate and the Sunda Plate. These plates (or microplates) are believed to have formerly been part of the larger Eurasian Plate, but were formed when transform fault activity intensified as the Indian Plate began its substantive collision with the Eurasian continent.
As a result, a seafloor spreading centre was created, which began to form the marginal basin which would become the Andaman Sea, the current stages of which commenced approximately 3-4 million years ago.
Yahoo News at http://news.yahoo.com/s/afp/20061223/sc_afp/indiaquakeandamans_061223052232
USGS News at http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/uswpav.php#details
The Andaman Sea is a so-called backarc basin. Back-arc basins form when an island arc is split longitudinally, approximately along the line of the island arc magmatic axis. This disrupts the magmatic arc and forms a remnant arc, which drifts away from the reforming arc axis. Back-arc basins are different from normal mid-ocean ridges because they are characterized by asymmetric seafloor spreading.
See also my blog Sumatra Fault.