Hi All. The M>8.9 quake that occurred in the area of Sumatra occurred along the Alpide belt. This is one of 3 belts in which earthquakes occur. The “moment tensor solution” show the quake to have had down slip.

Almost all the world's major earthquakes occur in two great belts. The first one is called the Circum-Pacific belt and the other one is called the Alpide belt. The Circum-Pacific belt sometimes called the Ring of Fire, accounts for more than 75 percent of the world's earthquakes. This belt runs on the West Coast of North and South Americas, the east coasts of Japan and China, Indonesia and other islands in the South Pacific.

Most of the other earthquakes occur in the Alpide belt, which cuts across Europe and Asia from Burma (Myanmar) to the southern Europe and North Africa with a starting point near Portugal and ending near Australia. Approximately 18-percent of all earthquakes occur in this area. Most of the quakes are the results of complex continental collisions. To say that it is a complex continental collisions is sort of an understatement. The various types of quakes that can occur in the area range from collision, under thrusting, indentation and extrusion. The last great quake to have occurred with 200 miles of the M>8.9 quake was on 11/21/1969 at 2.10N/94.60E and was a 8.20 Ms.

Other active earthquake areas include the mid oceanic ridges that form undersea mountain chains. In contrast, the flat parts of the continents and sea floor are stable regions that have few quakes.

This is speculation on my part, but it appears the Sumatra quake may have triggered a M>6.1 at Adaman Islands as they are about 700 miles north of the Sumatra quake. As for the M>7.3 at Nicobar Island it could be an aftershock, or it could be a triggered event and a main event in its own right. It’s really too early to tell one way or the other. Take Care…Don in creepy town