see link, there was just a 5.0 at 1.4 deg S in the area if the Sumatra subduction zone. This is within the "gap" between the March 2007 M8.7 and the 7.9 about a month ago. As in, most geologists, and maybe even seismologists, would think this zone was hazardous/stressed. I'd guess that if the focal mechanism suggested it was on a gently NE-dipping fault and it was thrust, this would be a little more alarming than if it was some other kind of quake (at some other 3D location). Could break any time, or maybe not for 100 years.
Chris

• Sumatra 5.0