i have updated the map i made this morning with 2 new maps. the first map is just like the original, but i have placed the epicenters to all the earthquakes from this morning (>M4 from the USGS website). the second map is more zoomed out and i have outlined some of the fracture zones that show up in the SRTM bathymetry (the gross bathy that forms the background of most of these maps).
these fracture zones are more successfully buried by Bengal fan sediments in the north, such that they are not generally visible. along the southern margin off Sumatra, these structures are more prominent.
the aftershocks seem to be trending a northwest-southeast strike, but there are no known structures with these configurations. there may be short faults that link fracture zones, probably generated when this crust was at the spreading ridge, but these would be short faults, compared to the fracture zones. the larger earthquake is the largest strike-slip earthquake in recorded history. given our knowledge about what regulates earthquake magnitude (area of the fault, the amount of fault slip, and the material properties of the crust, eg. how much “volume” of the crust moves during the eq), it is probable that these larger earthquakes are associated with a fracture zone (where faults of necessary length more likely exist).