The magnitude 8.6 earthquake that struck North Sumatra, Indonesia did not lead to a tsunami comparable to Indonesia's 2004 disaster for a couple of reasons, as said in a Discovery News story.
Today's temblor ripped along an oceanic transform fault, tearing the seafloor in a strike-slip motion as opposed to popping it apart.
Strike-slip motion carries less of an ability to push up on the entire water column above it and hence is less likely to form the same kind of tsunami wave as what hit Indonesia in 2004 and Japan in 2011.
The powerful undersea earthquake was a once in 2,000 years event and increases the risks of a killer quake in the region, Kerry Sieh, director of the Earth Observatory of Singapore, told Reuters.
"Besides it being the biggest strike-slip earthquake ever recorded, the aftershock is the second biggest as far as we can tell," said Sieh.
Strike-slip quakes involve the horizontal movement of colliding earth plates and are typically less powerful than those where there is vertical movement. They are also less likely to trigger big tsunamis.