Just heard about quake and would be concerned about Bangladesh and nearby parts of India from tsunamis....but if anything happened, it hapened already. CNN said a lot of fatalities on Sri Lanka...which means a large tsunami crossed a good chunk of the Indian ocean...there could be problems as far as ports on the African coast...again, if this was going to happen, it would have happened already, and I am not an expert on tsunamis and only have the same information you do online and on CNN. To answer Catheryn's question, the biggest recorded earthquake was Mw 9.5 in Chile in 1960...that ruptured 1000 km of subduction zone. Followed by 9.2 in Alaska in 1964...ruptured 600 km of subduction zone....so this is the biggest since then. The main shock was at latitude 3.3 North, with aftershocks as far as 8 something deg north...at 111 km/deg, if this was straight N-S, that would be 550 km of rupture, which is about right for a 8.9. but, it is a NW-SE subduction zone, so rupture is longer. The Adaman Islands quake are at 13 something N......so like Don suggests, must be separate triggered earthquakes...otherwise this would be largest recorded quake. The focal mechanism shows a very flat NE-dipping plane...which means that a very large downdip area ruptured...Magnitude is partly related to the area of the fault ruptured. I'll guess they upgrade this to a M9.

Again, I don't want to give myself any particular credibility, and if it is going to happen, it has already happened...but Bangladesh is very exposed to Cyclone storm surges which have killed up to 100s of thousands of people...hopefully this tsunami was refracted away form the upper Bay of Benglal and part of its energy absorbed in shallow shelf. I'd also worry about any low elevevation coral attols in Indian Ocean.

The earthquake was not a continental collision...it is a subduction zone of oceanic crust. But, the ocean plate motion is highly oblique to the subduction zone...and the slip is partitioned...so that the slip on this earthquake was not oblique...it was straight down...the remaining plate motion is taken up on a strike-slip fault...let's see..would be right-lateral like the San Andreas....is called the Great Sumatran Fault, I think...is on land. Someone may want to research when its last large ruptures were, and what the long term slip rate is, to see how "ripe" it is...if that concept has any validity these days.

I think it will be interesting to see if there are any global triggering of earthquakes....while having no statistical evidence beyond perhaps what Lowell W. has said/posted, I certainly do not think that the 8.1 south of New Zealand a few days before this one was a coincidence. So, it would not surprise me to see a global burst of earthquakes. Yo everyone...I should have no particular credibility on this...I am not a seismologist...I'm a hobbyist when it comes to this sort of things (although I am a research scientist as far as talking about active faults).

I invite John V. to express his professional opinion on some of this.
Chris