8.3!
Not that big as earthquakes go... However it's not the size of the earthquake that matters with tsunamis, it is the movement of the seabed itself, either due to the earthquake or a slump of material (off for example a continental shelf). The slump could in fact cause the earthquake.
Obviously not a huge amount of material was uplifted/moved in this case or the wave would have been much bigger.
(The boxing day 2004 earthquake was a biggy, almost ten times bigger, around 9.0 and caused uplift of several metres over tens-hundreds of miles)
Yeah, although reading someones comment on twitter, apparently it's the length of wave that does the damage. I suppose if it's 40cm, but 10x the volume or size of a normal 40cm wave, it could probably cause surges.
Yeah it's the length of the wave more than the height, the sheer volume of water pushing from behind the front is the main cause. A tsunami wave will only be a few cm-tens of cm in the open ocean, but 10-100km long, it's only when it hits the shallows that the front slows down and the back catches up making a higher wave with a huge amount of momentum.