Tsunami derection?

[Balanceofpower]

The huge quake off the coast of Japan last week caused a tsunami so big that it managed to travel the Pacific and hit the coast of California, if it was that big and strong to keep that momentum why didn`t it wipe-out Japan and devestate the whole of the eastern Russian and Chinese coasts, how was the havoc only confined to the Sendai area,Tokyo which lays just 200 mile away was untouched by the tsunami.

Experts tell us that when a quake happens in the ocean a ripple effect occurs which radiates from the epicentre in equal shockwaves.
It seems in this case that they are wrong and looked as though the plates slipped in an easterly derection and the main force was expelled that way and Sendai may have had a backdraught, which if this is the case it`s scary to think what would have happened if it had slipped in the direction of the mainland and the main force was directed there.

I understand that many tens of thousands have been killed but this is a scientific question as to how it was confined to a small area.

Anyone got any views on this theory?

[bednobs]

it went mainly in one direction owing to the force exerted when the sea floor "jumped up

[jomifl]

The horizontal direction that the plates move is irrelevant. What matters is the up/down movement of the ocean floor and the shape of this area. If it is elongated then the tsunami will be more pronounced as right angles to it's axis.Japan was the closest land mass and the worst affected areas were in bays which concentrate the tsunami and increase it's magnitude. This concentration effect occurs in the severn estuary and amplifies the spring tides to give the severn bore.

[beso]

I would have thought that derection would be the opposite of erection? How does that relate to a tsunami?