How Fast Does A Tsunami Travel?

Provoked by todays news of the Chilean earthquake…

Tsunami warnings are issued to Pacific inhabitants, for instance, Hawaii. Assuming the wave has a specific speed at which it travels, what is that speed, and what factors affect it, i.e., intensity of the earthquake, etc.

I would imagine that tidal waves all pretty much travel at the same speed, and vary only in the height of the wave, but I realize I don’t actually know squat. So, time to consult the Smartass Squad.

Speed will be affected by ocean depth.

In the open ocean a tsunami can travel up to some 5-600mph depending on depth and topography, but upon approaching landfall will slow to around 30mph, give or take 5-10mph. At those speeds the Chile earthquake tsunami could reach Japan in about 24 hours. An identical event occurred back in 1960:

A large tsunami, a la 2004 will typically require >6.75 earthquake or a large underwater volcanic event.

According to a couple of sites on Google, tsunamis can travel at 500 to 1000 kilometers per hour across the deep ocean, but slow as they enter shallower water.