Since we do have at least one person from India who reads this page (Shan), and because the Pacific northwest of the U.S. can have a tsunami the size of the Indian Ocean tsunami every 600 years or so, the following might be of interest. If you feel an earthquake and the shaking lasts more than a minute, you should get away from a low coast (like a beach or bay). It is most likely to have a large tsunami if the shaking lasts for more than 2 minutes. This does not rule out a large, but local tsunami from an underwater landslide from a much smaller quake. If you see the ocean withdraw over a period of minutes (not like the tides...something you have never seen before), it will certainly come rushing back as a tsunami. Tsunamis come in series....someone check here...probably separated by 5-15 minutes (??)...and the second one can be bigger than the first.

The following will be approximately correct but is from memory, and is not my study area, so will not be exactly correct: The Cascadia subduction zone extends from northern California (north of Cape Mendocino) through all of the Oregon and Washington coasts (I'm not sure of the exact northern limit...may be slightly into British Columbia). Paleoseismologic research by geologists suggest that it can have M9.0 quakes and large tsunamis. Tree rings of trees that were drowned by subsidence during one of these quakes show that the least one was within a year or so of 1700 (304 years B.P.), and a tsunami was recorded in Japan in that year...assumed to be from Cascadia great quake. I think the average recurrence is something like 600 years, but they can be spaced closer or longer in time....300 years is possible, but probably not really likely. It is likely that the subduction zone could break in pieces, so that the magnitude need not be as large as 9. Could be in the low 8s. But, geologists think that 9s have occurred, and thus are possible (the 1700 quake may have been a 9???). I think not a lot of people live at low elevation along the open ocean in the NW...thanks in part to big waves from ocean storms...so one question I might ask is whether the Juan de Fuca and Puget Sound areas would be prone to seiches....which is the slopping around of water in an enclosed body of water. I don't know what research has been done, if any, to see if this has occurred in the past.
Chris