Word out of Japan is that an elderly woman and a teenager were rescued from their collapsed home 9 days after it was damaged by the earthquake. That brings up a couple thoughts I'd like to share.
In a catastrophe, two scenarios develop. One is that you must evacuate, the other is that you can stick around and "shelter in place." Shelter in place is the term used when the building you're in when the crisis hits is suitable for your occupancy and there are no circumstances absolutely requiring that you evacuate.
The case in Japan is not what I would call sheltering in place, but the damaged residence did provide adequate shelter to keep these two alive for 9 days until they could be rescued. I must point out that this structure was damage by the earthquake, not the tsunami. There is no way to shelter in place when a tsunami is sweeping through the area — higher ground (or levels of a building above the waterline) must be reached.
I haven't seen photos of the building where these two were rescued, but my mind conjures scenes of rubble (probably because that's the kind of footage the media is providing) in which the two were trapped.
Still, there is a point to be made that even a badly damaged structure might be useful for shelter from the elements until the situation can be improved. Of course, if the structure is likely to continue collapsing around you, it is not a safe place and must be evacuated. But if the structural damage has settled and there is little risk of further collapse, perhaps it can be used to shield survivors from wind, rain and snow or hot sun.
Short of having the damaged building fall on you, the real shelter-related risks to survival are exposure to the elements. So being able to stay dry and out of the wind are two priorities. I remember seeing images of homes with blue tarps stretched over damaged roofs after hurricanes, and this same concept might apply after an earthquake. So a big tarp can be a valuable addition to survival supplies, because it might be used to help you shelter in place even though your home has been damaged.
A tarp, some rope and tent pegs are also useful if you have to evacuate. With a length of rope stretched between trees or other anchors to form a ridgeline, the tarp can be used as an emergency tent to get you out of the elements.
Before deciding to evacuate (unless there is a compelling reason - like a tsunami), consider the possibility of staying put and sheltering in place. You have a house full of resources to use, if that situation is possible. But if you decide that evacuation is the best course of action, do it early to avoid the rush.