Long term impacts of Tsunami's

Following the Tsunami that struck North East Japan earlier this year, the long term impacts are starting to emerge as quite significant. Rebuilidng the damaged coastal communities is expected to take many years.

http://www.bbc.co.uk/news/in-pictures-15789694

What causes Tsunami's?
What are the short term and long term effects of a tsunami?
Would it be possible to make 'Tsunami Proof' buildings? (Why do some survive and others don't? Is this pure luck?)
Is the cost of rebuilding communities worth the risk of having them destroyed by an event in one of the most sesmically active places on the planet?