About the word 'landslide'

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What we're dealing with is a case of metaphor, i.e. figurative language. In this case, the literal meaning has to do with the geological phenomenon. Without any surrounding context, the example you quote from findwords.info actually sounds like it's a case of this. (Note that, there, fault is also used in the geological sense.)

You ask whether "a person [...] can use the word", which sounds like you're asking for a judgment about what is correct. Academic linguists are more interested in describing what people out there in the real world actually do. I'll be doing the latter. (For further background, see this article.)

From this perspective, the question really becomes - what is the range of possible metaphorical extensions of the word 'landslide'? If you poke around online, you can find a continuum of definitions:

1. "lopsided electoral victory"
2. "any overwhelming victory"
3. "a large amount of something that happens quickly and forcefully"

People often cite the Oxford English Dictionary as authoritative. It gives only #1 ("a sweeping electoral victory"), with examples like the following:

• a veritable landslide in Mr. Hewitt's favor
• a great landslide of votes for McClellan.
• the Conservative landslide in 1906

But that doesn't mean that that's the limit of the possible metaphorical extension of the word. If you search for 'landslide' on the Corpus of Contemporary American English, you can see it used in a wide range of ways, many of which would fall under #2 above. One example is: The President's trade representative went so far as to predict a Clinton landslide in the vote on Wednesday. This is the closest one I can find to your example, "Landslide in social attitudes".

So, the bottom line - yes, saying 'landslide In social attitudes' is a somewhat atypical use of the word 'landslide', but it's perfectly within the envelope of natural variation in how the word is used. Metaphors are of course conventionalized, but they are to a large extent flexible, and the quick/forceful/overwhelming nature of a change in social attitudes makes a landslide an apt metaphor to use.