"Earthquake" is indeed a bad movie. Universal made-for-TV bad. But, it's David Lean caliber work compared to "Airport 1975," Universal's other monster hit for autumn 1974. I saw "Earthquake" the Friday eventing after Thanksgiving in the Skyway Theater in downtown Minneapolis. Across the street "Airport 1975" was at the Mann Theater (a 1960s roadshow house) and it too had a huge line down the block waiting to buy tickets. At the same time "The Godfather, Part II" was filling two downtown movies houses at the Academy and State theaters. So good taste was having a moment too.
I find that all films from the early to mid 70's had a TV movie feel to them. It was a style. An artistic choice. A particular esthetic. I don't look at them with the current perceptions of the here and now because I was there in that period--thus that feel doesn't bother me in the slightest.
To put it another way, you can't dislike an impressionist painting for not looking like a photograph.