Why do we say “Japan earthquake” and not “Japanese earthquake”?

Isn’t earthquake a noun and the preceding word an adjective? Isn’t “Japanese” the adjectival form of “Japan”?

Solution 1:

Because when we describe the earthquake we are talking about its location. Plus, earthquakes don't themselves, by their nature, have a connection with a specific nationality—they are not like Japanese food, clothes, tea, that are specific to the Japanese people.

Solution 2:

I suppose because it is referring to a place as in "an Atlantic storm" whereas to say a "Japanese earthquake" would imply there was something Japanese in its nature.

Solution 3:

Fewer syllables = Catchier headlines, once one media outlet has started using it everyone else jumps on the bandwagon and it becomes a meme.

Solution 4:

I'm not sure there is necessarily a rule for this type of situation - that is, when to use the name of the country and when to use the adjectival form. I think in many cases it's decided almost unconsciously based on what rolls off the tongue the easiest. The 'n' at the end of 'Japan' flows nicely into the vowel at the start of 'earthquake'. On the other hand, if an earthquake occurred in India it would feel odd to say "the India earthquake" - we may be more inclined to say "the Indian earthquake". English is riddled with these kinds of inconsistencies as we all know.