In my opinion, the following sentences are perfect (natural, grammatical English, with no need for any improvements at all):
1, 2, 3, 5a, 5b, 6b, 7, 8, 10a, 10b, 10c, 11, 12.
As for the ones not listed above, these are my comments / feedback:
4 - OK, but more natural to replace "a Japanese" with "a Japanese man", "a Japanese woman", or "a Japanese person".
6a, 9a, 9b - We do not usually use "attack" when describing an earthquake.
9a - "a big earthquake" means a one-time occurrence only, so you can not use it in this context.