If there is an earthquake, this building would probably collapse.
If an earthquake happens, this building probably won't be able to withstand it.
ご質問ありがとうございます。
① "If there is an earthquake, this building would probably collapse."＝「もし地震があったら、この建物は多分倒れるだろうね。」
② "If an earthquake happens, this building probably won't be able to withstand it."＝「もし地震が起きたら、多分、この建物は耐えられないだろうね。」
ご参考までに。
If an earthquake hits here, don't you think that building will fall over?
この場合、次のような言い方ができますよ。
ーIf an earthquake hits here, don't you think that building will fall over?
「地震が来たら、この建物倒れると思わない？」
..., don't you think that building will fall over? の代わりに I think that building will crumble.「その建物は崩れると思う」とも言えます。
ご参考まで！
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