This is the 18969th most frequent Korean word.
쓰러졌던
"Fallen" or "collapsed."
In this case, '쓰러졌던' is used to describe a building that physically collapsed due to the earthquake.
지진으로 인해 쓰러졌던 건물이 재건축되고 있습니다.
The building that had fallen due to the earthquake is being reconstructed.
In this sentence, '쓰러졌던' describes a tree that had fallen at a previous time.
어제 산책 중에 쓰러졌던 나무가 오늘 치워졌어요.
The tree that had fallen during the walk yesterday was cleared today.
Here, '쓰러졌던' metaphorically refers to a deteriorated or collapsed state of someone's health.