Thank you for your comment.

The earthquake was a natural event that had occurred before in the area, and in other parts of China. However, due to poor design and construction, it resulted in a man-made disaster.

Buildings may sustain major structural damage during major earthquakes (base isolation can result in very little structural damage). However, the building can be designed in a way that the upper floors do not collapse on the lower ones. Therefore, people was survive, even though the building may have to be demolished.