1,368. Blights, Falling Buildings
Hilchos Taaniyos 2:11
Regarding the various types of agricultural blights, a fast is convened and trumpets are sounded as soon as they affect the crops, even if only a small amount of grain the size of an oven’s opening is affected.
Hilchos Taaniyos 2:12
The case of falling buildings is as follows: if sturdy walls of three houses that are not situated on river banks should fall in a city, it is considered a type of trouble for which we fast and sound trumpets. The same is true should earthquakes or strong winds destroy buildings and kill people.