Amidst his discussion of the laws regarding public fast days, the Shulhan Aruch (Orah Haim 576:4) writes that a community must observe a public fast when confronting a situation of "Mapolet," or collapsing buildings. The Shulhan Aruch defines "Mapolet" for the purposes of this Halacha as the collapse of walls or buildings that are situated on firm ground with strong support. (According to the Ritba, at least three structures must fall for a fast to be required.) Included in this category, as the Shulhan Aruch mentions, are earthquakes and strong winds (such as tornadoes and the like) that cause walls or buildings to collapse.
Commenting on this Halacha, Rav Yaakob Haim Sofer (Baghdad-Israel, 1870-1939), in his work Kaf Ha’haim (576:26; listen to audio recording for precise citation), writes that in Jerusalem, no fast days are ever decreed on account of these kinds of phenomena, because they have never caused harm and destruction in this city. He records a remarkable incident that occurred on 11 Tammuz, 5687 (1927), when a destructive earthquake struck the area of Jerusalem. Although the surrounding villages sustained considerable damage and many gentile villagers perished in the disaster, no buildings or people in Jerusalem were harmed. The Kaf Ha’haim records that this event was looked upon as an overt miracle even by the scientists of the time who otherwise attributed all events to natural forces and denied God’s involvement. Everybody who witnessed the supernatural protection of Jerusalem had no choice but to acknowledge God’s role as the "Shomer Yisrael," the Guardian of Israel, who continuously protects His people from harm in each and every generation.
