an undeserved catastrophe; an undeserved ill turn; an unexpected calamity/1976年唐山大地震真是一場～。The big earthquake in Tangshan in 1976 was really an un expected calamity.
無妄之災(zāi)wu wang zhi zai
uncalled-for calamity
無妄之災(zāi)wú wànɡ zhī zāi
無妄：即“毋望”，意想不到的。形容意外的災(zāi)禍。an unexpected calamity, an undeserved ill turn, an unexpected disaster