To find basic information about ground subsidence and sinkholes, search the Library catalog for books on subsidence; karst; geological hazards; or geohazards. News articles on this subject may be found in Lexis Nexis. For academic articles, search such databases as the ASCE Digital Library and Academic Search Premier (subsidence AND "Mexico City") (ground AND sinking AND "Mexico City") (subsidence and Sagraria) (subsidence and cathedral and "Mexico City").  Additional information may also be found on the Internet in an online text posted by the US Geological Survey called: The Guidebook for Studies on Land Subsidence Due to Ground-water Withdrawal.  It contains a large amount of information on subsidence in Mexico City.