After an earthquake, landslides block river valleys, causing temporary lakes to form. Sometimes these lakes hold for a long time; in other cases, the earthen dam fails, causing flooding downstream.
The single best blog on the topic is Dave's Landslide Blog, from Dave Petley, who is the Wilson Professor at Durham University, UK. He's doing reporting on the Tangjiashan dam, and I won't even try to be up to date with that.
As a previous example:
Lake Sarez in Tajikistan is the result of a 1911 earthquake, forming the 600 meter long Usoi landslide dam. An article in GeoScienceWorld by Schuster and Alford discusses the risks of the dam failing. A 2003 risk mitigation project installed remote warning sensors to alert villagers of risks detected.
Quake Lake in Montana formed after a 1959 earthquake; the Billings Gazette captured memories of it in 1999. The US Army Corps of Engineers was quickly put into service to build a spillway for the dam.