The Sichuan earthquake caused huge landslides across the affected region. Some of these landslides fell into riverbeds and dammed the water - forming what are called "quake lakes." Quake lakes are extremely dangerous for two reasons: first, because the lake they create behind the landslide will severely flood nearby cities and farmland, and secondly because the landslide dam will usually fail after damming up a large amount of water, sending a huge wave of water downstream that will destroy anything in its path.
GIS was particularly important for identifying, mapping, and planning response strategies for quake lakes. The most common use of GIS for the quake lake problem was to combine imagery analysis with flood and water flow modeling.
In the wake of the disaster the GIS community responded with dozens of datasets and mashups. Harvard's Center for Geographic Analysis set up the China Earthquake Geospatial Research Portal, which collects GIS data and relevant newsfeeds and provides a web mapping service to display data from the Sichuan quake. I recommend you explore their site to see what is available. The mission of their site is simple - to widely disseminate geographic data related to the quake for research and relief purposes.
International cooperation like this can be extremely helpful. Many serious disasters make it difficult or impossible for local governments to assemble data and make even the simplest types of maps for response and recovery efforts. Outside observers who volunteer their time and data are capable of making a significant impact.
In September, 2008, GeoVISTA Center researchers went to China to attend a workshop on GeoCollaborative Crisis Management. We heard from several Chinese research scientists who told us how important it was to have outside help in the immediate aftermath of the disaster. As an example, the Chinese stated that their own remote sensing satellites did not provide adequate resolution or quick/complete coverage of the affected area, so it was essential to coordinate with other governments like the US and France to acquire high quality imagery in a very short timeframe.
One presenter at this conference told us about the frustration he and other GIS experts had with organizational barriers that prevented fast and efficient data sharing. Many of his colleagues were ashamed that on his way to the disaster area, China's president Wen Jiabao was only able to use an off-the-shelf paper map of the Sichuan region to begin planning response and recovery efforts.