The USGS announced today a new Website that displays the current probability of earthquake shaking in California. At http://pasadena.wr.usgs.gov/step/, maps show the likelihood of earthquake shaking over the next 24 hours. The maps combine information about recent earthquakes recorded by the CISN with information about known faults and earthquake history. The maps are updated at least hourly.
In addition to the real-time maps, the Web site also provides an archive of older maps, beginning in September 2004. Here is an example of the maps, comparing the probabilities in California before and after the M6.0 Parkfield earthquake on September 28, 2004. The forecast for September 29th at midnight shows the enhanced probability in the Parkfield area from the 9/28 event.
The maps and the methodology used to produce them are discussed in an article in the current issue of Nature, by Matthew Gerstenberger, Stefan Wiemer, Lucile Jones, and Paul Reasenberg. The article is available in the May 19th issue, along with a News and Views comment by Duncan Agnew.