Usually the USGS will first report a "tentative" or "preliminary" value for an earthquake's magnitude, and then will revise it as more data comes in from various seismograph stations.  It may go up or down as a result.

If you really want to get technical, a 4.7 is roughly 40% the strength of a 5.1.  (Sorry, I used to teach geology and went all geek mode there for a sec... weird smiley)

Nice little temblor though, sounds like.

Adam
Flathead Valley, MT, USA
1976 CT90 - Shiny Orange
1973 CT70 K3 - Candy Riviera Blue
1970 CT70 HK0 - Candy Blue Green (project)
1979 Z50R - Tahitian Red (project)
1964 CT200 - Scarlet Red (project + extras)
1968 CL175 K0 - Dark Blue (project)
1978 NC50 - Pal Green (project)
1982 & 1983 CT110s - Monza Red (projects + extras)