Curiosity can lead you into charted territories

Sometimes when I'm sitting at my desk at work, I get the distinct feeling my desk and the floor are vibrating. Kinda like an earthquake's after shock. Now for the most part, I get that these things happen on minute scales from time to time. Also, sometimes there are crews blasting in the vicinity of our office location due to the construction of the new casino, like we need another one of those here in St. Louis. But I digress.

So my curiosity got the better of me today and I decided to try and find a real time seismograph. Of course, I couldn't find one but I did find the SLU website showing screenshots for recent seismograph readings. Can anyone reading this blog help me interpret this reading from 8-3-09?

Seriously, that's freaky! What do the various colors mean? Other readings listed from around Missouri, Southern Illinois, Tennesee and the like, show similar activity at the same time. I'm sure this is more common that we are told but still. Freaky!