There is a whole field of study which attempts to discriminate between ground motion
caused by explosions and that caused by earthquakes. Although it seems that
it would be a simple observation that these seismograms had all first motions up
(compressive) then it would be an explosion as opposed to double-couple mechanism
which would indicate an earthquake this is not always the case. In fact some claim
that nations attempting to disguise underground explosions can easily hide those
explosions by setting them off in an area where an earthquake would be induced
by the explosion and you wouldn't be able to tell the difference with the seismographic
coverage.
The seismographic arrays around Colorado may not be dense enough to tell if
all first motions are the same, however, I will look at the on-line seismograms
of yesterday's Ml 4.5 and see if this is the case and let you know.