If you follow the link connected to the NPR article, it says they believe that the increase of M 3 quakes indicates there is a greater chance of a M 5.5 or greater quake occurring. Also, keep in mind that the "Magnitude" refers to how powerful the quake is at it's source, that is to say at the "hypocenter". When earthquakes are reported, the press often just reports where the "epicenter" was, which is the location in map view. It is also important to know the "focal depth", or how deep it was in the crust. The hypocenter is the point (under the epicenter at the focal depth) where the rock actually starts to rupture.

A small earthquake at a very shallow depth might be more damaging than a larger earthquake with a very deep hypocenter. If the quake is indeed triggered or influenced by hydraulic fracking, then it would presumably be at or near drilling depths. That is to say relatively shallow in seismic terms.