So, I downloaded some earthquake data from the USGS database. I then plotted the log of the number of earthquakes with magnitude greater than or equal to M versus the magnitude M. This should produce a nice linear trend as predicted by the Gutenberg-Richter law. However, there is an apparent dearth of earthquakes at low magnitude. Is this due to the sensitivity of instruments used to detect the earthquakes? Is this a well known occurrence? Is it affected by "declustering" of earthquakes at higher magnitudes?