I've discovered that there's two different sets of data for earthquakes - one for actual number of earthquakes, and ones for only significant numbers of earthquakes. For example, in January 2016 the USGS showed 11 earthquakes of magnitude 6.0 or greater, of which 5 were listed as significant; in February 2016 it showed 9 such earthquakes of which 2 were listed as significant.
I thought that this might explain why some people say that data shows that earthquakes are increasing, while others say the data shows that they are not.
I made a graph of the number of significant earthquakes of magnitude 6.0 and greater using USGS data for 2002 to 20015. There was a steady increase; for example, there were about 45 in 2007, 55 in 2011, 70 in 2014. I couldn't find any explanation for this, but I wondered if this increasing trend correlates to increasing population density in earthquake zones.
I couldn't find a set of historical data for actual (significant and insignificant) over the same period of time.