Does the increasing number of significant earthquakes relate to increasing population density in earthquake zones?
The only possible linkage between moderate earthquakes and population is that more people create increased groundwater extraction, and hence near-surface fault planes tend to dry out. This effectively increases the friction so that there are less frequent but more violent quakes. However, this would only affect near-surface earthquakes which seldom exceed about magnitude 3 or 4. The really big earthquakes originate at plate tectonic interfaces at depths from about 10 km to hundreds of kilometres. There is nothing that humanity can do to influence processes on this scale. 

Another issue is that micro-seismicity occurs all the time - millions of small quakes that go un-noticed every year. Some of these can certainly be caused by humans - but does this really count?