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.


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?

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