[...and still counting until 2014]
"this trend needs to be understood in relation to the increase in seismographs. Certainly, in the last 25 years, more lower intensity earthquakes have been noticed because of a general increase in the number of seismograph stations across the world and improved global communications. This increase has helped seismological centres to locate many small earthquakes which were undetected in earlier decades. Therefore, an upward trend is not unexpected in the graph, although the rise in the number of large earthquakes will be of more significance to our assessment of the trend.
By limiting the range of earthquakes being counted in this report to magnitude 7 or above, it means these earthquakes can easily be identified by a limited number of seismographs, and we have ensured that any increase in frequency for these larger earthquakes cannot be down to the increase in overall detection rates in this 25-year period, as all these larger earthquakes are able to be easily detected with fewer seismograph stations."
