Number of earthquake on the increase?

Let's assume that seismometer was able to detect any earthquake greater than 7.0 100 years ago, from http://www.moorlandschool.co.uk/earth/images/Earthquakefaq.htm
we get


the number of earthquake fluctuates quite widely where the peaks can be twice as large as the norm.We have less large earthquake for about 10 years.

Let's us look back at the smaller earthquake (ie 6.0-6.9)


There seems to be some increase at first glance for magnitude 6.0-6.9 since 1990. It is just 40-80% increase pre-1990. The question is why there is a sudden jump of number of earthquake after 1990 and persist somewhat at that level. One thing is certain, the earthquake doesn't increase over the years. The sudden jump is a unexplainable.