Whole lotta shakin' goin' on

By David Fuhs

There has been an increase in major seismic activity from 1973 to 2009 (the years for which there is online information at USGS.gov)

The following graph shows the total amount of "shaking" caused by all earthquakes of 7.0 magnitude or greater from 1973 to 2009. I assigned each 7.0 quake a value of one(1), each 8.0 quake a value of ten(10), and other magnitudes an appropriate Linear value.

The proper measure of the total amount of seismic activity each year should be the Total of the Linear value of each quake times the number of quakes of each magnitude. This is because the Richter Scale is Logarithmic. So, if you had three 6.0 earthquakes, two 7.0, and one 8.0 in "Year One", and in "Year Two" had three 6.0, two 7.0, and one 8.0 quake and one quake of 8.1; your graph would indicate an increase of 1 earthquake greater than 6.0 -- but in reality you would have experienced more than DOUBLE the amount of seismic activity ("shaking").

I took only those quakes of 7.0 magnitude or greater for each year and compared the seismic action on a linear scale (rather than the logarithmic Richter scale). Obviously, there are years of high seismic activity and years of low activity; but, when I ran an OLS regression the slope was +0.97 per year over 37 years. This is the equivalent of one additional magnitude 7.0 earthquake EACH YEAR! Keeping in mind that the quake that recently leveled Haiti was a 7.0 magnitude quake, there are 37 more 7.0 earthquakes per year in 2009 than there were in 1973. That's significantly more shaking now than in 1973.

More years of data would provide a better analysis of the normality/abnormality of recent seismic activity. But, given its limitations, anyone can do the same analysis that I did and get the same result.