As most of our faithful readers are aware, we’re curious about the exact nature of the relationship between solar activity and earthquakes. According to the USGS, solar activity does NOT induce seismicity. After speaking with them on several occasions and getting no real answers, I decided to plot the USGS NEIC earthquake database for the first quarter of 2011 against NOAA SWPC’s A-index.

As you can see here, the day of largest geomagnetic activity also coincides with the Sendai earthquake. We multiplied the A index by to attempt compensate for the amount (277+3!) of 5+ EQs daily and this shows that overall the correlation is roughly %33, but for 7+ mag quakes it is 96.5%, however there are only four data points.

Plotting ONLY 7+ magnitude quakes vs. the A-index from 1999 to 2010 seems to show an inverse relationship, puzzling! We have decided that due to the logarithmic scale of EQ, we should create an “EQ index” that is suitable for comparison to the A index and/or other factors.

Stay tuned for more.