What is the mean number of earthquakes of magnitude 6.0 to 6.9 over this 13 year period?

To determine the mean number of earthquakes of magnitude 6.0 to 6.9 over a 13-year period, you would first need the total number of such earthquakes recorded during that time. Then, divide this total by 13 to calculate the average per year. Without specific data, I cannot provide an exact figure, but this is the method to find the mean.