The combined factors or stress index used in the last blog didn't correlate well with the earthquake activity defined as the base 10 log of the number of earthquakes in a day.
Modifying the angle factors by adding one and dividing the result by two worked better.
One can use the correlation coefficient to estimate the number of earthquakes per day for a given stress index, SI. When we compare this estimate with the earthquake histogram we get a fairly good agreement for the background activity.
There is a deficit of earthquakes before the M7.1 earthquake and a surplus afterwards that may be associated with aftershocks. The new stress index lacks the peaks for when Moon's declination is negative.
The definition of the modified factors is as follows.
The stress index suggests that we might start to see a noticeable increase in earthquake activity in the next few days. The correlation coefficients for the individual factors with the earthquake activity have values similar to that of the SI.
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