> "As a final test, we wanted to check if the proton density catalogue is completely uncorrelated. We know, as stated above, that the seismic catalogue of strong earthquakes is non-Poissonian and internally correlated, so we have analyzed the proton density series to check if it were characterized by a white noise spectrum that would indicate an uncorrelated process. We simply computed the power spectrum, which is shown in Fig. 7 **(annotated below)**; it is clearly very different from a white spectrum, presenting at least two sharp peaks. We performed such a computation on the longest uninterrupted time window that has a 405 days length. This evidence testifies that neither the proton density distribution is random. So, this definitively confirms that the observed correlation between the seismic catalogue and the proton density cannot be likely obtained by chance; because the likelihood that two quantities, each of them internally correlated, show a clear mutual correlation only by chance is negligible."
The two triangles indicate the fortnightly and monthly tropical (~sidereal) lunar cycles which could potentially reflect tidal forcing effects which conflate with the 27-day sun rotation cycle, as described here https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008JD010499
Which is potentially bigger driver for triggering an earthquake? Tidal forcing or 2nd-order solar activity?