Let Roger look at Lowell's thesis (I'll try to, but I'm in a proposal crunch), but I think the correlation with Xray flares may have been immediate (within minutes of arrival), and perhaps on smaller quakes. So, you could try to plot, say, global M4s against X class flares-but in 1 hour (or less) bins. Or, try California quakes for M>2.5 and X class flares, or Xclass flares where California is sub or antisolar.

The other correlation was probably on the magnetic storms, or magnetic storms with a little delay-that is the Kp number. I do recall that Lowell said Loma Prieta coincided with a flare, but I forget how big and never checked this myself.

Maybe better to see what correlations Lowell did, and then instead of using an advanced statistical approach as he did, make simple graphs to try and reproduce the same correlation-to get a visual, and independent look at the correlations.
Chris