[Clinging Bitterly]

...his theory is that sunspots cause earthquakes.

I haven't read his theory but I can see how they might. No correlation has been established much less causation but solar activity is known to cause terrific disruptions in the earth's magnetic field. These disruptions are readily observed through various phenomena above the surface but their effect beneath the surface is largely unknown.

[crz]

All that Dr Casey has said that history has shown that during Minimums, some of the largest earthquakes in history have happened.

Of course a lot have happened in mean times also.