If gravity, in the form of tides, has almost no correlation with seismicity, then I fail to see how the much weaker force of magnetism could be expected to. Gravity, at least, operates on all matter within its field. A magnetic field will affect only ferrous materials, which are a small component of the Earth's crust. And, just as with gravity, the forces operate equally on both sides of a fault.

Finally, though magnetic field fluctuations, and even reversals, happen rather quickly on geologic timescales, they still are very slow changes on a human lifetime scale. There is no immediacy to any such concerns as increases or decreases in seismicity due to the reported changes.

Michael Williams
Arroyo Grande, CA USA