This doesn't weaken the argument. Scientists don't need to understand the exact mechanism causing these currents in order to be able to detect them and predict the right time to evacuate.

If anything, this strengthens the argument. If old detection methods have been based on weaker correlations, it seems more likely that this new method, based on a stronger correlation, will help local officials figure out more precisely when to evacuate.

This doesn't weaken the claim that this new method will help officials figure out when to evacuate. Regardless of how frequent major earthquakes have been, if they have been preceded by electrical current changes that can be detected by this new method, this method can still be useful to officials.

This weakens the argument. If this is true, then current changes could possibly occur very shortly before an earthquake, not leaving officials enough time to evacuate towns, which would weaken the claim that this method will aid officials in knowing \"exactly when\" to evacuate.

This doesn't weaken the argument. Even if there’s only one station capable of using this method, the method could still be employed and be helpful to officials.