 So when the field reverses, it's like you turn your magnet around, and now the crust is repelled from the mantle, and it can slip over it much more easily. And so in this condition, with the moon not synced to Earth's rotation, there's a torque, and that's what causes the tides. So it's the same thing that causes the tides, which could potentially pull on the crust and cause the crust to displace.