Drag related from hurricanes causing earthquakes is yes plausible. A hurricane is a huge coalescence of water vapor, which will have some density difference then the surronding enviorment. Remember the famous formula Mass over Volume, well hurricanes surely have a hefty mass, and volume but they're comprised up of similar gases, so the density difference is small. This causes wind to have an obstructed flow, and have three choices over, to the sides or through. This would slow down the prevailing atmospheric flow, to a point where the friction between the earth and atmosphere would increase, causing a slight decrease in rotational speed. After that I don't know how it would work, because if you were to slow down the rotational speed of Earth, angular momentum would decrease and gravity would increase, therefore causing all magma to be surpressed. That's my take on the whole thing, I know that many other factors contribute to having a volcano erupt, degassing, density of rock material, source of rock material etc. so gravity is just one small thing and besides gravity is a weak force when you think of it.