[Not a Bug] Earthquake Not Very Effective against Steelix?

[YoshiofRedemption 0]

I'm in the depths of Tanzan Mountain and have to fight the level 75 Steelix that dwells within it. Whenever I get to use Earthquake on it, the game text says "It's not very effective..." Unless I'm ignoring something vital with the field effect/weather/some other third thing, Steelix is a Steel/Ground type, and therefore should be weak to Earthquake. This isn't anything game-breaking, but it is more of something to note.

[Alextron 28]

The field effect adds bonus rock damage to earthquake.Better not use it against Steelix

[Ironbound 110]

Yes. In effect, it makes EQ like Flying Press: a dual-type move that is both Rock and ground, thereby first cancelling out the SEness because Steel resists Rock and is weak to ground, and then making it NVE because steelix's second type, ground, is neutral to ground but resists Rock. So all in all, Steelix is more resistant than weak to Ground+Rock, so the net effect is as if you use a NVE move that is resisted. Had you used only a rock move, it would've been doubly resisted, though.

Fire, Fighting and Water moves are your friends in that match.

[YoshiofRedemption 0]

Okay. Thanks everyone!