It doesn't have a floor, but I'm pretty sure solid ground counts as total cover.I was about to ask if a hemispherical wall of force had a floor, wondering if something could go under it, but then I remembered Crawford's "ruling" about tiny hut.
What follows of, course, is "what about Earthquake?" If you go by the way @Clint_L rules, a Wall of Force should block the effect of the Earthquake spell, even though that makes no sense. But then, so would a brick wall.
Of course, the rules are actually far from clear if total cover can block the effects of an area spell, or just the positioning of the point of origin.