Yucca Flats is more than 100 miles northwest of Las Vegas. It is east of Death Valley and probably more than 250 miles or more from the epicenter of the recent earthquake.
Hidden away off Nellis AFB, it is a relatively inactive tectonic area.
Even if there were a massive earthquake that destroyed the facility the waste would simply be trapped inside much as the uranium ore was trapped in the ground for billions of years before we mined it.