That the deal is reportedly done is no surprise. Sevilla have already acknowledged that a club has agreed to meet his buyout clause and Spurs' interest in the centerback was no secret. It always seemed like a matter of time before Fazio joined Tottenham, and it looks like he finally has.
The Fazio deal would come on the heel of Spurs' sale of Michael Dawson. With the Dawson deal for a reported £6 million and Fazio coming in for £8 million, it would be pretty great business by the club to improve the defense for a rather small cost. Fazio's wages have not yet been reported, but Dawson was not at Spurs on the cheap so it's unlikely that there is a giant gap between what Fazio will be paid and what Dawson was paid.
It is expected that Fazio will join Jan Vertonghen in Spurs' first choice center defense. That leaves Younes Kaboul and Eric Dier as backups, with young Milos Veljkovic as the fifth option. That means Vlad Chiriches should be on the way out, which is no surprise as he has been linked to several clubs.