Pythagorean Theorem: distance = sqrt(5.1^2 + 5^2) ≈ 1.005km.
With the actual depth, 4.94km, not 5km, 5.1 km would give distance = sqrt(5.1^2 + 4.94^2) ≈ 1.267km.
I guess you meant -, not +. Indeed, though I know the relevant formula, my intuition so violently failed me that I didn’t even calculate it before deciding it couldn’t be so large.