We prove the normality of minimal log canonical centers on threefold pairs whose residue fields are perfect of residue characteristics p ≠ 2 , 3 and 5 . We also show that the union of all log canonical centers on threefold pairs with standard coefficients are seminormal provided that the residue characteristics are large enough. In contrast, we provide an example of a non-seminormal log canonical center on a threefold in characteristic 3 , and give sufficient conditions to construct similar examples.
Arvidsson et al. (Thu,) studied this question.