  We consider a quantum circuit model describing the evaporation process of
black holes. We specifically examine the behavior of the multipartite
entanglement represented by this model, and find that the entanglement
structure depends on the black hole mass $M$ and the frequency of the Hawking
radiation $\omega$. For sufficiently small values of $M\omega$, the black hole
and the radiation system becomes a separable state after the Page time and a
firewall-like structure appears. On the contrary, for larger values of
$M\omega$, the entanglement between the black hole and the radiation is not
lost. These behaviors imply that owing to the monogamy property of the
multipartite entanglement, low frequency modes of the Hawking radiation
destroys the quantum correlation between the black hole and the emitted Hawking
radiation.
