  We consider a coupled system describing the interaction between acoustic and
elastic regions, where the coupling occurs not via material properties but
through an interaction on an interface separating the two regimes. Evolutionary
well-posedness in the sense of Hadamard well-posedness supplemented by causal
dependence is shown for a natural choice of generalized interface conditions.
The results are obtained in a real Hilbert space setting incurring no
regularity constraints on the boundary and almost none on the interface of the
underlying regions.
