  We establish the abstract and semi-abstract equations that translate the
conservation law for a totally-filled, or totally-empty basin of arbitrary
shape submitted to a SH plane seismic body wave. This law states that the input
flux is equal to the sum of the scattered and absorbed fluxes, the latter being
equal to zero when the filler medium is non-lossy. We show that the well-known,
exact, solutions for the case of a semi-circular basin indeed satisfy this law.
The latter can, and should, be employed to test the validity of any theoretical
or numerical solution one might propose for a basin of arbitrary shape.
