  We study microlocally the transmission problem at the interface between an
isotropic linear elastic solid and a linear inviscid fluid. We set up a system
of evolution equations describing the particle displacement and velocity in the
solid, and pressure and velocity in the fluid, coupled by suitable transmission
conditions at the interface. We show well posedness for the coupled system and
study the problem microlocally, constructing a parametrix for it using
geometric optics. This construction describes the reflected and transmitted
waves, including mode converted ones, related to incoming waves from either
side. We also study formation of surface Scholte waves. Finally, we prove that
under suitable assumptions, we can recover the s- and the p-speeds, as well as
the speed of the liquid, from boundary measurements.
