  We deal with the problem of the linearized and isotropic elastic inverse
scattering by interfaces. We prove that the scattered $P$-parts or $S$-parts of
the far field pattern, corresponding to all the incident plane waves of
pressure or shear types, uniquely determine the obstacles for both the
penetrable and impenetrable obstacles. In addition, we state a reconstruction
procedure. In the analysis, we assume only the Lipschitz regularity of the
interfaces and, for the penetrable case, the Lam{\'e} coefficients to be
measurable and bounded, inside the obstacles, with the usual jumps across these
interfaces.
