  Both electromagnetic shock-waves and gravitational waves propagate with the
speed of light. If they carry significant energy-momentum, this will change the
properties of the space-time they propagate through. This can be described in
terms of the junction conditions between space-time regions separated by a
singular, null hypersurface. We derived generic junction conditions for
Brans-Dicke theory in the Jordan frame, exploring a formalism based on a
transverse vector, rather than normal, which can be applied to any type of
hypersurfaces. In the particular case of a non-null hypersurface we obtain a
generalised Lanczos equation, in which the jump of the extrinsic curvature is
sourced by both the distributional energy-momentum tensor and by the jump in
the transverse derivative of the scalar. In the case of null hypersurfaces, the
distributional source is decomposed into surface density, current and pressure.
The latter however ought to vanish by virtue of the scalar junction condition.
