Approximate depth scales through the overburden are superimposed on the seismic sections.For the SS sections, two-way traveltimes were converted to depths using the borehole S-wave average velocity profile (Fig. 2), extrapolated below 18.5 m with the aid of the S-wave interval velocity depth section. For the P-wave section, we used a velocity model based on seismic refraction analyses presented in Section 4.3.1 below.