Translations:Wavefront for velocity linear with depth/4/en

We now can drop the subscript from $t_{D}$. As observed Slotnick (1959), the wavefronts are circles whose centers are along the y-axis at the points $\left({\rm {0,\ }}\left(v_{0}/a\right)\left({\rm {\ cosh\ \ }}at-{\rm {\ 1}}\right)\right)$ and whose radii are $\left(v_{0}/a\right){\rm {\ sinh\ }}$ at where t is the traveltime corresponding to each wavefront.