Fig. 3

Schematic of the slab convergence direction. The surface \(\Gamma _\text {slab}\) is colored by depth for visual aid. The plane defined by \(\hat{\varvec{r}} \times \hat{\varvec{d}}_\text {conv}\) and its intersection with \(\Gamma _\text {slab}\) are highlighted. The slab surface normal vector \(\hat{\varvec{n}}_\text {slab}\), the slab convergence direction \(\hat{\varvec{\tau }}_\text {conv}\) and the perpendicular vector \(\hat{\varvec{\tau }}^\bot _\text {conv}\) are drawn as arrows on the surface