Ok thanks to @temporal here is the diagram. It's a cross-section of a subduction zone, i.e. it's in a vertical plane (not map view).

               0
              0       depth (km)
  o->____====Δ== <-c  -0
         \            
  (fast)  * <-e       -50 
           \          
        d-> \         -100
  (slow)     \          
                      

The 'o' is the oceanic plate (thin line), the 'c' is the continental plate (double lines), 'd' points to the downgoing slab, 'e' points to where the earthquake occurred. O and C are the surface of the earth. 'fast' and 'slow' indicate that the slab is sinking/subducting fast at shallow depths and slower at deep depths. The Δ is an arc volcano that is smoking (like Mt. St. Helens or Fuji) that are always present above subduction zones because at ~100 km depths, the subducting slab loses some water which rises and then melts the upper mantle and lower crust of the continental crust above (these rocks are very hot and adding water lowers their melting temperature without changing the actual temperature much).