Starting from these distributions, an SGS co-simulation algorithm is used to generate the reference model of $V_p$, $V_s$, $\rho$ and $\phi$ that are shown in Figure \ref{fig:ref-model}. The model size is 1000m x 1500m with a cell size of 1m x 1m. The simulation algorithm is formulated in order to respect the natural transition between each group layer. 
    
  