Staad Foundation Advance Tank Ringwall Soil bearing calculation

Hi Technical Support,

Regarding the Tank foundation ring wall type design, Staad foundation is using the below equation to determine the stress under seismic conditions.

Can you please confirm the following: 

1. Whether the moments (Mrw) under seismic condition are derived at top of ring wall or at the bottom of ring wall.
2. Whether Seismic shear force multiplied by depth of ring beam to be considered in order to calculate the stress in soil at the bottom of ring wall due to additional moment on account of seismic shear force.

Thanks