The Potsdam Group lies unconformably upon the metamorphic Precambrian Grenville basement. It is comprised of the Covey Hill (Cambrian sandstones and conglomerates) and the Cairnside (lower Ordovician quartz sandstone) formations. The remainder of the section is all of Ordovician age. The Beekmantown Group includes the Theresa  (dolomitic sandstones) and the Beau\-har\-nois (dolostones) formations. The lower Chazy unit is composed of limestones, dolostones, and sandstones. The Trenton, Black River, and upper Chazy groups, are limestones. The Trenton Group is overlain by the Utica Shale and several hundred meters of interbedded shales, siltstones and sandstones of the Lorraine Group. The lower Utica Shale comprises limestone beds and is more calcareous than the upper Utica Shale. Deep saline aquifers are found in the Trenton, Beekmantown and Potsdam Groups. Figure \ref{fig:well-log} show synthetic well logs of $V_p$, $\rho$ and $phi$ representing the complete sedimentary sequence of the St.\ Lawrence Platform, compiled from a number of log data available in the studied area. $S$-wave velocity are computed using the Greenberg-Castagna relation \citep{Greenberg1992}. 
    
  