[Society of Exploration Geophysicists and Environment and Engineering Geophysical Society Symposium on the Application of Geophysics to Engineering and Environmental Problems 2015 - Denver, Colorado, USA (20 March to 24 March)] Symposium on the Application of Geophysics to Engineering and Environmental Problems 2015 - FORWARD GRAVITY MODELING FOR A VERTICAL PYRAMID MODEL OF FLAT TOP & BOTTOM WITH DEPTH-WISE PARABOLIC DENSITY VARIATION