ax1 = self.fig2.add_subplot(1,3,1)
    ax1.clear()
    ax1.set_xlabel('Density')
    ax1.set_ylabel('Vs')

    ax2 = ax1.twinx()
    ax2.clear()
    ax2.set_ylabel('Vp')

    ax1.plot(D1,Vs1, marker='o')
    ax2.plot(D1,Vp1, marker='o')

    self.fig2.tight_layout()
    self.canvas2.draw()