Using finished log widths of 1.25" and finished center width of 2.5" for a total finished block size of 12.5", which is only slightly bigger than you wanted, you would need the following yardage for 48 blocks of four lights and four darks (colors given are per your picture for mapping clarity):
centers (red) .375 yards
fabric 1 (light blue) .625 yards
fabric 2 (light brown) .875 yards
fabric 3 (medium light blue) 1.125 yards
fabric 4 (medium light brown) 1.25 yards
fabric 5 (medium dark blue) 1.25 yards
fabric 6 (medium dark brown) 1.75 yards
fabric 7 (dark blue) 2 yards
fabric 8 (dark brown) 2.25 yards
Hope that helps. 8)