1. get a topo map sheet from USGS sheets and a scale for the map and locate and draw the roughly parallel lines joining the shallowest isohypos of the same depth zones. Then draw a line perpendicular to two lines and compute the approximate drop per mile (or km). (Make sure you have the correct data planes for these depths
Remember that 1 degree is 92 ft per mile. Do the math, its really easy, my way
2as far as direction, cmon, are you a serious geology student or just taking "rocks for Jocks"