Focal depth of earthquakes along a subduction zone

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"

I was reffering to "Hypocenters" of earthquakes. Cascadia has a fairly uniform subduction plane that you can measure from these isohypos.

Thank you Farmerman!
I just took this course and this is 3rd chapter's exam.
I didnt have any geology background.