Unclos Tutorial P. Uncertainty

• Create alternative sediment thicknesses, either by

  A) Multiplying the thickness by 0.9 to produce a minimum thickness and multiply by 1.1 to produce a maximum thickness.

  or

  B) Change the depth conversion to produce an alternative thickness.

How to vary sediment thickness (uncertainty in thickness)

This document uses the Atlantis training/demo project for examples. The Atlantis project may be downloaded from http://www.geocap.biz/project (NB! Login required) or under the “Downloads” link on the top of the page.
The purpose is to show how you can adjust the thickness along a profile up and down in order to measure the horizontal effect on the 1%point (1%point is used in the following for the point used in Unclos art. 76 where the thickness of sediments are equal to 1% of the distance to the FOS). FOS = Foot of slope point.
If you have a seabed (in depth) and an interpretation of the base of sediments, you may use formulas or methods in Geocap to depth convert the base of sediments. If you have used Geocap methods with stacking velocities and Dix interval velocities described in chapter 17 in the user manual, you will end up with “Sediment profiles” and “Sediment thickness points” as present in the Atlantis project.

1. Find 3. Sediment Data > Sediment profiles > ATL-LOS-00-2

   Right-click > Table View
   This table contains x, y and z for the seabed bathymetry. The Scaler (S) contains the sediment thickness. The dataset also contains shotpoint numbers.

   
   Table view

   
   

2. OK – We want to create a thinner (minimum) profile and a thicker (maximum) profile.

   Right-click on ATL-LOS-00-2 > Copy
   Right-click on the Sediment profiles folder and “Paste” twice. Name the new datasets “ATL-LOS-00-2- max” and “ATL-LOS-00-2- min”

3. Right-click on “ATL-LOS-00-2- max” > Make active

   Go to the shell (in the toolbox and type:

   mul sca 1.1

   Now, the scalar (i.e. the thickness) is increased by 10%.

4. Right-click on “ATL-LOS-00-2- max” > Assign data from …> active

5. Right-click on “ATL-LOS-00-2- max” > Generate 1% dist to FOS area. (You may be asked for projection which is Mercator, central meridian 0.) You will be asked for foot of slope point(s), and you can select the FOS’s “Northern Plateau”.

6. Repeat this for “ATL-LOS-00-2- min” but multiply by 0.91.
   The two new datasets that are created have all points on the lines that falls within the 1% thickness criterion.