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Introduction

In order to use accurately calculate the sediment formula criterion in UNCLOS Article 76, we need a dataset containing the sediment thickness. This dataset can be based on seismic data and velocity information. This tutorial has some exercises which cover the basics for working with seismic data. In order to calculate the sediment thickness based on a seismic line we have to interpret the seabed surface and the base of sediments. This is done by using the Seismic Interpretation functionalitythickness we have to interpret the seabed surface and the base of sediments on seismic lines. In Geocap these two layers are called horizons. The distance between the seabed and basement horizons is the sediment thickness. 

When collecting seismic data a seismic wave travels from its source to a given reflector and returns to a receiver at the sea surface. The elapsed time is called two way travel time. In most cases this will be the depth unit (in milliseconds) of your seismic. Since the seismic is in time (milliseconds) and we need to calculate the sediment thickness in meters we need to do a conversion. This is called a depth conversion. The formula itself is simple: Distance = Speed * Time. The difficult part of the formula is finding the correct speed/velocity model, since the velocity changes through the different layers in the subsurface. In Geocap the interpretation is normally done in the time domain. This gives us the flexibility to change the velocity model and just update the sediment thickness calculation accordingly. We will have a look at different velocity models in the next section.

In this section we will visualize seismic data, import seismic and interpret seismic.

Exercises

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Display Seismic Lines and Interpretation

 

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Display a seismic line

  1. In the folder 3. Sediment Data / Seismic Data / ATL-99 right click the seismic line ATL-99-1 and click Seismic Display
  2. Right click the seismic line ATL-99-1 again and click Zoom to Data.
  3. Investigate the seismic line. Can you identify the Seabed and Sediment Base?
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Display the interpretation

  1. In the folder 3. Sediment Data / Seismic Interpretations right click the Ihorizon Seabed and click IHorizon Display.
  2. In the folder 3. Sediment Data / Seismic Interpretations right click the Ihorizon Sediment Base and click IHorizon Display.
  3. Investigate the interpreted horizons.

Interpret Seismic Lines

 

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Interpret a seismic line

In this exercise we are going to interpret the seabed and basement of the seismic line. First we need to display the seismic line we want to interpret.

  1. Right click the seismic line and select Seismic display.
  2. Right click the seismic line and select Zoom to Data

Next we open the Seismic Interpretation (Xi) dialog:

  • Locate Seismic Interpretation under Tools in the main menu.

First we need to select where our interpretations should be stored:

  1. Click Browse button to select the interpretation folder
  2. Select the seismic interpretation folder 3.Sediment Data / Seismic Interpretations

Next we need to specify the horizons we want to interpret:

  1. Click the button in order to create a new IHorizon. The IHorizon dialog will appear
  2. Type in Seafloor as the name of the new horizon, and click OK
  3. Click the Graphical Settings tab
  4. Set Line Width to 5
  5. Check the User Defined Color and pick a color for the horizon.
  6. Click OK
  7. Click the same new button again, and call the next horizon Sediment Base.

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