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Introduction

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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.

Illustration of a marine seismic survey using a towed streamer

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

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