Three Simple Models
This chapter shows you how to create 2-D geologic models, create synthetic shot gathers from the models, and examine the shot gathers for quality control (QC the gathers). Chapter 5 shows you how to use the models to “acquire” (create synthetic) seismic data sets.
Models developed in this chapter have layers that are homogeneous and isotropic. Each layer has a single acoustic (P-wave) velocity.
This chapter and the next are computer-intensive in two ways: (1) the scripts are complex and (2) it will probably take your computer two hours to most of a day to generate the shot gathers. If you want to skip this complexity, skim these two chapters to familiarize yourself with the geologic models, then simply use the synthetic data set generated from Model 4 (Chapter 6) that accompanies this Primer. Seismic data generated from Model 4 are processed in Chapters 7, 8, and 9.
Our first model consists of five homogenous, isotropic layers. In the x-direction, the model goes from zero to six kilometers. In the z-direction, the model goes from zero to two kilometers. In Figure 4.1, as with all the model images in this Primer, the model is drawn 1:1 (the horizontal units have the same length as the vertical units; the model is not stretched or squeezed). It is important to see a model 1:1 to assess the complexity of source-receiver raypaths.
Let's examine the script that created Model 1 and Figure 4.1. The numbers on the left are added for discussion; they