RAYPP

Introduction

The aim of the program is to calculate the travel-times of P-P reflections generated by flat earth model. The model consists of layers that have different velocities and thicknesses. The program produces common shot gather. The simple description of the model can be seen in the following figure :

The program is a FORTRAN object file. I have tested the program on my Pentium II 233 machine and it has been proved to work fast. To compute the travel-times of an earth model consisting of 26 layers with 401 receivers (more than 10,000 rays), for example, it takes 4.2 seconds approximately.

The program can be used by :

• A lecturer who wants to give some exercises on velocity analysis using Dix equation to the students. Using this program, he/she can easily produces travel-times of his/her own model and give them to the students who should determine the model from the given travel-times.
• Students that are doing research on algorithms, seismic processing techniques, etc.
• Industry workers who want to do quick calculations on a simple model as described above in field or in office where a commercial software for this purpose is not available.

Procedure

To run the program RAYPP you have to go through the steps below :

• Install Scilab on your computer.
• Download the program, and keep it in a directory of your choice. Let us assume that you put the file in directory /home/yourname/seislib.
  The size of the program is approximately 4.3 Kb.
• Write an ASCII file that contains commands to create the earth model, do ray tracing, and plot the travel-time curve. You can then modify the file to create new earth models to produce new travel-time curves. As an example, call the text editor, type the following lines, and save the lines in a file named exam1.sci in the directory you like.

  // Linking
  npp = link('raypp.o','raypp','f');
  
  // Model
  vp = [1000 2000 2500]';
  d  = [100 200 250]';
  x  = [0:50:500]';
  
  // Ray tracing
  nl = mini([length(vp) length(d)]);
  ns = length(x);
  tm = fort("raypp",vp,1,"r",d,2,"r",nl,3,"i",x,4,"r",ns,5,"i",...
       "out",[nl,ns],6,"r")
  
  // Plotting
  st = ones(1,nl);
  xbasc();
  plot2d1("onn",x,tm',st,"021");
  xtitle('P-P reflections','Offset (meter)','Waktu (detik)');
  xend();
  

• Go to directory that contains file exam1.sci and call Scilab by typing scilab in xterm.
• Type the following command in the Scilab command window :

  exec('exam1.sci')
  

• You'll be given the travel-times (matrice tm) and the figure below :

  

Run a new model

You can run a new model simply by replacing the lines in the modeling section in file exam1.sci. For example, you can write the lines below to represent a new model :

// Model
vp = [1000 1500 2000 2200 2500 2000 2500]';
d  = [100 100 50 100 100 50 100]';
x  = [0:50:500]';

To produce a split spread record, just type the next lines in the modeling section.

// Model
vp = [1000 2000 2200 2400 2500]';
d  = [50 50 50 50 100]';
x  = [-500:50:500]';