Fortran 77 package NET version 3.30

Ludek Klimes

Department of Geophysics, Charles University Prague, Ke Karlovu 3, 121 16 Praha 2, Czech Republic

E-mail: klimes@seis.karlov.mff.cuni.cz

Michal Kvasnicka

Formerly Department of Geophysics, Charles University Prague, Ke Karlovu 3, 121 16 Praha 2, Czech Republic

This is just a general overview, the detailed description of input data, procedures, and other important topics is included within the individual FORTRAN77 source code files.

General description of network ray tracing package NET

Purpose:
Network ray tracing is designed to calculate first-arrival travel times and the corresponding rays. For your application, please, do not confuse the first-arrival travel times with the ray-theory body-wave travel times. The first-arrival travel times from the given source of any shape are calculated at all grid points of a given rectangular grid of points. Together with the first-arrival travel times, also the maximum travel-time errors may be automatically estimated.

Model specification:
For network ray tracing, the seismic model is specified in terms of grid velocities at a rectangular grid. The density of the grid should correspond to the accuracy required and to the computer memory available. In a layered or blocky medium, also the indices of geological blocks at gridpoints are recommended to be specified in addition to the velocities, in order to improve accuracy considerably.
The model specification subroutine package MODEL is recommended to describe the models and to generate the grid values, unless the user prefers his own model specification system.

Programming language, error messages, screen output, etc.

Unified memory management.
Array dimensions MRAM, MFS, MSRC and MREC and MREFL in net.inc should be adjusted according to a particular computer memory and particular application. In the basic version delivered, arrays in 'net.for' are roughly dimensioned for a computer with 16MB of RAM (see ram.inc).

History files.

Alphabetical list of input parameters of all programs.

Compiling and linking programs of package NET

• Copy all files (or at least files ram.inc, error.for, sep.for, sep.inc, length.for, forms.for, eigen.for and f.pl) of package FORMS into your working directory. All the files including subdirectories may also be extracted using pkunzip -d forms.zip or tar -xvf forms.tar
• Edit include file ram.inc and Perl script f.pl according to the description in package FORMS.
• It is also recommended to compile and link all programs of package FORMS according to the description in forms.htm.
• Copy all files (or at least all *.for and *.inc files, net.fs2 and net.fs3) of package NET into your working directory. All the files including subdirectories may also be extracted using pkunzip -d net.zip or tar -xvf net.tar
• Now you may compile and link program net.for by entering command
  perl f.pl net
  All necessary subroutine files and include files are included by the Fortran 90 INCLUDE command. Fortran 77 subroutine files are included at the end of file 'net.for'.
  If you have no Perl interpreter, it should be available at www.perl.org

• You may also compile and link program netind.for by entering command
  perl f.pl netind
  All necessary subroutine files and include files are included by the Fortran 90 INCLUDE command. Fortran 77 subroutine files are included at the end of file netind.for.

Running programs of package NET

It is recommended to run the programs from the history files. The history files may contain the information how to execute the programs, the data read from standard input (Fortran) or from the command line (Perl) and the data read from the SEP parameter files.

Data from standard input *:
Main input data of each program are read from the standard input, and mostly consist of a single line containing filenames and at most few numerical parameters. For the description of input data of individual programs refer to the list of files below.

Application of the network shortest path ray tracing program NET in the models described in terms of model specification subroutines of package MODEL (ver. 5.40 or later is recommended):

• Install package NET into your working directory.
• Compile and link program grid.for of package MODEL. See package MODEL for details.
• Prepare the input data for package MODEL, describing the seismic model of the medium.
  Example: In the demo data of subdirectory
  len of package DATA, the model data file 'len-mod.dat' is assumed.

  Program 'grid.for' of the package MODEL generates the velocities and indices of geological blocks in the given rectangular grid of points. Example: In the demo data of subdirectory

  len, the input model file is 'len-mod.dat' and the grid is described within history file 'len-net.h'.

  Program 'net.for' of this package performs the network shortest path calculation of the first-arrival travel times in the generated discretized (raster) representation of the model. Example: In the demo data of subdirectory

  len, the input data file for 'net.for' is called 'len-net.dat'. Other input files are 'lenn-src.dat', 'lenn-rec.dat' and the output files of program 'grid.for'. The generated output files 'tt.out' and 'err.out' contain first-arrival travel times and their estimated maximum errors.

Two-point network ray tracing within Fresnel volumes

List of error messages

• Package FORMS
• Package MODEL
• Package CRT
• Package NET
• Package FD
• Package DATA

File list of package NET

(A) Documentation:

net.htm

This file. General documentation to NET (main HTML file containing basic description and links the files of this package).

netver.htm

List of released versions.

neterr.htm

List of error messages with the links to their descriptions.

(B) Network ray tracing program NET:

FORTRAN77 codes listed herein, together with auxiliary data files 'net.fs2' and 'net.fs3' containing template forward stars, form the complete and functional network ray tracing program 'NET'. Usually, no other files of this package are required to perform network ray tracing.

net.for

Fortran77 source code of the network ray tracing program NET. The source code also contains the description of the input and output data, and the brief comments on the program.

Description of input data (regular network ray tracing).

net.inc

Include file with most COMMON blocks for 'net.for'.

netnode.inc

Include file with a COMMON block for 'net.for'.

ttt.for

Part of the FORTRAN77 source code of the NET program responsible for the 2-D "second-order" grid travel-time tracing according to Klimes (1996).

ttt.inc

Include file with a COMMON block for 'ttt.for'.

net.fs2

Optimized circular 2-D forward stars.

net.fs3

Optimized spherical 3-D forward stars.

(C) Programs designed to generate forward stars for the NET program:

These programs are not required when using the NET program, because the forward stars for the net program are already generated and stored in 'net.fs2' and 'net.fs3'. They may be used if (1) larger forward stars than stored in the current versions of 'net.fs2' or 'net.fs3' are required (unlikely for most applications on most nowadays computers), or (2) if other than optimized forward stars are required for the purposes of comparing the performances of different algorithms or programs.

fs (subdirectory)

fs-opt2.for

Program generating 2-D optimized circular forward stars according to Section 4.3 of the paper by Klimes and Kvasnicka (1994).

fs-opt3.for

Program generating 3-D optimized spherical forward stars according to Section 4.3 of the paper by Klimes and Kvasnicka (1994).

fs-mcir2.for

Program generating 2-D circular Moser-Saito forward stars, containing all nodes within a circle except for the end nodes of the edges that would be parallel with shorter edges in a homogeneous medium.

fs-msph3.for

Program generating 3-D spherical Moser-Saito forward stars, containing all nodes within a sphere except for the end nodes of the edges that would be parallel with shorter edges in a homogeneous medium.

fs-msqr2.for

Program generating 2-D square Moser-Saito forward stars, containing all nodes within a square except for the end nodes of the edges that would be parallel with shorter edges in a homogeneous medium. Such forward stars have been used, e.g., by T-J.Moser or H.Saito.

fs-mcub3.for

Program generating 3-D cubic Moser-Saito forward stars, containing all nodes within a cube except for the end nodes of the edges that would be parallel with shorter edges in a homogeneous medium. Such forward stars have been used, e.g., by T-J.Moser or H.Saito.

(D) Demo data files for the network ray tracing program itself:

net.h

SEP parameter file describing the grid dimensions.

net.dat

Sample input data file for the 'net.for' program, to perform 2-D network ray tracing in a simple model without interfaces. The velocities are gridded in 'vel.dat'. The data correspond to the example described in Subsection 6.1 of Klimes and Kvasnicka (1994).

src.dat

Coordinates of a point source.

rec.dat

Receiver coordinates.

vel.dat

Grid velocities in a 1-D constant velocity gradient model by P.Podvin and I.Lecomte (1991), Geophys.J.int., 105, 271-284.

(E) Indexing of Fresnel volumes (accuracy enhancement of two-point rays by means of network ray tracing within Fresnel volumes):

netfv.htm

Notes on two-point network ray tracing within Fresnel volumes.

netind.for

Program NETIND to generate the index file mapping gridpoints onto the network nodes situated within the Fresnel volume corresponding to the maximum two-point travel-time error. It also may adjust the grid density in the input data for the 'net.for' program in order to achieve the best possible accuracy of network ray tracing.

Description of input data (network ray tracing inside Fresnel volumes).

Data files related to particular models

Acknowledgements

• Faculty of Mathematics and Physics, Charles University, Prague.
• Energy, Mines and Resources Canada, Ottawa, Ontario.
• Institute of Geotechnics, Czechoslovak Academy of Sciences, Prague.
• Geophysical Institute, Academy of Sciences of the Czech Republic.
• Grant Agency of the Academy of Sciences of the Czech Republic under Contracts 31223 and 346110.
• Grant Agency of the Charles University under Contracts 8/94 and 38/94.
• Grant Agency of the Czech Republic under Contract 205/95/1465.
• European Commission within the framework of the JOULE II Project "Integrated Structural Imaging of Seismic Data".
• Members of consortium "Seismic Waves in Complex 3-D Structures".

References

• Klimes L. and Kvasnicka M. (1994): 3-D network ray tracing. Geophys.J.int., 116, 726-738.
• Klimes L. (1996): Grid travel-time tracing: second-order method for the first arrivals in smooth media. PAGEOPH, 148, 539-563.