UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

Computer program modifications of Open-File Report 82-1065
A comprehensive system for interpreting seismic-refraction and
arrival-time data using interactive computer methods

by
Hans D. Ackermann

Leroy W. Pankratz
Danny A. Dansereau

Open-File Report 83-604

This report is preliminary and has not been reviewed for conformity with U.S.
Geological Survey editorial standards and stratigraphic nonmenclature. Any use
of trade names is for descriptive purposes only and does not imply endorsement
by the U.S. Geological Survey.

1 uses

1983


ABSTRACT

The computer programs published in Open-File Report 82-1065, A comprehensive
system for interpreting seismic-refraction arrival-time data using interactive
computer methods (Ackermann, Pankratz, and Dansereau, 1982), have been
modified to run on a mini-computer. The new version uses approximately 1/10
of the memory of the initial version, is more efficient and gives the same
results.

MODIFIED PROGRAMS

The computer programs of the initial report (Ackermann, Pankratz, and
Dansereau, 1982) were written for a large virtual-memory computer. They have
been modified to run on a mini computer (a Digital Equipment Corporation (DEC)
PDP 11-34A) in the DEC fortran IV-plus language.

The algorithms for the new set of programs are significantly different from
the initial version. They run much more efficiently and use roughly an order
of magnitude less memory. All of the test problems of the initial report have
been rerun and result in essentially identical answers. A tape copy of the
new version can be obtained upon request from the authors by sending a blank
tape. Their address is U.S. Geological Survey, Denver Federal Center MS 964,
Denver CO 80225.

Program execution is somewhat different from the old version and is explained
in a file named DOCUMENT.FTN. All of the essential modules (i.e., mainline

programs and subprograms) are documented in this file. The programs furnished
on tape are in the same order as listed in the file DOCUMENT.FTN, which is the

first file on tape.

The normal sequence for processing refraction data using these programs is
given below. It is assumed that the seismic lines are straight.

1. Determine a name FN for the line (8 characters or less).

2. Determine a reference point (distance and altitude) for the line. All
distances and altitudes will be with respect to this point.

3. Determine a reference number (k number) for each seismogram.

4, Digitize each seismogram (i.e., determine value of first-arrival time
for each trace).

5. Input digitized data into the disk file named FN.OTX, using incremental
values of distance (see documentation of program PERP). This may be
done using mainline program TXIN. However, it is usually more efficient
if digitizing is done on a digitizer and the data automatically input
into this file. (Programs for doing this are not included.)

6. Run program PERP for the data in file FN.OTX to change the incremental
distance values into actual distance values with respect to the
reference point, and to correct for perpendicular offsets of the
shotpoints with respect to the seismic line. The corrected values are
automatically re-entered into the file FN.OTX.

7. Prepare a time vs. distance (t-x) plot of all the data in file FN.OTX.
This is best done using an automatic plotting program. Automatic
plotting programs are not included in this package.


8. Approximate the t-x plots with straight line segments, using the
principals explained in the section titled manipulating arrival-time
curves (Ackermann, Pankratz, and Dansereau, 1982).

9. Digitize the end points of these straight line segments and input their
values into disk files FN.TL, FN.T2, . . ., FNeT15, (for example, the
data for layer one, the direct ray, are input into FN.Tl, for layer two
into FN.T2, and so on. See documentation of mainline programs TXIN and
TXIO in the file DOCUMENT.FTN). Input may be done using program TXIN.
However, it may be more efficient if digitizing is done on a digitizer
and the data automatically input into these files.

10. Input surface distances, altitudes, and velocities (i.e., layer one)
into disk file FN.MOD, using program MODLIN.

11. Run mainline program RUNCRIT or RECIP to obtain results for layer two.
Answers are output into disk files FN.Al, FN.A2, . . », FN.sAL5 depending
on the layer being computed.

12. Input distances, altitudes and velocities for layer two into disk file
FN.MOD using program MODLIN.

13. Run mainline program RAYTRACE, if desired to compare the computed
results against the t-x data.

lla., 12a., 13a. Repeat steps 11, 12, and 13 for layer 3.

1lb., 12b., 13b. Repeat steps 11, 12, and 13 for layer etc. until all
layers are determined.

REFERENCES CITED

Ackermann, H. D., Pankratz, L. W., and Dansereau, D. A., 1982, A comprehensive
system for interpreting seismic refraction arrival-time data using
interactive computer methods: U.S. Geological Survey Open-File Report
82-1065. 265 p.