FOUR REGIONAL SEISMIC LINES: 

NATIONAL PETROLEUM RESERVE— 

ALASKA (SUPPLEMENT TO U. S. Geological 

Survey Open-File Report 00-286) 

by Miller, J.J.1

, Agena, W.F. 1, Lee, M.W. 1, Zihlman, F.N. 1, Grow, J.A. 1, Taylor, D.J. 1, Killgore, 

Michele1

, and Oliver, H.L. 1 

Open-File Report 01-337 

2001 

This report is preliminary and has not been reviewed for conformity with the U.S. 

Geological Survey editorial standards or with the North American Stratigraphic Code. 

Any use of trade names is for descriptive purposes only and does not imply endorsement 

by the U.S. Government. 

U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

1

U.S. Geological Survey, MS 939, Box 25046, Denver Federal Center, Denver, CO 

80225-0046 
Four Regional Seismic Lines: National Petroleum Reserve—Alaska (Supplement To U. S. Geological Survey 

open-File Report 00-286) 

ABSTRACT 

This Internet site contains digital seismic data and associated support data for four regional seismic lines (736 

line-miles) recorded in the National Petroleum Reserve – Alaska (NPRA). These lines were created as a 

supplement to the data set contained on USGS-Open File Report 00-286 (Miller et al, 2000) which is a CD-ROM 

publication that contains stacked, migrated, 2-dimensional seismic reflection data and associated support 

information for 22 regional seismic lines (3,470 line-miles) recorded in the NPRA from 1974 through 1981. These 

22 regional lines, which form a grid covering the entire NPRA, were created by combining various individual lines 

recorded in different years using different recording parameters. The data were reprocessed by the USGS using 

modern, post-stack processing techniques, to create a data set suitable for interpretation on interactive seismic 

computer workstations. Reprocessing was done in support of ongoing petroleum resource studies by the USGS 

Energy Program. The grid of lines has a nominal spacing of 20 x 20 miles. However there are four intervals 

where the spacing between lines was much greater than 20 miles. To fill these grid spacing gaps, four additional 

regional lines (736 line-miles) were created using the same techniques as those used to create the lines on OFR 

00-286. These lines and associated support data are contained on this internet site in the following files: 1) Four 

files containing the digital seismic data in standard, SEG-Y format; 2) One file containing navigation data for these 

4 lines and for the original 22 lines contained on OFR 00-286, in standard SEG-P1 format; 3) Four small scale 

graphic images of the four seismic lines in Adobe Acrobat

®

 PDF format; 4) a graphic image of the location map, 

generated from the navigation file, 5) an ASCII text file with cross-reference information for relating the sequential 

trace numbers on each regional line to the line number and shotpoint number of the original component lines; and 

6) an explanation of the processing used to create the final seismic sections (this document). 

The SEG-Y format seismic files and SEG-P1 format navigation file contain all the information necessary for 

loading the data onto a seismic interpretation workstation. 

Miller, et al 1 
INTRODUCTION 

The USGS reprocessed twenty-six 2-D regional seismic transects across the National Petroleum Reserve – 

Alaska (NPRA) using current seismic data processing techniques. Twenty-two (22) of these lines are contained 

on the CD-ROM publication USGS Open File Report 00-286 (Miller, et al, 2000). To order the CD-ROM, contact 

the USGS Earth Science Information Center: 1-888-ASK-USGS (1-888-275-8747) or write to: Box 25286, Building 

810, Denver Federal Center, Denver, CO, 80225-0286. That CD-ROM includes the 20 original Regional 

Compressed Sections (RCS) (Ikelman, 1986) and 2 additional lines, totaling 3,470 line-miles in a nominal 20 x 20-

mile grid that cover the whole of NPRA. However, the nominal 20-mile spacing was greatly exceeded between 

lines r-4 and r-5, r-6 and r-7, r-7 and r-8, and r-11 and r-13 (Figure 1). To fill these grid spacing gaps, four 

additional regional lines (736 line-miles) were created using the same methodology and processing sequence as 

that used for the first 22 lines, and these data are presented on this Internet site. 

Although the complete NPRA seismic data set totals nearly 15,000 miles (Gryc, 1985, page C27) and is the 

largest public-domain onshore seismic data base in the United States, the 26 regional seismic lines presented 

here and on Open File Report 00-286 provide a useful summary of the NPRA data for understanding the overall 

geologic framework of the Brooks Range foreland basin and for assisting in research studies concerning the oil 

and gas potential of the region. 

The remainder of this section and all of the next two sections are excerpted directly from CD-ROM publication 

OFR 00-286 and describe the methodology for creating the regional lines the problems encountered and our 

approach to solving those problems. This information also applies to the 4 additional lines presented on this 

internet site. 

The original RCS lines were created by combining selected seismic lines into long regional lines that cover the 

whole of NPRA in a nominal 20 x 20-mile grid. Twelve (12) lines are oriented generally north-south and ten (10) 

lines are oriented generally east-west (Figure 1, Table 1). The seismic lines which composed each of the original 

RCS lines were the stacked, unmigrated, record sections that were processed by Geophysical Service, 

Incorporated (GSI) immediately after the data were collected (1974 through 1981.) 

Although the processing of the original RCS lines was done well, we encountered the following limitations when 

attempting to interpret the data: 

Miller, et al 2 
1. The data were not migrated. The probable reason for not migrating the data is that at the time of the original 

processing, migration was a time-consuming and expensive process. 

2. Except for a few lines, the magnetic tapes containing the original RCS lines could not be located and 

therefore we were unable to perform the migration process or to load these data into a modern seismic 

interpretation workstation for on-screen interpretation. We had digital versions of most of the stacked, 

unmigrated line segments which made up the RCS lines, but these had been processed by widely varying 

means and needed additional processing before being combined (discussed below.) 

3. The individual seismic lines which made up a single RCS line were recorded in different years using different 

recording parameters, the most significant parameter being different distances between geophones on the 

surface (“group intervals”.) These different group intervals meant that the horizontal resolution along each 

RCS line could change at the line segment boundaries. Within a single RCS line, the distance between 

seismic traces could be 165 ft. for one line segment, 110 ft. for another segment and 55 ft. for a third 

segment. To compensate for this difference in trace spacing, the original line segments were displayed on 

mylar film at different horizontal trace spacing scales and then physically spliced together by hand. The result 

was an RCS line having a constant horizontal scale which was sufficient for visual inspection of the data. 

However, in order to digitally process a seismic line through migration, the actual distance between traces 

must be constant. 

4. The data were processed using a “floating” datum that was a smoothed approximation of the surface 

elevations. The datum values used at line intersections were not always the same and therefore, the 

reflections did not tie in two-way travel time. 

REPROCESSING 

Because of the limitations described in the previous section, and in order to properly prepare the data set for 

migration and for interpretation on a computer workstation, we performed the processing steps described below. 

Two of the processing algorithms used were developed in-house and are noted below. All other processing was 

performed using the industry-standard ProMAX® seismic data processing system developed by Landmark 

Graphics®

. 

1. We reconstructed the RCS lines from the individual stacked, unmigrated seismic lines for which we had digital 

data (table 2). This “post stack” processing included amplitude scaling, frequency filtering, and noise burst 

editing, in order to create versions of the data that were relatively consistent in character from line to line. 

Miller, et al 3 
2. For those line segments for which we had no digital stacked data (table 2), we started with the raw field data 

and completely reprocessed each line through the steps described in #1, immediately above. The processing 

performed prior to stacking included editing of noisy data, amplitude scaling, spiking deconvolution, datum 

statics, Normal Moveout (NMO) corrections using velocities determined by interactive velocity analysis, and 

residual static corrections calculated by a surface consistent residual statics routine. 

3. For all the lines, we adjusted the datum to a common horizontal sea level datum. 

4. We converted the distance between traces to a constant of 110 ft., either by interpolation or decimation. A 

constant trace-to-trace interval is necessary in order to perform migration using the algorithms commonly 

available in commercial seismic data processing systems. 

5. We migrated the data using smoothed stacking velocities adjusted to the sea level datum. For the line 

segments that were processed using post-stack methods only, we used the stacking velocities that were 

printed at the top of each segment’s mylar display. For those line-segments that were processed beginning 

with the field tapes, we used the stacking velocities that we determined (refer to step #2, above.) 

6. After migration we applied post stack predictive deconvolution (using the 2nd zero crossing of the 

autocorrelation function as the predictive distance) in order to increase the temporal resolution of the data. 

The software used for this process was developed in-house. 

7. After predictive deconvolution, we applied a signature deconvolution process (sometimes referred to as 

wavelet deconvolution) to compensate for changes in the source waveform between lines and to further 

increase the temporal resolution of the data. The software used was developed in-house and was a version 

of Gray’s (1979) Variable Norm deconvolution method, adapted for post-stack data. 

This processing produced a data set that is well-suited for analysis on a seismic interpretation workstation. 

Reflections on the seismic lines tie in both travel-time and waveform at all line intersections and the distance 

between individual traces on all seismic lines is a constant 110 ft. 

Miller, et al 4 
Line Line-Miles Orientation 

R-1 96 N-S 

R1-ALT 137 N-S 

R-2 116 N-S 

R-3 129 N-S 

R-4 145 N-S 

R-5 190 N-S 

R-6 215 N-S 

R-7 149 N-S 

R-8 135 N-S 

R-9 125 N-S 

R-10 84 N-S 

R-11 109 E-W 

R-12 159 E-W 

R-13 203 E-W 

R-13ALT 26 E-W 

R-14 259 E-W 

R-15 292 E-W 

R-16 238 E-W 

R-17 180 E-W 

R-18 163 E-W 

R-19 88 N-S 

R-20 232 E-W 

R-21 166 N-S 

R-22 210 N-S 

R-23 140 N-S 

R-24 220 E-W 

Total: 4206 

Table 1. List of seismic lines contained in the data set with total mileage and geographic orientation of each line.. 

The four lines contained on this internet site are R-21 through R-24. Click on any of these four line names to 

display a graphic image in PDF-format of the stacked, migrated record sections. 

Miller, et al 5
R line Original 

Line 

R-21 65-76 

R-21 60-75 

R-21 66-75 

R-21 88-77 

R-22 45X-78 

R-22 45-77 * 

R-22 45-75 

R-22 678-79 

R-22 41-74 * 

R-22 42-74 * 

R-22 DS3-76 * 

R-22 672L-79 

R-22 628N-79 

R-23 U3-78 

R-23 70-75 

R-23 5X-75 

R-23 22-81 

R-23 35-74 

R-23 35-75 

R-23 684-79 

R-24 55-76 

R-24 55-75 

R-24 B22-78 

R-24 B19-78 

R-24 667-79 

R-24 77-75 

R-24 3-75 

R-24 32-75 

R-24 74-75 

R-24 75-75 

R-24 17-74 * 

R-24 18-74 

Table 2: List of the component lines that make up the 4 regional lines presented on this internet site. Asterisks (*) 

indicate those lines which were completely reprocessed from the field tapes. All other line segments were 

reprocessed from the stacked, unmigrated data previously processed by industry. 

Miller, et al 6 
NAVIGATION CONVENTION 

Interactive seismic interpretation software requires a unique index number to relate each seismic trace in a line to 

a surface position on a map. Further, migration algorithms assume that for each seismic line, the distance 

between consecutive traces is at some regular, constant interval and as described above, we reprocessed the 

data to meet this requirement, making the distance between any two seismic traces a constant of 110 ft. For 

many 2-D seismic surveys, the unique index number used is the line’s shotpoint number, but because the 

regional lines were created by combining different line segments, the original shotpoint numbers for any given 

regional line are not necessarily unique. For example, the first line segment of a regional line might have 

shotpoint numbers 10 through 50 and another line segment of the same regional line might have shotpoints 30 

though 80. In order to have a unique number for each trace in a regional line, we renumbered the traces starting 

at 1 for the first trace in the line and then increased the number by one, sequentially through the last trace in the 

line. We stored this unique number in the header of each seismic trace in the location (“trace-header word”) 

reserved for the Common Depth Point (CDP) number, and used this unique number as the index number for the 

navigation data. 

For each line segment, Latitude and Longitude coordinates for the surface position of each shotpoint were 

available. For each regional line, we combined the navigation data for the various line segments together and 

changed the shotpoint numbers to the associated, unique, CDP (index) number. The file NPRANAV.SEG 

contains location coordinates for all of the regional lines contained on both this Internet site and on OFR 00-286’s 

CD-ROM. The location map (figure 1) was generated directly from this file. Users loading these data into their 

own interpretation workstation should consider the unique CDP number to be the “shotpoint” number. 

There is no consistent formula to relate the original shotpoint number of each line segment to the CDP number of 

the regional line. Depending on the line and the interpolation needed, there could be 16, 12, 8, 4, or 2 CDP’s 

(traces) between shotpoints. However, file CDP_SP.TXT contains a table giving a cross-referenced list relating 

regional line number, to original line number, to original shotpoint number, and to CDP number for each regional 

line. 

DESCRIPTION OF THE DATA FILES CONTAINED ON THIS INTERNET SITE 

The following information is provided on this Internet site 

Miller, et al 7 
Seismic Data Files (Files R_21.SGY to R_24.SGY): These are the processed seismic data in SEG-Y format. 

The SEG-Y seismic data format standard was developed by the Society of Exploration Geophysicists (SEG) in 

1975 and has been in common use throughout the geophysical industry since that time. A complete description 

of the SEG-Y format is given in Barry and others (1975). All of the seismic data files in this publication are discimages of the SEG-Y data format described therein. That document assumes 9-track, magnetic tape recording 

media; naturally, the inter-record and inter-block gaps described for magnetic tape media will not exist on the 

disc-image. The disc-image is therefore a continuous file composed of a 3200-byte EBCDIC header, a 400-byte 

binary header, and data traces, each composed of a 240-byte trace-header followed by a fixed number of seismic 

data samples. The data samples are type 2: fixed-point integer (2 bytes (16-bits) per sample). The SEG-Y format 

provides a large number of trace header-words for the purpose of recording information related to each trace. 

Because the data are stacked, processed data, only the following two header words have valid information: 

1) CDP number: bytes 21-24, the standard trace header word reserved for the Common Depth Point (CDP) 

number. This CDP number begins at 1 for the first trace of each line and increases by 1 sequentially to the end of 

each line. These are the reference numbers used in the navigation file to define the location of each trace. 

2) Shotpoint Number: bytes 17-20, the standard trace header word reserved for the energy source point number. 

These shotpoint numbers are those from the original seismic lines which make up each regional line. As 

mentioned previously, file CDP_SP.TXT contains a table giving a cross-referenced list relating regional line 

number, to original line number, to original shotpoint number, and to CDP number for each regional line. 

Navigation File (NPRANAV.SEG): This is the location data in SEG-P1 format, the standard format for latitude, 

longitude, x, and y coordinates, and surface elevation, as defined by the Society of Exploration Geophysicists. 

Navigation information is given for the first and last trace of each line segment and traces within each line at an 

interval of 10 shotpoints. 

Digital Map Image (MAP.PDF): This file is a digital image in Adobe Acrobat®

 PDF format, containing a map view 

of the trace locations, generated directly from file NPRANAV.SEG. The label for each line number presented on 

this internet site (R-21 through R-24) is also a hyperlink that allows the user to view the associated digital image 

of the seismic line (see below). 

Miller, et al 8 
Cross Reference File (CDP_SP.TXT): A table giving a cross-referenced list relating regional line number, to 

original line number, to original shotpoint number, and to CDP number for each regional line. A printout of the first 

few lines in this file is given below: 

Line No. Original Original CDP 

Line No. Shotpoint No. 

R-21 65-76 290 2 

R-21 65-76 280 122 

R-21 65-76 270 242 

R-21 65-76 260 362 

R-21 65-76 250 482 

R-21 65-76 240 602 

R-21 65-76 230 722 

R-21 65-76 220 842 

R-21 65-76 210 962 

Digital Images of Seismic Displays (Files R21MT.PDF through R24MT.PDF): Small scale displays of each 

line, generated from a GEOGRAPHIX/SEISVISION®

 work station at a horizontal scale of 1:250,000 for distance 

and 1.5 inches/second for two-way travel time (“PRN” files). Although the vertical exaggeration of these displays 

is approximately 6:1 (assuming an average velocity of 10,000 ft/sec), the longest line (R-15) is about 78 inches 

long. The PRN files from SEISVISION were converted to compressed Adobe Acrobat®

 PDF files using the 

"Distiller" function in Adobe Illustrator®. The PDF files can be opened, viewed, and printed using the free 

downloadable version of Adobe Acrobat®

 Reader 4.0, which can be obtained from http://www.adobe.com. 

Notes on display annotation: There are two sets of numbers at the top of each display, one labeled Shot 

indicating Shotpoint number, the other CMP which is an acronym for Common Mid Point and is equivalent to the 

term CDP used elsewhere in this document. On the displays, these numbers are the same because as described 

above, we made the Shotpoint number equal to the CDP number in order to have a unique index number for each 

trace within a line. 

Miller, et al 9 
Display Software: No display software is provided on this Internet site. However, Open File Report 00-286 

contains an IBM P/C compatible seismic display program, PLOTSEIS.EXE and associated documentation for the 

purpose of displaying the SEG-Y data files. This display program is also published separately by Zihlman (1996). 

DISCLAIMER 

This Internet site was prepared by an agency of the United States Government. Neither the United States 

Government nor any agency thereof nor any of their employees makes any warranty, expressed or implied, or 

assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, 

product, or process disclosed in this report or represents that its use would not infringe privately owned rights. 

Reference therein to any specific commercial product, process, or service by trade name, trademark, 

manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring 

by the United States Government or any agency thereof. 

Although all data and software published on this internet site have been used by the USGS, no warranty, 

expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the 

functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is 

assumed by the USGS in the use of these data, software, or related materials. 

SYSTEM REQUIREMENTS 

Minimum hardware/software requirements are as follows: 

All platforms: Software capable of reading SEG-Y format data files, ASCII text files, and PDF-format graphics 

files.

FIGURES 

Figure 1. Digital image in Adobe Acrobat

®

 PDF format, containing a map view of the trace locations, generated 

directly from file NPRANAV.SEG. The label for each line number presented on this internet site (R-21 through R24) is also a hyperlink that allows the user to view the associated digital image of the seismic line in Adobe 

Acrobat®

 PDF format. 

Miller, et al 10 
TABLES 

Table 1. List of seismic lines contained in the data set with total mileage and geographic orientation of each line. 

The four lines contained on this Internet site are R-21 through R-24. Click on any of these four line names to 

display a graphic image in PDF-format of the stacked, migrated record sections. 

Table 2: List of the component lines that make up the 4 regional lines presented on this Internet site. Asterisks 

(*) indicate those lines which were completely reprocessed from the field tapes. All other line segments were 

reprocessed from the stacked, unmigrated data previously processed by industry. 

Miller, et al 11 
REFERENCES CITED 

Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, in Digital 

Tape Standards: Society of Exploration Geophysicists ["Recommended standards for digital tape formats"] 

reprinted from Geophysics, v. 32, p. 1073-1084; v. 37, p. 36-44; v. 40, p. 344-352, p. 22-30. 

Gray, W. C., 1979, Variable norm deconvolution: Ph.D thesis, Stanford University, Palo Alto, California. 101p. 

Gryc, G., 1985, The National Petroleum Reserve in Alaska, Earth-Science Considerations: U.S. Geological 

Survey Professional Paper 1240-C, 94p. 

Ikelman, J.A. (editor), 1986, Catalog of Geological and Geophysical Data for the National Petroleum Reserve in 

Alaska – Key to Geophysical Records Documentation No. 16 (Revised Edition): National Geophysical Data 

Center, Boulder, Colorado, p. 24-25. 

Miller, J.J., Agena, W.F., Lee, M.W., Zihlman, F.N., Grow, J.A., Taylor, D.J., Killgore, Michele, and Oliver, H.L., 

2000, Regional Seismic Lines Reprocessed Using Post-Stack Processing Techniques: National Petroleum 

Reserve—Alaska: U.S. Geological Survey Open File Report Open-File Report 00-286, 1 - CD-ROM disk. To 

order, contact the USGS Earth Science Information Center: 1-888-ASK-USGS (1-888-275-8747) or write to: Box 

25286, Building 810, Denver Federal Center, Denver, CO, 80225-0286. 

Zihlman, F.N., 1996, PLOTSEIS, A DOS display program for SEG-Y formatted seismic data: U.S. Geological 

Survey Open-File Report 95-516, 7p., 1 - 3/1/2" disk. 

Miller, et al 12