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Oz Yilmaz Shot Gathers

In the mid-1980s, Dr. Oz Yilmaz did research and taught seismic data processing at Western Geophysical, at the time a division of Litton Industries, but originally founded in 1933 by Henry Salvatori. During his teaching, Dr. Yilmaz often used 40 shot gathers that had been collected in seismic surveys around the world. Around the time Dr. Yilmaz wrote his 1987 book, "Seismic Data Processing" for the Society of Exploration Geophysicists (SEG), the company kindly made the 40 shot gathers available to the public.

 

 

Table 1.8. Parameter index of a worldwide assortment of common-shot gathers.

 

Adapted from "Seismic Data Processing" by Özdoğan Yilmaz,
Copyright 1987, Society of Exploration Geophysicists.

Record
Number		 Area Number of
Samples
per Trace1		 Number
of
Traces1		 Sampling
Interval,
ms		 Trace
Interval,
F or M		 Inner
Offset,
F or M		 Source Split-spread (SS),
Off-end near (OEN),
Off-end far (OEF)4
1 South Texas (1275) 1275 48 4 330 F 990 F Vibroseis * SS
22 West Texas (1025) 1000 120 4 100 F 400 F Vibroseis SS5
3 ** Louisiana (1500) 1500 24 4 340 F 340 F Dynamite OEN
42 Turkey (1275) 1250 48 4 100 M 250 M Vibroseis SS
5 South America (3000) 2535 48 2 100 M 200 M Dynamite SS
6 Far East (1250) 1250 48 4 100 M 150 M Dynamite OEF
7 South America (2600) 2535 48 2 100 M 300 M Vibroseis SS
8 Central America (1300) 1281 96 4 50 M 100 M Dynamite SS5
92 Alaska (1000) 1000 96 4 220 F 990 F Vibroseis SS
10 North Africa (1325) 1325 (120) 78 4 25 M 300 M Vibroseis OEN
112 Alaska (1000) 975 96 4 220 F 990 F Vibroseis SS
122 Mississippi (1275) 1250 (48) 483 4 330 F 990 F Vibroseis SS
13 Offshore Offshore (2025) 2025 48 4 220 F 875 F Air gun OEF
14 Offshore Texas (1525) 1525 48 4 220 F 690 F Aquapulse OEF
15 Offshore Canada (2500) 2500 48 2 25 M 360 M Air gun OEF
16 South America (1275) 1275 48 4 25 M 233 M Air gun OEF
17 South America (2000) 2000 48 4 50 M 250 M Air gun OEF
18 Offshore Louisiana (1500) 1500 120 4 82 F 716 F Air gun OEF
19 Turkey (1250) 1250 216 4 10 M 50 M Dynamite OEN
20 South Aleutians (2025) 2025 120 4 82 F 921 F Air gun OEF
212 Denver Basin (1550) 1500 48 2 220 F 220 F Vibroseis SS
222 Williston Basin (1550) 1500 48 2 110 F 110 F Vibroseis OEF
232 San Juaquin (1550) 1500 48 2 220 F 220 F Vibroseis OEF
24 Arctic (3000) 2535 48 2 220 F 220 F Aquaflex SS
25 Alberta (2000) 2000 96 2 50 M 50 M Dynamite SS
26 Alberta (1500) 1500 48 2 67 M 67 M Dynamite SS
27 Canada (1791) 1791 92 4 50 M (1-28) 200 M Air gun OEF
25 M (29-92)
28 Canada (2500) 2500 48 2 25 M 300 M Air gun OEF
29 Offshore Spain (2000) 1697 48 4 50 M 250 M Maxipulse OEF
30 Offshore Crete (2125) 2048 96 4 25 M 230 M Air gun OEF
31 North Sea (1550) 1536 96 4 25 M 228 M Air gun OEF
32 North Sea (1550) 1550 96 4 25 M 178 M Air gun OEF
33 North Sea (1625) 1536 96 4 25 M 200 M Air gun OEF
34 Celtic Sea (1500) 1485 60 4 50 M 253 M Air gun OEN
35 Denmark (2500) 2500 52 2 100 M 100 M Dynamite SS
362 Middle East (1024) 999 48 4 50 M 250 M Vibroseis OEF
372 Turkey (1000) 975 48 4 75 M 187 M Vibroseis OEN
38 North Africa (2500) 2500 60 2 100 M 100 M Vibroseis SS
39 Middle East (2500) 2500 60 2 50 M 100 M Geoflex OEN
40 West Africa (2600) 2535 96 2 30 M 120 M Dynamite OEN

* All vibroseis records have been correlated.
** Analog recording.
1 The value in parentheses is the value in the book; the value not in parentheses is the actual gather value.
2 Traces in these gathers have negative time samples; that is, SU keys delrt (bytes 109-110) and muts (bytes 111-112) are negative. For all gathers except 9, I removed the negative time samples. Gather 9 seems to have valid values before zero, so I shifted those values to positive time.
3 I found gather 12 to have 49 traces. I removed trace 49.
4 OEN means trace 1 is the nearest offset, OEF means trace 1 is the farthest offset.
5 These gathers are asymmetric split-spread.

 

 

Downloads

The Seismic Unix and SEG-Y tar files that are available below (click an image) are edited from the original archived seismic unix forty shot gathers that are on the Seismic Unix wiki. The two tar files below are edited in the following ways:

Click the image below to download a compressed tar file of my edited 40 Oz shot gathers (16 Mb) in Seismic Unix "little endian" format.

Click the image below to download a compressed tar file of my edited 40 Oz shot gathers (16 Mb) in SEG-Y "little endian" format.

Oz shot gather 25

Oz shot gather 25

Madagascar Users: Professor Sergey Fomel at The University of Texas at Austin created a Madagascar script for converting the SEG-Y files to RSF. The script is on github.

 

For the archive shot gathers in Seismic Unix "big endian" format, go to the Seismic Unix Wiki.

Click here to download a compressed tar file of images of the 40 Oz shot gathers (2.3 Mb)

To uncompress a .tgz file, use the following command

$   tar   -xvzf   data.tgz

The dollar sign ($) is the command line prompt, not part of the command.

Big Endian versus Little Endian

Big endian and little endian refer to byte order. For one technical description I refer you to a Wikipedia page: Endianness.

The difference between whether your installation of Seismic Unix will use big endian or little endian seismic data is how "XDR" is set in your Makefile.config file.

When you install Seismic Unix, when you run

$   make   install
$   make   xtinstall

and other "make" commands like these, these commands use the Makefile.config file.

For big endian configuration, use the XDR line as it appears in Makefile.config:

XDRFLAG   =  -DSUXDR

However, I want a little endian configuration. So, before I ran the "make" commands, I commented out the XDR line by putting the hash (#) sign at the beginning of that line. Then I added the next line that has "XDRFLAG" on the left side of the equal sign and a space on the right side of the equal sign:

#XDRFLAG   =  -DSUXDR
XDRFLAG   =  

How important is this? What is the data significance of big endian compared to little endian? At the beginning of the Makefile.config file, there is a comment that describes what it means to use XDR:

"forces all SU data to be big endian
independent of processor architecture"

Some years back, most computers were big endian; for example, computers made by Solaris and the IBM 360. However, personal computers that are x86 and AMD64 architecture are, natively, little endian. For my Seismic Unix installation on my Windows Surface Pro 3 OS, I commented out the XDR line in Makefile.config to let my SU datasets be created in the native little endian format. If you are using an x86 or AMD64 architecture, it is my opinion that you do the same.

Linux and suswapbytes

As I described above, you can choose whether the seismic data you create on your OS will be big endian or little. By default (if you do not comment out the XDR line in your Makefile.config file), your Linux data architecture will be big endian.

Can you use little endian datasets on a big endian OS? Can you use big endian datasets on a little endian OS?

Yes, you can, but you will have to use suswapbytes on the data file before you can process the file in Seismic Unix.

How will you know you have an "endian" problem? Typically, I find this out when I use surange on a data file. I use surange a lot.

SURANGE - get max and min values for non-zero header entries

My typed command is below. Under that is the computer response.

$   surange   <   oz.25.su

surange: fgettr.c: on trace #2 number of samples in header (4325) differs from number for first trace (13320)

That response does not make a lot of sense, but it is the normal Seismic Unix response to a mis-matched byte order data file.

Below, I use suswapbytes to create a new data file, then I use surange.

$   suswapbytes   <   oz.25.su   >   ozle25.su
$   surange   <   ozle25.su

96 traces

 

tracl

1 96 (1 - 96)

tracr

1 96 (1 - 96)

fldr

10025

tracf

1 96 (1 - 96)

cdp

25 120 (25 - 120)

cdpt

1

trid

1

nvs

1

nhs

1

duse

1

scalel

1

scalco

1

counit

1

delrt

2

muts

2

ns

2100

dt

2000

Now I have a successful output from surange. The endianness of my data file has been corrected for my machine by suswapbytes.