About SEG-Y

The SEG-Y (sometimes SEG Y or SEGY) file format is one of several data standards developed by the Society of Exploration Geophysicists (SEG) for the exchange of geophysical data. It is an open standard, and is controlled by the SEG Technical Standards Committee, a non-profit organization.

The format was originally developed in 1973 to store single-line seismic reflection digital data on magnetic tapes. The specification was published in 1975.

The format and its name evolved from the SEG “Ex” or Exchange Tape Format. However, since its release, there have been significant advancements in geophysical data acquisition, such as 3-dimensional seismic techniques and high speed, high capacity recording.

The most recent revision of the SEG-Y format was published in 2002, named the rev 1 specification. It still features certain legacies of the original format (referred as rev 0), such as an optional SEG-Y tape label, the main 3200 byte textual file header and a 400 byte binary file header [1].

Version

There are several version of SEG-Y, you can find the documents at SEG Technical Standards.

The marjor versions include:

All version compression (click here for source pdf version):

segy comparison

Structure

By comparing several versions of the SEG-Y files, we can observe that the SEG-Y file is primarily composed of the following mandatory parts: 3200 bytes Textual Header, 400 bytes Binary Header, 240 bytes Trace Headers and corresponding data traces. And there are several optional parts in version 1 and version 2: Optional 128 byte SEG-Y Tape Label, Extended Textual File Header, Data Trailer.

CIGSEGY only supports these mandatory parts, and other optional parts are currently not supported (this is because the vast majority of SEG-Y files only include these mandatory parts), i.e., cigsegy considers that a SEG-Y file contains one Textual Header, one Binary Header, N Trace Headers, N data traces, where N is the total number of traces.

Although the SEG-Y file structure and Version 0 closely resemble what cigsegy considers, this doesn’t imply that cigsegy can only handle Version 0 SEG-Y files. CIGSEGY takes into account the information from the binary header and trace headers of Version 1 and Version 2 as well.

Type of data

The seismic data can be devided into two categories: Poststack seismic data and Prestack seismic gather.

Inside the binary trace header of a SEG-Y file, there is a 2-byte integer stored at bytes 3229-3230. This integer describes the category to which this SEG-Y file belongs.

value

data type

post or pre stack

-1

Other

-

0

Unknown

-

1

As recorded (no sorting)

prestack

2

CDP ensemble

prestack

3

Single fold continuous profile

-

4

Horizontally stacked

poststack

5

Common source point

prestack

6

Common receiver point

prestack

7

Common offset point

prestack

8

Common mid-point

prestack

9

Common conversion point

prestack