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The SEG-Y (sometimes SEG Y)
file format A file format is a Computer standard, standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary format, pr ...
is one of several standards developed by the
Society of Exploration Geophysicists The Society of Exploration Geophysicists (SEG) is a learned society dedicated to promoting the science and education of exploration geophysics in particular and geophysics in general. The Society fosters the expert and ethical practice of geophy ...
(SEG) for storing
geophysical Geophysics () is a subject of natural science concerned with the physical processes and properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations acros ...
data. It is an
open standard An open standard is a standard that is openly accessible and usable by anyone. It is also a common prerequisite that open standards use an open license that provides for extensibility. Typically, anybody can participate in their development due to ...
, and is controlled by the SEG Technical Standards Committee, a non-profit organization.


History

The format was originally developed in 1973 to store single-line
seismic reflection Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismi ...
digital data on
magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic ...
s. 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 Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
techniques and high speed, high capacity recording. The most recent revision of the SEG-Y format was published in 2023, named the ''rev 2.1'' 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 The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
textual
EBCDIC Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding si ...
character encoded tape header and a 400 byte binary header.


Data structure

SEG-Y Files are stored in a hierarchical byte-stream format that combines both textual and
binary data Binary data is data whose unit can take on only two possible states. These are often labelled as 0 and 1 in accordance with the binary numeral system and Boolean algebra. Binary data occurs in many different technical and scientific fields, wh ...
segments. The following chart shows the byte stream structure of revision 1 (2002), with revision 2 (2017) only adding an optional data trailer for 1 or more 3200-byte records at the end: Since the first SEG-Y standard was published, many companies dealing with seismic data have produced variants of the SEG-Y standard which have run contrary to the aims of defining a standard for universal interchange, thus generally causing confusion and delay when data received by a company in expected SEG-Y format turns out to be a variant of that format. Initially, many of these derived from the fact that the format was based on the de facto standard of using IBM computers for digital processing where character data was coded in EBCDIC and number data in IBM Floating Point, whereas processing systems in use quickly evolved based on ASCII character and IEEE number representations. Even before the SEG-Y standard was agreed and published, earlier seismic data format standards published by the SEG such as SEG-A, SEG-B and SEG-C were modified by seismic acquisition companies, though not to the wide extent that the SEG-Y format has been modified by seismic acquisition and processing companies and oil companies using their own inhouse software. As magnetic tape technology developed, the original SEG-Y format using individual small data blocks for each distinct seismic trace became very inefficient in terms of tape performance so the first and subsequent revisions allowed for larger tape data blocks containing many individual traces. There have been many suggestions for including different kinds of metadata within the standard over the years, since when the standard was first proposed the processes of acquisition and processing were technologically much simpler. For example geographical positioning information either real world or relative wasn't stored in the trace header at acquisition or final processing whereas it is routine today. However, the relative simplicity of the SEG-Y format has meant that it has worked well for interchange of seismic data allowing anyone to read and understand data recorded in the 1970s on half inch magnetic tape as easily as reading it on modern tape media or from a disk file, as long as the standard has been adhered to. While SEG-Y format data is still stored on magnetic tape as a permanent archive, SEG-Y data is increasingly stored as disk files for online and near-line ease of access, and later format revisions allow for character and number data to be stored in native system representations as
ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
and
IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an American 501(c)(3) organization, 501(c)(3) public charity professional organization for electrical engineering, electronics engineering, and other related disciplines. The IEEE ...
.


See also

*
Reflection seismology Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflection (physics), reflected seismic waves. The method requir ...


References


External links


Downloadable SEG Technical Standards
including SEG Y revisions 0, 1 and 2 Computer file formats Geophysics Open formats {{geophysics-stub