SEG-Y

The SEG-Y (sometimes SEG Y) file format is one of several standards developed by the Society of Exploration Geophysicists (SEG) for storing geophysical data. It is an open standard, 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 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 2017, named the "rev 2.0" 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 EBCDIC character encoded tape header and a 400 byte binary header.
Data structure.
This image shows the byte stream structure of a SEG-Y file, with rev 1 Extended Textual File Header records.
Many SEG-Y programs do not totally follow the specification. For example, ODEC uses the opposite byte order and adds 320 bytes to the tail of each trace.
PASSCAL SEG-Y format.
A related format called "PASSCAL SEG-Y" is sometimes used to store continuous seismic records longer than a typical shot gather and should not be confused with the shot-gather focused "SEG-Y" format documented above. PASSCAL SEG-Y files contain a single trace, and therefore consist of solely a 240-byte trace header and a variable-length stream of binary integers (which can be much longer than the 32767-sample limit in shot-gather SEG-Y files).