SEG-Y: What is it?

The Society of Exploration Geophysicists Y Format, or SEG Y, has been the accepted exploration industry data format for digital seismic data since 1975.  Originally a magnetic tape-centric format, SEG Y has evolved over the years to remain the data format industry standard for data analysis and processing.  The latest revision (revision 1 .pdf format) to the format was released in 2002. 

The format can accommodate a variety of industry-specific metadata, for example, source sweep information and trace identification code (uphole, water break, etc), and legacy metadata, such as the tape reel number, in the binary header within the SEG Y file.  The format of SEGY files produced from PH5 data sets builds upon the revision 1 standard.

PASSCAL staff member Wille Zamora introduces volunteers to the datalogger and sensors deployed on the 2009 Batholiths Controlled Source experiment, Puntzi Lake, British Columbia, Canada

A SEG Y file typically contains all the traces which recorded a given source and is commonly referred to as a shot gather, or the file may contain traces from a single receiver which recorded a large number of sources and is known as a receiver gather.  Each trace within the gather is limited to 32767 samples.

The PASSCAL SEG Y trace file, in brief: a variation of the SEG Y format is the PASSCAL SEG Y trace file.  A PASSCAL SEG Y trace file contains one trace and accommodates an extended duration (greater than 32767 samples) by utilizing some of the unspecified words within the trace header.  Only a trace header is defined within the PASSCAL SEG Y trace file; there is no EBCDIC or textural file header nor is there a reel header.

Since much of the metadata are stored within the headers of the data traces of SEG Y gathers and PASSCAL SEG Y trace files, correcting the metadata is not practical and normally necessitates the reprocessing and reconstruction of the gather or file in order to reflect the change.