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SEGY Format Explained

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SEGY Format Explained

Introduction

SEGY is the most widely used format for storing and exchanging seismic data. Introduced in 1975 and updated in later revisions, SEGY provides a standardized structure for seismic traces, headers, and metadata. Whether you’re processing, interpreting, or managing seismic data, understanding SEGY is essential.

This article breaks down the SEGY format, its components, and why it remains the industry standard.

1. What Is SEGY?

SEGY is a digital file format used to store seismic traces and associated metadata. Defined by the Society of Exploration Geophysicists (SEG), it is used globally for:

  • Field data

  • Processed data

  • Pre‑stack gathers

  • Post‑stack volumes

  • Navigation and metadata

2. Why SEGY Matters

✔ Standardization

Ensures compatibility across software platforms.

✔ Metadata Preservation

Stores acquisition and processing information.

✔ Flexibility

Supports both 2D and 3D datasets.

✔ Longevity

SEGY has remained relevant for nearly 50 years.

3. Components of a SEGY File

A. Textual Header (3200 bytes)

Contains human‑readable metadata such as:

  • Survey name

  • Processing history

  • Coordinate system

  • Acquisition parameters

Traditionally stored in EBCDIC, but ASCII is now common.

B. Binary Header (400 bytes)

Stores global parameters such as:

  • Sample rate

  • Number of samples

  • Data format (e.g., 32‑bit float)

  • Coordinate units

C. Trace Headers (240 bytes each)

Each trace has its own header containing:

  • Source and receiver coordinates

  • Offset

  • CDP number

  • Elevation

  • Shot point

  • Inline and crossline numbers

Trace headers are essential for processing, navigation, and interpretation.

D. Trace Data

The actual seismic samples, stored in formats such as:

  • 32‑bit IEEE float

  • 16‑bit integer

  • 24‑bit integer

This is the bulk of the SEGY file.

4. SEGY Revisions

SEGY Rev 0 (1975)

The original standard.

SEGY Rev 1 (2002)

Adds:

  • Extended textual headers

  • Larger coordinate fields

  • Modern data types

SEGY Rev 2 (proposed)

Focuses on:

  • Larger file sizes

  • Modern metadata standards

  • Better coordinate handling

5. Common SEGY Issues

  • Incorrect byte positions

  • Missing navigation

  • Corrupted headers

  • Inconsistent coordinate units

  • Legacy formats

These issues often require reformatting, header repair, or metadata reconstruction.

Conclusion

SEGY remains the backbone of seismic data exchange. Understanding its structure and metadata is essential for processing, interpretation, and data management. As seismic datasets grow larger and more complex, SEGY continues to evolve to meet industry needs.

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