Polarity & Phase Helper

Determine seismic polarity convention (SEG/European) and phase rotation from known reflector observations. Essential quality control before amplitude interpretation, AVO analysis, or comparing datasets. Use a known geological interface to identify the polarity standard and phase of your seismic data.

Polarity Phase QC Conventions

Known Reflector Observation

1. Known Geology

Examples: shale-to-sand, water sand-to-gas sand, coal seam, top salt

2. Observed Seismic Character

Look at the seismic trace at the known interface
Confirm your display convention

3. Phase Analysis (Optional)

Compare seismic peak to well-tied interface depth
For advanced phase determination

Analysis Results

Polarity & Phase Background

Polarity Conventions

SEG (Society of Exploration Geophysicists) Convention:

  • Increase in acoustic impedance → Negative amplitude (trough)
  • Most common in North America and modern datasets
  • Also called "normal polarity" or "American convention"

European (Reverse) Convention:

  • Increase in acoustic impedance → Positive amplitude (peak)
  • Common in older data and some European datasets
  • Also called "reverse polarity"

⚠ Critical: Misidentifying polarity can lead to disastrous interpretation errors, especially for AVO and DHI analysis.

Phase Rotation

Zero Phase:

  • Peak/trough aligned with reflecting interface
  • Symmetric wavelet, best vertical resolution
  • Industry standard for interpretation

Minimum Phase:

  • Peak/trough occurs before zero-crossing
  • Asymmetric, front-loaded wavelet
  • Common in marine data before processing

Maximum Phase:

  • Peak/trough occurs after zero-crossing
  • Rarely used in practice

Mixed Phase: Common in real data; may need rotation to approximate zero phase

How to Check Polarity

  1. Use a known interface: Seafloor, well-tied horizons, or distinctive geological markers
  2. Predict impedance contrast: Calculate expected impedance change from logs or regional knowledge
  3. Compare observation to convention: Does the observed reflection match SEG or European?
  4. Check multiple reflectors: Verify consistency across multiple known interfaces
  5. Well calibration: Tie to synthetic seismograms from well logs

Best Practice: Always document polarity in your interpretation reports and when merging datasets.