page_title: Polarity reversal (seismology)
hierarchical_section_title: Polarity reversal (seismology)
caption_attribution_description: English: Diagram showing the acoustic relationship that results in a seismic polarity reversal.
context_page_description: In reflection seismology, a polarity reversal or phase change is a local amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator.
  It primarily results from the change in polarity of the seismic response when a shale overlies a brine-saturated zone, that becomes invaded with an oil/gas sand. This changes the acoustic impedance contrast from an increase to a decrease, resulting in the polarity of the seismic response being reversed - as per the normal convention adopted by the SEG.
context_section_description: In reflection seismology, a polarity reversal or phase change is a local amplitude seismic attribute anomaly that can indicate the presence of hydrocarbons and is therefore known as a direct hydrocarbon indicator.  
  It primarily results from the change in polarity of the seismic response when a shale (with a lower acoustic impedance) overlies a brine-saturated zone (with a high acoustic impedance), that becomes invaded with an oil/gas sand (with the lowest acoustic impedance of the three).  This changes the acoustic impedance contrast from an increase to a decrease, resulting in the polarity of the seismic response being reversed - as per the normal convention adopted by the SEG.
caption: Diagram showing the acoustic relationship that results in a seismic polarity reversal.
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