b'CommentarySeismic windowarrivals as a deflection downwards. This convention carried over into seismic reflection records. All very technical, but my favourite explanation is an anecdote from the days when seismic interpretation was drawn on paper sections using coloured pencils to pick reflectors which were most commonly at major increases in acoustic impedance. If the increase in impedance was displayed as a trough (an unfilled wiggle deflecting to the left) the coloured pencil line was easier to see. This convention also had the added bonus that the coals (common in the Gippsland and Cooper Basins) were displayed as black peaks and hence looked coally.This brings me back to my openingfor consistency we should all be using the SEG positive polarity standard and terms such as ASEG or Australian polarityshould be replaced with the correct term SEG negative polarity. Unfortunately, Ihavent seen any Figure 3. Example of AVO modelling results presented by an Australian operator. For comparison theevidence of willingnessin the industry display of modelled results has been inverted to account for the negative polarity convention of the seismicto move in this direction and there data (lower right). Inverting the graphical display to match the measured seismic response results inwill be more confusion when 4D unreadable text (arrows). seismic and shear wave data becomes morecommonplace.Figure 3 is an example of AVO modellingnot contain a definition for displayingFinally, Ill finish with an extract from from a recent prospect presentation thatthe data on paper or computer screens.a Schlumberger Petrel users guide. I attended. This company displays seismicAbout 1988 John Denham (ChiefThe polarity and colour conventions data as SEG negative polarity (an increaseGeophysicist BHP) queried the authorsdescribed in Petrel manuals are the in impedance is displayed as a trough)of the 1975 standard and they replieddefault color scale displays troughs as while their seismic modelling results areconfirming that the standard did notcold blue colors and peaks as hot red displayed with SEG positive polarity. Toinclude displaying the recorded dataand yellow colors. This appears to be enable the modelled and actual curves tofor interpretation. It was not until theagainst another popular convention be compared directly one of the displaysmid-90s that the later editions of theused, whereby positive amplitudes has been flipped. In this case the modelSEG Encyclopaedic Dictionary definedare usually displayed in blue tones. display was flipped and the curves canpolarity without any fanfaretheWhatever convention is chosen, it is be compared, but the text and labels aredefinition just appeared. The interveningup to each user to make this clear in difficult to read. gap of approximately 20years wasany resulting map or display showing plenty of time for various companies toamplitude related information. Thanks So what has brought about thisimplement their own polarity definition.for thatthis is exactly why the confusion? Generally, the US went for SEG positive,confusion continues.We can blame it on computerstheand Europe and Australia went negative introduction of digital recordingor reverse polarity. Referencesbrought about the need to define polarity, and this led to the SEG polarityThere are a number of reasons for theSimm, R., and White, R. 2002. Phase, polarity and standard being published in 1975negative polarity convention becomingthe interpreters wavelet. First Break 20.(Thigpen et al. 1975). This documentcommon place. Here are three. ProbablySchlumberger. 2013. Oilfield glossary.provided details of tests and standardsthe simplest reason is that a negativehttp://www.glossary.oilfield.slb.com/for seismic acquisition and includednumber on tape is simply displayed asSheriff, R. 2002. Encyclopedic Dictionary of this textAn increase in acoustica trough on paper. The second reasonApplied Geophysics. https://wiki.seg.org/impedancerecorded as a negativeharks back to seismic refraction records.wiki/Encyclopedic_Dictionary_of_Applied_number on tape. I understand thisRefraction seismic uses first arrivals whichGeophysicswas a pragmatic decision because mostare refracted along a boundary acrossThigpen, B. B., A.E. Dalby, and R. Landrum. manufacturers at the time wired theirwhich the seismic velocity (impedance)1975. Special report of the subcommittee on sensors in this way. But the standardincreases and commonly refractionpolarity standards. Geophysics 40(4): 694699. was for acquisition standards and didinstruments were wired to display firstdoi:10.1190/1.144056238 PREVIEWFEBRUARY 2024'