Geophysics cheatsheet
A couple of weeks ago I posted the first cheatsheet, with some basic science tables and reminders. The idea is that you print it out, stick it in the back of your notebook, and look like a genius and/or smart alec next time you're in a meeting and someone asks, "How long was the Palaeogene?" (21 Ma) or "Is the P50 the same as the Most Likely? I can never remember," (no, it's not).
Today I present the next instalment: a geophysics cheatsheet. It contains mostly basic stuff, and is aimed at the interpreter rather than the weathered processor or number-crunching seismic analyst. I have included Shuey's linear approximation of the Zoeppritz equations; it forms the basis for many simple amplitude versus offset (AVO) analyses. But there's also the Aki–Richards equation, which is often used in more advanced pre-stack AVO analysis. There are some reminders of typical rock properties, modes of seismic multiples, and seismic polarity.
As before, if there's anything you think I've messed up, or wrongly omitted, please leave a comment. We will be doing more of these, on topics like rock physics, core description, and log analysis. Further suggestions are welcome!
← Click to download the PDF (1.6MB)
cheatsheet, data, geophysics, tips in Workflows, Writing 
Reader Comments (6)
Great sheet this time around!
With respect to seismic polarity, you may want to specify which is SEG convention. I thought Euro was trough-negative-blue and peak-positive-red, e.g. the top of the sand appears as a blue trough and base of sand is a red peak, while SEG convention has it trough-negative-red and peak-positive-blue. Just checking.
@Maitri: Thanks for the comment. I will do my best to explain myself... That little picture started out as two: one on polarity (based on Figure 2 in Alistair Brown's great 2001 paper in Geophysical Prospecting 49, p729–733), and one on the convolutional model. Then they turned into one somehow. And now I am worried that it doesn't really serve either purpose; sorry if it's unclear.
As you say, Europeans represent a downward increase in impedance as a negative amplitude (trough). This trough is usually coloured red (as in the US and Canada). What we use in North America, where a downwards increase in impedance is a peak, is often called the 'SEG convention' or 'standard'. Brown points out in that paper that there isn't really a standard for the display of seismic data, but Sheriff's encyclopedia promotes it, so it will do!
I tried not to imply a lithology for the bed shown on my cheatsheet, it's just hard (fast and/or dense): a positive downwards increase in impedance. I did this because I usually describe polarity in terms of a downwards changes in impedance, even though it's not consistent with what many people think of as a sand (rightly or wrongly).
Hope that helps understand what I was trying to show there. I'm already working on an improved version.
Yup, understood. I was just advising that you may want to label the seismic figure in SEG/standard convention as such.
Having worked at several different oil companies with people from all over the world, the first question I ask now is: what's your polarity convention? I really think people should have that in a corner on their slides in general. Isn't that Brown paper just awesome? This blog and Chris Liner's are doing great things for the teaching of geophysics.
@Maitri: I agree: there should be some indication in every report or presentation. I made some little polarity cartoons at the last place I worked. You've inspired me to do something similar and put them up here... Keep an eye out.
And I have just added an annotation to the cheatsheet, indicating that the US/CAN convention is SEG 'standard'. Thanks for the suggestion. (And also for mentioning this little blog in the same sentence as Chris Liner's!)
I love this! I've stapled a copy of the basic cheatsheet into my personal notebook.
Would it be possible to create a version in which the elements of the sheet are in some vector format (rather than the rasters they're in now)?
Having a vectorized version would make it easier to rescale the sheet and print it at different sizes without a loss of fidelity.
@GeologyDave: Thanks for the nice comment! You're right, it needs to be in vector format. Although I create these things in Inkscape (an open source vector graphics package), much of the content is rasterized and I've had a spot of bother exporting PDFs that I like. So I have a couple of issues to work on...
I make the tables in MediaWiki and can't find a nice way to export them; I've been using screen caps, which is not optimal at all. I am trying to install a PDF writer on my MediaWiki, but it's not quite as easy as I was hoping it would be.
Too late to cut a long story short, but... watch this space!