The three virtues

Don’t forget the three virtues of a Geophysicist, namely:
True Love, True Friendship, True Amplitudes. ~ M. Tygel

This happens to be my favorite quote about geophysics.
A fellow writer asked me, what this quote was all about. So I began to elaborate on this.
The part about “True Love” appears to be the easiest to me. Having met the woman who is more than I ever dared to dream of, puts me in the position to say this true love gives me strength and support I need to move mountains. (What a lovely idiom for a geoscientist, right?!)
Now I hear some say “friends come and go”, but you should have your couple of friends that can count on you just like you can always count on them.
Those are the two ingredients that keep the geophysicist from going crazy when he’s entangled in some fancy dimension of Fourier- or Hilbertransforms. (Or maybe just missed the conversion from feet to meters?)?Now this part probably made my friends reading this quite happy, but didn’t solve the real puzzlement about the amplitudes.

Let’s see.
I work in seismics and I just happen to know the quote is from a fellow geophysicist in seismics. What we do in seismics is sending acoustic waves into the ground. Those waves waves get reflected at inconsistencies in the subsurface. So they get back to the surface and that’s where we set out our recorders to pick up an image of the earth we stand on.

There’s something wonderful about waves.

1 = Peak amplitude,
2 =?Peak-to-peak?amplitude,
3 =?RMS?amplitude,

4 =?Wave length?(not an amplitude)

They are characterized by very distinct featuresProperties of waves, such as the wavelength, polarization and amplitude. Now I’ll try not to make this too physical. When you hear sound, its pitch is determined by its frequency. The higher your frequency goes, the higher the pitch goes. However, if you want to figure out if this sound will burst your eardrums you should rather have a look at the amplitude. This will tell you how loud your sound is.
You might ask yourself why this is so interesting for us geophysicists. I mean, a reflector is a reflector right? So when there is something in the ground that will reflect your acoustic wave, you don’t need to care about it’s intensity. Well, first of all you can get a good estimate, how strong of a reflector you have in the underground. When there is a strong inconsistency in the ground, this will be shown by the amplitude of the reflected wave.Quantitative Seismic Interpretation – Stanford University But this isn’t all! The amplitudes of a seismic trace can be used as an indicator for carbohydrates in the underground. When a reservoir is filled with a fluid, this changes the behavior of our wave. The influence of the fluid on the wave increases by the time the wave travels through. Now it’s basic geometry to see that waves arriving with steeper angles have a shorter stay in the fluid filled sediments.

Changing angles result in changing ray path lengthsCC-BY-SA Nwhit :: Wikimedia User

This results in slight changes of the amplitude with increasing angles. For all of this you need the true amplitudes. Therefore, we call any process that works on seismic data and leaves the amplitudes intact “amplitude preserving” or “True Amplitude”.

Now you know about the three virtues of a geophysicist. And coincidentally, why I use the shorturl
What are your favorite geoscientific quotes?

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... is a geophysicist by heart. He works at the intersection of machine learning and geoscience. He is the founder of The Way of the Geophysicist and a deep learning enthusiast. Writing mostly about computational geoscience and interesting bits and pieces relevant to post-grad life.

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  1. Nice post! Definitely looking forward to more on this subject…

    As for quotes… I’m not certain he coined it, and I think it’s a snowclone, but Rob Stewart is often credited with this gem:

    “A day without seismic is like a day without sunshine.”

    But, as Steve Martin said, “A day without sunshine is like, you know, night.”

    • All good comments, thknas. It is certainly the case in the UK that there are contractors with poorly trained staff and people calling themselves geophysicists without a single geoscience qualification to their name. You wouldn’t use a builder to fix your teeth so why are archaeologists using these people to get their surveys? It seems possible that real geophysics by real archaeological geophysicists will soon become a thing of the past in the UK. If nothing else, real geophysicists won’t be able to afford to trade because we do have professional standards to maintain, CPD to fund, kit to invest in, research to contribute to, etc.We came across one outfit the other day who can’t spell magnetometer yet we know we have lost work to them!Point taken about shear, however, we don’t normally have that problem and in each case you have highlighted there are mitigating circumstances, like a steep bank in one for example. Fair enough comment though.

    • In my view the only person who shloud be able to call themselves a geophysicist is someone who has undertaken formal education in geophysics at graduate or post graduate level. We would not allow someone to call themselves a doctor just because they have been pescribing potions to people for 5 years and have not succeeded in harming anyone in the process would we? Geophysics is a broad church, archaeological prospection uses only a small part of it. Maybe there is scope for a term geophysical technician, (the accounting industry has such a term) which would signify someone has got loads of experience in field geophysics and processing (and maybe also interpretation) of data, but no formal qualification in it. This could also apply across other disciplins, for example in environmental and engineering surveys, but I suspect Archaeological prospection and utility detection is where the problem is most acute

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