Must-read geophysics blogs

Tuesday's must-read list was all about traditional publishing channels. Today, it's all about new media.

If you're anything like me before Agile, you don't read a lot of blogs. At least, not ones about geophysics. But they do exist! Get these in your browser favourites, or use a reader like Google Reader (anywhere) or Flipboard (on iPad).

Seismos

Chris Liner, a geophysics professor at the University of Arkansas, recently moved from the University of Houston. He's been writing Seismos, a parallel universe to his occasional Leading Edge column, since 2008.

MyCarta

Matteo Niccoli (@My_Carta on Twitter) is an exploration geoscientist in Stavanger, Norway, and he recently moved from Calgary, Canada. He's had MyCarta: Geophysics, visualization, image processing and planetary science, since 2011. This blog is a must-read for MATLAB hackers and image processing nuts. Matteo was one of our 52 Things authors.

GeoMika

Mika McKinnon (@mikamckinnon), a geophysicist in British Columbia, Canada, has been writing GeoMika: Fluid dynamics, diasters, geophysics, and fieldwork since 2008. She's also into education outreach and the maker-hacker scene.

The Way of the Geophysicist

Jesper Dramsch (@JesperDramsch), a geophysicist in Hamburg, Germany has written the wonderfully personal and philosophical The Way of The Geophysicist since 2011. His tales of internships at Fugro and Schlumberger provide great insights for students.

VatulBlog

Maitri Erwin (@maitri), an exploration geoscientist in Texas, USA. She has been blogging since 2001 (surely some kind of record), and both she and her unique VatulBlog: From Kuwait to Katrina and beyond defy categorization. Maitri was also one of our 52 Things authors. 

There are other blogs on topics around seismology and exploration geophysics — shout outs go to Hypocentre in the UK, the Laboratoire d'imagerie et acquisition des mesures géophysiques in Quebec, occasional seismicky posts from sedimentologists like @zzsylvester, and the panoply of bloggery at the AGU. Stick those in your reader!

Must-read geophysics

If you had to choose your three favourite, most revisited, best remembered papers in all of exploration geophysics, what would you choose? Are they short? Long? Full of math? Well illustrated? 

Keep it honest

Barnes, A (2007). Redundant and useless seismic attributes. Geophysics 72 (3). DOI:10.1190/1.2716717
Rarely do we see engaging papers, but they do crop up occasionally. I love Art Barnes's Redundant and useless seismic attributes paper. In this business, I sometimes feel like our opinions — at least our public ones — have been worn down by secrecy and marketing. So Barnes's directness is doubly refreshing:

There are too many duplicate attributes, too many attributes with obscure meaning, and too many unstable and unreliable attributes. This surfeit breeds confusion and makes it hard to apply seismic attributes effectively. You do not need them all.

And keep it honest

Blau, L (1936). Black magic in geophysical prospecting. Geophysics 1 (1). DOI:10.1190/1.1437076
I can't resist Ludwig Blau's wonderful Black magic geophysics, published 77 years ago this month in the very first issue of Geophysics. The language is a little dated, and the technology mostly sounds rather creaky, but the point, like Blau's wit, is as fresh as ever. You might not learn a lot of geophysics from this paper, but it's an enlightening history lesson, and a study in engaging writing the likes of which we rarely see in Geophysics today...

And also keep it honest

Bond, C, A Gibbs, Z Shipton, and S Jones (2007), What do you think this is? "Conceptual uncertainty" in geoscience interpretation. GSA Today 17 (11), DOI: 10.1130/GSAT01711A.1
I like to remind myself that interpreters are subjective and biased. I think we have to recognize this to get better at it. There was a wonderful reaction on Twitter yesterday to a recent photo from Mars Curiosity (right) — a volcanologist thought it looked like a basalt, while a generalist thought it more like a sandstone. This terrific paper by Clare Bond and others will help you remember your biases!

My full list is right here. I hope you think there's something missing... please edit the wiki, or put your personal favourites in the comments. 

The attribute figure is adapted from from Barnes (2007) is copyright of SEG. It may only be used in accordance with their Permissions guidelines. The Mars Curiosity figure is public domain. 

Update on 2013-01-11 13:29 by Matt Hall

The next post is more must-read geophysics, this time in the blogosphere. Enjoy!

Ten ways to spot pseudogeophysics

Geophysicists often try to predict rock properties using seismic attributes — an inverse problem. It is difficult and can be complicated. It can seem like black magic, or at least a black box. They can pull the wool over their own eyes in the process, so don’t be surprised if it seems like they are trying to pull the wool over yours. Instead, ask a lot of questions.

Questions to ask

1. What is the reliability of the logs that are inputs to the prediction? Ask about hole quality and log editing.
2. What about the the seismic data? Ask about signal:noise, multiples, bandwidth, resolution limits, polarity, maximum offset angle (for AVO studies), and processing flow (e.g. Emsley, 2012).
3. What is the quality of the well ties? Is the correlation good enough for the proposed application?
4. Is there any physical reason why the seismic attribute should predict the proposed rock property? Was this explained to you? Were you convinced?
5. Is the proposed attribute redundant (sensu Barnes, 2007)? Does it really give better results than a less sexy approach? I’ve seen 5-minute trace integration outperform month-long AVO inversions (Hall et al. 2006).
6. What are the caveats and uncertainties in the analysis? Is there a quantitative, preferably Bayesian, treatment of the reliability of the predictions being made? Ask about the probability of a prediction being wrong.
7. Is there a convincing relationship between the rock property (shear impedance, say) and some geologically interesting characteristic that you actually make decisions with, e.g. frackability.
8. Is there a convincing relationship between the rock property and the seismic attribute at the wells? In other words, does the attribute actually correlate with the property where we have data?
9. What does the low-frequency model look like? How was it made? Its maximum frequency should be about the same as the seismic data's minimum, no more.
10. Does the geophysicist compute errors from the training error or the validation error? Training errors are not helpful because they beg the question by comparing the input training data to the result you get when you use those very data in the model. Funnily enough, most geophysicists like to show the training error (right), but if the model is over-fit then of course it will predict very nicely at the well! But it's the reliability away from the wells we are interested in, so we should examine the error we get when we pretend the well isn't there. I prefer this to witholding 'blind' wells from the modeling — you should use all the data. 

Lastly, it might seem harsh but we could also ask if the geophysicist has a direct financial interest in convincing you that their attribute is sound, as well as the normal direct professional interest. It’s not a problem if they do, but be on your guard — people who are selling things are especially prone to bias. It's unavoidable.

What do you think? Are you bamboozled by the way geophysicists describe their predictions?

References
Barnes, A (2007). Redundant and useless seismic attributes. Geophysics 72 (3), p P33–P38. DOI: 10.1190/1.2370420.
Emsley, D. Know your processing flow. In: Hall & Bianco, eds, 52 Things You Should Know About Geophysics. Agile Libre, 2012. 
Hall, M, B Roy, and P Anno (2006). Assessing the success of pre-stack inversion in a heavy oil reservoir: Lower Cretaceous McMurray Formation at Surmont. Canadian Society of Exploration Geophysicists National Convention, Calgary, Canada, May 2006. 

The image of the training error plot — showing predicted logs in red against input logs — is from Hampson–Russell's excellent EMERGE software. I'm claiming the use of the copyrighted image is fair use.  

Great geophysicists #6: Robert Hooke

Robert Hooke was born near Freshwater on the Isle of Wight, UK, on 28 July 1635, and died on 13 March 1703 in London. At 18, he was awarded a chorister scholarship at Oxford, where he studied physics under Robert Boyle, 8 years his senior. 

Hooke's famous law tells us how things deform and, along with Newton, Hooke is thus a parent of the wave equation. The derivation starts by equating the force due to acceleration (of a vibrating particle, say), and the force due to elastic deformation:

where m is mass, x is displacement, the two dots denote the second derivative with respect to time (a.k.a. acceleration), and k is the spring constant. This powerful insight, which allows us to compute a particle's motion at a given time, was first made by d'Alembert in about 1742. It is the founding principle of seismic rock physics.

Hooke the geologist

Like most scientists of the 17th century, Hooke was no specialist. One of his best known works was Micrographia, first published in 1665. The microscope was invented in the late 1500s, but Hooke was one of the first people to meticulously document and beautifully draw his observations. His book was a smash hit by all accounts, inspiring wonder in everyone who read it (Samuel Pepys, for example). Among other things, Hooke described samples of petrified wood, forams, ammonites, and crystals of quartz in a flint nodule (left). Hooke also wrote about the chalk formations in the cliffs near his home town.

Hooke went on to help Wren rebuild London after the great fire of 1666, and achieved great respect for this work too. So esteemed is he that Newton was apparently rather jealous of him, and one historian has referred to him as 'England's Leonardo'. He never married, and lived in his Oxford college all his adult life, and is buried in Bishopsgate, London. As one of the fathers of geophysics, we salute him.

The painting of Hooke, by Rita Greer, is licensed under a Free Art License. It's a interpretation based on descriptions of him ("his chin sharp, and forehead large"); amazingly, there are no known contemporary images of him. Hear more about this.

You can read more about the relationship between Hooke's law and seismic waves in Bill Goodway's and Evan's chapters in 52 Things You Should Know About Geophysics. Download their chapters for free!

Units of geological time

I have an exercise in my writing course on scientific units. The last question is about units of geological time, and it always starts a debate. I favour ka, Ma, and Ga for all dates and spans of time, but I've never gone unchallenged. People like Ma BP, mya, m.y., myr, and lots of other things, and I've heard all sorts of rules for when to use which, and why. The sort of rules you can't quite remember the crucial details of.

Twitter isn't for everyone, but I think it has some real strengths — it's a great filter, a reliable connection finder, and a brilliant place to ask questions. So I asked Twitter, and compiled the responses in a storyboard:

The story exposed a useful blog post, an attempt to standardize (Aubry et al., 2009, Stratigraphy 6 (2), 100–105], another attempt [Holden et al., 2011, IUPAC–IUGS recommendation], and a firm rebuttal from Nick Christie-Blick. Many thanks to all my Twitter friends — one of whom I've actually met IRL!

Bottom line — there are regional variations and personal preferences. There's no consensus. Make your choice. Write unambiguously.

Segmentation and decomposition

Day 4 of the SEG Annual Meeting in Las Vegas was a game of two halves: talks in the morning and workshops in the afternoon. I caught two signal processing talks, two image processing talks, and two automatic interpretation talks, then spent the afternoon in a new kind of workshop for students. My highlights:

Anne Solberg, DSB, University of Oslo

Evan and I have been thinking about image segmentation recently, so I'm drawn to those talks (remember Halpert on Day 2?). Angélique Berthelot et al. have been doing interesting work on salt body detection. Solberg (Berthelot's supervisor) showed some remarkable results. Their algorithm:

1. Compute texture attributes, including Haralick and wavenumber textures (Solberg 2011)
2. Supervised Bayesian classification (we've been using fuzzy c-means)
3. 3D regularization and segmentation (okay, I got a bit lost at this point)

The results are excellent, echoing human interpretation well (right) — but having the advantage of being objective and repeatable. I was especially interested in the wavenumber textures, and think they'll help us in our geothermal work. 

Jiajun Han, BLISS, University of Alberta

The first talk of the day was that classic oil industry: a patented technique with an obscure relationship to theory. But Jiajun Han and Mirko van der Baan of the University of Alberta gave us the real deal — a special implementation of empirical mode decomposition, which is a way to analyse time scales (frequencies, essentially), without leaving the time domain. The result is a set of intrinsic mode functions (IMFs), a bit like Fourier components, from which Han extracts instantaneous frequency. It's a clever idea, and the results are impressive. Time–frequency displays usually show smearing in either the time or frequency domain, but Han's method pinpoints the signals precisely:

That's it from me for SEG — I fly home tomorrow. It's tempting to stay for the IQ Earth workshop tomorrow, but I miss my family, and I'm not sure I can crank out another post. If you were in Vegas and saw something amazing (at SEG I mean), please let us know in the comments below. If you weren't, I hope you've enjoyed these posts. Maybe we'll see you in Houston next year!

More posts from SEG 2012.

The images adapted from Berthelot and Han are from the 2012 Annual Meeting proceedings. They are copyright of SEG, and used here in accordance with their permissions guidelines.

Update on 2012-11-09 05:08 by Matt Hall

I just stumbled on another blog post about SEG! Laurent Duval has lots to read on his geophysicsy blog. Add it to your reader.

I was especially pleased to see him writing about Chuck Mosher's talk on the generalized windowed transform, because I was ill-equipped to write about it*, though it seemed 'important'. 

* I know what you're thinking — that doesn't usually stop me.

Brittleness and robovibes

Day 3 of the SEG Annual Meeting was just as rammed with geophysics as the previous two days. I missed this morning's technical program, however, as I've taken on the chairpersonship (if that's a word) of the SEG Online Committee. So I had fun today getting to grips with that business. Aside: if you have opinion's about SEG's online presence, please feel free to send them my way.

Here are my highlights from the rest of the day — both were footnotes in their respective talks:

Brittleness — Lev Vernick, Marathon

Evan and I have had a What is brittleness? post in our Drafts folder for almost two years. We're skeptical of the prevailing view that a shale's brittleness is (a) a tangible rock property and (b) a function of Young's modulus and Poisson's ratio, as proposed by Rickman et al. 2008, SPE 115258. To hear such an intellect as Lev declare the same today convinced me that we need to finish that post — stay tuned for that. Bottom line: computing shale brittleness from elastic properties is not physically meaningful. We need to find more appropriate measures of frackability, [Edit, May 2015; Vernik tells me the following bit is the opposite of what he said, apologies for my cloth ears...] which Lev pointed out is, generally speaking, inversely proportional to organic content. This poses a basic conflict for those exploiting shale plays. [End of public service announcement.]

Robovibes — Guus Berkhout, TU Delft

At least 75% of Berkhout's talk went by me today, mostly over my head. I stopped writing notes, which I only do when I'm defeated. But once he'd got his blended source stuff out of the way, he went rogue and asked the following questions:

1. Why do we combine all seismic frequencies into the device? Audio got over this years ago (right).
2. Why do we put all the frequencies at the same location? Viz 7.1 surround sound.
3. Why don't we try more crazy things in acquisition?

I've wondered the same thing myself — thinking more about the receiver side than the sources — after hearing about the brilliant sampling strategy the Square Kilometer Array is using at a PIMS Lunchbox Lecture once. But Berkhout didn't stop at just spreading a few low-frequency vibrators around the place. No, he wants robots. He wants an autonomous army of flying and/or floating narrow-band sources, each on its own grid, each with its own ghost matching, each with its own deblending code. This might be the cheapest million-channel acquisition system possible. Berkhout's aeronautical vibrator project starts in January. Seriously.

More posts from SEG 2012.

Speaker image is licensed CC-BY-SA by Tobias Rütten, Wikipedia user Metoc.

Smoothing, unsmoothness, and stuff

Day 2 at the SEG Annual Meeting in Las Vegas continued with 191 talks and dozens more posters. People are rushing around all over the place — there are absolutely no breaks, other than lunch, so it's easy to get frazzled. Here are my highlights:

Adam Halpert, Stanford

Image segmentation is an important class of problems in computer vision. An application to seismic data is to automatically pick a contiguous cloud of voxels from the 3D seismic image — a salt body, perhaps. Before trying to do this, it is common to reduce noise (e.g. roughness and jitter) by smoothing the image. The trick is to do this without blurring geologically important edges. Halpert did the hard work and assessed a number of smoothers for both efficacy and efficiency: median (easy), Kuwahara, maximum homogeneity median, Hale's bilateral [PDF], and AlBinHassan's filter. You can read all about his research in his paper online [PDF]. 

Dave Hale, Colorado School of Mines

Automatic fault detection is a long-standing problem in interpretation. Methods tend to focus on optimizing a dissimilarity image of some kind (e.g. Bø 2012 and Dorn 2012), or on detecting planar discontinuities in that image. Hale's method is, I think, a new approach. And it seems to work well, finding fault planes and their throw (right).

Fear not, it's not complete automation — the method can't organize fault planes, interpret their meaning, or discriminate artifacts. But it is undoubtedly faster, more accurate, and more objective than a human. His test dataset is the F3 dataset from dGB's Open Seismic Repository. The shallow section, which resembles the famous polygonally faulted Eocene of the North Sea and elsewhere, contains point-up conical faults that no human would have picked. He is open to explanations of this geometry. 

Other good bits

John Etgen and Chandan Kumar of BP made a very useful tutorial poster about the differences and similarities between pre-stack time and depth migration. They busted some myths about PreSTM:

• Time migration is actually not always more amplitude-friendly than depth migration.
• Time migration does not necessarily produce less noisy images.
• Time migration does not necessarily produce higher frequency images.
• Time migration is not necessarily less sensitive to velocity errors.
• Time migration images do not necessarily have time units.
• Time migrations can use the wave equation.
• But time migration is definitely less expensive than depth migration. That's not a myth.

Brian Frehner of Oklahoma State presented his research [PDF] to the Historical Preservation Committee, which I happened to be in this morning. Check out his interesting-looking book, Finding Oil: The Nature of Petroleum Geology. 

Jon Claerbout of Stanford gave his first talk in several years. I missed it unfortunately, but Sergey Fomel said it was his highlight of the day, and that's good enough for me. Jon is a big proponent of openness in geophysics, so no surprise that he put his talk on YouTube days ago:

The image from Hale is copyright of SEG, from the 2012 Annual Meeting proceedings, and used here in accordance with their permissions guidelines. The DOI links in this post don't work at the time of writing — SEG is on it. 

Update on 2012-11-20 13:28 by Matt Hall

Dave Hale kindly pointed me to a video he made, highlighting those weird conical faults. I think it's wonderful that it's characters like Jon Claerbout and Dave Hale that are leading a new dimension to our technical conferences. Thanks Dave!

Resolution, anisotropy, and brains

Day 1 of the SEG Annual Meeting continued with the start of the regular program — 96 talks and 71 posters, not to mention the 323 booths on the exhibition floor. Instead of deciding where to start, I wandered around the bookstore and bought Don Herron's nice-looking new book, First Steps in Seismic Interpretation, which we will review some time soon.

Here are my highlights from the rest of the day.

Chuck Ursenbach, Arcis

Calgary is the home of seismic geophysics. There's a deep tradition of signal processing, and getting the basics right. Sometimes there's snake oil too, but mostly it's good, honest science. And mathematics. So when Jim Gaiser suggested last year at SEG that PS data might offer as good resolution as SS or PP — as good, and possibly better — you know someone in Calgary will jump on it with MATLAB. Ursenbach, Cary, and Perz [PDF] did some jumping, and conclude: PP-to-PS mapping can indeed increase bandwidth, but the resolution is unchanged, because the wavelength is unchanged — 'conservation of resolution', as Ursenbach put it. Resolution isn't everything. 

Gabriel Chao, Total E&P

Chao showed a real-world case study starting with a PreSTM gather with a decent Class 2p AVO anomaly at the top of the reservoir interval (TTI Kirchhoff with 450–4350 m offset). There was residual NMO in the gather, as Leon Thomsen himself later forced Chao to admit, but there did seem to be a phase reversal at about 25°. The authors compared the gather with three synthetics: isotropic convolutional, anisotropic convolutional, and full waveform. The isotropic model was fair, but the phase reversal was out at 33°. The anisotropic convolutional model matched well right up to about 42°, beyond which only the full waveform model was close (right). Anisotropy made a similar difference to wavelet extraction, especially beyond about 25°.

Canada prevails

With no hockey to divert them, Canadians are focusing on geophysical contests this year. With the Canadian champions Keneth Silva and Abdolnaser Yousetz Zadeh denied the chance to go for the world title by circumstances beyond their control, Canada fielded a scratch team of Adrian Smith (U of C) and Darragh O'Connor (Dalhousie). So much depth is there in the boreal Americas that the pair stormed home with the trophy, the cash, and the glory.

The Challenge Bowl event was a delight — live music, semi-raucous cheering, and who can resist MC Peter Duncan's cheesy jests? If you weren't there, promise yourself you'll go next year. 

The image from Chao is copyright of SEG, from the 2012 Annual Meeting proceedings, and used here in accordance with their permissions guidelines. The image of Herron's book is also copyright of SEG; its use here is proposed to be fair use.

Ways to experiment with conferences

Yesterday I wrote about why I think technical conferences underdeliver. Coincidentally, Evan sent me this quote from Seth Godin's blog yesterday:

We've all been offered access to so many tools, so many valuable connections, so many committed people. What an opportunity.

What should we do about it? 

If we are collectively spending 6 careers at the SEG Annual Meeting every autumn, as I asserted yesterday, let's put some of that cognitive surplus to work!

I suggest starting to experiment with our conferences. There are so many tools: unconferences, idea jams, hackdays, wikithons, and other participative activities. Anything to break up sitting in the dark watching 16 lectures a day, slamming coffee and cramming posters in between. Anything to get people not just talking and drinking, but working together. What a way to build collaborations, friendships, and trust. Connecting with humans, not business cards. 

Unconvinced? consider which of these groups of people looks like they're learning, being productive, and having fun:

This year I've been to some random (for me) conferences — Science Online, Wikimania, and Strata. Here are some engaging, fun, and inspiring things happening in meetings of those communities:

• Speaker 'office hours' during the breaks so you can find them and ask questions. 
• Self-selected topical discussion tables at lunch. 
• Actual time for actual discussion after talks (no, really!).
• Cool giveaways: tattoos and stickers, funky notebooks, useful mobile apps, books, scientific toys.
• A chance to sit down and work with others — hackathons, co-writing, idea jams, and so on. 
• Engaged, relevant, grounded social media presence, not more marketing.
• An art gallery, including graphics captured during sessions. 
• No posters! Those things epitomize the churn of one-way communication.

Come to our experiment!

Clearly there's no shortage of things to try. Converting a session here, a workshop there — it's easy to do something in a sandbox, alongside the traditional. And by 'easy', I mean uncertain, risky and uncomfortable. It will require a new kind of openness. I'm not certain of the outcome, but I am certain that it's worth doing. 

On this note, a wonderful thing happened to us recently. We were — and still are — planning an unconference of our own (stay tuned for that). Then, quite unprovoked, Carmen Dumitrescu asked Evan if we'd like to chair a session at the Canada GeoConvention in May. And she invited us to 'do something different'. Perfect timing!

So — mark your calendar! GeoConvention, Calgary, May 2013. Something different.

The photo of the lecture, from the depressing point of view of the speaker, is licensed CC-BY-SA by Flickr user Pierre-Alain Dorange. The one of the unconference is licensed CC-BY-SA-NC by Flickr user aforgrave.