Burrowing by burning

Most kind of mining are low-yield games. For example, the world's annual gold production would fit in a 55 m2 room. But few mining operations I'm aware of are as low yield as the one that ran in Melle, France, from about 500 till 950 CE, producing silver for the Carolingian empire and Charlemagne's coins. I visited the site on Saturday.

The tour made it clear just how hard humans had to work to bring about commerce and industry in the Middle Ages. For a start, of course they had no machines, just picks and shovels. But the Middle Jurassic limestone is silicic and very hard, so to weaken the rock they set fires against the face and thermally shocked the rock to bits. The technique, called fire-setting, was common in the Middle Ages, and was described in detail by Georgius Agricola in his book De Re Metallica (right; aside: the best translation of this book is by Herbert Hoover!). Apart from being stupefyingly dangerous, the method is slow: each fire got the miners about 4 cm further into the earth. Incredibly, they excavated about 20 km of galleries this way, all within a few metres of the surface.

The fires were set against the walls and fuelled with wood, mostly beech. Recent experiments have found that one tonne of wood yielded about one tonne of rock. Since a tonne of rock yields 5 kg of galena, and this in turn yields 10 g of silver, we see that producing 1.1 tonnes of silver per year — enough for 640,000 deniers — was quite a feat!

There are several limits to such a resource intensive operation: wood, distance from face to works, maintenance, and willing human labour, not to mention the usual geological constraints. It is thought that, in the end, operations ended due to a shortage of wood.

Several archaeologists visit the site regularly (here's one geospatial paper I found mentioning the site: Arles et al. 2013), and the evidence of their attempts to reproduce the primitive metallurgical methods were on display. Here's my attempt to label everything, based on what I could glean from the tour guide's rapid French:

The image of the denier coin is licensed CC-BY-SA by Wikipedia user Lequenne Gwendoline


The hack is back: An invitation to get creative

We're organizing another hackathon! It's free, and it's for everyone — not just programmers. So mark your calendar for the weekend of 25 and 26 October, sign up with a frie, and come to Denver for the most creative 48 hours you'll spend this year. Then stay for the annual geophysics fest that is the SEG Annual Meeting!

First things first: what is a hackathon? Don't worry, it's not illegal, and it has nothing to do with security. It has to do with ideas and collaborative tool creation. Here's a definition from Wikipedia:

A hackathon (also known as a hack day, hackfest, or codefest) is an event in which computer programmers and others involved in software development, including graphic designers, interface designers and project managers, collaborate intensively on software projects.

I would add that we just need a lot of scientists — you can bring your knowledge of workflows, attributes, wave theory, or rock physics. We need all of that.

Creativity in geophysics

The best thing we can do with our skills — and to acquire new ones — is create things. And if we create things with and alongside others, we learn from them and they learn from us, and we make lasting connections with people. We saw all this last year, when we built several new geophysics apps:

The event is at the THRIVE coworking space in downtown Denver, less than 20 minutes' walk from the convention centre — a Manhattan distance of under 1 mile. They are opening up especially for us — so we'll have the place to ourselves. Just us, our laptops, high-speed WiFi, and lots of tacos. 

Sign up here. It's going to be awesome.

The best in the biz

This business is blessed with some forward-looking companies that know all about innovation in subsurface geoscience. We're thrilled to have some of them as sponsors of our event, and I hope they will also be providing coders and judges for the event itself. So far we have generous support from dGB — creators of the OpendTect seismic interpretation platform — and ffA — creators the GeoTeric seismic attribute analysis toolbox. A massive Thank You to them both.

If you think your organization might be up for supporting the event, please get in touch! And remember, a fantastic way to support the event — for free! — is just to come along and take part. Sign your team up here!

Student grants

We know there's a lot going on at SEG on this same weekend, and we know it's easier to get money for traditional things like courses. So... We promise that this hackathon will bring you at least as much lasting joy, insight, and skill development as any course. And, if you'll write and tell us what you'd build, we'll consider you for one of four special grants of $250 to help cover your extra costs. No strings. Send your ideas to


At home with Leonardo

Well, OK, Leonardo da Vinci wasn't actually there, having been dead 495 years, but on Tuesday morning I visited the house at which he spent the last three years of his life. I say house, it's more of a mansion — the Château du Clos Lucé is a large 15th century manoir near the centre of the small market town of Amboise in the Loire valley of northern France. The town was once the royal seat of France, and the medieval grandeur still shows. 

Leonardo was invited to France by King Francis I in 1516. Da Vinci had already served the French governor of Milan, and was feeling squeezed from Rome by upstarts Rafael and Michelangelo. It's nice to imagine that Frank appreciated Leo's intellect and creativity — he sort of collected artists and writers — but let's face it, it was probably the Italian's remarkable capacity for dreaming up war machines, a skill he had honed in the service of mercenary and cardinal Cesare Borgia. Leonardo especially seemed to like guns; here are models of a machine gun and a tank, alongside more peaceful concoctions:

Inspired by José Carcione's assertion that Leonardo was a geophysicst, and plenty of references to fossils (even Palaeodictyon) in his notebooks, I scoured the place for signs of Leonardo dablling in geology or geophysics, but to no avail. The partly-restored Renaissance floor tiles did have some inspiring textures and lots of crinoid fossils... I wonder if he noticed them as he shuffled around?

If you are ever in the area, I strongly recommend a visit. Even my kids (10, 6, and 4) enjoyed it, and it's close to some other worthy spots., specifically Chenonceau (for anyone) and Cheverny (for Tintin fans like me). The house, the numerous models, and the garden (below — complete with tasteful reproductions from Leonardo's works) were all terrific.

Check out José Carcione's two chapters about Leonardo and
his work in 52 Things You Should Know About Geophysics.
Download the chapter for free! [PDF, 3.8MB]


What I learned at Wikimania

As you may know, I like going to conferences outside the usual subsurface circuit. For this year's amusement, I spent part of last week at the annual Wikimania conference, which this year was in London, UK. I've been to Wikimania before, but this year the conference promised to be bigger and/or better than ever. And I was looking for an excuse to visit the motherland...

What is Wikimania?

Wikipedia, one of humanity's greatest achievements, has lots of moving parts:

  • All the amazing content on — the best encyclopedia the world has ever seen (according to a recent study by Rodrigues and Silvério).
  • The huge, diverse, distributed community of contributors and editors that writes and maintains the content.
  • The free, open source software it runs on, MediaWiki, and the community of developers that built it.
  • The family of sister projects: Wikimedia Commons for images, Wikidata for facts, WikiSource for references, Wiktionary for definitions, and several others.
  • The Wikimedia Foundation, the non-profit that makes all this amazing stuff happen.

Wikimania is the gathering for all of these pieces. And this year the event drew over 2000 employees of the Foundation, software contributors, editors, and consultants like me. I can't summarize it all, so here are a few highlights...

Research reviews

My favourite session, The state of WikiMedia scholarship, was hosted by Benjamin Mako Hill, Tilman Bayer, and Aaron Shaw. These guys are academics conducting research into the sociological side of wikis. They took it upon themselves to survey most of the 800 papers that appeared in the last 12 months, and to pick a few themes and highlights them for everyone. A little like the Geophysics Bright Spots column in The Leading Edge, but for the entire discipline. Very cool — definitely an idea to borrow!

A definition of community

Communities are one thing, but what sets the Wikimania community apart is its massive productivity. It has created one of the premier intellectual works in history, and done so in under 10 years, and without a leader or a Gantt chart. So it's interesting to hear about what makes this community work. What would you guess? Alignment? Collaboration? Altruism?

No, it seems to be conflict. Conflict, centered firmly on content—specifically sources, wording, accuracy, and article structure—is more prevalent in the community than collaboration (Kim Osman, WikiSym 2013). It's called it 'generative friction', and it underlines something I think is intuitively obvious: communities thrive on diversity, not homogeneity.

How to make a difference

The most striking talk, illustrating perfectly how the world today is a new and wonderful place, was by one of the most inspiring leaders I've ever seen in action: Clare Sutcliffe. In 2012, she discovered that kids weren't getting a chance to give computers instructions (other than 'post this', or 'buy that') in most UK primary schools. Instead of writing a paper about it, or setting up a research institute, or indeed blogging about it, she immediately started doing something about it. Her program, Code Club, is now running in more than 2000 schools. Today, less than 3 years after starting, Code Club is teaching teachers too, and has spread internationally. Amazing and inspiring.

Amusingly, here's a (paraphrased) comment she got from a computer science professor at the end:

I teach computer science at university, where we have to get the kids to unlearn all the stuff they think they know about programming. What are you teaching them about computer science and ethics, or is it all about making games?

Some people are beyond help.

The product is not the goal

I'll finish off with a remark by the new Executive Director of the WikiMedia Foundation, Lila Tretikov. Now that Wikipedia's quality issues are well and truly behind it — the enemy now is bias. At least 87% of edits are by men. She wondered if it might be time to change the goal of the community from 'the greatest possible article', to 'the greatest possible participation'. By definition, the greatest article is also presumably unbiased.

In other words, instead of imagining a world where everyone has free access to the sum of all human knowledge, she is asking us to imagine a world where everyone contributes to the sum of all human knowledge. If you can think of a more profound idea than this — let's hear it in the comments!

The next Wikimania will be in Mexico City, in July 2015. See you there!

Here's a thought. All this stuff is free — yay! But happy thoughts aren't enough to get stuff done. So if you value this corner of the Internet, please consider donating to the Foundation. Better still, if your company values it — maybe it uses the MediaWiki software for its own wiki — then it can help with the software's development by donating. Instead of giving Microsoft $1M for a rubbish SharePoint pseudowiki, download MediaWiki for free and donate $250k to the foundation. It's a win-win... and it's tax-deductible!


The Blangy equation

After reading Chris Liner's recent writings on attenuation and negative Q — both in The Leading Edge and on his blog — I've been reading up a bit on anisotropy. The idea was to stumble a little closer to writing the long-awaited Q is for Q post in our A to Z series. As usual, I got distracted...

In his 1994 paper AVO in tranversely isotropic media—An overview, Blangy (now the chief geophysicist at Hess) answered a simple question: How does anisotropy affect AVO? Stigler's law notwithstanding, I'm calling his solution the Blangy equation. The answer turns out to be: quite a bit, especially if impedance contrasts are low. In particular, Thomsen's parameter δ affects the AVO response at all offsets (except zero of course), while ε is relatively negligible up to about 30°.

The key figure is Figure 2. Part (a) shows isotropic vs anisotropic Type I, Type II, and Type III responses:

Unpeeling the equation

Converting the published equation to Python was straightforward (well, once Evan pointed out a typo — yay editors!). Here's a snippet, with the output (here's all of it):

For the plot below, I computed the terms of the equation separately for the Type II case. This way we can see the relative contributions of the terms. Note that the 3-term solution is equivalent to the Aki–Richards equation.

Interestingly, the 5-term result is almost the same as the 2-term approximation.

Reproducible results

One of the other nice features of this paper — and the thing that makes it reproducible — is the unambiguous display of the data used in the models. Often, this sort of thing is buried in the text, or not available at all. A table makes it clear:

Last thought: is it just me, or is it mind-blowing that this paper is now over 20 years old?


Blangy, JP (1994). AVO in tranversely isotropic media—An overview. Geophysics 59 (5), 775–781.

Don't miss the IPython Notebook that goes with this post.