# Tune in to Undersampled Radio

Back in the summer I mentioned Undersampled Radio, the world's newest podcast about geoscience. Well, geoscience and computers. OK, machine learning and geoscience. And conferences.

We're now 25 shows in, having started with Episode 0 on 28 January. The show is hosted by Graham 'Gram' Ganssle, a consulting and research geophysicist based in New Orleans, and me. Appropriately enough, I met Gram at the machine-learning-themed hackathon we did at SEG in 2015. He was also a big help with the local knowledge.

I broadcast from one of the phone rooms at The HUB South Shore. Gram has the luxury of a substantial book-lined office, which I imagine has ample views of paddle-steamers lolling on the Mississippi (but I actually have no idea where it is).

To get an idea of what we chat about, check out the guests on some recent episodes:

### Better than cable

The podcast is really more than just a podcast, it's really a live TV show, broadcasting on YouTube Live. You can catch the action while it's happening on the Undersampled Radio channel. However, it's not easy to catch live because the episodes are not that predictable — they are announced about 24 hours in advance on the Software Underground Slack group (you are in there, right?). We should try to put them out on the @undrsmpldrdio Twitter feed too...

So, go ahead and watch the very latest episode, recorded last Thursday. We spoke to Tim Hopper, a data scientist in Raleigh, NC, who works at Distil Networks, a cybersecurity firm. It turns out that using machine learning to filter web traffic has some features in common with computational geophysics...

You can subscribe to the show in iTunes or Google Play, or anywhere else good podcasts are served. Grab the RSS Feed from the UndersampledRad.io website.

Of course, we take guest requests. Who would you like to hear us talk to?

Comment

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# Working without a job

I have drafted variants of this post lots of times. I've never published them because advice always feels... presumptuous. So let me say: I don't have any answers. But I do know that the usual way of 'finding work' doesn't work any more, so maybe the need for ideas, or just hope, has grown.

Lots of people are out of work right now. I just read that 120,000 jobs have been lost in the oil industry in the UK alone. It's about the same order of magnitude in Canada, maybe as much as 200,000. Indeed, several of my friends — smart, uber-capable professionals — are newly out of jobs. There's no fat left to trim in operator or service companies... but the cuts continue. It's awful.

The good news is that I think we can leave this downturn with a new, and much better, template for employment. The idea is to be more resilient for 'next time' (the coming mergers, the next downturn, the death throes of the industry, that sort of thing).

### The tragedy of the corporate professional

At least 15 years ago, probably during a downturn, our corporate employers started telling us that we are responsible for our own careers. This might sound like a cop-out, maybe it was even meant as one, but really it's not. Taken at face value, it's a clear empowerment.

My perception is that most professionals did not rise to the challenge, however. I still hear, literally all the time, that people can't submit a paper to a conference, or give a talk, or write a blog, or that they can't take a course, or travel to a workshop. Most of the time this comes from people who have not even asked, they just assume the answer will be No. I worry that they have completely given in; their professional growth curtailed by the real or imagined conditions of their employment.

More than just their missed opportunity, I think this is a tragedy for all of us. Their expertise effectively gone from the profession, these lost scientists are unknown outside their organizations.

Many organizations are happy for things to work out that way, but when they make the situation crystal clear by letting people go, the inequity is obvious. The professional realizes, too late, that the career they were supposed to be managing (and perhaps thought they were managing by completing their annual review forms on time) was just that — a career, not a job. A career spanning multiple jobs and, it turns out, multiple organizations.

I read on LinkedIn recently someone wishing recently let-go people good luck, hoping that they could soon 'resume their careers'. I understand the sentiment, but I don't see it the same way. You don't stop being a professional, it's not a job. Your career continues, it's just going in a different direction. It's definitely not 'on hold'. If you treat it that way, you're missing an opportunity, perhaps the best one of your career so far.

### What you can do

Oh great, unsolicited advice from someone who has no idea what you're going through. I know. But hey, you're reading a blog, what did you expect?

• Do you want out? If you think you might want to leave the industry and change your career in a profound way, do it. Start doing it right now and don't look back. If your heart's not in this work, the next months and maybe years are really not going to be fun. You're never going to have a better run at something completely different.
• You never stop being a professional, just like a doctor never stops being a doctor. If you're committed to this profession, grasp and believe this idea. Your status as such is unrelated to the job you happen to have or the work you happen to be doing. Regaining ownership of our brains would be the silveriest of linings to this downturn.
• Your purpose as a professional is to offer help and advice, informed by your experience, in and around your field of expertise. This has not changed. There are many, many channels for this purpose. A job is only one. I firmly believe that if you create value for people, you will be valued and — eventually — rewarded.
• Establish a professional identity that exists outside and above your work identity. Get your own business cards. Go to meetings and conferences on your own time. Write papers and articles. Get on social media. Participate in the global community of professional geoscientists.
• Build self-sufficiency. Invest in a powerful computer and fast Internet. Learn to use QGIS and OpendTect. Embrace open source software and open data. If and when you get some contracting work, use Tick to count hours, Wave for accounting and invoicing, and Todoist to keep track of your tasks.
• Find a place to work — I highly recommend coworking spaces. There is one near you, I can practically guarantee it. Trust me, it's a much better place to work than home. I can barely begin to describe the uplift, courage, and inspiration you will get from the other entrepreneurs and freelancers in the space.
• Find others like you, even if you can't get to a coworking space, your new peers are out there somewhere. Create the conditions for collaboration. Find people on meetup.com, go along to tech and start-up events at your local university, or if you really can't find anything, organize an event yourself!
• Note that there are many ways to make a living. Money in exchange for time is one, but it's not a very efficient one. It's just another hokey self-help business book, but reading The 4-Hour Workweek honestly changed the way I look at money, time, and work forever.
• Remember entrepreneurship. If you have an idea for a new product or service, now's your chance. There's a world of making sh*t happen out there — you genuinely do not need to wait for a job. Seek out your local startup scene and get inspired. If you've only ever worked in a corporation, people's audacity will blow you away.

If you are out of a job right now, I'm sorry for your loss. And I'm excited to see what you do next.

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# What will people pay for?

Many organizations in the industry are asking this question right now. Software and service companies would like to sell product, technical societies would like to survive diminished ad sales and conference revenue, entrepreneurs would like to find customers. We all need to make a living.

I was recently asked this very question by a technical society. However, it's utterly the wrong question. Even asking this question reveals a deep-seated misunderstanding of what technical societies are for.

The question is not "What will people pay for?", it's "What do people need?".

### The leaders of our profession

Geoscientists and engineers are professionals. Our professional contributions are defined by our work and its purpose, not by our jobs and its tasks. This is essentially what makes a professional different from other workers: we are purpose-oriented, not task-oriented. We're interested in the outcome, not the means.

But even professionals benefit from leadership. Professional regulators notwithstanding, our technical societies are the de facto leaders of the profession. The professional regulator is the 'line manager' of the profession, not the 'chief geoscientist'.

Leadership is about setting an example, inspiring great work, and providing the means to grow and make the best contributions people can make. Societies need to be asking themselves how they can create the conditions for a transformed profession, a more relevant and resilient one. In short, how can they be useful? How can they serve?

### OK, so what do people need?

I don't claim to have all the answers, or even many of them, but here are some things I think people need:

• Representation. Get serious about gender and race balance on your boards and committees. There is recent progress, but it's nowhere near representative. Related: get out of North America and improve global reach.
• Better ways to contribute and connect. Experiment more — a lot more, and urgently — with meetings and conferences. Help people participate, not just attend. Help people connect, not just exchange business cards.
• New ways to contribute and connect. Get serious about social media. Get scientists involved — social media is not a marketing exercise. Think hard about how you can engage your members through blogs and other content.
• Reproducible science. Go further with open access, open data, and open source code. Make your content work harder. Make it reach further. Demand more of your authors to make their work reproducible.
• A bit less self-interest. Stop regarding things you didn't organize or produce as a threat. Other people's events and publications may be of interest to your members, and your mission is to serve them.

Don't listen to my blathering. The AGU and the EGU are real leaders in geoscience — be inspired by them, follow their lead. Pay more attention to what's happening in publishing and conferences in other technical verticals, especially technology.

### Pie in the sky is still pie

People will say, "That's all great Matt, but right now it's about survival." I get this a lot, but I'm not buying it. When times are good, you don't need to do the right thing; when times are hard, you can't afford to. True, all this would be easier if you'd started doing the right thing when times were good, but you didn't, so here we are.

Sure it's tough now, but are you sure you can afford to wait till tomorrow?

I've written lots before on these topics. Suggested reading:

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# x lines of Python: read and write SEG-Y

Reading SEG-Y files comes up a lot in the geophysicist's workflow. Writing, less often, but it does come up occasionally. As long as we're mostly concerned with trace data and not location, both of these tasks can be fairly easily accomplished with ObsPy.

Today we'll load some seismic, compute an attribute on it, and save a new SEG-Y, in 10 lines of Python.

ObsPy is a rare thing. It demonstrates what a research group can accomplish with a little planning and a lot of perseverance (cf my whinging earlier this year about certain consortiums in our field). It's an open source Python package from the geophysicists at the University of Munich — Karl Bernhard Zoeppritz studied there for a while, so you know it's legit. The tool serves their research in earthquake and global seismology needs, and also happens to handle SEG-Y files quite nicely.

Aside: I think SixtyNorth's segpy is actually the way to go for reading and writing SEG-Y; ObsPy is probably overkill for most applications — it's about 80 times the size for one thing. I just happen to be familiar with it and it's super easy to install: conda install obspy. So, since minimalism is kind of the point here, look out for a future x lines of Python using that library.

### The sentences

As before, we'd like to express the process in just a few sentences of plain English. Assuming we just want to read the data into a NumPy array, look at it, do something to it, and write a new file, here's what we're doing:

1. Read (or really index) the file as an ObsPy Stream object.
2. Stack (in the NumPy sense) the Trace objects into a single NumPy array. We have data!
3. Get the 99th percentile of the amplitudes to make plotting easier.
4. Plot the data so we can see it.
5. Get the sample interval of the data from a trace header.
6. Compute the similarity attribute using our library bruges.
7. Make a new Stream object to hold the outbound data.
10. Write a new SEG-Y file with our computed data in it!

There's a bit more in the Jupyter Notebook (examining the file and trace headers, for example, and a few more plots) which, remember, you can run right in your browser! You don't need to install a thing. Please give it a look! Quick tip: Just keep hitting Shift+Enter to run the cells.

If you like this sort of thing, and are planning to be at the SEG Annual Meeting in Dallas next month, you might like to know that we'll be teaching our Creative Geocomputing class there. It's basically two days of this sort of thing, only with friends to learn with and us to help. Come and learn some new skills!

The seismic data used in this post is from the NPRA seismic repository of the USGS. The data is in the public domain.

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# x lines of Python: synthetic wedge model

Welcome to a new blog series! Like the A to Z and the Great Geohpysicists, I expect it will be sporadic and unpredictable, but I know you enjoys life's little nonlinearities as much as I.

The idea with this one — x lines of Python — is to share small geoscience workflows in x lines or fewer. I'm not sure about the value of x, but I think 10 seems reasonable for most tasks. If x > 10 then the task may have been too big... If x < 5 then it was probably too small.

Python developer Raymond Hettinger says that each line of code should be equivalent to a sentence... so let's say that that's the measure of what's OK to put in a single line.

### Synthetic wedge model

To kick things off, follow this link to a live Jupyter Notebook environment showing how you can make a simple synthetic three-rock wedge model in only 9 lines of code.

The sentences represented by the code that made the data in these images are:

1. Set up the size of the model.
2. Make the slanty bit, with 1's in the wedge and 2's in the base.
3. Add the top of the model as 0; these numbers will turn into rocks.
4. Define the velocity and density of rocks 0 to 2.
5. Distribute those properties through the model.
6. Calculate the acoustic impedance everywhere.
7. Calculate the reflection coefficients in the model.
8. Make a Ricker wavelet.
9. Convolve the wavelet with the reflection coefficients.

All of the notebooks we share in this series will be hosted on mybinder.org. I'm excited about this because it means you can run and edit them live, without installing anything at all. Give it a go right now.

You can see them on GitHub too, and fork or clone them from there. Note that if you look at the notebook for this post on GitHub, you'll be able to view it, but not change or run code unless you get everything running on your own machine. (To do that, you can more or less follow the instructions in my User Guide to the TLE tutorials).

Please do take this notion of x as 'par' as a challenge. If you'd like to try to shoot under par, please do — and share your efforts. Code golf is a fun way to learn better coding habits. (And maybe some bad ones.) There is a good chance I will shoot some bogies on this course.

We will certainly take requests too — what tasks would you like to see in x lines of Python?

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# What's that funny noise?

Seismic reflections are strange noises. Around 50 Hz, narrow band, very quiet, and difficult to interpret. It is possible to convert seismic traces (active or passive) into audible sound with a shift in pitch and a time stretch.

Made by the legendary Emory Cook, who recorded everything from steel bands to racing cars to ionospheric noises to this treatment of Hugo Benioff's earthquake recordings. Epic.

Curiously the audification thing has never really caught on in exploration geophysics — a bit surprising, given the fascination with spectral decomposition over the last 15 years or so. And especially so when you consider that our hearing has a dynamic range of about 100 dB, which is comparable to, indeed slightly greater than, our vision (about 90 dB).

Paolo Dell'Aversana of ENI wants to change that. Rather than listening to 'raw' seismic, he's sending it to a MIDI interface and listening to it as a piano roll. Just try to imagine playing seismic on a piano for a second, then listen to his weird and wonderful results — at 9:45 in this EAGE video:

In this EAGE E-Lecture Paolo Dell'Aversana discusses how digital music technology can support geophysical data analysis and interpretation. If you've read any of Dell'Aversana's articles, you'll know he has one of the most creative minds in exploration geophysics. Skip to 9:45 for the crazy seismic piano roll.

On the subject of weird sounds, one of my favourite Wikipedia pages is List of unexplained sounds. I especially love the eerie recordings of mysterious underwater noises, like this one called Upsweep:

No-one knows what makes that noise! My money's on a volcanic vent, but that doesn't explain the seasonality. Maybe we should do a hackathon on these unexaplained sounds some time. If you know of any others — I'd love tohear about them.

If you enjoy strange infrasound as much as I do, I recommend following these two scientists on Twitter:

f you really like strange noises, don't forget to check out the Undersampled Radio podcast!

1 Comment

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# Hooke's oolite

52 Things You Should Know About Rock Physics came out last week. For the first, and possibly the last, time a Fellow of the Royal Society — the most exclusive science club in the UK — drew the picture on the cover. The 353-year-old drawing was made by none other than Robert Hooke

The title page from Micrographia, and part of the dedication to Charles II. You can browse the entire book at archive.org.

The drawing, or rather the engraving that was made from it, appears on page 92 of Micrographia, Hooke's groundbreaking 1665 work on microscopy. In between discovering and publishing his eponymous law of elasticity (which Evan wrote about in connection with Lamé's $$\lambda$$), he drew and wrote about his observations of a huge range of natural specimens under the microscope. It was the first time anyone had recorded such things, and it was years before its accuracy and detail were surpassed. The book established the science of microscopy, and also coined the word cell, in its biological context.

Sadly, the original drawing, along with every other drawing but one from the volume, was lost in the Great Fire of London, 350 years ago almost to the day.

### Ketton stone

The drawing on the cover of the new book is of the fractured surface of Ketton stone, a Middle Jurassic oolite from central England. Hooke's own description of the rock, which he mistakenly called Kettering Stone, is rather wonderful:

I wonder if anyone else has ever described oolite as looking like the ovary of a herring?

These thoughtful descriptions, revealing a profundly learned scientist, hint at why Hooke has been called 'England's Leonardo'. It seems likely that he came by the stone via his interest in architecture, and especially through his friendsip with Christopher Wren. By 1663, when it's likely Hooke made his observations, Wren had used the stone in the façades of several Cambridge colleges, including the chapels of Pembroke and Emmanuel, and the Wren Library at Trinity (shown here). Masons call porous, isotropic rock like Ketton stone 'freestone', because they can carve it freely to make ornate designs. Rock physics in action!

You can read more about Hooke's oolite, and the geological significance of his observations, in an excellent short paper by material scientist Derek Hull (1997). It includes these images of Ketton stone, for comparison with Hooke's drawing:

Reflected light photomicrograph (left) and backscatter scanning electron microscope image (right) of Ketton Stone. Adapted from figures 2 and 3 of Hull (1997). Images are © Royal Society and used in accordance with their terms.

I love that this book, which is mostly about the elastic behaviour of rocks, bears an illustration by the man that first described elasticity. Better still, the illustration is of a fractured rock — making it the perfect preface.

References

Hall, M & E Bianco (eds.) (2016). 52 Things You Should Know About Rock Physics. Nova Scotia: Agile Libre, 134 pp.

Hooke, R (1665). Micrographia: or some Physiological Descriptions of Minute Bodies made by Magnifying Glasses, pp. 93–100. The Royal Society, London, 1665.

Hull, D (1997). Robert Hooke: A fractographic study of Kettering-stone. Notes and Records of the Royal Society of London 51, p 45-55. DOI: 10.1098/rsnr.1997.0005.

1 Comment

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# 52 Things... Rock Physics

There's a new book in the 52 Things family!

52 Things You Should Know About Rock Physics is out today, and available for purchase at Amazon.com. It will appear in their European stores in the next day or two, and in Canada... well, soon. If you can't wait for that, you can buy the book immediately direct from the printer by following this link.

The book mines the same vein as the previous volumes. In some ways, it's a volume 2 of the original 52 Things... Geophysics book, just a little bit more quantitative. It features a few of the same authors — Sven Treitel, Brian Russell, Rachel Newrick, Per Avseth, and Rob Simm — but most of the 46 authors are new to the project. Here are some of the first-timers' essays:

• Arthur Cheng, How to catch a shear wave.
• Peter Duncan, Mapping fractures.
• Paul Johnson, The astonishing case of non-linear elasticity.
• Chris Liner, Negative Q.
• Chris Skelt, Five questions to ask the petrophysicist.

It's our best collection of essays yet. We're very proud of the authors and the collection they've created. It stretches from childhood stories to linear algebra, and from the microscope to seismic data. There's no technical book like it.

### Supporting Geoscientists Without Borders

Purchasing the book will not only bring you profund insights into rock physics — there's more! Every sale sends \$2 to Geoscientists Without Borders, the SEG charity that supports the humanitarian application of geoscience in places that need it. Read more about their important work.

It's been an extra big effort to get this book out. The project was completely derailed in 2015, as we — like everyone else — struggled with some existential questions. But we jumped back into it earlier this year, and Kara (the managing editor, and my wife) worked her magic. She loves working with the authors on proofs and so on, but she doesn't want to see any more equations for a while.

If you choose to buy the book, I hope you enjoy it. If you enjoy it, I hope you share it. If you want to share it with a lot of people, get in touch — we can help. Like the other books, the content is open access — so you are free to share and re-use it as you wish.

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# Q is for Q

Quality factor, or $$Q$$, is one of the more mysterious quantities of seismology. It's right up there with Lamé's $$\lambda$$ and Thomsen's $$\gamma$$. For one thing, it's wrapped up with the idea of attenuation, and sometimes the terms $$Q$$ and 'attenuation' are bandied about seemingly interchangeably. For another thing, people talk about it like it's really important, but it often seems to be completely ignored.

A quick aside. There's another quality factor: the rock quality factor, popular among geomechnicists (geomechanics?). That $$Q$$ describes the degree and roughness of jointing in rocks, and is probably related — coincidentally if not theoretically — to seismic $$Q$$ in various nonlinear and probably profound ways. I'm not going to say any more about it, but if this interests you, read Nick Barton's book, Rock Quality, Seismic Velocity, Attenuation and Anistropy (2006; CRC Press) if you can afford it.

### So what is Q exactly?

We know intuitively that seismic waves lose energy as they travel through the earth. There are three loss mechanisms: scattering (elastic losses resulting from reflections and diffractions), geometrical spreading, and intrinsic attenuation. This last one, anelastic energy loss due to absorption — essentially the deviation from perfect elasticity — is what I'm trying to describe here.

I'm not going to get very far, by the way. For the full story, start at the seminal review paper entitled $$Q$$ by Leon Knopoff (1964), which surely has the shortest title of any paper in geophysics. (Knopoff also liked short abstracts, as you see here.)

The dimensionless seismic quality factor $$Q$$ is defined in terms of the energy $$E$$ stored in one cycle, and the change in energy — the energy dissipated in various ways, such as fluid movement (AKA 'sloshing', according to Carl Reine's essay in 52 Things... Geophysics) and intergranular frictional heat ('jostling') — over that cycle:

$$Q \stackrel{\mathrm{def}}{=} 2 \pi \frac{E}{\Delta E}$$

Remarkably, this same definition holds for any resonator, including pendulums and electronics. Physics is awesome!

Because the right-hand side of that relationship is sort of upside down — the loss is in the denominator — it's often easier to talk about $$Q^{-1}$$ which is, more or less, the percentage loss of energy in a single wavelength. This inverse of $$Q$$ is proportional to the attenuation coefficient. For more details on that relationship, check out Carl Reine's essay.

This connection with wavelengths means that we have to think about frequency. Because high frequencies have shorter cycles (by definition), they attenuate faster than low frequencies. You know this intuitively from hearing the beat, but not the melody, of distant music for example. This effect does not imply that $$Q$$ depends on frequency... that's a whole other can of worms. (Confused yet?)

### The frequency dependence of $$Q$$

It's thought that $$Q$$ is roughly constant with respect to frequency below about 1 Hz, then increases with $$f^\alpha$$, where $$\alpha$$ is about 0.7, up to at least 25 Hz (I'm reading this in Mirko van der Baan's 2002 paper), and probably beyond. Most people, however, seem to throw their hands up and assume a constant $$Q$$ even in the seismic bandwidth... mainly to make life easier when it comes to seismic processing. Attempting to measure, let alone compensate for, $$Q$$ in seismic data is, I think it's fair to say, an unsolved problem in exploration geophysics.

Why is it worth solving? I think the main point is that, if we could model and measure it better, it could be a semi-independent measure of some rock properties we care about, especially velocity. Actually, I think it's even a stretch to call velocity a rock property — most people know that velocity depends on frequency, at least across the gulf of frequencies between seismic and acoustic logging tools, but did you know that velocity also depends on amplitude? Paul Johnson tells about this effect in his essay in the forthcoming 52 Things... Rock Physics book — stay tuned for more on that.

For a really wacky story about negative values of $$Q$$ — which imply transmission coefficients greater than 1 (think about that) — check out Chris Liner's essay in the same book (or his 2014 paper in The Leading Edge). It's not going to help $$Q$$ get any less mysterious, but it's a good story. Here's the punchline from a Jupyter Notebook I made a while back; it follows along with Chris's lovely paper:

Top: Velocity and the Backus average velocity in the E-38 well offshore Nova Scotia. Bottom: Layering-induced attenuation, or 1/Q, in the same well. Note the negative numbers! Reproduction of Liner's 2014 results in a Jupyter Notebook.

Hm, I had hoped to shed some light on $$Q$$ in this post, but I seem to have come full circle. Maybe explaining $$Q$$ is another unsolved problem.

References

Barton, N (2006). Rock Quality, Seismic Velocity, Attenuation and Anisotropy. Florida, USA: CRC Press. 756 pages. ISBN 9780415394413.

Johnson, P (in press). The astonishing case of non-linear elasticity.  In: Hall, M & E Bianco (eds), 52 Things You Should Know About Rock Physics. Nova Scotia: Agile Libre, 2016, 132 pp.

Knopoff, L (1964). Q. Reviews of Geophysics 2 (4), 625–660. DOI: 10.1029/RG002i004p00625.

Reine, C (2012). Don't ignore seismic attenuation. In: Hall, M & E Bianco (eds), 52 Things You Should Know About Geophysics. Nova Scotia: Agile Libre, 2012, 132 pp.

Liner, C (in press). Negative Q. In: Hall, M & E Bianco (eds), 52 Things You Should Know About Rock Physics. Nova Scotia: Agile Libre, 2016, 132 pp.

van der Bann, M (2002). Constant Q and a fractal, stratified Earth. Pure and Applied Geophysics 159 (7–8), 1707–1718. DOI: 10.1007/s00024-002-8704-0.

### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).

# The sound of the Software Underground

If you are a geoscientist or subsurface engineer, and you like computery things — in other words, if you read this blog — I have a treat for you. In fact, I have two! Don't eat them all at once.

### Software Underground

Sometimes (usually) we need more diversity in our lives. Other times we just want a soul mate. Or at least someone friendly to ask about that weird new seismic attribute, where to find a Python library for seismic imaging, or how to spell Kirchhoff. Chat rooms are great for those occasions, Slack is where all the cool kids go to chat, and the Software Underground is the Slack chat room for you.

It's free to join, and everyone is welcome. There are over 130 of us in there right now — you probably know some of us already (apart from me, obvsly). Just go to http://swung.rocks/ to sign up, and we will welcome you at the door with your choice of beverage.

To give you a flavour of what goes on in there, here's a listing of the active channels:

• #python — for people developing in Python
• #sharp-rocks — for people developing in C# or .NET
• #open-geoscience — for chat about open access content, open data, and open source software
• #machinelearning — for those who are into artificial intelligence
• #busdev — collaboration, subcontracting, and other business opportunities
• #general — chat about anything to do with geoscience and/or computers
• #random — everything else

If you have a long commute, or occasionally enjoy being trapped in an aeroplane while it flies around, you might have discovered the joy of audiobooks and podcasts. You've probably wished many times for a geosciencey sort of podcast, the kind where two ill-qualified buffoons interview hyper-intelligent mega-geoscientists about their exploits. I know I have.

Well, wish no more because Undersampled Radio is here! Well, here:

The show is hosted by New Orleans-based geophysicist Graham Ganssle and me. Don't worry, it's usually not just us — we talk to awesome guests like geophysicists Mika McKinnon and Maitri Erwin, geologist Chris Jackson, and geopressure guy Mark Tingay. The podcast is recorded live every week or three in Google Hangouts on Air — the link to that, and to show notes and everything else — is posted by Gram in the #undersampled Software Underground channel. You see? All these things are connected, albeit in a nonlinear, organic, highly improbable way. Pseudoconnection: the best kind of connection.

Indeed, there is another podcast pseudoconnected to Software Underground: the wonderful Don't Panic Geocast — hosted by John Leeman and Shannon Dulin — also has a channel: #dontpanic. Give their show a listen too! In fact, here's a show we recorded together!

Don't have an hour right now? OK, you asked for it, here's a clip from that show to get you started. It starts with John Leeman explaining what Fun Paper Friday is, and moves on to one of my regular rants about conferences...

In case you're wondering, neither of these projects is explicitly connected to Agile — I am just involved in both of them. I just wanted to clear up any confusion. Agile is not a podcast company, for the time being anyway.

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### Matt Hall

I am a geoscientist in Nova Scotia, Canada. Founder of Agile Geoscience, co-founder of The HUB South Shore. Into geology, geophysics, programming in Python, and knowledge sharing (especially wikis).