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Tectonics and Structural Geology

Tectonics and Structural Geology

Features from the Field: Boudinage

Features from the Field: Boudinage

The Features from the Field series is back! In our previous posts, we have shown how rocks can deform during ductile deformation, producing folds. Folds very commonly develop in rocks when rock layers are shortened by tectonic forces in a specific direction. On the other hand, when layers are extended, we develop boudins.

Saucisson is a dry cured sausage (boudin) from France. Did you know that geology is full of food analogies? Indeed, we love barbecues. Photo credits © Nate Grey (Flickr)

Boudins – the term comes from the French word for ‘sausage’ – are fragments of original layers that have been stretched and segmented. They develop in layers that are stronger and more resistant to deformation (i.e. more competent) than the surrounding rocks. In the example shown at the top of the page, the boudinated layer is made up of ‘strong’ amphibolites that are surrounded by relatively weaker quartzites. As you can see, the layering of the quartzites is deflected in the ‘pinches’, as if they where flowing in the gaps of the boudins during the extension. That’s it! During ductile deformation, rocks flow over millions of years in a plastic way.

Different rock types are characterized by a different strength during deformation, which is significantly influenced by temperature, pressure or -very important- presence of water. Boudinage is a very common structure which helps  the geologist understand ‘who is stronger than who?’ and helps them guess the physical conditions at which deformation took place.

Boudinage style can also vary enormously. For example, the eye-shaped boudins shown at the top of the page are called ‘pinch-and-swell’ structures. Indeed, you can notice that the boudins are not entirely separated and are connected by a very thin amphibolite layer, as if they were ‘pinched’ by a finger. This structure suggest that both the boudinated layer and the surrounding rocks are deforming in a ductile way.

However, fracturing can also play an important role in boudinage. In the example shown below, the top layer consists of strong quartz-metaconglomerate that has been boudinated within very weak phyllites (the bottom layer). The quartz-metaconglomerate is fragmented along symmetric (dextral and sinistral) fractures with an offset of several centimeters. The white material filling the gaps are vein of quartz that were deposited during the boudinage process. Note how the fractures are restricted to the metaconglomerate.

 

Symmetric boudinage of a quartz metaconglomerate in phyllites. The gaps of the boudins are filled with white quartz veins (Punta Bianca, La Spezia, Italy). Photo credits © Samuele Papeschi

 

Boudins can be symmetric, as in the example above, or asymmetric, as in the example below, where the boudinated layer is an amphibolite surrounded by weaker micaschists and quartzites. The boudins are separated by small scale sinistral shear fractures and systematically rotated clockwise. In this case, the geologist can obtain information about rock strength during deformation, but also on the sense of shear – which here is top to the right.

 

Asymmetric boudinage of amphibolite (the blackish layer) in dark grey biotite-micaschists and white quartzites (Elba Island, Italy). The amphibolite layers is fragmented by several, sinistral shear fractures. Photo credits © Samuele Papeschi

 

Rocks are not stretched in a single direction. Layers can also be flattened and stretched along 2 directions. When this occurs, you get fragmented boudins surrounded by 2 sets of fractures, as in the last example below. You already know that geologists like food analogies, so are you able to guess the name of this last structure? Yes, it is a chocolate tablet boudinage.

 

Chocolate tablet boudinage: a grey dolomite vein has been stretched along two, nearly-perpendicular, directions. The gaps between the boudins are filled by calcite deposited by fluids (Punta Bianca, La Spezia, Italy). Photo credits © Samuele Papeschi.

 

To sum it up, boudinage is a very important structure when studying rocks in the field, which gives us important insights about deformation, rock strength, pressure and temperature conditions and the sense of shear. Together with folds, lineations and foliations, it represents one of the most important features that can be described in the field.

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Meeting Plate Tectonics – Francis Albarède

Meeting Plate Tectonics – Francis Albarède

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Francis Albarède


Francis Albarède started his career as an undergraduate student in Natural Sciences at the University of Montpellier in southern France. He moved to Paris to get a PhD in Geochemistry, supervised by Claude Allegre, at the Institut de Physique de Globe de Paris (IPGP). After his PhD he remained at IPGP as researcher and teacher. He then moved to Caltech, where he stayed for two years. The National School of Geology in Nancy, France, offered him a professorship, a position he happily fulfilled for 12 years. In 1991 he switched to the Ecole Normale Superieure in Lyon, France where he holds a director position of the department of earth and life sciences until today.

 

Hi Francis, could you briefly introduce your research interests and methods?

Francis Albarède. Credit: Francis Albarède.

Sure. I’m a geochemist, and I apply geochemistry to understand mantle dynamics and the evolution of the mantle. I also use geochemistry to investigate other planets and work on ocean dynamics. Besides geochemistry, I also use isotopes and trace elements to understand the mantle dynamics and I use models to predict the complexness of magmatic and oceanic processes. Besides earth scientific questions, my methods can be used in archaeological problems or medical issues. My interests are mainly within the field of earth sciences, but I sometimes venture to different fields of research.

Interdisciplinary research needs to be enhanced.

You have quite an extensive career. What do you consider your biggest accomplishment in your field?

The introduction of geochemical modelling I consider one my most significant achievements. And of course, the introduction of the MC-ICP Mass Spectrometry in the mid-’90s within geosciences had tremendous success. At the time it was a new technique and it has become one of the most dominant geochemical tools in many different laboratories around the world. In geodynamics, the idea that continents grow from the head of superplumes was also successful.

Besides these big accomplishment, do you have personal projects too?

Yes, I do have a couple fun projects of my own. They often have to do with introducing new data. For example, I am currently working on using a panel of isotopes (silver, lead, copper) to understand the origin of money.

Science is actually quite hard work.

You have seen many changes in your field. What do you consider one of the biggest challenges in your field nowadays?

Interdisciplinary research needs to be enhanced. The geochemists are good at their own job, and so are the geophysicists. But we need more people that are knowledgeable in both geochemistry and geophysics, a gap that is difficult to bridge. In addition, few scientists ask the right questions. Always ask yourself why other people should care about your own research.

A two-stage history of He in the marble-cake mantle made of fertile (e.g., U- and Th-rich “pyroxenite” in beige) and refractory (e.g., U- and Th-poor “dunite” in green) rocks. Francis Albarède, 2008. Rogue Mantle Helium and Neon, Science, Vol. 319, Issue 5865, pp. 943-945, DOI: 10.1126/science.1150060

 

When you were at the early stages of your career, what were your expectations?

I never expected to be successful at an international level, but it happened anyway. I was craving to make great discoveries, and, even though the road to it was very bumpy, it happened, at least to the best of my capacities.

The most important is to think out of the box.

What is the most valuable advice you have received in your career?

As an early career scientist, I was very arrogant, even more than today. I received the advice, mainly from foreigners, to be more rigorous or demanding to myself. I was told that science is not just a quick effort, or that you do not get important results with a snap of your fingers. It is actually quite hard work. Claude Allegre, my PhD supervisor predicted I would always be a student and sure enough, I still am a student. I am not sure if I became less arrogant, but I definitely took his advice to work harder and to become more rigorous.

So, as the last question, do you have any advice for Early Career Scientists that are aiming for a career in science?

An Early Career Scientist needs to be exposed to other groups and individuals, preferably those who think differently. Perk is the great strength of being young but the danger is to reinvent the wheel. Do not think that something understood 50 years ago is necessarily obsolete. The most important is to think out of the box. This is not an easy thing to do, but if you manage it will make you a different scientist and therefore much more valuable to the community. Being scholarly will multiply and enlarge your sources of information. Read a lot, cultivate your memory, and most of all, have faith in your own capacities.

 

Francis Albarède. Credit: Société Française d’Exobiologie.

Interview conducted by Anouk Beniest

Meeting Plate Tectonics – Eric Calais

Meeting Plate Tectonics – Eric Calais

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Eric Calais


Eric Calais is Professor of Geophysics and Head of the Geosciences department at the Ecole Normale Supérieure in Paris, France. He was a postdoctoral researcher at Scripps Institution of Oceanography, then became a professor of geophysics at Purdue University (USA) where he remained for 12 years. He is renowned for his work on the kinematics and dynamics of active tectonic processes in Asia, Africa, and the Caribbean. Further, Prof. Calais is highly interested in geo-communication. He has served multiple times as expert-consultant in seismic hazard and risk reduction and was a scientific advisor to the United Nations in Haiti from 2010 to 2012.

We tend to be academics and nothing else, that is not sufficient

Where lies currently your main research interest?
My main goal is to understand the present day deformation of the Earth crust, but not only at tectonic plate boundaries, also in plate interiors.

Eric Calais standing next to a GPS antenna at the Cherry Lane meteorological station of Purdue University. Credit: Purdue University

We have known for 50 years about Plate Tectonics. We know how to describe the motion of plates at the surface of our planet and we know that this has been going on for hundreds of millions of years. There are two questions I am interested in:  What drives these motions? What is the engine? The second one is focused on the idea that the earthquake’s energy is released at plate boundaries, so they are linked to plate tectonics, but we really haven’t said much about why earthquakes occur. What is the mechanic of earthquake faulting? How is that driven by friction, stress, fluids? We are perhaps close to a significant transition in our understanding of earthquakes.

For part of my research, I look at the earthquake process from an angle that is different from that of most of my colleagues, who work in areas where there are a lot of earthquakes. I am interested in areas that are not deforming very rapidly or not at all, the internal parts of tectonic plates, but that do produce earthquakes from time to time. Sometimes very large ones. I try to understand why earthquakes occur within plate interiors and what does it mean in general. Of course, that could be then applied to any kind of earthquake.

What would you say is the favourite aspect of your research?

Fieldwork. That’s the reason why I went to Earth science instead of biology. Because I had the opportunity to be outside, not being confined to the lab. Another one is lectures with students and postdocs, with younger people. The older I grow, the more important the connection with them becomes. There is this notion that the younger generation is never as good as the previous one, I think this is wrong. They are as good, and probably much better than we were. I always learn from my students and PostDocs. Having the blessing of interacting with them, is something that is very important to me.

It’s really hard to make big changes in the real world as a scientist and influence some of the decisions […]

Why is your research relevant? What are the possible real world applications?

The real world applications of my research are twofold.

Calais & Minster (1995). GPS detection of ionospheric perturbations following the January 17, 1994, Northridge Earthquake. Geophysical Research Letters, 22(9), 1045–1048.

People like me who try to understand why earthquakes happen make measurements, calculations and models. Thanks to this we are able, not to make predictions, but to make assessments about how big the next earthquake may be. And this is already an important step towards earthquake safety. Because if you know what to expect you can integrate that information in seismic hazard models, then an engineer or an architect will be able to use this information to design earthquake-safe buildings. There is a strong link between the observations in the field, the measurements and the calculations we make, and the applications for earthquake safety.

The second aspect is communication with the broader public and with decision makers. It’s awareness raising amongst the population as a whole and also amongst the decision makers. That is the most difficult part of the job, really. The first part, converting measurements into something an engineer can use to better design a building, that’s the “easy” part, it’s doable and it is tractable, it is something that is very tangible for scientists and engineers.

The second one is much more difficult and it requires a lot of energy and you never know whether or not you succeed in making a point, in influencing decisions. Nevertheless, I think that scientists, as a whole, and in particular scientists working on earthquakes, have to step outside of their comfort zone. We tend to be academics and nothing else, that is not sufficient. We need to go out and speak about what we know and speak at the proper level to raise awareness amongst the population.

 

What do you consider to be your biggest academic achievement?

Post-2010 earthquake measurements in Haiti – Credit: Ecole Normale Supérieure, Eric Calais

It’s hard to tell… I think that we have been able to change the way one thinks about earthquakes within plate interiors over the past years. It’s hard to talk about achievement at this point but I would say there is a trend. If that trend continues, I have high hopes that it will lead us to a better understanding of why earthquakes occur, not only within plate interiors. Many people might not be interested, or they might not even be aware that there are significant earthquakes in plate interiors.

In France, we care a lot about that because 70% of the energy we use comes from nuclear power and we want those nuclear power plants to be earthquake safe. So what is the potential of an earthquake hitting one of those in France or Germany or anywhere in the world is a multibillion-dollar question. It is very interesting to study the earthquake process within plate interiors where you do not have to worry about plate motions or complications, the system is quite simple. I think it’s a system that is more tractable than the plate boundary system, which is more complicated. Trying to make progress in understanding this particular type of earthquakes is something I am pushing hard for right now in my research, with colleagues, PhD students and postdocs. I think that if we understand them better, we will have progressed towards understanding earthquakes as a whole.

Again, I’m not sure this is an achievement, but I am happy I worked with the Haitian Government under the United Nations as a scientific advisor after the earthquake in 2010 in Haiti. The earthquake was not that big, magnitude 7.1, but it had a large impact on the population and the economy. I am happy that I was able to step in and trigger some small changes. It’s really hard to make big changes in the real world as a scientist and influence some of the decisions that were made during the reconstruction that followed the earthquake. In a way, this was an achievement, but again very hard to measure quantitatively.

Do we ever solve problems or do we discover more problems?

What would you say is the main problem that you solved during your most recent project?

Do we ever solve problems or do we discover more problems? (laughs) I think the problems that I’ve solved are easy problems. I would take two recent examples:

Installation of a GPS measurement site in Haiti after the 2010 earthquake. Credit: Eric Calais

One of the problems we were facing a few years ago, was whether there is or not an accumulation of deformation in some areas inside continents that will lead to earthquakes in the future. At plate boundaries we see that faults accumulate elastic energy that is measurable. And we know that this energy will be released during earthquakes to come. The system is simple in a way. But what about geologically stable continents? There was a big debate some years ago whether or not the same would occur inside continents.

We were able to show, and I think everyone agrees on that now, that this is not the case. Areas in stable continents that are prone to earthquakes are not building up seismic energy as we speak. Which means that if earthquakes happen in those areas, and they do, they are releasing elastic energy that is stored in the crust over a very long time. Although this is not yet proven –it is hard to do so but we are working on it!. I think that we have made a significant step forward in showing that earthquakes in plate interiors are releasing a sort of “fossil” elastic energy. I think this is helping us a great deal in understanding earthquakes.

Another important result, which is more regional, is the question that was standing for many years about the Africa-Somalia plate boundary, which coincides with the East African Rift, a 4000 km series of basins and volcanoes. What is going on across the East African Rift? Is it a plate boundary? If it is a plate boundary, how fast are plates moving across that boundary? What can we tell about the distribution of deformation across that plate boundary? My group was fortunate enough to make significant steps thanks to field measurements. It is very interesting to make measurements that tell you about the ways the Earth works, and something new about it. In particular, on such an impressive geological feature as the East African Rift.

 

What would you change to improve how science in your field is done?
That requires some thinking… I guess the easy answer is more funding. But I think it’s not the right answer. I think most people would say “Give us more money to be able to do a better job”…

I think that at least in the US and even in Europe –obviously, I can not speak for every European country– there is a decent amount of funding to do research in geosciences. One of the problems that I see, at least in France, is that as a discipline we are not attracting as many students as we should. We are the discipline that is going to make our planet a place where we can live –or not– in the next few hundred years. There should be many more students interested in the geosciences, whether this is earthquake hazards, climate change, water resources… I feel that it’s much harder to find interested students than it should be. We need to do a better job at motivating students into geoscience research because this is one of the fields of study that will help make the Earth a sustainable planet for the future.

My colleagues will kill me for saying that.

What you just exposed, goes to some extend in line with my next question: What are the biggest challenges right now in your field?

Installation of a geodetic benchmark for campaign GPS measurement, Klein’s Camp, Serengeti National Park, Tanzania. Credit: Eric Calais

There is always this back and forth in our field between more measurements and more models. Should we make more measurements? Or should we stop, stand back and think about what these measurements actually mean before we set up new instruments somewhere? I think that finding this balance is a challenge in a way, not only in Earth Sciences. Finding the right balance between, how much is invested into developing measurement systems and producing data and how much investment should be made into making sense of the data. At the moment, there is progress being made, but we are underestimating the data revolution in Earth Sciences.

Right now you hear about machine learning and big data and all those words are out and about in the Earth Sciences, as in any other science. But, we need to be much better prepared to what’s already there in terms of data and what is going to come. It’s very challenging to have not only the right algorithms and the code etc, but also the right mindset in place to accept that in the near future a lot of our thinking will be driven by data, perhaps more so than by physics – My colleagues will kill me for saying that (laughs). It’s a challenge and an opportunity.

I could have done something completely different and have been equally happy.

What were your motivating grounds starting as an Early Career Researcher? Did you always saw yourself staying in academia?

It’s important for the younger generation of ECR to realize that 25 years have made a big difference in terms of the job market, to begin with. When I was a PhD student in France, having done a postdoc was absolutely not mandatory to get a job. I did one, but a lot of my colleagues did not. Right now, most early career students go through 1, 2, 3, 4, 5 postdocs and it’s still hard to find a job. Things have changed dramatically.

My expectation was academia. There was nothing else to think about, really. I barely had a thought for a career in the private sector. It was so much driven by my passion and things were going fine, so I could not see myself doing something else. That being said, now, in retrospective, when I think about myself looking forward in terms of an academic career and nothing else, I know that I was wrong in the sense that I could have done something completely different and have been equally happy. The job I did in Haiti with the UN, for example, a few years ago opened my eyes. There are lots of great, fulfilling, and useful things to do as a geoscientist, or with a geoscientific background, outside of the pure academic domain.

There are lots of great, fulfilling, and useful things to do as a geoscientist […] outside of the pure academic domain. […] Be an actor of change, not just a scientist.

What advice would like to you give to Early Career Students?

I’m trying to stay away from the typical advice: be persistent, be creative. That is true, those are important… Both are easy to say, but not easy to do… One advice that I would give, that I was never given is: be a scientist who is a part of this planet. Be an actor of change, not just a scientist.

 

This map illustrates the horizontal surface motions of sites in Asia. Eric Calais, a Purdue associate professor of geophysics, used global positioning systems to measure the precise movements of hundreds of points on the continent to determine how they react to collisions of the underlying tectonic plates. (Purdue graphic/Calais laboratory) – Credit: Purdue University

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Dietmar Müller

Meeting Plate Tectonics – Dietmar Müller

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Dietmar Müller


Dietmar Müller is Professor of Geophysics at the University in Sydney and leads the EarthByte research group. He started his academic career in Germany at the University of Kiel and obtained his PhD in Earth Science at the Scripps Institution of Oceanography, UC San Diego, in 1993. Throughout his career he has straddled the boundary between geology, geophysics and computing.

Figure out what you actually enjoy doing and just go and do that.

You were educated in Germany and in the USA. How did you end up in Australia?

After I finished my PhD in 1993, I saw an advert for a lectureship in geophysics at the University of Sydney in EOS. I had never been to Australia and had no idea what life in Sydney might be like, but I thought, I might as well send off an application. A couple of months later I got a postcard from Sydney University, informing me that I had been shortlisted for the position. I thought this was vaguely interesting, but as a fresh PhD graduate, I mainly had my eyes on a couple of postdoctoral fellowships in Europe. Then I got a phone call for an interview. They had clearly decided that flying me to Sydney, all the way across the vast Pacific Ocean, was far too expensive. But they seemed to be interested in my vision for the future, and at the end of the phone interview they asked me: “If we offered the position to you, would you take it?” The thing is, this was the first real job anyone offered to me, so I thought, it’s probably a good idea to say “sure, why not”. Soon they faxed me a contract (these were not yet the days of the internet). Then I thought, hmm, what is this place actually like? So I went to the public library in San Diego and borrowed a VHS tape on Sydney. It included footage of Bondi Beach, Sydney Harbour and the Blue Mountains, with a few kangaroos and koalas thrown in for good measure. I thought this looks ok, it could be a liveable place. After I finally got my visa, I booked a 1-way flight to Sydney, and in late October 1993 I showed up in the Department of Geology and Geophysics and ran into a guy who turned out to be the Head of Department. He looked at the Scripps T-shirt I was wearing, and said: You must be the guy we hired! Of course, he had never seen me, so my T-shirt was my main identifying feature. Remarkably, over 25 years later, I am still there.

Dietmar settling into life in Australia in the 90s, mapping Devonian carbonates in Yass. Credit: unknown.

What is your main research interest? How would you describe your approach and methods?

I lead an Australian research effort, with many international links, to develop and continue to refine something that could be called a virtual Earth Laboratory. I have been an advocate for open-source software and open-access data during my entire career to make science transparent and reproducible. Based on these principles we have spearheaded the development of custom software and global data sets to reconstruct the Earth through time. To understand the Earth’s evolution we need to change our geographic reference system as we go back in time, because of plate tectonics. The plate tectonic revolution in the late 60s and 70s established the principles of how plate tectonics works. Applying these principles to build an Earth model is essentially what I have focussed my career on. I have always had a fascination with Earth evolution over geological time because its comprehension lies so far outside the everyday experience of humans. Most people cannot grasp the relevance of processes on vastly longer timescales than our own lifetime. But understanding the rhythms of Earth’s deep past and thinking about time like a geologist can perhaps give us the perspective we need for a more sustainable future. To dive into the Earth’s past, plate tectonics is indispensable. We need to be able to reconstruct geological data to their original environments. Doing this effectively requires open-source software and open-access data sets that can be shared amongst the community, enabling collaboration.

How do you build an open-source software system from scratch?

Dietmar Müller and Mike Gurnis in Altadena, 2006, taking a break from planning GPlates development. Credit: Melanie Symonds.

When I arrived in Sydney (over 25 years ago) there was no open software to build plate tectonic models, let alone to link plate motions to mantle convection models so that we can investigate the evolution of the entire plate-mantle system. I assembled a small team, partnering with Michael Gurnis at Caltech, to build the community GPlates software. This effort was initially supported by the Australian Partnership for Advanced Computing (APAC) enabling the development of GPlates1.0 on Linux and PCs and its Geographic Markup Language-based information model. In 2005, we managed to get a small educational grant from Apple Computers to develop the GPlates for Macs. We are lucky that shortly afterwards the AuScope National Collaborative Research Infrastructure was established which has supported GPlates development since 2007. That allowed us to fully develop reconstructions of plate boundary networks through time, which is essential for coupling plate tectonics to mantle convection models, as well as the 3D interactive visualisation of mantle volumes and lastly the functionality to model plate deformation, a key step beyond the classical rigid plate tectonic theory. We also developed a python library, pyGPlates, that allows users to link our plate models to many other forms of spatiotemporal data analysis and to other types of models, including geodynamic and paleoclimate models.

The slow carbon cycle is like slow cooking… over millions of years

What would you say is your favourite aspect of doing research?

Understanding the Earth as a system. I am interested in integrating observations from Plate Tectonics and mantle convection with landscape evolution and surface environments through time. I would like to adopt a definition of Earth System Science that actually includes the entire solid Earth, as well as the atmosphere, oceans and biosphere.

What are the real world applications of your research?

There are many applications of plate tectonics. They include understanding solid Earth evolution, palaeogeography, paleoclimate, paleoceanography, paleobiology, and spatiotemporal data mining, for instance for resource exploration. Most mineral deposits are associated with plate boundaries, so being able to link ore deposit formation with plate motions and the kinematic and geodynamic history of plate boundaries allows us to start understanding why certain mineral deposits form at specific windows in space and time, something we have recently started doing using the Andes as a case study.

Students will be entering a transformed workplace unlike any their parents knew

What do you consider to be your biggest academic achievement?

I am most well-known for my work on the age and palaeophysiogeography of the ocean basins. I started working on this as a PhD student. My thesis supervisor, John Sclater, made a name for himself with the first isochron map of the ocean basins. But there was no digital map. Having a digital grid, linked to a global plate model, was going to be critical for studying a whole range of processes from subduction, plate-mantle interaction, the evolution of ocean gateways through time, dynamic surface topography, and many others. I decided to synthesize all the data that we had available at the time to create the first digital map of the ocean basins, followed by a set of reconstructed paleo-age maps. This has enabled a lot of research, both my own and that of the community. For example, it has allowed us to look at the volume of the ocean basins through time (via the connection between the age and the depth of the ocean floor). A more recent achievement, fresh off the press, represents an epic decadal effort on part of the EarthByte group to complete a global plate model for the Mesozoic/Cenozoic period that includes plate deformation. Classical plate tectonics requires plates to be rigid and separated by narrow boundaries. It’s astonishing that it’s taken about 30 years since diffuse deformation was first widely recognised in the 80s to get to the point of systematically building a global model incorporating diffuse deformation for the geological past (soon to appear in Tectonics). It reveals that about a third of the continental crust has been deformed since the breakup of Pangea, about 77 million km2, partitioned into 65% extension and 35% compression. That roughly corresponds to the total area of North and South America and Africa together. The model can be used to investigate the evolution of crustal strain, thickness, topography, temperature, and heat flux, globally.

Total distributed continental deformation accumulated over 240 million years of rifting and crustal shortening. In Dietmar et al. (to come in 50th anniversary plate tectonics volume in Tectonics). A global plate model including lithospheric deformation along major rifts and orogens since the Triassic.

What would you say is the main problem that you solved during your most recent project?

Recently, I became involved in the Deep Carbon Observatory. There are a few quite exciting problems involved in understanding the Earth’s deep carbon cycle and, being an area I have not traditionally worked in, it’s a new adventure for me to try to understand how plate tectonic drives the geological carbon cycle. One of the problems that we tackled in the course of connecting plate tectonics to the “slow carbon cycle” is to investigate seafloor weathering. The slow carbon cycle takes place over tens of millions of years, driven by a series of chemical reactions and tectonic activity and is part of Earth’s life insurance, as it has maintained the planet’s habitability throughout a series of hothouse climates punctuated by ice ages. We were able to build on ocean drilling results and laboratory experiments from other groups to understand how of the storage of C02 and carbon in the ocean crust changes through time, as a function of the age of the ocean crust and of the bottom water temperature, which is quite important, because temperature strongly modulates this process. This is something we published in Science Advances in 2018.It is quite a cool paper!

We actually need geochemists and geophysicists to work together

After being many years active in the academia, looking back, what would you change to improve how science in your field is done?

The biggest change in my time in academia is the emergence of artificial intelligence (AI) and data science as a universal, rapidly growing research area and set of tools to analyse big or complex data, to assimilate data into models and to quantify uncertainties in process models and predictions. There is an urgent need for all Earth science students to become literate in these areas. By the time this year’s first-year students will graduate, they will be entering a transformed workplace unlike any their parents knew. However, the need for changing staff profiles and undergraduate curricula are often recognised and implemented much more slowly than the evolution of the world outside of our ivory towers. But this change needs to happen.

What you just exposed, goes to some extent in line with my next question: What are the biggest challenges right now in your field?

Most of the problems that we are left with are complicated problems that aim at understanding the complexity of the Earth system. That could be anything from structural geology to understanding physical and chemical problems. An example is the field of geodynamics. It is mostly dominated by looking at the physics of mantle convection. And then there is another bunch of people who look at the chemistry of the mantle. These fields have not been properly connected. We actually need geochemists, geophysicists and geologists to work together to try to understand how the Earth system works. Then we need to connect deep Earth evolution to surface environments, understand the exchange of fluids and volatiles between the solid Earth and the oceans and atmosphere.

You actually have to be in for the long game

Building a geological time machine at the University of Sydney, 2009. Credit: Rhiannon McKeon

What was your motivation, starting as an Early Career Researcher? Did you always see yourself staying in academia?

As a kid I was inspired to become a scientist by taking long walks along Germany’s Baltic Sea beaches, picking up unusual rocks and fossils along the way, none of which really belonged there. They had all originated in Scandinavia, where they had been scraped off by moving glaciers and dropped much further south after being transported in the ice over 1000 km. I still have a small collection of these rocks and fossils which include remains of sea urchins and squids from the Cretaceous period and over 400 My old pieces of ancient reefs that had once been buried deeply in the Scandinavian crust. I always wanted to be an academic, I wanted to understand how the Earth works, over geological time. I never had any second thought about that. I can see today that students are often quite confused about what they want to do. Because they are unsure about where the future might take them, they don’t end up focussing on any one subject and are not necessarily inclined to acquire skills that are deep and broad enough to excel. If you want to be successful at anything, you need to become really good at something, and persevere. Be good at something that you actually enjoy, and be in it for the long game.

Who inspires you?

I am inspired by the pioneers of open source software and open access data. Open science is the key to forming global research teams and advancing studies of the Earth system. I am inspired by Paul Wessel at the University of Hawaii, who, together with his colleagues, built one of the most extensive geo-software systems, the Generic Mapping Tools, over the past ~30 years; I started using an early version of it during my PhD and am still using it! In terms of open access data, one of my heroes in Earth Sciences is David Sandwell at the Scripps Institution of Oceanography, who revolutionised our knowledge of the deep structure of the ocean basins by making his global satellite gravity maps freely available to the community. On the geochemistry side, Kerstin Lehnert at the Lamont-Doherty Earth Observatory has accomplished an amazing feat by leading the EarthChem database effort, and now the Interdisciplinary Earth Data Alliance, a nice example for bringing geochemistry and geophysics together.

What is the best advice you ever received?

Not long after I arrived at the University in Sydney, the then professor of geophysics pulled me aside and said: “I have one piece of advice for you: Stay away from University politics and just do your own thing“. That’s exactly what I have done and that’s the best advice I have ever received. It is easy to get carried away with politics at many different levels…

Stay away from University politics

What advice would you give to students?

You have to figure out what you enjoy and what you would like to do. You should not choose a career because you think this career will pay more money than another one, or it may seem there are more jobs in one field than another. The advice I would give to students is to try to figure out what you actually enjoy doing and just go and do that. The future will be driven by big and complex data analysis and simulation and modelling, but there will still be a need for people who can identify a rock. If you can do both, you’ll have a job without any doubt!

 

Dietmar Müller, November 2018 in his office. Credit: Jo Condon, AuScope

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Cesar Ranero

Meeting Plate Tectonics – Cesar Ranero

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Cesar Ranero


Prof. Cesar Ranero is an Earth Science researcher, currently Head of Barcelona Center for Subsurface Imaging (Barcelona-CSI). He owns a degree in Structural Geology and Petrology from the Basque country and he later completed his PhD in Barcelona, emerging himself in Geophysics. Prof. Ranero’s research is marked by a multidisciplinary approach, applying physical methodologies to understand geological processes.

Scientist also have to look for collaboration with the industry.

Ranero giving an outreach talk on fossil fuels at the Centre de Cultura Contemporània de Barcelona (CCCB). Credit: Cesar Ranero

Hi Cesar, after doing research for few decades, what is, at present, your main research interest?

My research interest covers mainly active processes, I am not so interested in regional geology. I see regional geology as a necessary step to understand processes but the main goal of our group is to understand geological processes. For instance, a great interest in our group is the seismogenic zone and the generation of great earthquakes. We have very good examples in the Iberian peninsula, such as the famous 1755 Lisbon earthquake. Yet, nobody knows where the big fault that created this earthquake is located. We have a lot of research to do. But, often to understand local geology you need to integrate it in the big-picture view of processes. This is why we are mainly interested in those processes rather than in regional geology.

The more you know, the more you realize that nearly everything is to be discovered.

Further, I am interested in interacting with the industry. The geological/geophysical community is a relatively small community (compared to medicine, for example). There is out there quite a few industry groups that are doing very similar things in terms of methodologies and approaches (communities working in oil & gas exploration, or the ones working on carbon sequestration, or geothermal energy production…) All these communities have quite a bit of history in the development of methodologies. They usually have much more money and very talented people developing new methodologies. It is very necessary that we participate in their interests. They are often showing interest in what we do. By going to their meetings and talking to them, you can build fruitful interactions. Scientists also have to look for collaboration with the industry, because at the end of the day it is a place where some of our students can find a good job and make a career.

How would you describe your approach and methods?

The approach in our group is multidisciplinary, we combine complementary methodologies. But it is also important to be aware of proper methods to interpret geophysical data (you have to understand different geological methods, for instance, the methods used in structural geology).

Poststack finite-difference time migration line showing the structure of the Cocos plate across the ocean trench slope. Ranero et al., 2003, Bending-related faulting and mantle serpentinization at the Middle America trench, Nature, 425, 6956, 367.

 

What would you say is your favorite aspect of your research?

What stroke me since I started my PhD is how much good work has been done, but how much more needs to be done.
We know a lot because there were many talented people before doing a lot of work. But actually, if you have a sceptical mind, the more you know, the more you realize that nearly everything is to be discovered. If you look at the last 10 years, you realize that a lot of what has been published is incremental science and much had been laid down in previous publications. But also, there are a whole series of new topics coming out and you have to pay attention because those are the topics that really mean a substantial jump forward. Every year there are several new interesting things coming. For example, earthquake phenomena have been an amazing topic in the last years, all these new phenomena explaining how plate boundaries slip. You have to keep a sceptical mind and at the same time search for those topics.

You have to have a sceptical mind.

Why is your research relevant, what are the real world applications?

This is always a good question. We do a lot of basic research and there is always the philosophical question on whether basic research is relevant… When we discovered the laser, nobody knew how relevant this would be in the future. Now, we can not live without it! I am sure that there is a percentage of basic science discovery that might not have any real-world application. But in many cases, it does. Much of what we do contributes to the understanding of natural hazards. But also, we contribute to resolving problems industries and society are concerned with.

Prestack depth migration of a Sonne-81 line projected on bathymetry perspective. Ranero & von Huene, 2000, Subduction erosion along the Middle America convergent margin, Nature, 404, 6779, 748.

 

At this point of your career, what do you consider to be your biggest academic achievement?

I would like to think that it is the next one! (laughs)

I am proud to have been elected as a fellow of the American Geophysical Union. It means I have done something relevant that is appreciated by my peers, and at the same time, it is a great motivation to work even harder in the future.

Also, I have some nice papers that I am proud of (tectonics of subduction zones, the role of fluids on earthquakes, serpentinization of the outer rise). My view is that for most people, after you finish your career and you look back at your many publications, probably only 3-4 papers are really worth it and seriously contributed brand new material.

What would you say is the main problem that you solved during your most recent project?

Since I came back to Spain, 12 years ago, I started to work a lot in the Mediterranean. For many years, the Mediterranean had been a place where people did not want to work because it is too complex. With the help of German groups and others, our group has been able to characterize for the first time the nature of the crust in many systems in the Mediterranean. We have added a new layer of information to understand the evolution of the whole Mediterranean region. I am quite happy with that, we are producing quite a few papers and have some very new ideas, and we have also started to put that together with fieldwork. There has been a lot of on-land work all around the Mediterranean, but rather limited modern geophysical data on the nearby basins. For example, the Apennines are very well known, but the nearby Tyrrhenian, not so much… We worked with the Italian and the German groups and found some new, interesting geological observations.

Cartoon showing a conceptual model of the structure and metamorphic evolution of subducting lithosphere formed at a fast spreading center. Ranero et al., 2005, Relationship between bend-faulting at trenches and intermediate-depth seismicity, Geochem. Geophys. Geosyst., 6, Q12002, doi:10.1029/2005GC000997.

The biggest challenge is to have time to think about new observations of
high quality that challenges the conventional view
.

After being many years active in the academia, looking back, what would you change to improve how science in your field is done?

I think there are significant differences depending on the country, even within Europe, in terms of funding: how research is done, how research careers develop… Some countries, like Germany and France, are doing relatively good in terms of funding. Other countries, like Spain, Italy or Portugal are not. These countries do not have a well-organized structure for funding, so for researchers is difficult to know how to organize funding around their research to succeed. The people that do well, that work hard, that produce, should have the certainty that they will be able to move forward. But today there is a lot of uncertainty, and in these countries, there’s no warranty that people who deserve it, will have their chances. This is a major problem for ECR, and I think a better structure funding and more funding opportunities for ECR are needed.

Regarding European-funded projects, as for example those of the European Research Council, these programs are extremely prestigious, and only the very top are getting these very well funded grants. And yet, it is unclear to me, at least in my community, that the results and papers produced in the context of these programs are of higher quality than those in other funding programs. So, is it unclear to me that this is a system that we should sustain, but that we shall see in the next years. Talking to others, I get the perception that it is now becoming somewhat too prestigious, people even hesitate to submit proposals because they have to invest loads of time into it and is a huge effort that might not even pass the first evaluation, and review comments appear somewhat indecisive. But I might be wrong on this one.

What you just exposed, goes to some extent in line with my next question: What are the biggest challenges right now in your field?

As for the scientific challenges, I think we can look back at the Plate Tectonic revolution. How did it happen? Before it happened, many observations did not have a good explanation because we were lacking the right data. Then, almost suddenly, we got three datasets that nobody had seen before: magnetometers and echo sonars of higher quality coming from the second-world-war related research, and a worldwide seismological network for monitoring within the frame of the Nuclear Weapon Ban Treaty. And of course, these data landed on the right people. But, in my opinion, it was the access to the right data that provided a whole new view on geology.

So, perhaps the biggest challenge we have now is to be able to produce new methodologies of high resolution to look deeper into the Earth. We need to use high-quality new data sets and new observations that could allow to actually challenge the conventional views.

This is very complicated, particularly in the academic world we live in now. Currently, people have to write several papers for their PhD, and immediately after, in the postdoc period, they have to produce a massive number of papers to at least have a chance. In these circumstances, you can simply not think long enough in a complicated problem. There’s little time to think about what the main fundamental problems are that you want to solve. You have to be a paper-producing machine, and this is detrimental to their quality. You might manage to be someone that is highly productive but, in that frame, it is unlikely that you will often produce major quality. There’s too much pressure on ECRs. So, a challenge is to have time to think about how to obtain new observations of high quality that can change conventional views.

Pre-stack depth-migrated line IAM11, with arrows and numbers indicating the average dips of the block-bounding fault segments exhumed during rifting. Ranero & Pérez-Gussinyé, 2010, Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins, Nature, 468, 7321, 294.

You have to be a paper-producing machine, and this is detrimental to their quality.

What were your motivating grounds, starting as an Early Career Researcher? Did you always saw yourself staying in academia?

I actually thought of going to the industry when I finished university. But I was lucky enough to be introduced to Enric Banda, my PhD supervisor, who had a big picture of geosciences, and he made a real impression on me and made me change my goals. Once I started my career in science, I quickly realized that there was a lot to be done. After two-three years into my PhD, thanks to a nice data set and some good results that were coming out, I definitely saw myself staying in academia. I looked for funding before finishing my PhD and I was lucky to get a Marie Curie, which was not even called like that at the time. I was lucky to work with relatively large groups, and with good funding. There was a good moment, also for industry. Funding was not a major issue for me for many years, so I could spend my time doing the research I wanted. At present, early careers are much more complicated, and you have to really like it to keep on pushing for it.

What advice would you like to give the ECS?

Be ambitious, think big. Don’t be afraid of making mistakes. And above all, be sceptical, completely sceptical about everything. Don’t pretend you know more about what you know, but be sceptical. Because, almost for sure, no matter who did the work, it can be improved, and in most cases, to a great extent. And be open, talk to everybody.

 

Researchers of the Barcelona Center for Subsurface Imaging. Credit: Cesar Ranero

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Anne Davaille

Meeting Plate Tectonics – Anne Davaille

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Anne Davaille


Anne Davaille majored in Physics and continued with a PhD in Theoretical Physics of Fluids, jointly at the University Pierre et Marie Curie and the Institut de Physique du Globe de Paris (IPGP). She investigates convection in strongly temperature-dependent fluids. After her PhD, she went to Yale for a postdoc and she currently holds a CNRS-position at the FAST Laboratory of University Paris-Sud, France.

Research is ideas plus craftmanship. It should be fun and you have to enjoy it to do it.

Anne Davaille. Credit: Anne Davaille.

Anne, what are your research interests and what methods do you use for your research?

Fluid mechanics is my main research area. I study convection in complex fluids, and I use this framework to understand mantle convection and the convective evolution and cooling of planets. My main approach is through laboratory experiments. But then I use and/or build some theory to interpret the experimental results, to derive a physical understanding, and finally to make inferences for geodynamics. All the way, numerics are also involved, to treat the experimental results, or to quantitatively apply the results to planets.

 

No matter what fancy stuff you do, if your data is not good, you are losing on what you are going to get

You have significantly advanced fluid dynamics within the geosciences. Up until now, what do you consider your biggest scientific achievement?

It is probably the works that we did on thermo-chemical plumes in two-layer convection models. We showed that convection in a mantle heterogeneous in density and viscosity could produce several types of plumes, and therefore several types of hotspots. More recently, we have been able to observe different ways of subduction initiation from convection in complex fluids. Plume-induced subduction could be occurring on Venus right now, and might have been important in the Archean Earth. On the side, I am also very happy with the techniques we developed to measure simultaneously and in situ the temperature and velocity fields in the experiments. It really helped us to push lab experiments forward and get a quantitative understanding of the processes we observed.

Different types of plumes and hotspots, depending on the presence of density heterogeneities in the mantle. From Davaille, Nature, 402, 756-760, 1999; and Davaille, Girard & Le Bars, EPSL, 203, 621-634, 2002.

 

After all the time you have spent in science, you have seen many questions answered and more questions rise. What is the biggest challenge in your field that we face today?

Until now, we still have not solved the question ‘why do we have plate tectonics?’ from a physical point of view. On what scale do we need to look for that answer? Grain scale? Or meso-scale, since the lithosphere is quite heterogeneous (e.g. faults, dikes,…)? To get plate tectonic behavior, and therefore the strong localization of deformation, we need a non-Newtonian rheology. From my experience, fluids presenting this particular behaviour are very often mixtures, and their effective behaviour on the large scale can be quite different from their local microscopic behaviour. Moreover, the history of this structure can also strongly influence the large-scale behaviour. With the theoretical understanding we have today, we still cannot model well these behaviours, and therefore answer the plate-tectonics question. I don’t know if we shalll find the answer in theory first, I don’t think that is necessary. It will require most probably a mix of theory, numerics, and data, both experimental (where you can observe and measure all the scales, from the grain to convection) and geological (the “field truth”). Once we do have that answer, we shall gain a better understanding of the other planets and satellites as well.

Plume-induced subduction obtained in FAST laboratory in a climatic chamber. From Davaille, Smrekar & Tomlinson, Nature Geosc., 10, 349-355, 2017.

The one thing we really should stop doing is having this frantic will to publish

Your field of expertise has changed over the years. Is there something you would still like to change?

Oh yes, there are some things I would like to change. The one thing we really should stop doing is having this frantic will to publish. It is an extremely bad habit and it does not generate good research. Especially for the young people that still need to develop ideas and skills, they need time to think and make mistakes, which is not possible with the current mindset of fast publishing. Fast publishing is not beautiful, nor efficient for creative research. Even though the world wants things always faster, doing it faster is not human. We should stop this. What I find the most important is that my work should be strong enough so that people understand what I did and can use this to build on it and move further. For this we need time.

Different regimes of convection in strongly temperature-dependent fluids as a function of the viscosity ratio and the intensity of convection (Rayleigh number). The temperature structure in the sugar syrups is visualized by Thermochromic Liquid Crystals. From Androvandi, Davaille, Liamre, Fouquier & Marais, Phys. Earth Planet. Int., 188, 132-141, 2011.

 

When you were in the Early Stages of our career, what were your expectations for your future?

When I was 7 years old, I learned about plate tectonics. Later, the operation FAMOUS was happening and at this young age I found that fantastic and I wanted to know more. That was one of the reasons why I went into physics. I think that during my career I have been very lucky. Once I got my degree, I thought that before getting a job, I wanted to do a PhD in a very specific topic ‘Convection in complex fluids and planets’. After that we would see. I did not really have any expectations, but I thought, if I can do it maybe it will work and that would be great. Somehow it worked and so I continued working in it, and it is still great fun!

You have to be very demanding, very rigorous if you want to succeed

The last question for today’s Early Career Scientists: what advice would you like to give the ECS that would like to stay in science?

Well, first I think that research is ideas plus craftmanship. It should be fun and you have to enjoy it to do it. But craftmanship is demanding. I have a small anecdote here. I once did an internship at Schlumberger. I worked with experiments and my supervisor at the time told me ‘if you put shit in, -(meaning noise)-, you will get shit out’. My advice would therefore be that no matter what fancy stuff you do, if your data is not good, you are losing on what you are going to get. So for experimental or numerical modelling, if you are not demanding, or only short-term, you may get away with it for a while, but on the long run, you will not last. You have to be very demanding, very rigorous. I think that’s the best way to succeed.

 

Anne Davaille. Credit: Anne Davaille.

Interview conducted by Anouk Beniest

Minds over Methods: Mineral reactions in the lab

Minds over Methods: Mineral reactions in the lab

 

Mineral reactions in the lab

André Niemeijer, Assistant Professor, Department of Earth Sciences at Utrecht University, the Netherlands

In this blogpost we will go on a tour of the High Pressure and Temperature (HPT) Laboratory at Utrecht University and learn about some of the interesting science done there.

André Niemeijer next to a striated fault surface. Credit: André Niemeijer.

André’s main interest is fault friction and all the various processes that are involved in the seismic cycle. This includes the evolution of fault strength over long and short timescales, the evolution of fault permeability and the effects of fluids. His current research is aimed at understanding earthquake nucleation and propagation by obtaining a better understanding of the microphysical processes that control friction of fault rocks under in-situ conditions of pressure, temperature and fluid pressure.

Most of the deformation in the Earth’s brittle crust occurs on and along faults. Fault movement produces fine-grained wear material or gouge, which is very prone to fluid-rock interactions and mineral reactions (Wintsch, 1995). It has long been recognized that the presence of a fluid allows for deformation to occur at much lower differential stresses than without.

Pressure solution

One of the mechanisms by which this deformation occurs is pressure solution (alternatively termed “solution-transfer creep” or “dissolution-precipitation creep”). This mechanism operates through the dissolution of materials at sites of elevated stress, diffusion along grain boundaries and re-precipitation at low stress sites (e.g. pores). Pressure solution is an important diagenetic process in sandstones and carbonates as evidenced by the presence of stylolites in many carbonate rocks, which are often used as counter tops and floors (particularly in banks, I noticed). In addition, it has been suggested that pressure solution plays an important role in the accommodation of (slow) shear deformation of faults (Rutter & Mainprice, 1979) and possibly in controlling the recurrence interval of earthquakes (Angevine, 1982).

Fluid-rock interactions in the lab

Experimentally, it is challenging to activate pressure solution or mineral reactions in the laboratory, because they are typically slow processes. Moreover, it is difficult to find evidence of their operation. We have used a unique hydrothermal rotary shear apparatus, which is capable of temperatures up to 700 °C to activate pressure solution in fine-grained quartz gouges. We were able to prove that new material was precipitated by using a combination of state-of-art electron microscopy techniques that involve cathodoluminescence (CL).

The hydrothermal rotary shear apparatus at the HPT laboratory at Utrecht University, the Netherlands. Credit: André Niemeijer.

Signature of pressure solution

The CL signal of a mineral depends on the type and level of impurities and defects that are present. We used quartz derived from a single crystal which showed relatively uniform CL. Because our apparatus has various metal alloy parts, small amounts of aluminium are present in the fluid. Aluminium can be incorporated in newly precipitated quartz, which gives a different CL signal. This allows us to map the locations where quartz has newly formed and link this to the experimental data. Taken together, we can use these to derive and constrain microphysical models for fault slip that can be used to extrapolate to natural conditions (e.g. Chen & Spiers 2016, van den Ende et al., 2018).

RGB overlay of secondary electron and cathodoluminescence signals in a deformed quartz sample. Newly precipitated quartz shows up in a blue colour. Credit: Maartje Hamers.

Mineral reactions

Outcrops of natural faults often show evidence for enhanced mineral reactions with increasing shear strain. For instance, the Zuccale fault (Isle of Elba, Italy) has a high content of talc in the highest strained portion of the fault (Collettini & Holdsworth, 2004). Talc is a frictionally weak mineral and its presence in the Zuccale fault provides an explanation for the possibility of slip along this low-angle normal fault. We were able to produce talc experimentally from mixtures of dolomite and quartz in only 3-5 days of shearing at low velocity. This shearing was accompanied by major weakening, with friction dropping from 0.8 to as low as 0.3. The reaction to talc is sensitive to temperature and fluid composition. At slightly higher temperature, we produced diopside and forsterite which are frictionally unstable and generated audible laboratory earthquakes.

Identifying reaction products

We tried a whole range of different analytical techniques to identify the reaction products. Despite the obvious frictional weakening that we observed, talc was only observed in two samples with x-ray diffraction (XRD). Fourier-transform Infrared analysis, on the other hand, proved to be very sensitive to talc and has the big advantage that only a small amount of material is needed (~70 mg). Electron microscopy with EDS-analysis (Energy Dispersive X-ray Spectroscopy) proved helpful to some extent, because it shows the phase distribution. However, the small size of reaction products gives a mixed chemistry, which complicates the identification of reaction products. Finally, to positively identify the various phases in the different samples, we employed Raman mapping.

RGB overlays of EDS analyses of samples deformed at 300 °C (left) and 500 °C (right). Dolomite appears in yellow, quartz in blue, calcite in red, talc in cyan in the left image, while dolomite is orange, calcite is red, diopside is purple and forsterite is cyan in the right image. Credit: André Niemeijer.

Outlook

Our studies have shown that reactions can be quite rapid in fine-grained fault gouges. These reactions can have a profound effect on both fault strength and stability but are typically ignored in large-scale models of the seismic cycle. Incorporating reactions requires models that can account for the effect of stress and grain size reduction on the development of faults, which is not an easy task, but is a necessary ingredient to understand the long-term behavior of faults.

References

  • Angevine, C. L., Turcotte DL, Furnish MD. (1982) Pressure solution lithification as a mechanism for the stick-slip behavior of faults. Tectonics 1 (2), 151-160 doi:10.1029/TC001i002p00151.
  • Chen, J. and Spiers CJ. (2016) Rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model. Journal of Geophysical Research: Solid Earth 121 (12), 8642-8665 doi:10.1002/2016JB013470.
  • Collettini, C. and Holdsworth RE. (2004) Fault zone weakening and character of slip along low-angle normal faults: Insights from the Zuccale fault, Elba, Italy. Journal of the Geological Society 161 (6), 1039-1051 doi:10.1144/0016-764903-179.
  • E H Rutter, D H Mainprice (1979)On the possibility of slow fault slip controlled by a diffusive mass transfer process. Gerlands Beitr. Geophysik, Leipzig 88 (1979) 2, S. 154-162.
  • van den Ende, M. P. A., Chen J, Ampuero J., Niemeijer AR. (2018) A comparison between rate-and-state friction and microphysical models, based on numerical simulations of fault slip. Tectonophysics 733, 273-295 doi:10.1016/j.tecto.2017.11.040.
  • Wintsch, R. P., Christoffersen R, Kronenberg AK. (1995) Fluid-rock reaction weakening of fault zones. Journal of Geophysical Research: Solid Earth 100 (B7), 13021-13032 doi:10.1029/94JB02622.

Meeting Plate Tectonics – Roger Buck

Meeting Plate Tectonics – Roger Buck

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Roger Buck


Roger Buck is a Research Professor at the Lamont-Doherty Earth Observatory at Columbia University, in New York. His interest lies in developing theoretical models for processes that affect the solid earth. He also studies deformation patterns and topography on other planets, such as Venus.

The key is to look for areas where new data shows that there are important things we don’t understand, things that still surprise us.

After being active for several decades, what is currently your main research interest? How would you describe your approach and methods?

Broadly, I work in Geodynamics. In a lot of different aspects to it. I started doing work on planetary science and mantle convection. Now I work mostly on the mechanics of faulting and of magmatic dike intrusions, particularly focussed on continent breakup and mid-ocean ridges.

 

Roger Buck – Deploying GPS instruments to understand the mechanics of dike intrusions in Afar, Ethiopia. Credits: Roger Buck

 

What would you say is the favourite aspect of your research?

What I find really satisfying is trying to find geologic phenomena or structures that look very complicated, but where there is actually a fairly simple underlying physical mechanism. It is particularly satisfying to find a fairly simple mathematical expression describing the mechanics of processes that otherwise might look quite complicated.

I always hope that, on the long term, explaining things better is good in itself

Why is your research relevant? What are the possible real world applications?

That’s difficult to say in a lot of cases. Just explaining how structures got to be there might not have immediate effects. But, I always hope that on the long term explaining things better is good in itself. Understanding how the Earth works can help us dealing with hazard mitigation. Some of the work that we are doing recently deals with the tectonic processes that are related with earthquakes. That might help us understand the different kinds of earthquakes that happen in different areas.

 

Roger Buck – Physical experiment with gelatin, testing how magma intrusion could trigger continental breakup. Credit: Roger Buck

What do you consider to be your greatest academic achievement?

In airplanes, I tell people that “I work on areas that are splitting apart and on what allows them to split apart”. Probably the single cleanest example was a controversy that came up in the 1980s about what people often refer to as “low angle normal faults” that are associated with rocks brought up from great depth in the crust in core complexes. Over a number of papers, we showed that a lot of these structures that are low angle now, probably initiated at high angles, in ways that are very easy to understand mechanically. They evolved in a way that it’s just a consequence of normal extensional faults extending over long distances. It was very satisfying to chip away that problem from a kinematic viewpoint, and then from a more basic, mechanical point of view. Much of his work was done with excellent colleagues, like Luc Lavier and lately with Jean-Arthur Olive, on numerical simulations of these processes.

 

What would you say is the main problem that you solved during your most recent project?

I’ve been working with a very bright student on the Tōhoku earthquake that happened in March 2011 in Japan, where there was really unprecedented data (the Japanese had many geophysical instruments both on land and underwater). One of the things that was unexpected was that in the upper plate, in the lithosphere above the subduction interphase, the predominant aftershocks over a broad region (about 200 km wide) were extensional earthquakes. This had never been seen before. We have been working with simple ideas and numerical models to explain these extensional earthquakes. Our idea is that it is related to the long term (millions of years timescale) changes in the dip angle of subduction that basically bend the upper plate. We don’t have a clear connection with the extensional deformation that might have been related to the excessive size of the tsunami that was produced, but there could be some relationship. We certainly have not solved this problem but we have a promising hypothesis for one part of the Tōhoku earthquake.

It is very important to continue support for very basic work.

After being many years active in academia, looking back, what would you change to improve how science in your field is done?

Oh, that’s a hard question. A lot of things over the years have been done very well, I think. Like fostering international collaboration in science and that there has been fairly healthy support for science, in a lot of countries, including the United States. It is very important to continue support for very basic work. There has been a retreat from supporting multi-channel seismic work in the ocean in recent years, but this is one of the best ways for us to illuminate the structures produced by tectonic processes. At the same time, increased computer power allows us to get better resolution of structures, based on essentially the same data. However, we still need to collect new data.

The key for big advances is often new technologies

Roger Buck – Deploying seismometers across the Okavango Rift. View on the Victoria Falls. Credit: Roger Buck

 

What you just exposed, goes to some extent in line with my next question: What are the biggest challenges right now in your field?

Uh! These are pretty challenging questions, that’s for sure!

I think there are great and exciting challenges in things I don’t work on myself. The fact that geodesy has improved so much in recent decades and we are learning so much more about plate boundaries. I remember the wonderful talk of Jean-Philippe Avouac during the symposium in Paris, he emphasized how much we have learned. Many seismic gaps are in places where we don’t see traditional seismic activity: large earthquakes or fast earthquakes. We now know that they are slow earthquakes and slow slip events. Understanding where they occur and why we have different kinds of earthquakes in different places along subduction zones is an area that a lot of people have recognized is very important. I think the key to big advances is often new technologies. Geodesy, both on land and submarine, combined with imaging offers terrific hope for a better understanding of major earthquakes. For example, we don’t have a good clue on why some big subduction earthquakes produce very large tsunamis and others not so large tsunamis. These are huge challenges.

 

What were your motivating grounds, starting as an Early Career Researcher? Did you always see yourself staying in academia?

I was always kind of academically oriented. I liked the idea of doing research. I started in Physics and liked it a lot, and then I started taking Geology and liked Geology a lot! I was at university in the mid-1970s and there was a lot of excitement about applying plate tectonics to solve different problems and it seemed very exciting… I am definitely not a good field geologist, but I love being in the field. I think it is important for people doing theoretical work to actually understand the data that they are working with and where it comes from, and the great skill it takes to collect and interpret data. But I realized very quickly that this wasn’t my strength. The key is to look for areas where new data is showing that there are important things we don’t understand, things that still surprise us. That is one of the encouraging things that I’ve seen through my career: repeatedly, with new measurements, we had total surprises. We have seen things we did not expect.

Follow things where you have the potential to make some contribution

What is the best advice you ever received and what advice would like to you give to Early Career Students?

Oh boy!  One piece of advice I got about writing papers that deal with models is particularly good:  You should very clearly separate observations from model assumptions and model interpretations. Not mixing these three things up is something that I certainly struggle with it, but it is something that keeps papers clear and crisp.

The obvious piece of advice that you hear very often and that I certainly tell people: You are typically going to like things that you have some aptitude for. So, follow things where you have the potential to make some contribution. Find something that you really do feel good about doing and you are going to feel good about it if you are somewhat capable of doing it.

 

Roger Buck in Egypt – Credit: Roger Buck

 

Interview conducted by David Fernández-Blanco

Meeting Plate Tectonics – Roland Bürgmann

Meeting Plate Tectonics – Roland Bürgmann

These bi-weekly blogs present interviews with outstanding scientists that bloomed and shape the theory that revolutionised Earth Sciences — Plate Tectonics. Stay tuned to learn from their experience, to discover the pieces of advice they share, to find out where the newest challenges lie, and much more!


Meeting Roland Bürgmann


 

Roland Bürgmann is Professor of Geophysics at the University of California, Berkeley. He has been teaching and doing research in Berkeley for around 20 years. He started studying Geology in Germany (Universität Tübingen) and then continued his studies in the US, obtaining his PhD in Geomechanics and Crustal Deformation from Stanford University.

 

After being active for several decades in your field, where is your main research interest currently? How would you describe your approach and methods?

My current research is on active tectonics. Really the idea is to study deformation processes in the Earth related to fault systems and the earthquake cycle, but also all kinds of systems that produce active deformation like volcanoes, landslides, or land subsidence. We study those especially with geodetic tools, and also with seismology and field observations. So, I don’t tie myself to any particular observational technique, I’m really just interested in better understanding the kinematics and dynamics of deformation processes of all kinds in the Earth.

The key indication that you are doing the right thing is that you love what you’re doing

What would you say is your favourite aspect of your research?

Research really means being able to work with people. Research is not a solitary thing, a lot of it is about thinking of problems and trying to solve them. Not by yourself, but by having the opportunity to work with students and postdocs. That really enriches research immensely. I see this as one of the most enjoyable and valuable aspects of academic research.

Why is your research relevant? What are the possible real-world applications?

I guess with what we do it is relatively easy to point out real-world applications because we address natural hazards. Earthquakes, volcanoes, landslides… everybody is somewhat worried about those. On the other hand, we have to admit that often the research we do is not going to directly impact or save lives. My wife is a cancer surgeon and she might have improved or even saved a life or two every week. For us, it is much more like we are pushing on a research problem, and we do see the long-term relevance when it comes to ultimately being able to mitigate and better understand earthquake hazards and some of these other hazardous processes.

Research is not a solitary thing

Roland with his group after running a trail race (an annual tradition) Credit: Roland Bürgmann

 

What do you consider to be your biggest academic achievement?

Bürgmann, Hilley, Ferretti, & Novali (2006). Resolving vertical tectonics in the San Francisco Bay Area from permanent scatterer InSAR and GPS analysis. Geology, 34(3), 221.

My biggest academic achievement, I’m sure is still to come (laughs). That’s a tough question… you couldn’t really say, well this is “the one” finding or study that is the most important one… I think overall the work I’ve done that relates to better understanding the whole earthquake cycle; we’ve done a lot of work on postseismic deformation, fault slip, stress interactions, rheology… but it’s all incremental. I don’t feel like we have made “this one” discovery that people would always associate with me.

What would you say is the main problem that you solved during your most recent project?

One of my most recent projects is related to landslide physics. We use InSAR to study the landslide deformation, and rely on precipitation records and pore-pressure diffusion models to calculate what the fluid pressure is in the landslides. We can quite directly relate that and explain the time lag between precipitation and landsliding.

I think that this is a useful contribution. In a paper that we are about to publish, we were able to do that in the years prior to a landslide that then failed catastrophically. So there the hope is that this will actually allow us to understand what is it that gets a landslide over the brink. Landslides can keep moving steadily over the years, decade for decade, but what is it that makes one fail catastrophically? So this study, we hope can help to contribute to better understanding that.

 We should do more […] interdisciplinary studies

Looking back, what would you change to improve how science in your field is done today?

Something that we are doing already, which I think is really important and we should do more of, are truly interdisciplinary studies. I’m a strong believer in that, and I do think that geomorphologists need to talk to geophysicists, and to the modellers … Ideally, all of us should know enough about these other fields so that we can really optimize how we can see the whole system. I do think there is much more left to be done when it comes to that. Allowing us to speak the same language and joining forces when it comes to really understanding how the Earth works, not to limit oneself to just one problem, one process, and therefore one approach to understand it.

 

After all the time you have spent in science, you have seen some questions answered and more questions raised. What are the biggest challenges right now in your field?

Bürgmann, Rosen & Fielding (2000). Synthetic Aperture Radar Interferometry to Measure Earth’s Surface Topography and Its Deformation. Annual Review of Earth and Planetary Sciences, 28(1), 169–209.

Scientifically, we like to understand what we study in the simplest possible way. We try not to “over-model” what we observe, really just trying to get at the key underlying processes and principles. On the other hand, we got so much data now from all kinds of observational systems that seem to be trying to tell us much more. This suggests we should be upscaling the model complexity, and try to understand multiple processes at the same time. That is both exciting and seems dangerous. Whenever I see climate scientists with their models that incorporate hundreds of different processes, everything from turbulence in the atmosphere to particles in the air and many other things, that just seems scary and something that you would not want to do with what we study in geophysics. But I do see the need that we have to make our models and ways of understanding the Earth more complicated. Doing that consciously but well, that’s a big challenge.

 

What were your motivating grounds, starting as an Early Career Researcher?

The biggest influences ultimately are people. It was highly enthusiastic role models that made me get really excited about what I’m doing and made me change my career path. I wanted to study other things in my freshman year when I started studying geology. Over the years, I got to work with enthusiastic and inspiring mentors that made all the difference. Ultimately we are social animals and it does make a huge difference to have those kinds of influences in your early career.

We all have our insecurities

So you always saw yourself staying in academia?

I wasn’t sure. I definitely considered alternative career paths. I meant to do an industry internship, which ended up not working out because I ended up working at the US Geological Survey that summer instead. I think I kind of knew I wanted to be in academia, but you really don’t know. You don’t know if you are good enough. We all have our insecurities and everything that comes with that, from impostor syndrome to what not. But it certainly always felt natural to me. The key indication that you are doing the right thing is that you love what you’re doing.

 

Following to what you just exposed, is there any other advice would you give to Early Career Students?

When it comes to giving advice, I always say, research in academia is the best possible job. Period. But only if you enjoy doing that. If research stresses you beyond normal stress levels, if it does not give you true pleasure, then maybe it is not the right thing. I totally appreciate how that is not necessarily true for everybody. Maybe you are meant for a more structured environment, where you don’t have to make up your days’ work on your own, every day. But if you are happy with that, it really is the greatest thing in the world. It does not feel like a job.

 

Credit: Roland Bürgmann

Interview conducted by David Fernández-Blanco