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Geotalk: Steven Smith on fossil faults and fantastic faulting

24 Apr

This week in Geotalk, we’re talking to Steven Smith, a Lecturer from the University of Otago. Steven takes us on an Earth-shaking journey, explaining how ancient faults reveal what’s happening under the Earth’s surface and delving into the future of fault zone research.

First, could you introduce yourself and tell us a little about what you are currently working on?

Last September I started as a Lecturer at the University of Otago in New Zealand. My work focuses on understanding the structure and evolution of tectonic fault zones in the continental crust. I graduated from Durham University (England) back in 2005 and remained there to complete my PhD, studying a large fault zone exposed on Italy’s Island of Elba. My Italian connection continued as I then moved to Rome for 4 years to undertake a post-doc with Giulio Di Toro and Stefan Nielsen at the INGV (National Institute of Geophysics and Volcanology). In Rome I was working on a large group project funded by the European Union. The project involved integrating field and experimental work to better understand some of the extreme deformation processes that occur in fault zones during earthquakes. When my post-doc finished, I relocated to New Zealand, attracted by the research opportunities available here and the wonderful places waiting to be explored!

Steve on the summit of Lobbia Alta (3,195 m), a peak in the Adamello area of the Italian Alps. This area is part of a large Tertiary magmatic batholith that is cut by several fault zones Steve studied as part of his post-doc work. (Credit: Steven Smith)

Steve on the summit of Lobbia Alta (3,195 m), a peak in the Adamello area of the Italian Alps. This area is part of a large Tertiary magmatic batholith that is cut by several fault zones Steve studied as part of his post-doc work. (Credit: Steven Smith)

Last year, you received a Division Outstanding Young Scientists Award for your work on the structure of shear zones. Could you tell us a bit more about your research in this area?

I work mainly on so-called “exhumed” fault zones – those that were once active and have been brought to the surface of the Earth by millions of years of uplift and erosion. By studying the structure of exhumed fault zones we can understand a lot about the physical and chemical processes that are active when faults slip. I have worked on fault zones in Europe that were exhumed from both the middle and upper crust. I’m particularly interested in the crushed-up rocks in the cores of fault zones (better known as fault rocks) and what these can tell us about fault zone rheology and deformation processes.

In the last few years, we have identified a number of previously-unrecognised textures in the cores of large normal and thrust faults in Italy. These include faults with highly reflective “mirror-like” surfaces and small rounded grains resembling pellets. Our work focused on trying to understand the significance of these textures, and in doing so we had to develop new experimental methods to deform fault zone materials under more realistic conditions. By comparing our field observations to the experimental data, we realised that the textures we identified probably represent ancient “fossil” earthquakes preserved in the rock record.

When thinking of a fault zone, you don’t often think small. How can you scale down what’s going on to create a laboratory-sized experiment?

That’s a very good question, and something that experimentalists have to be aware of all the time. It’s generally not possible to reproduce in the laboratory all of the conditions that a natural fault enjoys, which is why laboratory work ideally has to be integrated with other data, such as field observations of natural faults and theoretical modelling. But it is possible to perform experiments at quite realistic pressures and temperatures, and some deformation apparatus can deform fault zone samples over a very wide range of slip velocities – the sort you would expect during the seismic cycle along natural faults.

Laboratory experiments allow us to produce data on rock strength and fault zone behaviour that simply wouldn’t be possible by any other means. At the same time, it’s important to bear in mind that a small laboratory experiment might represent the behaviour of only a single point on a much larger fault surface – that’s where complementary field and geophysical observations come in. Looking at fault geometry and fault zone evolution over time helps put lab studies into context.

Admiring the inner workings of a fantastic fault on the Italian Island of Elba. (Credit: Bob Holdsworth, Durham University)

Admiring the inner workings of a fantastic fault on the Italian Island of Elba. (Credit: Bob Holdsworth, Durham University)

How does deformation differ across the world’s fault zones?

In the last few years, seismologists have detected different types of slip behaviour along active faults, from those that creep along steadily at rates of a few millimetres per year to those that fail catastrophically in earthquakes. In between there are other types of slip behaviour seen in seismological signals (such as seismic waves) from the deeper parts of fault zones like the San Andreas fault and the Alpine fault in New Zealand. Understanding the basic controls of this rich variety in fault slip behaviour is one of the key goals of modern earthquake science. Geologists studying exhumed fault zones have also long recognised that fault zone structure in the crust is very complex and highly dependent on factors like the type of host rock, level of exhumation, availability of fluids and so on. A future goal for geologists like me is trying to understand whether different types of fault slip behaviour recognised in modern-day seismic signals are preserved in the structure of fault zones in some way. 

Is digital mapping an essential tool for the modern-day structural geologist? How does it help?

As in most branches of science, digital technologies are now increasingly used for geological mapping purposes, although a majority of universities still favour the traditional pen-and-paper approach to training students in geological mapping. In many mapping situations – ranging from reconnaissance-scale mapping to detailed surface topography measurements – there are a number of benefits to a digital approach, the main one being that field data are automatically located using GPS or laser-based technology. This opens up a range of possibilities to map and study 3D structures that would be difficult and time-consuming, if not impossible, using more traditional approaches.

I certainly think that digital technologies will play an increasingly important role in geological mapping and research in the future, and the technology will inevitably become more fit-for-purpose and affordable. I recently taught a short workshop on digital mapping to a group of 4th year students in Otago; after a few days they were all quite confident using handheld computers and GPS devices to map, and I think they were impressed by the ease with which the digital data could be analysed to better understand the inherent complexities of geological structure.

Finally, will you be working on faults in the future or moving on to pastures new?

I think there are a lot of important research problems to tackle in fault zones, so it’s likely I’ll continue working on faults in a broad sense in the future. The devastating Tohoku-oki earthquake and tsunami in Japan in 2011 highlighted that our understanding of fault zones is far from complete. My post-doc experience has convinced me that integrating field and experimental work is a promising way to understand fault zone processes. At the moment I’m particularly interested in the very-small scale frictional processes that occur on fault surfaces during earthquakes, and I’m currently using some of the analytical equipment here in Otago to study experimental samples that were deformed under earthquake-like conditions.

If you’d like to suggest a scientist for an interview, please contact Sara Mynott.

GeoEd: Why fieldwork is essential to training the next generation of Geoscientists

3 Apr

Our latest GeoEd article is brought to you by Simon Jung, a lecturer and palaeoceanographer from the University of Edinburgh, who highlights what makes fieldwork a brilliant way to understand Earth processes…

Studying geosciences involves training across a broad range of natural sciences. Only equipped with such background knowledge will students be able to grasp key concepts in the various sub-disciplines that geosciences has to offer. So what’s the best way to get ahold of such knowledge?

A substantial part of the theoretical background in geosciences can be delivered via lectures and/or practicals. Using this standard teaching approach, for example, knowledge of the various rock types and the minerals they contain can be conveyed clearly and effectively. Background information on different soil types, or shapes of rivers, can also be passed on in this fashion.

For something more visual, geological or geomorphological maps can create a great 2D representation of a 3D structure, giving basic insights into the relationship between larger sets of strata or geomorphological features in a given region.

There are, however, important limitations as to the level of understanding students can possibly reach through a classroom-only approach. And these can only be overcome through field training.

Viewing a landscape from an elevated spot – or otherwise suitable location – in the field allows much better comprehension of the processes that have shaped a region. For the first time, truly understanding the nature of the succession of different rock types is an eye-opening and life changing event. Similarly, grasping the role of time in allowing long-term erosion to shape a region can only be attained in the field. A visit to the northwest of Scotland is one way to achieve these goals.

Studying an outcrop in northwest of Scotland. (Credit: Simon Jung)

Studying an outcrop in northwest of Scotland. (Credit: Simon Jung)

Geological and geomorphological research in northwest Scotland has been instrumental in laying the foundations of many crucial concepts in geosciences. The area offers easy access to a unique set of rock sequences documenting Scotland’s early geological history, the explosion of life on Earth, as well as how rivers and ice have shaped the modern landscape. Students from the University of Edinburgh are frequently taken out here, where they are exposed to a huge variety of geological and geomorphological phenomena.

The more specific learning outcomes center around three main areas:

  1. Hands on training in the field helps refining all aspects related to fieldwork (e.g. observational skills, mapping)
  2. Using self-generated field data regarding rock sequences and their 3D orientation allows students to comprehend the long-term geological history
  3. Students also obtain a greater understanding of the role of erosion in shaping the landscape in a region. How? By determining river runoff at a number of locations and making measurements of the sediments being transported

Such excursions allow students to develop an improved understanding of the local geological and geomorphological history of a region.  At a larger scale, they will also develop a more comprehensive view of the processes having shaped the Earth. As the video below documents, this journey is not only educating, but fun too!

By Simon Jung, Lecturer in Palaeoceanography, University of Edinburgh

 

Imaggeo on Mondays: A rolling stone gathers no moss

31 Mar

Philippe Leloup brings us this week’s Imaggeo on Mondays, with tales from a mountain trail that show a geologist can never resist a good rock!

In reality, this shiny slab of rock is about 20 centimetres across. Polished to perfection, the layers of marble and amphibole are beautiful to behold. (Credit: Philippe Leloup via imaggeo.egu.eu)

In reality, this shiny slab of rock is about 20 centimetres across. Polished to perfection, the layers of marble and amphibole are beautiful to behold. (Credit: Philippe Leloup via imaggeo.egu.eu)

This image is that of a polished slab of a rock composed of interlayered marbles and amphibolites. The sample was once part of a small dry-stone wall bordering an outdoor kitchen along a trail along the Ailao Mountain Range in China (or Ailao Shan in Chinese).

As I passed by, a small black eye looked at me, and I couldn’t resist asking the owner to give me that stone – one that could easily be replaced by any other rock nearby, and he kindly agreed. The rock was special for me because I felt that its structure would be spectacular.

The Ailao Range is part of the Ailao Shan – Red River shear zone, a region that stretches for more than 1000 kilometres – from southeast Tibet to the Tonkin Gulf. During the Oligo-Miocene, the Indochina bock (encompassing Vietnam, Cambodia, Laos and Thailand) was pushed away from the collision between the Indian and Asian continents and moved several hundreds of kilometres towards the southeast along that ~10 kilometre-wide shear zone. Today, evidence that intense ductile deformation occurred are found in gneiss and marbles showing steep foliation, horizontal lineation, and numerous left-lateral shear features – a type of deformation that leaves rocks looking like this:

 A thin section microphotograph (total width ~0.5 mm) showing several feldspar crystals with bended tails. These tails show that they have slowly rotated counter-clockwise. These rolling structures are characteristic of left-lateral ductile deformation. (Credit: Philippe Leloup via imaggeo.egu.eu).

A thin section microphotograph (the total width is about 0.5 mm) showing several feldspar crystals with bended tails. These tails show that they have slowly rotated counter-clockwise. These rolling structures are characteristic of left-lateral ductile deformation. (Credit: Philippe Leloup via imaggeo.egu.eu).

When I cut the rock it turned out that the amphibole layer had a very special shape, like a Swiss roll, resulting from simple shear – something that revealed spectacular colours and a stunning shape when seen in section.

By Philippe Leloup, University of Lyon

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Pitter-patter of little paws in Patomsky crater

10 Feb

This week’s Imaggeo on Mondays is brought to you by Dmitry Demezhko, who describes how Patomsky crater may have formed and why it keeps scientists puzzling…

Patomsky crater, also known as Patomskiy crater or the Patom cone, sits in the Irkutsk Region of Eastern Siberia. The site is a curious cone with a crater at the top and a small mound in the center. The cone totals some 39 metres in height and stretches more than 100 metres in diameter (at the base of the cone).

Patomsky crater – view from a helicopter. (Credit: Dmitry Semenov)

Patomsky crater – view from a helicopter. (Credit: Dmitry Semenov)

The crater was discovered in 1949 by Russian geologist Vadim Kolpakov and for a long time it was considered to be an impact structure with a meteoric origin. Later, Viktor Antipin suggested it could be a nascent volcano. But neither meteoritic nor volcanic matter was found there. The crater consists of proterozoic limestone and sandstone debris and, to date, there is no consensus among scientists regarding the crater’s origin.

View from the crater. (Credit: Dmitry Demezhko, distributed via imaggeo.egu.eu)

View from the crater. (Credit: Dmitry Demezhko, distributed via imaggeo.egu.eu)

During a short expedition in August 2010 we conducted a gravimetric survey at the crater and surrounding area, aiming to evaluate its internal structure. The gravity field shows that surface negative anomalies, where the gravity is unusually low, have deep “roots” and a joint source at depth. But the crater’s gravity field differs greatly from the fields of other well-known impact structures, suggesting that it may not have formed during a meteoric impact.

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right). (Credit: Demezhko et al., 2011)

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right), (click for larger). (Credit: Demezhko et al., 2011)

We suggest this structure formed in two stages. During the first stage tectonic processes similar to mud volcanism created a porous vertical channel. In the second stage, cryogenic processes would have played an important role in breaking apart the rocks to form the cone and crater.

There is a lot of mysticism and superstition surrounding Patomsky. Local residents call the crater “a fabulous Eagle’s Nest” and say that both people and animals bypass it. We didn’t sense anything mystical while working in the crater though – and this cute little animal lives quite comfortably there.

Downward continuation of the Patomsky crater (left) and Popigay impact structure gravity fields (right). (Credit: Demezhko et al., 2011)

“Inside Patomsky crater: a chipmunk” by Dmitry Demezhko. This image is distributed via imaggeo.egu.eu.

By Dmitry Demezhko, Institute of Geophysics UB RAS, Yekaterinburg

References:

Alekseyev, V. R.  Cryovolcanism and the mystery of the Patom Cone, Geodynamics and Tectonophysics, 3, 289-307, 2012 (in Russian)

Demezhko D.Y., Ugryumov I.A., Bychkov S.G.: Gravimetric studies of Patom Crater. In: Patom Crater. Research in the 21st Century. Publishing House of the Irkutsk State University, Irkutsk, p. 42–50, 2011 (in Russian)

If you are pre-registered for the 2014 General Assembly (Vienna, 27 April – 2 May), you can take part in our annual photo competition! Up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image on any broad theme related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

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