Geophysics

Interview with Dr. Pascal Audet

Matt Herod July 3, 2013

Today’s post is a special treat! An interview style post with one of the newest professors in the Department of Earth Science at the University of Ottawa: Dr. Pascal Audet.

What is your background? e.g. What was your undergrad in, PhD.

I graduated with a degree in physics from the Université de Montréal. By that time I knew I wanted to work in applied physics and I had always been curious about how the Earth works, so I enrolled in a Master’s program in Earth Sciences at the Université du Québec à Montréal, where I worked on gravity and topography modeling. I then decided that I wanted to do a career in geophysics, so I moved to Vancouver and started studying seismology at UBC. I graduated in 2008 and moved to California to do a postdoc at the University of California at Berkeley.

What was your PhD research about?

My PhD research was focused on the structure of subduction zones, especially the Cascadia subduction zone that is threatening the coastal cities of the Pacific Northwest (Vancouver, Victoria, Seattle, Portland). During my PhD I installed a few dozen seismic stations to record the ground motions caused by earthquakes from around the world. I used the information contained in the seismic records to study the structures deep below the stations. My results showed that the oceanic plate subducting beneath North America contains trapped pore-water at very high pressures, which could help explain some odd slip behavior of the subduction zone thrust fault.

Pascal had to chop all those trees down just to put in his seismic station. (Just kidding)

What field of geoscience do you study?

I consider myself a geophysicist, in that I use physical principles and techniques to investigate interesting questions about the Earth. My specialties are in seismology (the study of earthquakes and the waves they generate) and in gravimetry (study of the gravitational field of the Earth and other planets). I mostly deal with geophysical signals – seismic waves of gravity fields – and I develop processing techniques to obtain important information on Earth structures and dynamics.

How did you end up becoming interested in seismology and subduction zones?

At the time I started my PhD, I thought that studying seismology was the coolest job in the world, and subduction zones were the most interesting objects to study. Indeed, this is where a vast oceanic plate grinds past another tectonic plate on its way down to the Earth’s deep interior, producing the Earth’s most energetic events (e.g., the magnitude 9 Japan earthquake in 2011) in the process. I also had the good fortune to work with Michael Bostock at UBC, one of the best subduction zone seismologists. My interest never faded and here I am, doing research, teaching and training the next generation of geophysicists. I have the best job in the world!

What sort of techniques do you use to study seismology?

As I said, I use information contained in seismic records to obtain information on Earth structures. In a nutshell, earthquakes generate waves that propagate through the interior of the planet, and are recorded by very sensitive seismic instruments all around the globe. The signals contain information on the earthquake itself, but also on all the structures that the waves propagated through (via various wave effects that are well known in physics, such as refraction, reflection, diffraction, etc.). If we can remove the signature of the source from the seismic records, we are left with signals that contain information on structure alone. These signals then give us information on the seismic velocity of the medium, which is interpreted in terms of the geometry, temperature, composition and fluid content.

What sort of field work is involved in the study of seismology?

During my PhD I installed a few dozen seismic instruments in the northern part of Vancouver Island. Each station consists of the sensor, the data logger (recording device), and the power system. The sensor is typically buried about 2 meters in the ground and the power system is provided by solar panels that recharge a couple of car batteries. Carrying all this equipment and digging holes in clear cuts was quite challenging!

Join Pascal in the Yukon! He is looking for grad students. The field work is great.

What do you do with the data once you have gotten it from the field?

The data are recorded continuously on a disk. After collecting the disks at the end of the experiment, the data are archived at one of the data archiving centers and is available immediately to any researcher on the planet. With the right software, anybody can download seismic data from any seismic station. Some stations even provide real-time data, where a satellite connection is used to send the data seamlessly to the archiving center.

You are also interested in planetary tectonics. How do we study this field?

I am also very interested in the structure of planets and satellites within our solar system (e.g., the Moon, Mars, Venus). Since it is quite difficult and expensive to land on other planets and install seismometers (the Apollo Missions did install a few seismometers in the 1970s, but they only worked for a very brief period of time), one of the best tools to study their internal structure is to use the attraction from their gravitational field. Even though the gravity field appears to be uniform across the surface of the Earth (and other planets), there are minute variations that arise from small changes in the density structure of the deep interior. By studying these small variations in gravity, we can therefore obtain information on the internal structure of the planet. On remote planetary bodies, the gravity field is known by tracking satellites that orbit the planet. My current works is aimed at developing the tools to study the lateral variations in the gravity field.

What are your plans for future research?

This summer I am going back in the field to install 7 seismic stations in the Yukon and Northwest Territories, across the MacKenzie Mountains. These stations will use the satellite connection to send the data in real-time. The stations will be in the ground for 5 years, and the data collected will be used to study the structure and seismicity of the northern Canadian Cordillera – an area where we know very little about tectonic processes. This experiment is timed perfectly with the installation of stations in Alaska as part of the US Earthscope experiment (http://www.earthscope.org/). I will be spending a lot of time processing the data and will hopefully make interesting discoveries about the tectonics of this spectacular area.

Thanks so much Pascal!

By the way! Pascal is actively seeking graduate students interested in joining him in this exciting work in the Yukon or on planetary gravitational fields. If you would like to hear more about the MSc. and PhD. opportunities that Pascal has available post in the comments and I can put you in touch with him directly! He is also fully bilingual and a top notch hockey player.

Guest Post: Dr. Sam Illingworth – To Boldy Go

Matt Herod May 2, 2013

Satellites are now so ubiquitous in our lives that there is something of a precedent to take them for granted. A normal daily routine for may people across the world may include watching television (satellite) as you check your twitter account (satellite) and have a look at the weather (satellite), all before you’ve even eaten your breakfast (not a satellite); whilst for those of us in the remote sensing community, whose work consists of analysing data from a large plethora of Earth-observing satellites, it can often seem that our lives are intertwined with those majestic flying machines as they dance their cosmic waltz far above the confines of planet Earth. It is almost staggering to believe that just over 50 years ago there was not a single manmade satellite in space, especially when you take into the consideration the fact that since its conception in 1957 the United States Satellite Surveillance Network (SNN) has chartered some 8,000+ anthropogenic obiters.

Sputnik 1 (souce: www.interestingfacts.org)

After the Second World War, the two global powerhouses of that era, the USA and the USSR, found themselves locked in a conflict of attrition that will come to be known as the Cold War. A war whose victors are judged not by the more conventional markers of land gain or battle tallies, but rather through the accumulation of weaponry and the rapid advancement of technology, of which the race to get into space plays a key and pivotal role. Most people, if asked who they considered to be the winners of the Space Race, would tell you that it was of course the USA, taking one small step for man and one giant leap for capitalism when Neil Alden Armstrong walked across the lunar landscape on July 21^st 1969. Ask another group of people from a certain vintage or scientific persuasion, and they would probably tell you that the true winners of the Space Race were the Soviets, seeing as they were the first to actually get something up there with the launch of Sputnik 1 on October 4^th 1957. But for me there can only be one winner, and it is neither Apollo 11 nor Sputnik 1, but instead the much less lauded US satellite: Explorer 1.

The Sputnik satellite may have been the first into space, and the Apollo missions may have bee the first to demonstrate the capability of manned spaceflight, but as an Earth observational scientist it was the Explorer 1 satellite that I find to be the most intriguing, being as it was the first to carry a scientific payload; a set of instrumentation which would be used to make the first great scientific discovery from space.

The achievements of the Russian polymaths in ensuring that the Soviets were the first into space should of course never be overlooked, nor would it be strictly fair to say that the scientific significance of Sputnik 1 disappeared as soon as it had successfully reached the edge of the atmosphere – by measuring the drag on the satellite, scientists were able gain useful information about the density of the upper atmosphere – but I like to think of Sputnik 1 as that valiant guest at a wedding, who wishing to get the party started with suitable aplomb, makes a line straight for the empty dance floor only to find that once there they lack any of the necessary moves to do anything of particular note. Explorer 1 on the other hand can be thought of as the louder, more eccentric cousin of Sputnik 1, strutting up to the dance floor without a tie (incredibly there was no tape recorder installed on Explorer 1, meaning that data could only be analysed in near real time as it was transmitted back down the scientists on the ground) before starting to cut shapes that would make even a computerised lathe turn green with envy.

From left to right: William H. Pickering, director of the Jet Propulsion Laboratory, which designed and built Explorer 1. James A. Van Allen, University of Iowa physicist who directed the design and creation of Explorer’s instruments.
Wernher von Braun, head of the U.S. Army Ballistic Missile Agency team that designed and built the Jupiter-C rocket (Source: Smithsonian National Air and Space Museum).

Explorer 1 was launched on the 31^st January 1958, becoming the first of the USA’s forays into the vast unknowns of the surrounding cosmos. The design and build of the scientific payload was Lead by Dr. James Van Allen of the University of Iowa, its purpose being to measure cosmic rays as they made their way from the Supernovae explosions of distant stars within our galaxy and towards the Earth. The instrumentation was effectively a Geiger-Müller counter, set up to count the number of high energy cosmic rays as they passed through the relatively fragile shell of the satellite’s metallic exterior, and it was expected that the instrument would return values of approximately 30 rays per second. However, the scientists noted that at certain points in its orbit the instrumentation was returning values of 0 rays per second. Upon closer inspection of the data (along with the measurements taken by Explorer 3, launched on 26^th March 1958, and complete with requisite tape recorder) it turned out that these zero values all seemed to be concentrated around South America, and that they only seemed to be present when the satellite was flying at an altitude of greater than 2000 km; at altitudes less than this the instrument recorded the expected 30 counts per second. The team at Iowa soon deduced that these zero counts weren’t zero counts at all, rather they were errors in the data brought about by the instrumentation being bombarded by a powerful stream of highly energised particles that were beyond its measuring capabilities. Van Allen (and others at the University of Iowa) proposed that the reason for this localised concentration was a doughnut-shaped belt of highly energized particles, trapped in formation as a result of the Earth’s magnetic field. These belts have since been named after their discoverer (and not as I had assumed, much to the amusement of one of my undergraduate lecturers, after US rock-hero Eddie van Halen), becoming the first scientific discovery to be made from space.

The Van Allen belts (source: Wikipedia

It was this monumental achievement that formed a significant contribution towards the potential of satellites to inform on the many wonders of our home planet, and it is for this reason that I put forward the Explorer 1 (and by association the USA – sorry soviet fans) team as the true winners of the Space Race, a worthy recipient of a truly intergalactic (well ok, monogalactic) battle.

Sam is a postdoctoral research assistant at the University of Manchester, where he spends most of his time working on the development of an algorithm for the retrieval of trace and greenhouse gas measurements from aircraft measured spectra, an algorithm that he affectionately refers to as MARS (the Manchester Airborne Retrieval Scheme). In his spare time Sam enjoys convincing scientists that they can learn to communicate their research more effectively by embracing theatrical technique in all its many guises.

Thanks for reading!

It’s rainin’ isotopes…

Matt Herod March 27, 2013

This post is kind of a continuation of Laura Roberts excellent guest post on the Solar Storms and the Earth’s Magnetic field. However, this is a bit of a different spin on it. I am not writing about what get’s kept out, but rather what slips by the shield and gets in. Of course, I am speaking about cosmic rays and the wonderfully useful isotopes they produce that rain down upon us. Yes, it is literally raining isotopes…all the time! I know that this sounds weird, when I first learned about this phenomenon it came as a complete surprise to me. Not only are isotopes raining down all the time, but there is a lot that we can learn about our planet by analyzing these amazing by-products of cosmic ray collisions.

What are cosmic rays?

Cosmic rays are incredible things. The Earth is constantly being bombarded by them and we are protected from this massive influx of extra-terrestrial radiation by our magnetic field and atmosphere, which deflects about 90% of the low energy cosmic rays. Check out last weeks awesome guest post about Earth’s magnetic field. There are two types of cosmic rays. Primary cosmic rays generally originate outside of our solar system and travel throughout space occasionally bumping into things like planets. In fact, it has only recently been discovered exactly where they come from. In February, 2013 a paper came out in Science called: Evidence Shows That Cosmic Rays Come From Exploding Stars that (surprise) stated primary cosmic rays are produced by exploding stars aka. supernovae in which an ancient star blows up, releasing massive amounts of energy, elements and cosmic rays!

Kepler’s Supernova (Source)

Primary cosmic rays are 99% protons and alpha particles (two protons and two neutrons) and the remaining 1% are the nuclei of heavy atoms or beta particles (electrons). These bits of atoms and radiation fly around in space and bang into everything. Sometimes, actually more often than sometimes, they bang into the Earth. In fact, they bang into the Earth a lot! There are billions of collisions every day. Some of the particles crashing into the Earth have low energies while others have high energies. The frequency that these low energy particles collide is many times greater than high energy ones. There are about 10,000 collisions per square meter per second for giga-eletronvolt particles. For the higher energy rays the rate of collision is less. They might arrive with a frequency of 1 per square metre per second, as is the case with tera-electronvolt particles. The decrease in collision frequency continues as energy increases up until the very highest energy of the exa-electronvolt which collides about 0nce per square kilometre per century.

When cosmic rays pass through the Earth’s magnetic field is when things start to get really interesting, from a geochemical perspective that is. When primary cosmic rays enter the Earth’s atmosphere they start banging into all of the molecules and atoms floating around up there and produce secondary cosmic rays. Basically imagine a bowler throwing a strike. The bowling ball represents the primary cosmic ray and the pins are the molecules in the atmosphere. When the ball collides with the pins they fly off in every direction, which is analogous to the process occurring constantly in our atmosphere. When this takes place in the atmosphere the collision is so energetic the molecules and atoms can actually break apart. This is called spallation and results in a cascade of neutrons, protons and atoms called an air shower.

A simulation of a cosmic ray shower formed when a proton with 1TeV (1e^12 eV) of energy hits the atmosphere about 20km above the ground. The ground shown here is a 8km x 8km map of Chicago’s lakefront. This visualization was made by Dinoj Surendran, Mark SubbaRao, and Randy Landsberg of the COSMUS group at the University of Chicago, with the help of physicists at the Kavli Institute for Cosmological Physics and the Pierre Auger Observatory. (Source)

What is produced?

Air showers produce all sort of radioactive isotopes that are formed no other way. Some are very short lived and decay away quickly, while others are extremely long lived and have half lives of millions of years, allowing them to accumulate in the environment.

A list of the major cosmic ray isotopes and their half lives. The ones in bold have geologic applications.

Other isotopes are produced when cosmic rays reach the ground and collide with minerals. This can cause other isotopes to form within the mineral crystal lattice. For example, the cosmogenic isotope, aluminum-26 is produced when a cosmic rays strikes a quartz crystal and transforms some of the silicon in the quartz structure into aluminum. These are referred to as in-situ cosmogenic isotopes.

The next part of the process concerns what happens to all of these isotopes once they have sprung into existence thousands of metres above our heads. The fate of these isotopes is varied and they all live in the atmosphere for a little while before becoming part of the hydrologic cycle. Eventually they fall down to Earth either stuck onto aerosols or incorporated into rain and begin to interact with water bodies, enter groundwater, stick to soil particles or get absorbed into people, plants or animals. Essentially, they begin cycling through the environment until they decay away. Since these isotopes get cycled through various parts of the environment we can use them as tracking tools to trace the pathways they take and learn about their interactions with other components of environmental cycles.

What is the use?

Cosmic rays isotopes are useful for more than just getting a good tan! In fact, the list of possible questions that can be applied to cosmogenic isotopes just goes on and on. I’ll just briefly cover a few of them since each one of these applications is a whole blog post by itself I’ll just give the highlights here.

Exposure age dating: Exposure age dating is one of the principle uses of cosmogenic isotopes and several different ones have been employed to this end. Exposure age dating is when we use cosmogenic isotopes to date how long something has been exposed to secondary cosmic rays at the Earth’s surface. For example, a rock at the toe of a glacier may have just been exposed to cosmic rays a year ago and its exposure age date will tell us this. Another rock, 20 metres further from the glacier toe may have been exposed 5 years ago and this difference will be recorded. Basically, the clock starts ticking once cosmic rays are able to reach the rock or bone, or whatever material is being dated. Exposure age dating has the power to date materials that range from only a few thousand years to millions of years depending on the half lives and concentrations of the nuclides in question. The way exposure dating works is that when a secondary cosmic ray impacts a rock containing Si (silicon) or O (oxygen) some of the neutrons on the silicon or oxygen are knocked off and the result is the production of aluminum-26 or beryllium-10 right in the mineral lattice. One common mineral that contains both silicon and oxygen is quartz. Quartz is pretty much everywhere and in everything, which opens the door for a wide range of materials that can be exposure age dated. All they have to contain is a bit of quartz. The decay of 26Al and 10Be allows the material to be dated. There are other isotopes that can be used for exposure age dating besides these two and other minerals that contain Si or O can also be used as well. The figure below shows the wide range of applications that exposure age dating can be applied to. For example, if you want to date a volcanic eruption it is easy to exposure age date the lava or ash, both of which have a lot of Si. It is also possible to date landslides, erosion rates, burial ages, the list goes on and on. There are many other isotopes that can be used as well besides 26Al and 10Be.

Figure showing all of the different applications of exposure age dating. Ivy-Ochs, S., & Kober, F. (2008). Surface exposure dating with cosmogenic nuclides. Quaternary Science Journal, 57(1-2), 179–209.

CLOUD Project: The CLOUD project is a CERN experiment that is investigating the possible linkage between cosmic rays and cloud formation. It has been hypothesized that cosmic rays can cause clouds to form by forming aerosols and it has been noticed by satellites that an increase in the cosmic ray bombardment can increase the amount of cloud cover. Cloud cover has a profound influence on the Earth’s energy balance and hence climate. It has been proposed that throughout geologic time changes in the cosmic ray flux have been responsible for climate change. However, proving this is difficult given the length of time in question and the evolving states of the cosmic ray flux and Earth’s magnetic field. However, CLOUD has set out to find the linkage between cosmic rays, clouds and climate if one exists.

Carbon-14: Carbon 14 is unquestionably the most used of any of the cosmogenic isotopes. It has applications in geology, archaeology, paleontology, anthropology, hydrogeology, and many other -ologies as well. 14C is produced primarily when neutrons collide with nitrogen in the atmosphere replacing a proton in the nitrogen nucleus and transforming it into carbon-14, although atmospheric nuclear weapons testing also produced a substantial amount of 14C. The primary use of 14C, or radiocarbon, is radiocarbon dating. Once radiocarbon is produced it enters the global carbon cycle and disperses throughout the environment. Since it is part of the carbon cycle it becomes incorporated into all living things, including people and animals. 14C continues to enter our bodies while we are alive. Once we die, there is no further addition of 14C and therefore, the clock starts ticking on its use as a dating tool. 14C has a 5,730 year half life and is therefore useful as a dating tool for biological materials up to ~45,000 years ago.

Cosmic rays are some of the most mysterious, yet useful phenomena on our planet and have allowed for incredible advances in many sciences. As new, more sensitive technology becomes available look for the use of cosmic rays and the isotopes they produce to accelerate as we find new questions they can be used to answer.

Cheers and thanks for reading,

Matt

Guest Post: Solar Storms and the Earth’s Protective Shield – Laura Roberts Artal

Matt Herod March 15, 2013

I am a PhD student at the University of Liverpool Geomagnetism Laboratory. My current research project is the palaeomagentic study of 3.5-3.2 billion year old rocks from South Africa. The aim of my research is to improve our understanding of the long term evolution of the Earth and the surface conditions under which the first forms of life originated through using palaeomagnetic records. The rocks of the Barberton Greenstone Belt are excellently preserved and have only been subjected to low grade metamorphism (greenschist facies), making them good candidates for paleomagnetic studies. I also undertook my undergraduate studies at Liverpool University, where I studied monogenetic volcanism on Tenerife. Between my undergraduate and PhD I had a brief stint in the world of industry as an environmental consultant. I’m a keen science communicator and am involved in a number of outreach projects.

An article last month in the U.K’s Guardian Newspaper reported on the findings of the Royal Academy of Engineers who warned the U.K government of the need to set up an expert panel which could generate plans on how the country should prepare and cope in the event of a large solar storm or corona mass ejection (CME). What was not reported in the article and is often unknown, is that we already have a shield that goes some way to protect us from the harmful effects of out giant neighbour; but I’m getting ahead of myself. Let start with a few basics.

In essence, a solar flare is a large release of energy at the Sun’s surface, which can be followed by a CME. Solar flares tend to be short lived events and eject a cloud of charged particles, including protons, electrons and atoms. CMEs often follow flares and tend to emit considerable gusts of solar wind and magnetic fields. When the winds and charged particles reach the proximity of planet Earth, they interact with the Earth’s magnetic field causing a magnetic storm with the charged particles being preferentially deflected towards the Earth’s magnetic poles. Magnetic storms can cause disruption to electronic grids and communication systems, including satellites, aircraft, GPS navigation systems and mobile phone networks, amongst others. The Royal Academy of Engineer’s report was making reference to these potential harmful effects and arguing that the U.K. should prepare itself against them. In truth, they don’t exaggerate, the damage that solar flares can cause is not negligible: In September 1859, a large solar flare caused telegraph wires in both the United States and Europe to spontaneously short circuit, causing numerous fires; Northern Lights were seen as far south as Rome, Havana and Hawaii, with similar effects at the South Pole. More recently, in March 1989, a large solar flare caused a blackout in the whole of the Quebec province of Canada, whilst the Canadian television network and newspapers were disrupted by damage caused by a solar flare to communication satellites orbiting the Earth in 1994. I won’t go into the details of how and what we ought to be doing to protect ourselves against these (this is not my field!). Instead, I’ll tell you about the Earth’s Magnetic field and its role in protecting us against the harmful storm winds and particulate clouds.

My research focuses on some of the oldest rocks in the world. I study the Barberton Greenstone Belt (BGB), which is located in North Eastern South Africa and is one of a few Archean aged terrains located across the globe.

The BGB is characterised by volcanic sequences which are interspersed with layers of sediments. It has been subjected to a number of tectonic events which have led to folding and low-grade metamorphism in the area. The world famous type-section of Komatiite lavas, as discovered by the Viljoen brothers in 1969, is exposed in the BGB. My research is concentrated on three Complexes of the Onvenwacht Suite, with rocks showing ages between 3.5 and 3.2 billion years (geological map modified from de Wit et al. 2011). But, how can these rocks tell us anything about solar storms, CMEs and the Earth’s magnetic field?

We now that the Earth’s magnetic field acts a shield against the harmful particles ejected by solar flares, deflecting them pole wards. In addition, it protects us against atmospheric erosion and water loss caused by solar wind. The lack of a magnetic field on Mars (generate by a geodynamo in the core), leaves the planet barren with no atmosphere or water. The early Earth was able to retain its atmosphere and water and so became habitable (with early forms of life being reported in the BGB). However, we know little about the Earth’s magnetic field during this time. Studying the paleomagnetic signature of the rocks of the BGB might enlighten us about the processes that were taking place in the core, mantle and crust during the Archean. My research focuses on the directions of the magnetic field recorded in the BGB during its formation. Recent studies (Tarduno et al, 2010) have attempted to understand the strength of the field during the Archean and what bearing that might have on the ability of the planet to protect itself against solar winds. In their study, Tarduno and collegues, report paleointensities (obtained from single silicate crystal bearing magnetic inclusions) that are ~50-70% lower than the intensity of the present day field. How much then, could the Earth’s magnetic field reasonably be expected to shield the planet from the Sun? Tarduno et al. argue that solar particles would have greater access to the Earth’s atmosphere during this period, due to an increased polar cap area. During the Archean, the stand-off distance between the Sun and the Earth could also be estimated to be smaller. These two facts combined would promote loss of volatiles and water, suggesting that the early Earth had a larger water inventory than presently. Overall, the young Earth was able to produce a magnetic field strong enough to protect the planet from large scale atmospheric erosion and water loss, it is likely that there were important changes to these in the first billion years of the Earth’s history.

I find it reassuring that there is this invisible shield that is protecting us humans, (perhaps not our technology), and has been doing for most of the Earth’s history. The Magnetic field has contributed to the conditions being right for evolution to happen. I think we should give it a lot more credit!

Please see below for a selection of links that might be of interest for those who might want a bit more reading on the subject!

http://www.geomagnetism.org/

http://www.peeringintobarberton.com/project.html

http://news.bbc.co.uk/1/hi/sci/tech/8659019.stm

http://www.nasa.gov/topics/earth/features/sun_darkness.html

http://science.nasa.gov/science-news/science-at-nasa/2003/23oct_superstorm/

Laura Roberts Artal