Nearly 20 years ago, researchers at Oregon State University began leading an effort to collect information about the structure and evolution of the North American continent using electromagnetic energy. That effort is finally complete. The new map can be used to protect the electrical grid during extreme solar storms and identify geohazards. It can also help target locations for tapping natural resources, including geothermal power and critical minerals. Adam Schultz led the effort at OSU and joins us to explain what we can learn from a better understanding of the Earth’s geoelectric properties.
The following transcript was created by a computer and edited by a volunteer:
Geoff Norcross: This is Think Out Loud on OPB. I’m Geoff Norcross. 20 years ago, researchers at Oregon State University started an effort to map out the North American continent using electromagnetic energy. It’s like an MRI of the earth beneath our feet. That map is out now, and it can be used to protect the electrical grid during big solar storms like the one we had earlier this year. It can also help pinpoint important natural resources for extraction.
Adam Schultz led the effort for OSU. He’s a professor of geophysics at the school and he joins us now. Adam, welcome to Think Out Loud.
Adam Schultz: Thanks, Geoff.
Norcross: 20 years ago when this project started, what was the goal? What were you trying to see?
Schultz: Originally, this was a big part of a big initiative by the US academic geophysical community through the National Science Foundation to study the structure and evolution of the North American continent. So it was a pure geological sciences project, where a number of different geophysical techniques, seismic techniques, electromagnetic techniques, studies of ground deformation, etc., were used to overlay all of these results and to try to really understand how the continent was put together. So again, it was just a pure science and discovery project at the time.
Norcross: How do you do it though? How do you map out what is going on underneath the surface of the earth?
Schultz: You said it was like an MRI, and that’s a good analogy. It’s not an MRI, it’s not a CT scan, but it’s the equivalent of what happens in a hospital. But now your target is something on the scale of a continent. So the method we use has a curious name – magnetotellurics. That refers to using measurements of the earth’s magnetic field. And tellurics is a Greek term referring to earth currents or the electrical currents in the earth. So by measuring the natural time variations at a whole grid of different locations, we can generate an image if you wish, like an MRI or a CT scan, of the electrical properties of the rocks and minerals, at every location underneath that grid of stations, all the way from the surface down to about 300 kilometers. So that’s covering the crust and the uppermost mantle underneath, in this case, continental North America.
Norcross: How many stations did you have to put out there in order to get these readings?
Schultz: It was a little bit shy of 1,800. And a station is a temporary recording station. It might be there for several weeks to two or three months, depending on signal levels and noise levels at each site.
Norcross: Just to kind of get a sense of how big an area one station can measure, where did you park your station to measure what’s happening here in the Northwest?
Schultz: We have a grid of station locations, spaced roughly 70 kilometers apart. It’s not an exactly rectangular grid, but nearly. And every 70 kilometers, we’ll sit there temporarily with one of these recording stations for that period of time. And that gives us sensitivity not only to depths down to about 300 kilometers, but also laterally over a region covering the space between the 70 kilometers between station points. So you’re talking about, for the Cascadia region, from the crest of the Cascades to the coast, many, many tens of stations in Oregon, similarly Washington and California.
Norcross: And did you just drive these stations out into the landscape and just take a reading, and then move to the next? I’m not quite clear on how it works.
Schultz: It’s kind of like we’re running a logistics operation like UPS or FedEx where we have multiple field crews, up to four at a time driving their four wheel drive trucks, and going to designated locations. And I say designated because this is the United States and somebody owns the land everywhere. Could be the federal government, could be private landowners. So we have to get permits for every single one of these stations.
The first job is to see where are we in our 70 kilometer grid? And within about 15 kilometers of that location, can we find a site that we think will be suitable, away from noise sources? And then can we find who owns the land and will we get permission? It’s a huge operation just from the backend of handling that, and also running all these trucks and minimizing driving distances when you’re paying crews by the hour. So you can imagine it becomes a big deal over a 20 year project to execute this on time and on budget.
Norcross: So after 20 years, you have a map, and you can see things like mineral deposits or areas to explore for geothermal power. With the push to electric vehicles and the batteries needed to run them, and the move away from fossil fuels for power, that sounds huge.
Schultz: Well yeah, from two perspectives. The first is looking at the natural resources. So what we’re really looking at is the deep roots of where these natural resources, like you’re saying, geothermal energy or critical minerals, might lie. And then that gives companies the information they need to maybe prospect in higher resolution to the depth where they might want to extract those minerals. But first they need to know the most likely areas. So this plays an important role in that.
And also, it plays an important role that turns out in protecting critical infrastructure against certain natural hazards, particularly space weather. And it also provides information on other natural hazards. Curiously enough, even though we’re looking at the electrical properties of the rocks and minerals underneath crust and mantle, it actually is giving us some additional information that might be relevant to where and how likely it is to see big earthquakes.
Norcross: Well, that brings up Cascadia. I know you were looking at the crest and the mantle underneath the continent. But we’ve got the Cascadia subduction zone about 100 miles off the coast, and when all the energy is released out there it’s going to be a very bad day. Did you learn anything about the subduction zone in your research here?
Schultz: Yeah, our data is definitely sensitive to it. We can see the subducting plates. And in particular, there’s a region of great interest which is, as the oceanic plate subducts underneath North America, the very top of that plate all the way up to the base of the crust is an area called the mantle wedge. And in this intermediate area, we’re able to image areas that are highly electrically conductive, and other areas that are resistive. And we believe that the primary reason for this difference in electrical properties is the presence or absence of fluids. The magnetotelluric method, where we’re measuring the magnetic and electric fields, is very sensitive to the presence of fluids. And as the oceanic plate subducts underneath the edge of the continent where we all live, fluids are constantly and slowly trickling up from the subducting plate. And we believe that the presence or absence of fluids has a role in lubricating the interface between the two plates, how stress builds up, and whether or not there’s a higher or lower probability of a megathrust earthquake of the sort we’re always talking about here in Cascadia.
Norcross: Adam, you learned about areas in the continent that are vulnerable to solar storms and electromagnetic pulses. Can you explain that to me?
Schultz: Yeah, certainly. When the power grid in this country was built – we were one of the first countries to have a power grid – it wasn’t really known that there were geomagnetically induced currents flowing through the ground. And so when solar flares get big enough, you get an ejection of charged particles called a coronal mass ejection from the sun that streams out into space. And this is happening all the time, and to some extent we’re always seeing the influence of this in the earth’s magnetic field.
But every now and then there’s a big blast. And when that happens, the earth’s magnetic field is disturbed greatly. And also some of those charged particles are captured above the atmosphere in the earth’s ionosphere. So this causes electric currents to flow above the atmosphere. And from some physics, that leads to electric and magnetic fields and electric currents to flow in the ground and below, in the crust and mantle. And that’s something that we can measure.
And it turns out that the power grid, the transmission system is grounded, as you can imagine. And so when these geomagnetic induced currents flow in the ground, they also flow in the transmission network. And the transmission network for the power grid wasn’t designed for that. So that means the big monster transformers that underpin the U.S. power transmission network are under stress from time to time from these geomagnetic induced currents. Sometimes the stress can be really severe. A good example was 1989 – up in the province of Quebec, there was a big solar storm, we had a big geomagnetic disturbance, and the Quebec power grid failed. It wasn’t just a Canadian problem because the US and Canadian power grids are interconnected, so that had ramifications across the continent. And there’s also stress in U.S. transmission networks as well.
So that was one example. In 2012, there was a near miss, there was an enormous coronal mass ejection, and if the earth had been slightly ahead or behind in its orbit, it would have hit us head on. Fortunately, there was just a glancing miss. If it had hit us head on, the estimates were it was sufficiently big to substantially bring down sec big sections of our power grid. And it’s not just a theoretical possibility, because the earliest known one of these events is called the Carrington Event – it was in the 1850s – the highest technology system we had was the new telegraph network. And one fine day, when there were auroras down in the tropics, there were sparks flowing through all the telegraph stations. So it took some years to understand what was going on. It was these geomagnetic induced currents. So the 2012 near miss got everyone’s attention. It got the attention of the utilities of the regulators, and it made it all the way up to the White House level …
Norcross: I’m afraid we have to stop you, Adam. I’m sure there is a lot to be said about this. But thank you so much for your time. Adam Schultz is a professor of geophysics out of Oregon State University.
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