AILSA CHANG, HOST:
For almost two decades, geologists have been setting up sensors all over the U.S., measuring the deep underground structure of the continent beneath us. Along the way, they discovered relics of a lost continent, mineral deposits and clues to the electrical conductivity of the Earth's crust. And this month, they finally revealed their new maps and models of the U.S. in the journal Reviews of Geophysics. Paul Bedrosian of the U.S. Geological Survey is part of that team and joins us now. Welcome to ALL THINGS CONSIDERED.
PAUL BEDROSIAN: Yeah. Thank you very much, Ailsa. A pleasure to be here.
CHANG: Pleasure to have you. OK, my very first question out of the box is - we already have a whole bunch of maps of the U.S. Why did we need a new one?
BEDROSIAN: The study which we undertook is really examining a different physical property, that being electrical conductivity or how well the rocks beneath our feet conduct electricity. And this physical property allows us to sort of see the world through a different lens.
CHANG: And just explain why is it important for us to know the electrical conductivity of what's beneath our feet?
BEDROSIAN: Yeah. Well, electrical conductivity allows us to determine the type of rocks that are down there. And once we can determine the type of rocks, we can kind of get a picture of how the continent was assembled over billions of years of geologic time.
CHANG: Wow.
BEDROSIAN: It also allows us to understand the hazards associated with space weather in particular to critical infrastructure. So when we think of space weather, we often think of things like the aurora, which gives us those beautiful displays in the night sky. But the same phenomena that gives rise to these aurora can also wreak havoc with critical infrastructure - things like the power grid, which we rely on. So one of the things which impacts the effect on things like the electric power grid is the conductivity - that is how well those rocks conduct electricity beneath our feet.
CHANG: So fascinating. And how far down beneath the surface are these structures that you were mapping?
BEDROSIAN: So the data that we collected, they're really able to image clear through the Earth's crust and lithosphere. So that's down to depths of about 200 kilometers or about 150 miles.
CHANG: Whoa. And I mentioned that one of the things you discovered were relics of a lost continent. What? Like, what did you discover exactly?
BEDROSIAN: Yeah. So, you know, one of the surprising things that came out of these models and data is that there's this large resistive block sitting beneath the Eastern U.S., basically from the crest of the Appalachians east across the coastal plain. And we think that this block is actually representing, you know, part of the supercontinent Pangaea that formed and was left behind when the Atlantic opened.
CHANG: Wow.
BEDROSIAN: And this resistor also has really important implications when we think of space weather hazards.
CHANG: Yeah, let's talk more about that. Like, can you give an example of a time when a solar storm affected technology on Earth?
BEDROSIAN: Yeah, so probably the most recent example that comes to mind is in 1989. There was a magnetic storm that was actually not a very large magnetic storm, but it actually brought down much of the power grid in Quebec for a number of hours. But there have been considerably larger storms in the past, and there will be in the future. And one of the ones that is often discussed is the so-called Carrington event. And this was a large magnetic storm in 1859. And, you know, back in those days, it was telegraph networks. We didn't really have an...
CHANG: Yeah.
BEDROSIAN: ...Electric power grid.
CHANG: Right.
BEDROSIAN: And, you know, reports from the days where there were fires at telegraph stations and operators getting shocked.
CHANG: Oh, my God.
BEDROSIAN: But, you know, if an event like that were to occur today, there are estimates that have been made that the impacts could be in the trillions of dollars.
CHANG: All right, so the stakes of what you're doing are quite, quite high. Can electrical utilities use this map to help prepare for future solar storms, then?
BEDROSIAN: Yeah, so these sorts of maps and these sorts of data can be used for power flow simulations and try to understand which areas are more or less vulnerable in the event of a magnetic storm.
CHANG: Research geophysicist Paul Bedrosian with the U.S. Geological Survey, thank you very much. This was fascinating.
BEDROSIAN: Thanks. Pleasure talking to you.
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