Under Our Feet-Faults, Quakes & Ancient Forces

🌎Minnesota doesn't do earthquakes. Right? Think again. 👀 Beneath the snow, the lakes, and the sleepy farm fields, the ground holds secrets—ancient ones. And every so often, it lets us know it's there.

Dr. Aaron Hirsch of the Minnesota Geological Survey reads the ground the way most of us read a book. He takes us down through the dirt, past the glaciers, and into rock billions of years old.

What's that boom💥 on the coldest January night? What would we find if we pulled the plug on Lake Superior? Could the Great Lakes ever slosh like a bathtub? 🛁

You'll hear about a rock that fooled a young boy, a seismologist who missed his own earthquake, and a river that did the impossible.

By the end, you may never look at a Minnesota rock—or the earth beneath your feet—the same way again.🌎👣

🪏Want To Dig Deeper? 

Minnesota Geological Survey

USGS Earthquake Hazards Program 

EarthScope Consortium :  For excellent free animations and educational material explaining earthquakes

Children's Books:

• Earthquake! by Marion Dane Bauer
• Earthquakes by Seymour Simon
• Earthquakes by Franklyn M. Branley

Today's episode is brought to you by the Joan of Arc Scroll Medal, a beautiful brass alloy medal, designed by award-winning artist, Pat Benincasa. This uniquely shaped medal is ideal for holiday or as a special occasion gift!    Visit www.patbenincasa-art.com

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Please Note: The views expressed by our guests do not necessarily reflect the views of the podcaster.

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Transcript

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Pat

Fill to Capacity where heart grit and irreverent humor collide. A podcast for people too stubborn to quit and too creative not to make a difference. 

Hi, I'm Pat Benincasa. This is Fill To Capacity. I'm glad you're here. Episode 147, "Under Our Feet- Faults, Quakes, and Ancient Forces." Most folks think of the Midwest as a place of snowstorms, thunderstorms. maybe hail and downpours, and the occasional tornado, but earthquakes in Minnesota? Turns out there's a lot going on underground. Ancient faults, buried structures, and forces that have been at work for billions of years. My guest today is Dr. Aaron Hirsch. He's with the Minnesota Geological Survey at the University of Minnesota. And he spends a lot of time looking at what's going on under Minnesota and around the Great Lakes So what causes an earthquake? Why do they even happen in places like Minnesota where we don't expect them?

And what the heck is going on beneath Lake Superior? And our guest is the person to ask. Welcome, Dr. Aaron Hirsch. So glad you're here.

Aaron

Thank you for having me. 

Pat

Before we get into earthquakes, what is the Minnesota Geological Survey and what is your role there?

Aaron

So the Minnesota Geological Survey is the research and stewardship arm of the Earth and Environmental Sciences Department. So we are a pseudo-state agency. We provide information and data to the public as it relates to water. minerals, land surfaces, and the geology beneath our feet.

I'm the geophysicist, so what that means is I use particular data sets as it relates to physical rock properties. So how dense a rock relates to a gravity signature. how fast seismic waves travel through a rock, I can use seismic waves to analyze those. I can use how much of a rock will be induced by a magnetic field to look at what's underneath our feet. We look at the electrical properties, how conductive a rock might be, how resistive it is, their electromagnetic signals.

And because Minnesota is covered mostly by glacial material, sands and gravels the bedrock is a little bit harder to see. And so we can use those properties to elucidate the subsurface where we don't have direct information from a borehole. 

Pat

Okay, so I've got to ask you, what's the first rock you remember picking up that you just had to know more about it?

Aaron

That's a good question. So I grew up in Minnesota. The first rock I remember was actually not a rock at all. It was slag. So there's iron smelting that was done up north from the iron mines. And I found this really cool rock I thought it was a rock, but all it was is kind of like the leftover bits from that iron smelting that made it look like almost like a ruby. But it was just kind of like silica glassy material. So after looking at books, kind of came to that conclusion. Besides that one, I would say uh my grandma used to snowbird down to Arizona and we'd visit her and we uh kept little pebbles of obsidian. That really kind of drew my attention. So I have still have like a big container of of all the those rocks. And I still have that  flag as well.

Pat

Well, that beautiful inky black obsidian. I understand.

Okay, now let's go underground. When the ground shakes, what's going on down there?

Aaron

If the ground is shaking like from an earthquake, you have three primary waves that are generated. You have a P and an S wave, so a primary and a secondary wave. That primary wave is kind of a compressional wave, so kind of like an accordion traveling through the earth. So kind of things get squished and relaxed and squished and relaxed like a sound wave through the air. The secondary wave, so the second wave that is also traveling. So the primary wave moves the fastest, so that's what we feel first.

The secondary wave is the second fastest we feel that second. That is a shear wave. So that will actually is shearing the ground. It's kind of instead of moving in a compression, it's moving past each other. The last one is what we really feel in an earthquake because it moves the slowest, and those are surface waves. And surface waves are complicated. Those are generated when some of those waves touch the surface and then they are kind of  transformed into a wave that kind of travels along the surface itself.

Pat

Is it like throwing a pebble in a pond and it ripples out?

Aaron

So that pebble- if you imagine instead of like if we're on the surface and we drop that pebble on the ground, that's the surface as it ripples across. That can be represent all the different kinds of waves because they're all radiating out in that kind of pattern. The P and the S waves, they move really fast, so you feel those first, but you feel them very little. Those surface waves are very slow. And those are really what you see a lot of the shaking in the the videos you see from different earthquakes um from different places like Thailand or in California.

Pat

So Aaron, I was digging through recent earthquake records and found a magnitude three point three event recorded this year, April 30th, about sixty miles north of Duluth. Was that actually an earthquake?

Aaron

Probably not. That might have actually probably been related to mining.

Pat

Really?

Aaron

So they are actively mining Up along the North Shore, there's the Masabi Range of Minnesota. So that's a lot of iron mining. They will set off thousands and thousands of pounds of explosives to break up the iron-rich rocks that they can then take big dozers and scoop those up and separate the iron-rich rocks and make tacanite. Which then gets transported for making into steel. I only say probably not based on the location you gave me. It's still possible. I've not looked into that earthquake itself. But yeah, those kind of size earthquakes. Generally we're not going to see even if it was a real earthquake anything really above a four that we've seen in the more recent past, last 50 years.

Pat

I want to go right into the cold weather because yes, this is Minnesota. Okay, you know where I'm going. On the coldest winter nights , people across Minnesota hear loud booms. Some call them frost quakes. Now are those real earthquakes?

Aaron

No. So an earthquake has to do with the ground, like a large chunk of ground moving. So there's kind of three general types of of forces that will create an earthquake along a fault. There's what's called a normal fault where one side is dropping down. from the other. Those are places like the basement range of Nevada. Those are normal faults. 

So those are like a extensional environment, things that are pulling apart. You'll get a reverse or thrust faults. And that's where things are kind of coming together, pushing against each other. One kind of gets pushed up over the other. And then you get strike slip or kind of California San Andreas example where things are moving past each other.

Pat

Aaron, let me stop you. Excuse me. What is a fault?

Aaron

A fault is an area of weakness between two different forces where you're seeing that movement. So if you have an area like for this, for example, the San Andreas Fault, that is a fault because on one side you have the North American plate and on the other side you have the Pacific Plate.

Pat

A plate is a massive, irregularly shaped slab of solid rock that makes up the Earth's outer shell.

Aaron

In simplistic terms, they're moving past each other very slowly, but they get locked up. And then over time that kind of stress builds up. Where it can then surpass the strength of those rocks being next to it, and then they quickly slide past each other, generating an earthquake.

When it gets really cold, we're seeing very, very near surface, surficial, you know, the ice is like spanning, kind of getting these cracks. So not a not a real earthquake itself. So it's really the ice cracking out loud. Or even trees. You can get like World War II, the trees were exploding. It was so cold, the sap the water inside the trees was so cold the trees would actually explode.

Pat

I want to shift gears. Before we head to the Great Lakes, a little context here. Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario. Form the largest freshwater lake system on Earth by surface area. Now, Aaron, if we could drain Lake Superior What would we see at the bottom?

Aaron

Initially, if you rate at the bottom, it'd probably be pretty mucky. There's gonna be a lot of kind of fine silts and and clay material right there at this at the bottom. There will be some bare rock, but you will, yeah, initially you're gonna have that very fine silt. Underneath that, you'll probably then have many tens of meters, if not hundreds of meters, of lake sediments.

So things that have accumulated over thousands and thousands of years below that, you actually will get into old, much, much older rocks, like kind of the origins of Lake Superior. You'll get into the basalt and the igneous rocks that kind of helped form Lake Superior itself. During the ice age this whole region sat under enormous glaciers.

Pat

When all that ice disappeared, what happened to the land underneath it? Like, is the ground Still adjusting today and the image I get is pressing my hand into a foam mattress for a long time and then taking it away, the mattress slowly comes back. So what happens to that land when the glaciers disappeared?

Aaron

No, that's a great question. That's a great analogy too. We use that exact same analogy when we describe it. So that is what we call isostatic adjustment or glacial isostatic adjustment, so GIA. And yeah, it's that exact same thing. So you have a kilometer thick pile of ice sitting directly on top of Minnesota, or most of Minnesota and it's been there for a thousand plus years. And then it suddenly retreats and it's gone.

The mattress is Minnesota. But don't think of it as like one, it's the same foam everywhere. It's not that same foam mattress. It's different kinds of foam because different rocks will compress differently. And so, and it's not going to respond like any film matrix because it's a very heavy rock. It's a very dense rock. It will relax and kind of come back up, but over geologic time. thousands of years. We're still experiencing that today.

And they can measure that. They measure those with very high precision GPS units Where they can measure, you know, this moved up a millimeter over the last year versus maybe somewhere else it went down a millimeter.

Pat

Well, that's fascinating. Okay, now this is in the realm of what could happen. Could a significant earthquake happen under one of the Great Lakes? And could it move enough water to create a tsunami or what I've heard geologists call sayche? Where the water sloshes back and forth across the lake? Could that happen with one of the Great Lakes?

Aaron

You can get one of those sayches- those have happened in the Great Lakes. That's more of a tidal response. So you have very calm water and then suddenly you get kind of like a tidal response where you just get like a a small little wave, like a ripple that we talked about before where you drop that rock in the pond and that just kind of like moves across and then it comes back-gentle. We're not talking your classic tsunami like thing happening. You can have those in smaller lakes as well. I had a person contact me. asking about, yeah, was there an earthquake in this area? Cause that happened to them on a lake. And after research I I kind of determined it was probably one of those sayches. And next time they're out in the lake, try and get that on video because it would be super interesting as it relates to a possible earthquake under the Great Lakes.

I'm gonna go with a probably not, I've not investigated earthquakes under the Great Lakes specific. In Lake Superior, for the most part, it's tectonically very calm and stable. We're in what's called the Craton. So we're in the oldest and coldest, most stable parts of the continent. Everything that underneath our feet, to go past the glaciers for the most part, is over a billion years old. Very tectonically stable. We do get earthquakes associated with that isostatic adjustment.

Pat

Isostatic adjustment is the land slowly rising or sinking when a huge amount of weight is added or taken away. Think foam mattress example.

Aaron

And the most recent one was a 4. 4, don't quote me on the magnitude, over by like western Minnesota, kind of the hump of Minnesota. And that was in 1994. That was felt pretty widely because of how old and stable our rocks are, those seismic waves can be felt further afield. They're very cold and stable, so the seismic waves travel very nicely through them. They're not attenuated, unlike in San Andreas fault.

Pat

The San Andreas Fault is a seven hundred- and fifty-mile-long crack in the earth beneath California, where two huge pieces of the earth's crust slowly grind past each other.

Aaron

Everything's more new, it's all jumbled up and broken to pieces, so those seismic waves get attenuated and and distributed, so you're not gonna feel it as as far.

Pat

You know, I couldn't help but think when you talked about the stability of what's underneath Minnesota, I thought to myself, oh, that's so Minnesota.

 Now you talked about 1994. I want to go back almost 20 years. In 1975, there was an earthquake near Morris, Minnesota. Tell me about that one, because what I was reading is that it was felt in neighboring states.

Aaron

Yeah. Well, it's relatively close to North and South Dakota, but because of how competent and old our rocks are. Those seismic waves can travel really far. I don't know if you remember there was an earthquake in Washington, D. C. in like early 2000s. That was felt very far away. Because if you go east of the Rockies, everything for the most part is very old and cold. But up there it's still very old and cold. So the side wings can travel really far away and still be felt. And so, yeah, in 1975, that was the same area as the 1994 earthquake and also felt very widespread.

They now use a scale. It's an intensity scale. It's like how did it feel? You fill out a form and it's kind of like did the plates fall? Did your door move? Did windows rattle? And kind of gives you an estimate of how intense the shaking was in your area and then how widespread that earthquake was felt. They didn't have that in 1975 They might have had it in 1994.

If there's an earthquake in Minnesota, it's going to be felt more widespread, but it should not be damaging We're not gonna get these large earthquakes.

Pat

Okay, so I'm sitting in my house. It's Sunday morning. I'm drinking my coffee, and all of a sudden the dishes start rattling. How big, let's say, in a metropolitan area could an earthquake possibly be here?

Aaron

The largest we've really seen is in the 4's. So what you have to think of when you think of earthquakes, it's not a linear scale either. So a three is about 32 times bigger than a two So we like to use uh it's the spaghetti analogy. So think of like thin spaghetti noodles. So a magnitude one is one piece of spaghetti noodle. Very easy to break and rupture and create a magnitude 2. Now you have 32 pieces of spaghetti that you have to break and rupture. And and now you have to have 64 and it's you're just ever increasing. And because most of these earthquakes that are happening in Minnesota are related to this isostatic adjustment. 

There's not a lot of stress that is building up. It's these kind of like little pops. We can probably see really small earthquakes, earthquakes that you can't even feel. We use seismometers to to look at those. But that 4   it's gonna be a quick little rattle and then they're like, what was that?

And then you start talking to your neighbors, and then they felt it. So it wasn't just you, it wasn't just the it wasn't just that dump truck that drove past or Something like that wasn't a plane overhead that kind of rattled things and then you see it on the news like, oh, and then suddenly everyone's talking about it and it's now been felt widespread. It's not gonna be damaging buildings falling over chaos in the streets kind of situation. Not like the movies. Not in Minnesota at least.

Pat

Have you ever experienced an earthquake yourself?

Aaron

So yes and no. I say this so when I was in graduate school in Boston, there was an earthquake in May. And my office is, this is down in like off of Commonwealth in the Back Bay area of Boston. If you know anything about Boston, the back bay was built up from a marshy area. They literally put pylons of wood and then built on top of that. So it's very soft ground.

In those areas where you have the softer surficial material, earthquake waves kind of get, they kind of accentuate. They kind of get bigger. They slow down so the waves get larger. I wasn't there. I was at home. And my house at the time was sitting directly on top of bedrock. Bedrock is very hard and competent. So side of the waves travel very quickly through there.

So all my colleagues were talking about all their doors were swinging shut and they felt rattling. And at home like I didn't feel anything. Apparently there were the earthquake went past us as a seisism. As a traditionally  trained  seismologist, so that was  very disappointing for me.

Pat

Yeah, how crushing.

Aaron

I know how crushing.

Pat

No pun intended. I think the question that people always want to ask, and they probably have asked you a thousand times, can earthquakes be predicted?

Aaron

That's a loaded question as a seismologist, because you know, anyone could then take my statement and then suddenly it's now all over the news. I'm gonna go with the careful answer and say we cannot predict an earthquake, but we can use probability and statistics to estimate where the next one would occur. And we have to use a lot of information to do that.

I kind of use the California example because it's an everyone kind of can relate or at least understands the San Andreas fault. Where there are earthquakes. Those earthquakes are releasing stress. If there's more earthquakes, more stress is being released.

If along the San Andreas Fault there's an area where there are not earthquakes happening. But we know there is stress building up. Probability states that that's an area more likely to have an earthquake So that's what they use. They use kind of like these probability maps of where an earthquake will happen over a certain amount of time. Think like a weather map. Oh, it's a 30% chance of rain. It's like that, but it's like over the next 50 years, what's the probability of like a 7. 0 occurring along the San Andreas Fault in any particular area?

So for example, Minnesota, we had an earthquake in like 1975. We had an earthquake in 1994. We didn't have one in 2004. Are we overdue? You know, it's that kind of scenario. Or like Yellowstone, oh we're overdue for a large eruption, are we?

Statistically, not so much So we could do something like that. No one has done that for Minnesota just because the number of earthquakes are very, very small and very few. But we do have infrastructure that we do need to be concerned about if there was a large earthquake in Minnesota. Nuclear power plants are one example.

Pat

Okay. Well that leads me to my next question. Does climate change and mining affect probability or possibility of earthquakes happening?

Aaron

That's a great question. I will also add in their oil and gas, not just mining, but oil and gas, because that is one thing that has led to an increase in seismicity. And what it's not necessarily the extraction of oil and gas, but it's where they've done fracking. So when they frack, they pump down all that water. They then bring that water back out. They leave a lot of the sand to keep the fractures open so they can pull out that gas or oil. Well that gas, that water that they use now is like mixed with all that fluid that's in there. And that fluid is oil-based, so there might be some pretty gross chemicals. So they need to get rid of it. They can't just throw it in the lake or river.

So what they have done in what they continue to do is they will find a someplace where there's a water source that is confined. A place where they could put it that is confined and is not potable water. It's too saline, maybe it's got a bunch of other gross things in it already. So they will put water down there. But now they're pumping a bunch of water into a system, and that has generated earthquakes in Oklahoma, has generated earthquakes in Ohio. 

And they've done that also with geothermal activity. Like, oh, we're going to put a geothermal well bore here. And so they're going to pump water down. Heat it up and then pull it out as steam. Well, they've now lubricated that rock down there and it happened to be an old fault and that then fault had ruptured. Mining not a whole lot can happen with that. You will experience mining related seismicity from just their blasting. So pretty small related things.

Climate change. I actually had to kind of do a little bit of research on that question. I's kind of a yes and a no. It's currently being looked at and it's more of a situation where it's climate change. We're warming up. Glaciers are retreating, it'd be the similar situation that we have in Minnesota where we have that isostatic adjustment. So glaciers are retreating now that load is off the foam. The foam is now rebounding, so you have that increase in earthquake potential there. 

You can also get earthquakes where that water's, that ice is not melting. So now you have an increased amount of water that could be seeping down into the rocks and lubricating some of those faults So it's an area of active research.

I've only found a couple articles about it. So it's going to be something that people will investigate further, but there is the possibility. In terms of large earthquakes, probably not. 

But look at the situation in Nepal. That wasn't necessarily an earthquake generated, but it was a landfall. situation where that glacier fell or the rock that was probably ice, it was probably held together more by permafrost than anything else because a really steep slope. And when that fell and then went down those valleys and killed what I think we're at the now almost 1,400 people have died from that. That created an earthquake from just it falling. So they originally did not know whether it was an earthquake or a landslide Uh now they know it was a landslide that they generated the earthquake, but that was more than likely climate change related.

Pat

On August 26th of this year, near the Nepal-Tibet border What was first reported as an earthquake turned out to be something very different. As Aaron pointed out, A massive amount of rock and glacial ice broke loose, plunging more than 3,300 feet down a Himalayan mountainside the collapse created a seismic signal roughly equivalent to a magnitude 5. 2 earthquake.

I want to shift gears and head south. In the winter of 1811 and 1812. A string of powerful earthquakes struck along the Mississippi River near where Missouri, Arkansas, Tennessee and Kentucky meat. And as I was reading it, it even said briefly that the Mississippi w started to flow backwards Yeah, I couldn't believe that, Aaron. I thought the mighty Mississippi flowing backwards. Okay, I digress. It's called the New Madrid Seismic Zone. And some of those quakes were felt hundreds of miles away.

And you've explained earlier, given the nature of what's under there, the type of rock and stone. Some transmit the waves faster than others. You've explained that beautifully. So could something like that happen again within the new Madrid seismic zone? And would we feel it this far north?

Aaron

An earthquake along the New Madrid seismic zone could definitely happen. That is an area where people are studying it quite a bit. It's an area of weakness within the crust of the US. So whether we feel it or not really will depend on a size, how large. And I just would have to go back and look to see did was it felt in Minnesota back in 1811? 

I don't remember if it was, but it would be possible. If it was felt here, it would be, oh, did that you know the plate rattled kind of syndrome? It would be very slight. It would be very minimal. We were so far away from it. People down there, they would feel it a lot. The river flowing backwards for an hour, yeah, that just always blows my mind. It really puts things in perspective of how powerful an earthquake can be. Yes. And the after-effects Unbelievable.

Pat

Okay, now I'm an artist and I do a lot of construction work. I built my own studio. I'm going to ask you a question. It may be the dorkiest question you've ever heard. I'm going to risk that. Okay You talk about these plates coming together, these fault lines. Now, in construction, you can put something between two boards if there's a gap, like caulk. You can put a foam. Could we have the technology where we could go in and inject some kind of fluid or movable foam or caulk?

Aaron

Between those fault lines? You could. Are you looking to lubricate or are you looking to try and stop it?

Pat

Well actually I'm thinking of a shock absorber idea.

Aaron

Okay. Oh, like in the in within the fault itself. Yeah. I'm sure you could try. I think Mother Nature is way stronger. than we really can fathom on those scales. The the amount of engineering that it would take. We're talking the order of scale.

The thing's not just rupturing like right at the surface, but it's like a long a thing like a plane. So it might rupture, a large earthquake could rupture 60 plus miles. 20 kilometers deep and ship that whole thing six feet. The amount of energy in that is, you know, they they measure that in the number of like nuclear bombs. It's that kind of scale. I don't know if you would be able to do it. 

And then I I would even go uh further and go, would what's the insurance policy on that? So if you if you start to do that going like, oh, we're gonna lubricate it and make it so it's it's like a shot goes over it and it made it worse.

Or it locked it up further so that even more stress built up on it. And an even larger earthquake. 

Pat

All right. All right. Then let's go from underneath to on top. And I know this is a little bit out of your wheelhouse, but I love studying and looking at different forms of architecture. And around the world, they are now designing architecture that's earthquake proof. And especially I think in Japan, where they use a lot of paper and cardboard reprocessed in their structures. They build shock absorbers underneath the house.

Aaron

Yeah, the shock absorbers are always really cool.

Pat

I mean, what is your thought about that? I know you spend time underneath, but what do you think about that whole approach?

Aaron

I think it's necessary if you're gonna live in an area where there's active earthquakes, California, Japan, many places around the world. you have to build to a level where they can withstand certain kinds of earthquakes. I wouldn't go so far as call them earthquake proof. I would go earthquake resistant.

Just because depending on the structure and maybe depending on how the earthquake waves come through, maybe the earthquake would be good against something that's coming right at you because the way you've built it it can withstand shaking maybe more north-south than east-west.

But the problem is a lot of people in different parts of the world their homes are older, maybe they don't have the funding or there's they don't have the mechanism to be able to do that. And so it becomes kind of this modal distribution of we have really big high rises that can withstand these you know giant earthquakes but then you go into you know, for lack of a better word, the slums of the area and they're living in tin buildings and those things will collapse with a you know strong breeze, let alone an earthquake. 

But yeah, I think those those buildings are are crazy now that they build with the shock absorbers or the the inner inertial dampers where you have something in the center that sways with it. Things are super interesting.

Pat

I think they call it shape memory. And in some of that architecture they're using this high grade, if you want to think, rubber bands. And so shape memory means it can move, as you're saying earthquake resistant -those structures can move. I think in Australia they use a type of concrete that is pre-formed that they're using

And I can't help but think about the city of Venice. When they had to build their buildings in water, they created a concrete that had linseed oil in it. So it could expand and contract with and around the water. So Those are the kinds of things I think about when we talk about earthquakes. Since we can't go under, okay, scale. We can't use giant caulk because of cost. Maybe we better focus on what's on top. Yeah, it's it's the cheaper and and more logical solution. Yeah, I think so.

After spending so much time studying what's under Minnesota, is there something going on beneath our feet? That you wish the rest of us understood or even knew was there?

Aaron

That's a really good question. We need in Minnesota?

Pat

Yeah, like where you with the area that you know.

Aaron

It would be great if people understood just how old I think the rocks are. So if you went underneath, you dug through the sediments. all the sands and the gravels to get to the depth like true bedrock. First, those sediments, those were deposited 12, 14,000 years ago. at the earliest.

There's some older, some like three, fourteen thousand, maybe a hundred thousand years ago. But depending on where you're on the state, your first bedrock might be Cretaceous. So last age of the dinosaurs 65-million-year-old rock.

You might find shark teeth in there because we're an inland sea. Other parts state the first bedrock might be Paleozoic rock, so 250 million years old. You're going to find fossils that, you know, of ancient organisms that no longer are around, trilobites, these really weird little snaily looking things. Nautiluses, uh things like that.

Or you could go to areas where first bedrock is a billion years old. You go up on the North Shore, 1 billion years old. A lot of the rocks up on the North Shore. You might go to other parts of Minnesota. That rock is over two billion years old. You go to southwestern Minnesota near Morton, the Morton Gnice kind of rock, that's over three billion years old.

So just people understanding the scale and understanding how old the rocks are, I think that would be great. Because it's such a hard concept. You say three billion, what does that mean? As a geologist, geophysicist, we go back to geology 101 and go, how do you explain deep time to people? And you do like the classic example is you go, you are to take your arms completely outstretched. On your one fingertip on your left hand, that is the start of Earth. That's 4. 6 billion years ago. Human existence is the very fingertip, the very end of your fingernail on your other hand. That's how long we've been around. Couple million years, all just on the very tip of that finger. You do the same thing with a calendar, January 1st, 12 a. m. That's the start on Earth. Humans pop out at 1159 p. m. December 31st So this whole span without humans, just kind of understanding just like how big that is.

I always find that very fascinating. I think it'd be for other people to be able to see or understand that, I think would be great. Puts things in perspective. 

Pat

I have to ask this. Most of us, Erin, think about time like today Parents, grandparents, great grandparents, and if you're lucky you can go far back. Our sense of time is just that within our own capability of understanding. But you live with a profound understanding of what you call deep time. I mean what you just described, how does that affect the way you are in the world?

Aaron

I still get stressed about very near-term things. I can't be late for things. That stresses me out. I still live in the very near term. So I was like sitting here at my at my computer ten, fifteen minutes ahead of time for this this meeting, just so I would not be late, because that would have stressed me out if I was like, I'm five minutes, oh, it's gonna start in a couple minutes, I'm not ready.

I start to get very imaginative because I go, what's gonna happen in a million years? What's going to happen in 10 million years? What is the things going to look like? Is Minnesota gonna look very similar? How things are gonna change? Yeah, I think you can appreciate and get an idea for what things look like in the past based what we see today.

So I see an active beach I can then go someplace in Minnesota and be like, that sandstone right there, that was at a beach 300 million years ago Because we have modern analogs. So we know what that looks like. I don't know if I necessarily appreciate it more. I would like to hope I do, but I just can kind of put things in a slight perspective.

Whether that helps with anything or not, I'm not sure.

Pat

The jury's still out.

Aaron

The jury's still out, yeah.

Pat

Well, Aaron, I want to thank you for coming on Filter Capacity. You've made earthquakes accessible to us in the way that you explained it. And I don't know if I can go out my door now and look at Minnesota the same way after talking to you.

Aaron

I hope not. I hope this was informative. If you see a rock, you can pick it up and go like, where did you come from and how did you form?

Pat

I gotta tell you, Aaron, my house and my studio are filled with jars of rocks. I have rocks everywhere.

Aaron

I love them.

Pat

I love them too. I can look at them and just like you say, where have you been? How old are you? Yep. Thank you for coming on today.

Aaron

You're welcome.

Pat

Listeners, thank you for joining us and take care of yourselves and each other. Bye.