How Seismological Equipment Works

the Mississippi. Hey, nice Mississippi. Yeah, you know what. That's the site of several faults, actually one great, big fault. There are lots of faults everywhere, and it's not my fault. No, before we get into whose fault it is, let's talk about listener mail. By the way, this is not his fault. This listener mail comes from Joe, and Joe says earthquake. No,

just kidding. I live in Christchurch, New Zealand, and I've been through two major earthquakes and I was wondering if you could do a podcast on how they measure earthquakes. Cheers Joe, Joe, we're very glad that you are okay. Definitely, so definitely, So that was a scary situation if you don't know. Um uh, just a few weeks ago, as I when we're recording this, in very late February two eleven, there was a pretty significant earthquake, to say the very least,

that hit New Zealand. Um and uh, you know, several people lost their lives as a result of this. Um And of course these things are very damaging, both to people and property. So it's a it would be nice if we could do a lot of prediction and give you a heads up from when these things are coming, but I'm afraid at this point about the best we can do is let you know how big they were and maybe get an idea of what you might expect

from an aftershock. Yeah. As it turns out, predicting an earthquake is not exact science, but we have learned quite a bit about earthquakes. And before we get too far into this, I should just point out that a couple of our sister podcasts have covered similar topics. Stuff you Should Know has done an entire episode on how earthquakes work.

It's actually one of their older episodes, but it's it's excellent, so you can listen to that if you are interested in the topic and the stuff of Genius did an episode about an early pioneer in seismology, which and we'll talk about him in a little bit, just because it's it's too cool not to talk about, right, Oh yeah, yeah, definitely so so an earthquake. You know, we most of us probably know exactly what someone means when they say earthquake. It's it's an event in which the ground is shaking

right right, the earth thing. Yeah, yeah, Um, they can be caused from from many many different related types of movement in the Earth. Um, it's pretty well, uh, pretty well known at this point that the Earth's crust is made up of many plates, and there are different kinds of they're they're moving in different ways. Um. I'm going back to my undergraduate days when I actually took a geology class, which I found fascinating but didn't go into it obviously as a career field. But um, in some cases,

one plate is going underneath another plate. In other cases, they're rubbing against one another in a and you know along you know, one is going north while the other is going south. And and gradually what happens is tension builds up. I'm oversimplifying here, but tension builds up, and when the tension is released, that causes an earthquake. And they can be you know, small enough that you don't even notice it. Um. But some of the equipment we're

going to talk about today can detect that. Of course, others, um, like the earthquake in New Zealand and and famous earthquakes like in Haiti and uh in California, in Japan, um and and my favorite fault, the New Madrid fault in the middle of the United States. Again, that would be the one near Mississippi and all the others around it. Um.

You know, those can can be very very serious. So uh, you know, scientists have been trying to figure out for a long time, we'll say a very very very long time millennia in fact, yes, exactly how to measure the effect of the earth shaking. So let's talk about what actually happens and then we can talk about how we how we measure it. Now you gave a good overview. Yeah, there's, like I said, that's just a nutshell, very very very basic version, right, Yeah, three basic ways that plates move

against each other. Right, they either move apart, or they move together, or they slide against each other. Right, that's about it. The by the way, if you're talking about a plate going underneath another, that's called subducting. Um, just so you guys know. And when plates, when plates meet, uh, it pushes rock and dirt together. That's what actually forms mountains. Besides, there's also volcanic mountains, so there's some mountains that are

formed through volcanic activity. But in general, mountains are formed when two plates pressed up against each other and they crinkle essentially. Um. Now, when these these uh, these events happen, these these plate events. By the way, there are other things that can cause an earthquake, like an explosion can cause the essentially a localized earthquake, and meteoric impact can cause an earthquake, that kind of thing. But most of

them are caused by these these plate movements. Um. There's about eight thousand of them each day, and most of them are uh beneath our level of being able to perceive them. And of course lots of them are happening in places where there's really little to know human habitat there, so we wouldn't necessarily notice it even if it were a significant earthquake, because one is there, right, might be

under the ocean or anything like that. Um. And like you were saying, where the plates meet, that's a fault. That's you know, any place where two two plates are meeting, that's a fault. When when there is an earthquake, energy radiates out from the center of that earthquake in seismic waves. Yes, and these waves are what you would you know, when you think of a wave, that's what we're talking about. It's energy moving in a wavelength. There's there's a peak

and there's a trough through this wave. And uh, there's actually two waves that move out from an earthquake. Yes, he's talking about the PEA wave in which those those waves move in the direction that they're they're being propagated. Um and then the S wave, which is perpendicular to that, right, And the PEA wave moves faster than the S wave. It actually goes about between one to five miles per second. It tends to be one point seven times faster than the than the S wave. So this has become a

key for us to figure out where earthquakes are originating. Right, because you measure the time between the primary wave and the secondary wave, and that will tell you, in general how far away the focus is. It doesn't tell you the direction. It will just tell you. You know, you feel a shaking, and then you feel a second shaking. You take the time between that, you do a little calculation.

You figured, all right, so the center of this earthquake is fifty miles away, but it could literally be fifty miles in any direction on the surface. You can discount the directions that are directly below you and directly above you, and all that like anything in the air, not gonna matter. Um. So that's that's the basics of earthquakes. We'll talk a little bit about the measuring. Let's let's let's take a little walk back into history by a couple of millennia.

This is the guy that we were talking about and the stuff of genius who came up with an interesting seismoscope. Now, a seismoscope is a an instrument, any instrument that indicates that motion has occurred. But it does not give you more information than that, right right. It can't necessarily tell you where it was coming from. It can't necessarily tell you, um, it can't give you like a reading over a duration of time, it just tells you, hey, stuff moved around.

So basically, if you've seen Jurassic Park, when that dinosaur is coming up on you and you watch the motion in the glass of water, in the glass of water, that wop. Yes, it's a very primitive seismoscope, but as slightly and I stress slightly more sophisticated seismoscope was invented by a Chinese philosopher named Chong Hang Yes, and one thirty two. Yeah, one thirty two a d Yes, that's not that, that's not one thirty two in the afternoon. That's the year. Um No, Chang hangg came up with

this really cool design. And we we've actually seen examples of this and you know, uh, not just it's it's not just a theory that these things actually existed. Though they're they're actual, the way they worked is somewhat of a mystery. We've got a couple of ideas of how they could have worked, but but we'll get to that. So basically, what you had was a wine jar. Yes, it was. It was cylinder. You know, think of it as a sort of cylindrical shape standing on in so

like a jar. Yes, six ft in diameter, so we're not talking like a little jar, No, this would be a big jar. And mounted to the jar on the jar were eight dragon head spouts that faced in the cardinal directions. Yes, and that would be at the very top of the jar from what from what I understand, it can be anywhere from the above the middle to the top of anything on the top half of the jar.

Is that's because I've actually seen pictures of these. There are images of these on the Internet of various people have made recreations of these things. Um. So within that each dragon's mouth there's essentially a marble or stone, and so those are balanced within the mouths of the dragons. And then underneath the dragon mouths are these little ceramic

frogs with open mouths. And the idea here is that if there's an earthquake that is significant enough for it to set this seis muscope off, it'll rattle the pebbles, and the pebbles that are facing the direction that the earthquake is coming from, uh would theoretically fall out the dragon's mouth into the frog mouth. So then you could look in and say, all right, this is coming from somewhere the north northeast region. Um, it doesn't tell you

how far away it's gonna the earthquake was. But let's say that you're in ancient China and you are overseeing a large amount of land. Communication is not fast. But seeing something like that happened, you could say, well, now I know that there's some problems to the north of us. I should expect some people to come and ask me for help, or maybe I should send Uh perhaps it

came from the direction that an enemy is in. Perhaps you would want to send a group of troops out there to see, like, hey, were they weakened enough for us to kind of come in and mop up? Right? So this isn't this isn't just a diversion, uh, you know, just something that you do for fun. They really had a practical use. Now, now, the point where I said it might be a bit of a mystery is that we're not sure what was inside the jar. There are some who think that the jar had perhaps a pendulum

suspended from the top of the jar. That so it's it's actually you know, the base of the weight of the pendulum would be inside the jar. That's funny that you have mentioned that, because I have the feeling that will come up again. Yes, and this is because you

need an inertial mass in most of these seismoscopes. You need something that is not going to move in relation to the rest of the instrument because one of the big challenges of measuring earthquakes, I mean it sounds silly, but it's true, is that you have to design a tool that can measure something even when the uh the tool itself is moving right like, you know, if the earth is quaking and the tool is on the earth,

then how do you get a reliable measurement. Well, this idea of an inertial mass becomes very important with later size seismometers. So um, yeah, there was one possibility. Another possibility was a reverse pendulum. And a reverse pendulum is essentially a flexible pole with a weight at the end

of it. The weight is on the top right, And the idea here is that a significant UH quake would cause the pendulum to swing, perhaps hitting the inside of the jar, and that's what would then cause the stone in that dragon's mouth to fall into the the frog's mouth, and then it's six more weeks of winter. Uh, okay, stuff, I'm a little bit I'm on cold medication. So yeah, And in doing some research I read in in Britannica that in Italy in the seventeenth century, um a seismoscope.

They're used spilling water to show you know what was going on, whether there was an earthquake taking place. And another they also used a lot of mercury. I know that's probably not a surprise, but yeah, a cup of mercury, which would be would probably be a pretty good indicator given its color. Um. Yeah, too bad, you'd be crazy by the time the earthquake hit. Now see you're getting into the tiny details that are just just ruined them

the magic for me. Um and uh. And then there was a Luigi Palmieri who had a seized seismometer to detect, you know, the motion during an earthquake. He had a series of use you shaped tubes that again used mercury. Um. And then there was a clock hooked up to that and um, what would happen is the motion would cause an electrical clock to stop and to start a recording drum. Um. Basically, there was a float on top of the mercury and the drum was keeping track of the floats motion as

it moved. It would tell you the time and intensity of the earthquake. That makes it more that. That's why we would refer to that as a seismoment or even a seismograph, because seismograph essentially that that graph means to draw, but it's it's essentially meaning that you are recording the event of the earthquake and there's some element of time there or you can actually see the earthquakes movements over time and be able to say this is when it started,

this is when it ended, and um. And that's what sets it apart from the seismoscopes, which essentially just tell you, hey, something's moving out there, yes, which you know a lot of us can do on a good day. I can do it. The rabbits, they're agitated. So let's let's talk a little bit about what it takes to get uh. One of some of the challenges in creating a seismic graph, Well, there's one very big challenge, which is to overcome friction.

That's a big one because see, and in a seismograph, in a lot of cases, especially the earlier seismographs, you would want to use a marketing device, a pen and a piece of paper essentially, um and uh. The problem is that the in order to be sensitive, the pen is marking on the paper right right to record the

Earth's motion UM. But the problem is that it has to overcome the friction of the pen on the paper right and if it's a very very subtle quake, then the friction may be too great for the pen to move UM. And that that is a very big challenge. It it doesn't seem like it would be that big, but if you think about it, uh, you know, if you had a UM I would imagine too for older

pens before ballpoint type technology it's created. If you had something like some of these UM seismographs where it was constantly moving UM, when the paper was constantly moving under the pen, I'm not sure how you would distribute inc to it unless it worked sort of like a fountainin And I didn't actually research that. I wish I had

because now I'm kind of intrigued the podcast. But yeah, I mean that the seismograph is not a twentieth century innovation, and you know the ballpoint pen, well it wasn't either, but the seismograph goes back farther. So another big challenge is that you have to you have to segregate the seismograph from other structures. Yes, So for example, here in our building, it wouldn't do us much good to have a seismograph here because the vibrations that we would create

in the building, the vibrations from traffic passing outside. The seismograph would pick all that up and we get a lot of false readings, false positives. Yeah, if you've ever been on the top floor of a parking deck when people are leaving at rush hour, I mean you'll feel the motion of the cars moving and sometimes they'll you know, you can bounce around a little bit, depending on the

parking deck. So the key to having a very good seismograph is finding a way so that you can you can connect it to the bedrock of whatever region you're in. I will I will try to do flint stones. I hated that cartoon really, Yeah, despised it with the heat of a thousand exploding suns. Well, we won't get into that um. But yes, you have to connect it to the bedrock and then once sits connect to the bed

bedrock and and completely separate from other buildings. So it's not getting essentially uh pollution really because vibration vibration, then you can be more more sure that the readings you get reflect what's actually going on with the Earth as opposed to localized events. And it's interesting, this idea of the inertial mass ends up being really really important. Yes, and there's it's it's funny because um pendulums have been used for a very very very long time in UH

seismological circles. UM. Because if you have a pendulum hanging and and it's free of vibration pollution, then um, it's just going to hang there until something acts on it because of the laws of inertia. Basically, an object at rest tends to stay at rest. Um. But there's something else too. You also have to have a damper because of the laws of inertia, because an object in motion

tends to stay in motion. So you have to have both if you're going to have an accurate UH seismometer, because you if once the pendulum starts to move with the earth as it starts to shake, it will continue to do that. And from from what i've from what I understand, you need some kind of dampening material in order for it to get an accurate representation of how much the Earth is moving, which is kind of funny.

I wouldn't necessarily have thought about that, but yes, the pendulum is just gonna keep swinging and you'll you really won't have an idea and it's okay, well, this is it. Was it a serious earthquake or was it a very very mild earthquake? And you can tell both from the pendulum moving and the inertial damper that's that stops it from moving as much. Right, Uh. One one way to imagine there are a couple of different variations on the

seize mobter basic design. But one way to imagine it is imagine you've got a stand and from the stand hangs a very very sense of spring, a very tight spring, and there's a weight on the end of that spring, so it's above the ground. It's just it's hanging there. It's not moving up and down. It's it's at rest. It's just the weight is hanging from the spring, not moving at all. There is a pen attached to the weight, and the pens the top of the pen is or the the ink is rested the nib thank you like

words gone, Jonathan. The ap upset. The nib of the pen is resting against a piece of paper that's on a spool that's constantly turning giving fresh paper to the pen. So when there's an earthquake, if there's up and down motion, this is, you know, a vertical seismometer. There are different kinds, so the weight tends to stay still. Uh. You're you have to step outside the context of the Earth, which is kind of weird to say, but you have to

do it. Like the Earth, the the mass is maintaining its space, uh, and then the the everything else is moving up and down in relation to the weight. And that's the basis for most seismometers. There's also a kind where it's similar except the the it's it's a horizontal seismometer, in which there's a imagine a stand. Okay, but now you've got a long pole that sticks out halfway through the stand, right, So it's a horizontal pole that's connected.

It's got a it's got a hinge on it so it can move left and right in relation to the stand. And then there's also a spring attached from the top of the stand to the the far end of the pole. Right. All right, You've got you've got your weight there at the far end of the pole. And again you've got your pen attached to it. The pen's nib is against the paper. Now, when there's an earthquake that does side to side motion, the lever can swing to the left

and to the right. The the spring acts as the dampener it amount because it's it's a high tension spring. So the weight will move back and forth again again. Really, the the paper is moving back and forth against the weight. Uh. And that's how you get your readings for horizontal waves. UM. Now, a good seismometer actually has will have a three axes

UH detector on it. Yes, Now, what do you were just I'm sorry, go ahead, and I was gonna say what you were describing before was the strained seismograph if I'm not mistaken. Yes, Um, from from some of the research that I had done, I understand that it really you really need to measure basically, just for the simplification of this and and the fact that we're trying to describe it in an UH in an audio track, left to right, up and down, so I'm not up and

down but left and right, north to south. Uh. So you have two different directions, and X axis and y axis you're measuring those two and then you do have a vertical access to UM. And you're you have pendulums for each of those three and so really we should say instead of left right, we should say north south east west. Sorry, yes, that's much better, UM and UM

And yes, so I totally lost my train of thought. Sorry, but yes, you have to have the three axes to be able to detect, uh, what kind of earthquake is hitting you, like, what kind of waves are moving through the ground. Yes, And they have found another way to solve the pen on paper UH problem because some optical seismographs use mirrors to reflect light onto photosensitive paper has mounted on the drum. Now there the drum in in UH.

Seismographs that use a drum of paper basically have a if you think about it as a recording point that is gradually moving around the drum. So it starts it. It's sort of like a recording drum that you might see UM in those early audio recorders or a version of the long playing vinyl record. It starts at one point and gradually goes in a spiral around as the drum goes So it's recording the movement of the as

time goes on, and the the fact that it is moving. UM. And distance to shows you roughly when those uh, those seismological waves are taking place. UM, And I think that's really that the optical seismograph is an elegant solution to the problem. Of course, es since you're using photosensitive paper, that means you also have to be recording this in the dark. Yeah, there are there are quite a few seismic uh seismoscopes and seismommits that no longer use pen

or paper at all. They're just using various sensors, so that I mean, there's some where they have the paper counterpart as well to show off to the public whenever the public wants to watch it, because it's a lot more interesting to see the pen against paper, especially since

that's such an iconic image for size seismographs. I remember seeing the little needle like pens, you know then and watching the paper tape scroll through any united is scratching seismology and light detectors many so it is a very it is there is something very satisfying about seeing that. But the truth is is that a lot of the modern ones just use sensors. Now, let's talk about um identifying where the focus of an earthquake is, because here's

another thing. You can have the most advanced seismicograph or seismometer in the world, and it's not necessarily going to tell you where the focus is. What it's gonna tell you is how far away the earthquake is, right, and we're how far away the focus of the earthquake is right. And I think that's um that's sort of a frustrating point for geologists because as much as they know, they

still have difficulty um being pinpoint accurate too. And they're they're very good at what they do, but they're very good at measuring, yes, But there I think the material inside the earth is difficult for them. Makes it makes life because when you talk about the epicent of the earthquake, you're not saying, well, you know it's down at the corner of Fifth and Maine. You also have to figure

out how deep within the earth it is. And that also it's you know, once it gets down to a certain point, it's very very it's sort of is a fustcutory. You can't really tell as accurately as you would like to. Um. Yeah, and then that just that just makes these tools the more accurate they become. There's still an element of difficulty, and and and to make matters even more difficult. Um, the primary waves and secondary waves have different different traits.

Primary waves can move through anything. They move through solids, liquids, and gas. Secondary waves, however, can only move through solids. So once they hit the liquid center, the delicious liquid center of the Earth, that they don't go any further than that. Um. But you know, there are there seismographs out there that are sensitive enough to, at least in theory, detect an earthquake even if it's happening on the other side of the world. So how do earthquake scientists figure

out where the epicenter of an earthquake is. They have to consult multiple seismic graphs, and they they do it with three of them. And this is going to be familiar to anyone who has done any kind of navigation. UM. The reason here is that, like I said before, that you measure the difference between the primary wave that the time it takes a primary wave and a secondary wave to hit you, and that's how you can figure out how far away the thing is. Right. Well, that creates

a sphere, a virtual sphere around the seismic graph. Okay, let's say that we know that the epicenter of the earthquake is twenty five miles away from our seismic graph, So that's twenty five miles in every direction. We we don't know the origin of this. Now, of course, you can go ahead and say, all right, it's not gonna be the sky, but at any rate, can imagine that. So you then call up your buddy who's a couple of cities away, and say, hey, we just had an earthquake.

Do you guys have an earthquake registered on there too? And he says, yeah, yeah, it's seventy five miles away. Well, now you take the intersection of your sphere and their sphere at every point where it's you know where where those two spheres connect, and say, okay, the epicenter is somewhere in here. Then you call up a third well, a third person. It's your second buddy. You call up your second buddy, he's in another city. He said, hey,

we have an earthquake. Do you guys notice anything? So, yeah, it was thirty miles away. And you take those three uh, those those three measurements, and that's going to give you a point on the map. It'll actually give you two you'll get two connections that it could possibly be, but one of them is going to be in the sky, and that means you can count that one out. The one that's in the earth. That's the epicenter of the

earthquake's triliteration. Okay, I'll try it. No, no, no no, that's t r I. But yeah, it's you know, it's this idea of it's something that we've used, like I said, in navigation, where you it's like triangulating. It's the same sort of principles that you need three points and from those three points, once you've made the measurements, you can figure out where that epicenter is. Yeah, and that's that's important.

That's why so many scientists, especially around the uh what is known as the Ring of Fire, an area of intense geologic activity. They're scientists all over the world who have access to this kind of equipment and that's so very important to determining um. There are a lot of things that that go into this in addition to just

the earthquake and finding out where the epicenter is. Because if you have earthquakes, say off the coast in the middle of the ocean, they might produce tsunami and uh, knowing roughly where the epicenter is can give you an idea of where you might expect to see a tsunami and and roughly how long you might have until you would expect it on shore. UM. So that's very very important, UM, and is really really useful in enable you know, in

enabling people to do that. UM. And you can use you can use a seismological equipment to do all kinds of other things too. They use it in patroleum exploration, monitoring volcanic activity. Of course, these these two are actually very very closely related. UM. That's because sound will move at a different speed depending upon the medium it's moving through.

And by knowing the speeds that sound moves in and the various medium or media that it can that you could possibly encounter, you can start to narrow down like, oh, this is a likely place for oil versus this it is unlikely that we would find oil it were we to drill here. And we talked about a little bit about that in our Auto Tune podcast. Yeah yeah, and the oil drilling episode two. UM. So yeah, these are these are certainly very important devices and UM, you know,

can you think of anything else that we need to. Yeah, let's let's talk really quickly about the Richter scale. Oh, the Richter scale, we haven't even touched on that. So Richter scale is you may have heard about the Richter scale, about that being a way of measuring the magnitude of an earthquake. The Richter scale is a scale in which each whole number is uh ten times more powerful. I guess you could say or has a magnitude of ten

times the previous whole number. So a magnitude to earthquake has ten times the magnitude of a one earthquake excellent, and three would have ten times that the two and um, So these numbers get big really quickly. Anything below of four is pretty much a minor earthquake, and in fact three or lower you're not likely to feel. Anything that's a seven or higher is a major earth wake. That's that's going to cause lots of damage should it hit

any populated area. Um and some serious side effects can happen to We're talking about things like a fissure opening up and magma pouring out, or the tsunami, as Chris was mentioned, that could also be a byproduct. Those are those are the really bad ones. Anything that's in the six to seven range is still bad bad, it's just not considered a major earthquake. Now, that's not the only scale we used to measure earthquakes, or at least not

the effects of earthquakes. Do you know of the Marcali scale? No, I don't, Okay, So the Richter scale is more it's scientific, right, you are actually taking measurements of the earthquake and you're saying, based upon this magnitude, this is how powerful this earthquake was. So it's a scientific measurement. The Marcali scale is more of a subjective measurement. Marcali scale is the scale of

damage done by an earthquake. Now, for earthquakes where where you can feel the earth shaking, but but it's not strong enough to actually damage anything. That would be a category two on the Mercaulli scale. So one would be an earthquake you couldn't even feel. Now it goes up to all the way up to twelve. That's a quake that's so powerful that's doing major structural damage in the area. So let's look, I'm gonna finish up here with one other thing that we we talked that I wanted to

talk about. There was a discussion recently online about the possibility that solar flares could somehow induce earthquakes and predict earthquakes. Yes, we we had a solar flare not too long ago, and then there was the earthquake in christ Church, and so some have said that that that the solar flare in in effect predicted the earthquake. I'm not so quick to jump on this. I've done some research, alcoholic preliminary.

I've done some preliminary research into this, and I can't find any um accepted scientific study that really points to a connection. There's some that seemed to say there's some sort of uh connection there, but nothing that's actually, you know, really like, nothing that that really grabs me and says this is this is proof. Most of it seems circumstantial. A lot of it has confirmation bias written all over it,

which is a logical fallacy. And I was trying to search around to find because I saw things saying that that that the solar flare did in effect predict the earthquake in christ Church. One of them, one of the sources I found made at error that I just wanted to point out. And I'm not saying that this is necessarily the the crux of the entire argument, or that this is the source. But it was a blog that that quoted a NASA UM scientist, and you think, okay,

NASA people, they know a lot about solar flares. Well, the quote was the total energy in a space quake, which, by the way, that's what happens when the energy from a solar flare and encounters the Earth's magnetosphere. The total energy in a spacequake can rival that of a magnitude five or six earthquake. Now, the blogger chose to interpret this as saying that space quakes cause magnitude five or

six earthquakes. That's not the case. What the scientist said was that the amount of energy is equivalent to an earthquake,

not that one causes the other. Right, And I made a I just made up an analogy that said, if we said that a redwood, fully mature redwood falling in the forest and hitting the ground had the same amount of of energy to it, the same amount of force to it that a locomotive moving at seventy five miles per hour has, we would not say that a tree falling in the forest causes the locomotive to go seventy

five miles per hour. There's no connection between the two other than the fact that the magnitude of the energy is the same. Aim. So now I'm not saying that there is no connection. I'm saying I can't find any scientific study that gives me a very definitive answer, or even a semi definitive answer. So but from the geologists that I referenced, most of them seem skeptical, saying that really earthquakes mostly that mostly are caused by these plate movements,

which are not affected by magnetic phenomena. Okay, I just wanted to head that off a well, let's clarified nicely. Yeah, well, I didn't write a blog post this time. At least I've been doing that. Jonathan responds to people who have no interest in what he has to say. I guess that's what blogging is all about, really, when I get down to it. Okay, so let's wrap this up, guys. Uh,

that's our our discussion on seismology and seismological equipment. If you have any questions or you want to share some stories, if you've been in an earthquake and you got some some tales to hell. You can let us know on Facebook and Twitter are handled. There is tech Stuff hs W, or you can shoot us an email. That address is tech stuff at how stuff works dot com and Chris and I will taught to you again really soon. For more on this and thousands of other topics, visit how

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