Speaker 1: Brought to you by the reinvented two thousand twelve Camray.
Speaker 1: It's ready. Are you get in touch with technology? With
Speaker 1: tech Stuff from how stuff works dot com. Hello again, everyone,
Speaker 1: and welcome to tech stuff. My name is Chris Poulette
Speaker 1: and I am an editor at how stuff works dot com.
Speaker 1: Sitting across from me, as always, is senior writer Jonathan Strickland.
Speaker 1: The governor and I aren't even in the same party.
Speaker 1: If this turns out to be a false alarm, he'll
Speaker 1: make me out to be the biggest fool west of
Speaker 1: the Mississippi. Hey, nice Mississippi. Yeah, you know what. That's
Speaker 1: the site of several faults, actually one great, big fault.
Speaker 1: There are lots of faults everywhere, and it's not my fault. No,
Speaker 1: before we get into whose fault it is, let's talk
Speaker 1: about listener mail. By the way, this is not his fault.
Speaker 1: This listener mail comes from Joe, and Joe says earthquake. No,
Speaker 1: just kidding. I live in Christchurch, New Zealand, and I've
Speaker 1: been through two major earthquakes and I was wondering if
Speaker 1: you could do a podcast on how they measure earthquakes.
Speaker 1: Cheers Joe, Joe, we're very glad that you are okay. Definitely,
Speaker 1: so definitely, So that was a scary situation if you
Speaker 1: don't know. Um uh, just a few weeks ago, as
Speaker 1: I when we're recording this, in very late February two eleven,
Speaker 1: there was a pretty significant earthquake, to say the very least,
Speaker 1: that hit New Zealand. Um and uh, you know, several
Speaker 1: people lost their lives as a result of this. Um
Speaker 1: And of course these things are very damaging, both to
Speaker 1: people and property. So it's a it would be nice
Speaker 1: if we could do a lot of prediction and give
Speaker 1: you a heads up from when these things are coming,
Speaker 1: but I'm afraid at this point about the best we
Speaker 1: can do is let you know how big they were
Speaker 1: and maybe get an idea of what you might expect
Speaker 1: from an aftershock. Yeah. As it turns out, predicting an
Speaker 1: earthquake is not exact science, but we have learned quite
Speaker 1: a bit about earthquakes. And before we get too far
Speaker 1: into this, I should just point out that a couple
Speaker 1: of our sister podcasts have covered similar topics. Stuff you
Speaker 1: Should Know has done an entire episode on how earthquakes work.
Speaker 1: It's actually one of their older episodes, but it's it's excellent,
Speaker 1: so you can listen to that if you are interested
Speaker 1: in the topic and the stuff of Genius did an
Speaker 1: episode about an early pioneer in seismology, which and we'll
Speaker 1: talk about him in a little bit, just because it's
Speaker 1: it's too cool not to talk about, right, Oh yeah, yeah,
Speaker 1: definitely so so an earthquake. You know, we most of
Speaker 1: us probably know exactly what someone means when they say earthquake.
Speaker 1: It's it's an event in which the ground is shaking
Speaker 1: right right, the earth thing. Yeah, yeah, Um, they can
Speaker 1: be caused from from many many different related types of
Speaker 1: movement in the Earth. Um, it's pretty well, uh, pretty
Speaker 1: well known at this point that the Earth's crust is
Speaker 1: made up of many plates, and there are different kinds
Speaker 1: of they're they're moving in different ways. Um. I'm going
Speaker 1: back to my undergraduate days when I actually took a
Speaker 1: geology class, which I found fascinating but didn't go into
Speaker 1: it obviously as a career field. But um, in some cases,
Speaker 1: one plate is going underneath another plate. In other cases,
Speaker 1: they're rubbing against one another in a and you know
Speaker 1: along you know, one is going north while the other
Speaker 1: is going south. And and gradually what happens is tension
Speaker 1: builds up. I'm oversimplifying here, but tension builds up, and
Speaker 1: when the tension is released, that causes an earthquake. And
Speaker 1: they can be you know, small enough that you don't
Speaker 1: even notice it. Um. But some of the equipment we're
Speaker 1: going to talk about today can detect that. Of course, others, um,
Speaker 1: like the earthquake in New Zealand and and famous earthquakes
Speaker 1: like in Haiti and uh in California, in Japan, um
Speaker 1: and and my favorite fault, the New Madrid fault in
Speaker 1: the middle of the United States. Again, that would be
Speaker 1: the one near Mississippi and all the others around it. Um.
Speaker 1: You know, those can can be very very serious. So uh,
Speaker 1: you know, scientists have been trying to figure out for
Speaker 1: a long time, we'll say a very very very long
Speaker 1: time millennia in fact, yes, exactly how to measure the
Speaker 1: effect of the earth shaking. So let's talk about what
Speaker 1: actually happens and then we can talk about how we
Speaker 1: how we measure it. Now you gave a good overview. Yeah, there's,
Speaker 1: like I said, that's just a nutshell, very very very
Speaker 1: basic version, right, Yeah, three basic ways that plates move
Speaker 1: against each other. Right, they either move apart, or they
Speaker 1: move together, or they slide against each other. Right, that's
Speaker 1: about it. The by the way, if you're talking about
Speaker 1: a plate going underneath another, that's called subducting. Um, just
Speaker 1: so you guys know. And when plates, when plates meet, uh,
Speaker 1: it pushes rock and dirt together. That's what actually forms mountains. Besides,
Speaker 1: there's also volcanic mountains, so there's some mountains that are
Speaker 1: formed through volcanic activity. But in general, mountains are formed
Speaker 1: when two plates pressed up against each other and they
Speaker 1: crinkle essentially. Um. Now, when these these uh, these events happen,
Speaker 1: these these plate events. By the way, there are other
Speaker 1: things that can cause an earthquake, like an explosion can
Speaker 1: cause the essentially a localized earthquake, and meteoric impact can
Speaker 1: cause an earthquake, that kind of thing. But most of
Speaker 1: them are caused by these these plate movements. Um. There's
Speaker 1: about eight thousand of them each day, and most of
Speaker 1: them are uh beneath our level of being able to
Speaker 1: perceive them. And of course lots of them are happening
Speaker 1: in places where there's really little to know human habitat there,
Speaker 1: so we wouldn't necessarily notice it even if it were
Speaker 1: a significant earthquake, because one is there, right, might be
Speaker 1: under the ocean or anything like that. Um. And like
Speaker 1: you were saying, where the plates meet, that's a fault.
Speaker 1: That's you know, any place where two two plates are meeting,
Speaker 1: that's a fault. When when there is an earthquake, energy
Speaker 1: radiates out from the center of that earthquake in seismic waves. Yes,
Speaker 1: and these waves are what you would you know, when
Speaker 1: you think of a wave, that's what we're talking about.
Speaker 1: It's energy moving in a wavelength. There's there's a peak
Speaker 1: and there's a trough through this wave. And uh, there's
Speaker 1: actually two waves that move out from an earthquake. Yes,
Speaker 1: he's talking about the PEA wave in which those those
Speaker 1: waves move in the direction that they're they're being propagated.
Speaker 1: Um and then the S wave, which is perpendicular to that, right,
Speaker 1: And the PEA wave moves faster than the S wave.
Speaker 1: It actually goes about between one to five miles per second.
Speaker 1: It tends to be one point seven times faster than
Speaker 1: the than the S wave. So this has become a
Speaker 1: key for us to figure out where earthquakes are originating. Right,
Speaker 1: because you measure the time between the primary wave and
Speaker 1: the secondary wave, and that will tell you, in general
Speaker 1: how far away the focus is. It doesn't tell you
Speaker 1: the direction. It will just tell you. You know, you
Speaker 1: feel a shaking, and then you feel a second shaking.
Speaker 1: You take the time between that, you do a little calculation.
Speaker 1: You figured, all right, so the center of this earthquake
Speaker 1: is fifty miles away, but it could literally be fifty
Speaker 1: miles in any direction on the surface. You can discount
Speaker 1: the directions that are directly below you and directly above you,
Speaker 1: and all that like anything in the air, not gonna matter. Um.
Speaker 1: So that's that's the basics of earthquakes. We'll talk a
Speaker 1: little bit about the measuring. Let's let's let's take a
Speaker 1: little walk back into history by a couple of millennia.
Speaker 1: This is the guy that we were talking about and
Speaker 1: the stuff of genius who came up with an interesting seismoscope. Now,
Speaker 1: a seismoscope is a an instrument, any instrument that indicates
Speaker 1: that motion has occurred. But it does not give you
Speaker 1: more information than that, right right. It can't necessarily tell
Speaker 1: you where it was coming from. It can't necessarily tell you, um,
Speaker 1: it can't give you like a reading over a duration
Speaker 1: of time, it just tells you, hey, stuff moved around.
Speaker 1: So basically, if you've seen Jurassic Park, when that dinosaur
Speaker 1: is coming up on you and you watch the motion
Speaker 1: in the glass of water, in the glass of water,
Speaker 1: that wop. Yes, it's a very primitive seismoscope, but as
Speaker 1: slightly and I stress slightly more sophisticated seismoscope was invented
Speaker 1: by a Chinese philosopher named Chong Hang Yes, and one
Speaker 1: thirty two. Yeah, one thirty two a d Yes, that's
Speaker 1: not that, that's not one thirty two in the afternoon.
Speaker 1: That's the year. Um No, Chang hangg came up with
Speaker 1: this really cool design. And we we've actually seen examples
Speaker 1: of this and you know, uh, not just it's it's
Speaker 1: not just a theory that these things actually existed. Though
Speaker 1: they're they're actual, the way they worked is somewhat of
Speaker 1: a mystery. We've got a couple of ideas of how
Speaker 1: they could have worked, but but we'll get to that.
Speaker 1: So basically, what you had was a wine jar. Yes,
Speaker 1: it was. It was cylinder. You know, think of it
Speaker 1: as a sort of cylindrical shape standing on in so
Speaker 1: like a jar. Yes, six ft in diameter, so we're
Speaker 1: not talking like a little jar, No, this would be
Speaker 1: a big jar. And mounted to the jar on the
Speaker 1: jar were eight dragon head spouts that faced in the
Speaker 1: cardinal directions. Yes, and that would be at the very
Speaker 1: top of the jar from what from what I understand,
Speaker 1: it can be anywhere from the above the middle to
Speaker 1: the top of anything on the top half of the jar.
Speaker 1: Is that's because I've actually seen pictures of these. There
Speaker 1: are images of these on the Internet of various people
Speaker 1: have made recreations of these things. Um. So within that
Speaker 1: each dragon's mouth there's essentially a marble or stone, and
Speaker 1: so those are balanced within the mouths of the dragons.
Speaker 1: And then underneath the dragon mouths are these little ceramic
Speaker 1: frogs with open mouths. And the idea here is that
Speaker 1: if there's an earthquake that is significant enough for it
Speaker 1: to set this seis muscope off, it'll rattle the pebbles,
Speaker 1: and the pebbles that are facing the direction that the
Speaker 1: earthquake is coming from, uh would theoretically fall out the
Speaker 1: dragon's mouth into the frog mouth. So then you could
Speaker 1: look in and say, all right, this is coming from
Speaker 1: somewhere the north northeast region. Um, it doesn't tell you
Speaker 1: how far away it's gonna the earthquake was. But let's
Speaker 1: say that you're in ancient China and you are overseeing
Speaker 1: a large amount of land. Communication is not fast. But
Speaker 1: seeing something like that happened, you could say, well, now
Speaker 1: I know that there's some problems to the north of us.
Speaker 1: I should expect some people to come and ask me
Speaker 1: for help, or maybe I should send Uh perhaps it
Speaker 1: came from the direction that an enemy is in. Perhaps
Speaker 1: you would want to send a group of troops out
Speaker 1: there to see, like, hey, were they weakened enough for
Speaker 1: us to kind of come in and mop up? Right?
Speaker 1: So this isn't this isn't just a diversion, uh, you know,
Speaker 1: just something that you do for fun. They really had
Speaker 1: a practical use. Now, now, the point where I said
Speaker 1: it might be a bit of a mystery is that
Speaker 1: we're not sure what was inside the jar. There are
Speaker 1: some who think that the jar had perhaps a pendulum
Speaker 1: suspended from the top of the jar. That so it's
Speaker 1: it's actually you know, the base of the weight of
Speaker 1: the pendulum would be inside the jar. That's funny that
Speaker 1: you have mentioned that, because I have the feeling that
Speaker 1: will come up again. Yes, and this is because you
Speaker 1: need an inertial mass in most of these seismoscopes. You
Speaker 1: need something that is not going to move in relation
Speaker 1: to the rest of the instrument because one of the
Speaker 1: big challenges of measuring earthquakes, I mean it sounds silly,
Speaker 1: but it's true, is that you have to design a
Speaker 1: tool that can measure something even when the uh the
Speaker 1: tool itself is moving right like, you know, if the
Speaker 1: earth is quaking and the tool is on the earth,
Speaker 1: then how do you get a reliable measurement. Well, this
Speaker 1: idea of an inertial mass becomes very important with later
Speaker 1: size seismometers. So um, yeah, there was one possibility. Another
Speaker 1: possibility was a reverse pendulum. And a reverse pendulum is
Speaker 1: essentially a flexible pole with a weight at the end
Speaker 1: of it. The weight is on the top right, And
Speaker 1: the idea here is that a significant UH quake would
Speaker 1: cause the pendulum to swing, perhaps hitting the inside of
Speaker 1: the jar, and that's what would then cause the stone
Speaker 1: in that dragon's mouth to fall into the the frog's mouth,
Speaker 1: and then it's six more weeks of winter. Uh, okay, stuff,
Speaker 1: I'm a little bit I'm on cold medication. So yeah,
Speaker 1: And in doing some research I read in in Britannica
Speaker 1: that in Italy in the seventeenth century, um a seismoscope.
Speaker 1: They're used spilling water to show you know what was
Speaker 1: going on, whether there was an earthquake taking place. And
Speaker 1: another they also used a lot of mercury. I know
Speaker 1: that's probably not a surprise, but yeah, a cup of mercury,
Speaker 1: which would be would probably be a pretty good indicator
Speaker 1: given its color. Um. Yeah, too bad, you'd be crazy
Speaker 1: by the time the earthquake hit. Now see you're getting
Speaker 1: into the tiny details that are just just ruined them
Speaker 1: the magic for me. Um and uh. And then there
Speaker 1: was a Luigi Palmieri who had a seized seismometer to detect,
Speaker 1: you know, the motion during an earthquake. He had a
Speaker 1: series of use you shaped tubes that again used mercury. Um.
Speaker 1: And then there was a clock hooked up to that
Speaker 1: and um, what would happen is the motion would cause
Speaker 1: an electrical clock to stop and to start a recording drum. Um. Basically,
Speaker 1: there was a float on top of the mercury and
Speaker 1: the drum was keeping track of the floats motion as
Speaker 1: it moved. It would tell you the time and intensity
Speaker 1: of the earthquake. That makes it more that. That's why
Speaker 1: we would refer to that as a seismoment or even
Speaker 1: a seismograph, because seismograph essentially that that graph means to draw,
Speaker 1: but it's it's essentially meaning that you are recording the
Speaker 1: event of the earthquake and there's some element of time
Speaker 1: there or you can actually see the earthquakes movements over
Speaker 1: time and be able to say this is when it started,
Speaker 1: this is when it ended, and um. And that's what
Speaker 1: sets it apart from the seismoscopes, which essentially just tell you, hey,
Speaker 1: something's moving out there, yes, which you know a lot
Speaker 1: of us can do on a good day. I can
Speaker 1: do it. The rabbits, they're agitated. So let's let's talk
Speaker 1: a little bit about what it takes to get uh.
Speaker 1: One of some of the challenges in creating a seismic graph, Well,
Speaker 1: there's one very big challenge, which is to overcome friction.
Speaker 1: That's a big one because see, and in a seismograph,
Speaker 1: in a lot of cases, especially the earlier seismographs, you
Speaker 1: would want to use a marketing device, a pen and
Speaker 1: a piece of paper essentially, um and uh. The problem
Speaker 1: is that the in order to be sensitive, the pen
Speaker 1: is marking on the paper right right to record the
Speaker 1: Earth's motion UM. But the problem is that it has
Speaker 1: to overcome the friction of the pen on the paper
Speaker 1: right and if it's a very very subtle quake, then
Speaker 1: the friction may be too great for the pen to
Speaker 1: move UM. And that that is a very big challenge.
Speaker 1: It it doesn't seem like it would be that big,
Speaker 1: but if you think about it, uh, you know, if
Speaker 1: you had a UM I would imagine too for older
Speaker 1: pens before ballpoint type technology it's created. If you had
Speaker 1: something like some of these UM seismographs where it was
Speaker 1: constantly moving UM, when the paper was constantly moving under
Speaker 1: the pen, I'm not sure how you would distribute inc
Speaker 1: to it unless it worked sort of like a fountainin
Speaker 1: And I didn't actually research that. I wish I had
Speaker 1: because now I'm kind of intrigued the podcast. But yeah,
Speaker 1: I mean that the seismograph is not a twentieth century innovation,
Speaker 1: and you know the ballpoint pen, well it wasn't either,
Speaker 1: but the seismograph goes back farther. So another big challenge
Speaker 1: is that you have to you have to segregate the
Speaker 1: seismograph from other structures. Yes, So for example, here in
Speaker 1: our building, it wouldn't do us much good to have
Speaker 1: a seismograph here because the vibrations that we would create
Speaker 1: in the building, the vibrations from traffic passing outside. The
Speaker 1: seismograph would pick all that up and we get a
Speaker 1: lot of false readings, false positives. Yeah, if you've ever
Speaker 1: been on the top floor of a parking deck when
Speaker 1: people are leaving at rush hour, I mean you'll feel
Speaker 1: the motion of the cars moving and sometimes they'll you know,
Speaker 1: you can bounce around a little bit, depending on the
Speaker 1: parking deck. So the key to having a very good
Speaker 1: seismograph is finding a way so that you can you
Speaker 1: can connect it to the bedrock of whatever region you're in.
Speaker 1: I will I will try to do flint stones. I
Speaker 1: hated that cartoon really, Yeah, despised it with the heat
Speaker 1: of a thousand exploding suns. Well, we won't get into
Speaker 1: that um. But yes, you have to connect it to
Speaker 1: the bedrock and then once sits connect to the bed
Speaker 1: bedrock and and completely separate from other buildings. So it's
Speaker 1: not getting essentially uh pollution really because vibration vibration, then
Speaker 1: you can be more more sure that the readings you
Speaker 1: get reflect what's actually going on with the Earth as
Speaker 1: opposed to localized events. And it's interesting, this idea of
Speaker 1: the inertial mass ends up being really really important. Yes,
Speaker 1: and there's it's it's funny because um pendulums have been
Speaker 1: used for a very very very long time in UH
Speaker 1: seismological circles. UM. Because if you have a pendulum hanging
Speaker 1: and and it's free of vibration pollution, then um, it's
Speaker 1: just going to hang there until something acts on it
Speaker 1: because of the laws of inertia. Basically, an object at
Speaker 1: rest tends to stay at rest. Um. But there's something
Speaker 1: else too. You also have to have a damper because
Speaker 1: of the laws of inertia, because an object in motion
Speaker 1: tends to stay in motion. So you have to have
Speaker 1: both if you're going to have an accurate UH seismometer,
Speaker 1: because you if once the pendulum starts to move with
Speaker 1: the earth as it starts to shake, it will continue
Speaker 1: to do that. And from from what i've from what
Speaker 1: I understand, you need some kind of dampening material in
Speaker 1: order for it to get an accurate representation of how
Speaker 1: much the Earth is moving, which is kind of funny.
Speaker 1: I wouldn't necessarily have thought about that, but yes, the
Speaker 1: pendulum is just gonna keep swinging and you'll you really
Speaker 1: won't have an idea and it's okay, well, this is it.
Speaker 1: Was it a serious earthquake or was it a very
Speaker 1: very mild earthquake? And you can tell both from the
Speaker 1: pendulum moving and the inertial damper that's that stops it
Speaker 1: from moving as much. Right, Uh. One one way to
Speaker 1: imagine there are a couple of different variations on the
Speaker 1: seize mobter basic design. But one way to imagine it
Speaker 1: is imagine you've got a stand and from the stand
Speaker 1: hangs a very very sense of spring, a very tight spring,
Speaker 1: and there's a weight on the end of that spring,
Speaker 1: so it's above the ground. It's just it's hanging there.
Speaker 1: It's not moving up and down. It's it's at rest.
Speaker 1: It's just the weight is hanging from the spring, not
Speaker 1: moving at all. There is a pen attached to the weight,
Speaker 1: and the pens the top of the pen is or
Speaker 1: the the ink is rested the nib thank you like
Speaker 1: words gone, Jonathan. The ap upset. The nib of the
Speaker 1: pen is resting against a piece of paper that's on
Speaker 1: a spool that's constantly turning giving fresh paper to the pen.
Speaker 1: So when there's an earthquake, if there's up and down motion,
Speaker 1: this is, you know, a vertical seismometer. There are different kinds,
Speaker 1: so the weight tends to stay still. Uh. You're you
Speaker 1: have to step outside the context of the Earth, which
Speaker 1: is kind of weird to say, but you have to
Speaker 1: do it. Like the Earth, the the mass is maintaining
Speaker 1: its space, uh, and then the the everything else is
Speaker 1: moving up and down in relation to the weight. And
Speaker 1: that's the basis for most seismometers. There's also a kind
Speaker 1: where it's similar except the the it's it's a horizontal seismometer,
Speaker 1: in which there's a imagine a stand. Okay, but now
Speaker 1: you've got a long pole that sticks out halfway through
Speaker 1: the stand, right, So it's a horizontal pole that's connected.
Speaker 1: It's got a it's got a hinge on it so
Speaker 1: it can move left and right in relation to the stand.
Speaker 1: And then there's also a spring attached from the top
Speaker 1: of the stand to the the far end of the pole. Right.
Speaker 1: All right, You've got you've got your weight there at
Speaker 1: the far end of the pole. And again you've got
Speaker 1: your pen attached to it. The pen's nib is against
Speaker 1: the paper. Now, when there's an earthquake that does side
Speaker 1: to side motion, the lever can swing to the left
Speaker 1: and to the right. The the spring acts as the
Speaker 1: dampener it amount because it's it's a high tension spring.
Speaker 1: So the weight will move back and forth again again. Really,
Speaker 1: the the paper is moving back and forth against the weight. Uh.
Speaker 1: And that's how you get your readings for horizontal waves. UM. Now,
Speaker 1: a good seismometer actually has will have a three axes
Speaker 1: UH detector on it. Yes, Now, what do you were
Speaker 1: just I'm sorry, go ahead, and I was gonna say
Speaker 1: what you were describing before was the strained seismograph if
Speaker 1: I'm not mistaken. Yes, Um, from from some of the
Speaker 1: research that I had done, I understand that it really
Speaker 1: you really need to measure basically, just for the simplification
Speaker 1: of this and and the fact that we're trying to
Speaker 1: describe it in an UH in an audio track, left
Speaker 1: to right, up and down, so I'm not up and
Speaker 1: down but left and right, north to south. Uh. So
Speaker 1: you have two different directions, and X axis and y
Speaker 1: axis you're measuring those two and then you do have
Speaker 1: a vertical access to UM. And you're you have pendulums
Speaker 1: for each of those three and so really we should
Speaker 1: say instead of left right, we should say north south
Speaker 1: east west. Sorry, yes, that's much better, UM and UM
Speaker 1: And yes, so I totally lost my train of thought. Sorry,
Speaker 1: but yes, you have to have the three axes to
Speaker 1: be able to detect, uh, what kind of earthquake is
Speaker 1: hitting you, like, what kind of waves are moving through
Speaker 1: the ground. Yes, And they have found another way to
Speaker 1: solve the pen on paper UH problem because some optical
Speaker 1: seismographs use mirrors to reflect light onto photosensitive paper has
Speaker 1: mounted on the drum. Now there the drum in in UH.
Speaker 1: Seismographs that use a drum of paper basically have a
Speaker 1: if you think about it as a recording point that
Speaker 1: is gradually moving around the drum. So it starts it.
Speaker 1: It's sort of like a recording drum that you might
Speaker 1: see UM in those early audio recorders or a version
Speaker 1: of the long playing vinyl record. It starts at one
Speaker 1: point and gradually goes in a spiral around as the
Speaker 1: drum goes So it's recording the movement of the as
Speaker 1: time goes on, and the the fact that it is moving. UM.
Speaker 1: And distance to shows you roughly when those uh, those
Speaker 1: seismological waves are taking place. UM, And I think that's
Speaker 1: really that the optical seismograph is an elegant solution to
Speaker 1: the problem. Of course, es since you're using photosensitive paper,
Speaker 1: that means you also have to be recording this in
Speaker 1: the dark. Yeah, there are there are quite a few
Speaker 1: seismic uh seismoscopes and seismommits that no longer use pen
Speaker 1: or paper at all. They're just using various sensors, so
Speaker 1: that I mean, there's some where they have the paper
Speaker 1: counterpart as well to show off to the public whenever
Speaker 1: the public wants to watch it, because it's a lot
Speaker 1: more interesting to see the pen against paper, especially since
Speaker 1: that's such an iconic image for size seismographs. I remember
Speaker 1: seeing the little needle like pens, you know then and
Speaker 1: watching the paper tape scroll through any united is scratching
Speaker 1: seismology and light detectors many so it is a very
Speaker 1: it is there is something very satisfying about seeing that.
Speaker 1: But the truth is is that a lot of the
Speaker 1: modern ones just use sensors. Now, let's talk about um
Speaker 1: identifying where the focus of an earthquake is, because here's
Speaker 1: another thing. You can have the most advanced seismicograph or
Speaker 1: seismometer in the world, and it's not necessarily going to
Speaker 1: tell you where the focus is. What it's gonna tell
Speaker 1: you is how far away the earthquake is, right, and
Speaker 1: we're how far away the focus of the earthquake is right.
Speaker 1: And I think that's um that's sort of a frustrating
Speaker 1: point for geologists because as much as they know, they
Speaker 1: still have difficulty um being pinpoint accurate too. And they're
Speaker 1: they're very good at what they do, but they're very
Speaker 1: good at measuring, yes, But there I think the material
Speaker 1: inside the earth is difficult for them. Makes it makes
Speaker 1: life because when you talk about the epicent of the earthquake,
Speaker 1: you're not saying, well, you know it's down at the
Speaker 1: corner of Fifth and Maine. You also have to figure
Speaker 1: out how deep within the earth it is. And that
Speaker 1: also it's you know, once it gets down to a
Speaker 1: certain point, it's very very it's sort of is a fustcutory.
Speaker 1: You can't really tell as accurately as you would like to. Um. Yeah,
Speaker 1: and then that just that just makes these tools the
Speaker 1: more accurate they become. There's still an element of difficulty,
Speaker 1: and and and to make matters even more difficult. Um,
Speaker 1: the primary waves and secondary waves have different different traits.
Speaker 1: Primary waves can move through anything. They move through solids, liquids,
Speaker 1: and gas. Secondary waves, however, can only move through solids.
Speaker 1: So once they hit the liquid center, the delicious liquid
Speaker 1: center of the Earth, that they don't go any further
Speaker 1: than that. Um. But you know, there are there seismographs
Speaker 1: out there that are sensitive enough to, at least in theory,
Speaker 1: detect an earthquake even if it's happening on the other
Speaker 1: side of the world. So how do earthquake scientists figure
Speaker 1: out where the epicenter of an earthquake is. They have
Speaker 1: to consult multiple seismic graphs, and they they do it
Speaker 1: with three of them. And this is going to be
Speaker 1: familiar to anyone who has done any kind of navigation. UM.
Speaker 1: The reason here is that, like I said before, that
Speaker 1: you measure the difference between the primary wave that the
Speaker 1: time it takes a primary wave and a secondary wave
Speaker 1: to hit you, and that's how you can figure out
Speaker 1: how far away the thing is. Right. Well, that creates
Speaker 1: a sphere, a virtual sphere around the seismic graph. Okay,
Speaker 1: let's say that we know that the epicenter of the
Speaker 1: earthquake is twenty five miles away from our seismic graph,
Speaker 1: So that's twenty five miles in every direction. We we
Speaker 1: don't know the origin of this. Now, of course, you
Speaker 1: can go ahead and say, all right, it's not gonna
Speaker 1: be the sky, but at any rate, can imagine that.
Speaker 1: So you then call up your buddy who's a couple
Speaker 1: of cities away, and say, hey, we just had an earthquake.
Speaker 1: Do you guys have an earthquake registered on there too?
Speaker 1: And he says, yeah, yeah, it's seventy five miles away. Well,
Speaker 1: now you take the intersection of your sphere and their
Speaker 1: sphere at every point where it's you know where where
Speaker 1: those two spheres connect, and say, okay, the epicenter is
Speaker 1: somewhere in here. Then you call up a third well,
Speaker 1: a third person. It's your second buddy. You call up
Speaker 1: your second buddy, he's in another city. He said, hey,
Speaker 1: we have an earthquake. Do you guys notice anything? So, yeah,
Speaker 1: it was thirty miles away. And you take those three uh,
Speaker 1: those those three measurements, and that's going to give you
Speaker 1: a point on the map. It'll actually give you two
Speaker 1: you'll get two connections that it could possibly be, but
Speaker 1: one of them is going to be in the sky,
Speaker 1: and that means you can count that one out. The
Speaker 1: one that's in the earth. That's the epicenter of the
Speaker 1: earthquake's triliteration. Okay, I'll try it. No, no, no no, that's
Speaker 1: t r I. But yeah, it's you know, it's this
Speaker 1: idea of it's something that we've used, like I said,
Speaker 1: in navigation, where you it's like triangulating. It's the same
Speaker 1: sort of principles that you need three points and from
Speaker 1: those three points, once you've made the measurements, you can
Speaker 1: figure out where that epicenter is. Yeah, and that's that's important.
Speaker 1: That's why so many scientists, especially around the uh what
Speaker 1: is known as the Ring of Fire, an area of
Speaker 1: intense geologic activity. They're scientists all over the world who
Speaker 1: have access to this kind of equipment and that's so
Speaker 1: very important to determining um. There are a lot of
Speaker 1: things that that go into this in addition to just
Speaker 1: the earthquake and finding out where the epicenter is. Because
Speaker 1: if you have earthquakes, say off the coast in the
Speaker 1: middle of the ocean, they might produce tsunami and uh,
Speaker 1: knowing roughly where the epicenter is can give you an
Speaker 1: idea of where you might expect to see a tsunami
Speaker 1: and and roughly how long you might have until you
Speaker 1: would expect it on shore. UM. So that's very very important, UM,
Speaker 1: and is really really useful in enable you know, in
Speaker 1: enabling people to do that. UM. And you can use
Speaker 1: you can use a seismological equipment to do all kinds
Speaker 1: of other things too. They use it in patroleum exploration,
Speaker 1: monitoring volcanic activity. Of course, these these two are actually
Speaker 1: very very closely related. UM. That's because sound will move
Speaker 1: at a different speed depending upon the medium it's moving through.
Speaker 1: And by knowing the speeds that sound moves in and
Speaker 1: the various medium or media that it can that you
Speaker 1: could possibly encounter, you can start to narrow down like, oh,
Speaker 1: this is a likely place for oil versus this it
Speaker 1: is unlikely that we would find oil it were we
Speaker 1: to drill here. And we talked about a little bit
Speaker 1: about that in our Auto Tune podcast. Yeah yeah, and
Speaker 1: the oil drilling episode two. UM. So yeah, these are
Speaker 1: these are certainly very important devices and UM, you know,
Speaker 1: can you think of anything else that we need to. Yeah,
Speaker 1: let's let's talk really quickly about the Richter scale. Oh,
Speaker 1: the Richter scale, we haven't even touched on that. So
Speaker 1: Richter scale is you may have heard about the Richter scale,
Speaker 1: about that being a way of measuring the magnitude of
Speaker 1: an earthquake. The Richter scale is a scale in which
Speaker 1: each whole number is uh ten times more powerful. I
Speaker 1: guess you could say or has a magnitude of ten
Speaker 1: times the previous whole number. So a magnitude to earthquake
Speaker 1: has ten times the magnitude of a one earthquake excellent,
Speaker 1: and three would have ten times that the two and um,
Speaker 1: So these numbers get big really quickly. Anything below of
Speaker 1: four is pretty much a minor earthquake, and in fact
Speaker 1: three or lower you're not likely to feel. Anything that's
Speaker 1: a seven or higher is a major earth wake. That's
Speaker 1: that's going to cause lots of damage should it hit
Speaker 1: any populated area. Um and some serious side effects can
Speaker 1: happen to We're talking about things like a fissure opening
Speaker 1: up and magma pouring out, or the tsunami, as Chris
Speaker 1: was mentioned, that could also be a byproduct. Those are
Speaker 1: those are the really bad ones. Anything that's in the
Speaker 1: six to seven range is still bad bad, it's just
Speaker 1: not considered a major earthquake. Now, that's not the only
Speaker 1: scale we used to measure earthquakes, or at least not
Speaker 1: the effects of earthquakes. Do you know of the Marcali scale? No,
Speaker 1: I don't, Okay, So the Richter scale is more it's scientific, right,
Speaker 1: you are actually taking measurements of the earthquake and you're saying,
Speaker 1: based upon this magnitude, this is how powerful this earthquake was.
Speaker 1: So it's a scientific measurement. The Marcali scale is more
Speaker 1: of a subjective measurement. Marcali scale is the scale of
Speaker 1: damage done by an earthquake. Now, for earthquakes where where
Speaker 1: you can feel the earth shaking, but but it's not
Speaker 1: strong enough to actually damage anything. That would be a
Speaker 1: category two on the Mercaulli scale. So one would be
Speaker 1: an earthquake you couldn't even feel. Now it goes up
Speaker 1: to all the way up to twelve. That's a quake
Speaker 1: that's so powerful that's doing major structural damage in the area.
Speaker 1: So let's look, I'm gonna finish up here with one
Speaker 1: other thing that we we talked that I wanted to
Speaker 1: talk about. There was a discussion recently online about the
Speaker 1: possibility that solar flares could somehow induce earthquakes and predict earthquakes. Yes,
Speaker 1: we we had a solar flare not too long ago,
Speaker 1: and then there was the earthquake in christ Church, and
Speaker 1: so some have said that that that the solar flare
Speaker 1: in in effect predicted the earthquake. I'm not so quick
Speaker 1: to jump on this. I've done some research, alcoholic preliminary.
Speaker 1: I've done some preliminary research into this, and I can't
Speaker 1: find any um accepted scientific study that really points to
Speaker 1: a connection. There's some that seemed to say there's some
Speaker 1: sort of uh connection there, but nothing that's actually, you know,
Speaker 1: really like, nothing that that really grabs me and says
Speaker 1: this is this is proof. Most of it seems circumstantial.
Speaker 1: A lot of it has confirmation bias written all over it,
Speaker 1: which is a logical fallacy. And I was trying to
Speaker 1: search around to find because I saw things saying that
Speaker 1: that that the solar flare did in effect predict the
Speaker 1: earthquake in christ Church. One of them, one of the
Speaker 1: sources I found made at error that I just wanted
Speaker 1: to point out. And I'm not saying that this is
Speaker 1: necessarily the the crux of the entire argument, or that
Speaker 1: this is the source. But it was a blog that
Speaker 1: that quoted a NASA UM scientist, and you think, okay,
Speaker 1: NASA people, they know a lot about solar flares. Well,
Speaker 1: the quote was the total energy in a space quake, which,
Speaker 1: by the way, that's what happens when the energy from
Speaker 1: a solar flare and encounters the Earth's magnetosphere. The total
Speaker 1: energy in a spacequake can rival that of a magnitude
Speaker 1: five or six earthquake. Now, the blogger chose to interpret
Speaker 1: this as saying that space quakes cause magnitude five or
Speaker 1: six earthquakes. That's not the case. What the scientist said
Speaker 1: was that the amount of energy is equivalent to an earthquake,
Speaker 1: not that one causes the other. Right, And I made
Speaker 1: a I just made up an analogy that said, if
Speaker 1: we said that a redwood, fully mature redwood falling in
Speaker 1: the forest and hitting the ground had the same amount
Speaker 1: of of energy to it, the same amount of force
Speaker 1: to it that a locomotive moving at seventy five miles
Speaker 1: per hour has, we would not say that a tree
Speaker 1: falling in the forest causes the locomotive to go seventy
Speaker 1: five miles per hour. There's no connection between the two
Speaker 1: other than the fact that the magnitude of the energy
Speaker 1: is the same. Aim. So now I'm not saying that
Speaker 1: there is no connection. I'm saying I can't find any
Speaker 1: scientific study that gives me a very definitive answer, or
Speaker 1: even a semi definitive answer. So but from the geologists
Speaker 1: that I referenced, most of them seem skeptical, saying that
Speaker 1: really earthquakes mostly that mostly are caused by these plate movements,
Speaker 1: which are not affected by magnetic phenomena. Okay, I just
Speaker 1: wanted to head that off a well, let's clarified nicely. Yeah, well,
Speaker 1: I didn't write a blog post this time. At least
Speaker 1: I've been doing that. Jonathan responds to people who have
Speaker 1: no interest in what he has to say. I guess
Speaker 1: that's what blogging is all about, really, when I get
Speaker 1: down to it. Okay, so let's wrap this up, guys. Uh,
Speaker 1: that's our our discussion on seismology and seismological equipment. If
Speaker 1: you have any questions or you want to share some stories,
Speaker 1: if you've been in an earthquake and you got some
Speaker 1: some tales to hell. You can let us know on
Speaker 1: Facebook and Twitter are handled. There is tech Stuff hs W,
Speaker 1: or you can shoot us an email. That address is
Speaker 1: tech stuff at how stuff works dot com and Chris
Speaker 1: and I will taught to you again really soon. For
Speaker 1: more on this and thousands of other topics, visit how
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