Richter scale The basics of the logarithmic Richter and Moment Magnitude Scales to measure earthquakes
- I've been doing a bunch of videos about logarithmic scale
- and we've also -- unfortunately -- had many notable earthquakes this year
- so I thought I would do a video on the Richter Scale,
- which is a way to measure - which is a way to measure earthquake magnitudes.
- And just to be clear, although we associate the Richter Scale as the way we measure earthquakes now
- the one we actually use now is the Moment Magnitude Scale,
- and the reason why most people don't make a huge differentiation between the two is that
- the Moment Magnitude scale was calibrated to the Richter Scale
- for the whole reason why we moved to the Moment Magnitude Scale
- is that the Richter Scale starts to kind of max out at around magnitude 7 earthqukes.
- So this gives us a much better way to measure things that are above a magnitude 7.
- So this right here is a picture of Charles Richter, he's passed away,
- but this is from an interview that he gave, and it's interesting because it kinda
- gives the rationale for how he came up with the Richter Scale.
- "I found a paper by Professor K. Wadati of Japan in which he compared
- large earthquakes by plotting the maximum ground motion against the distance to the epicenter."
- So this Professor K. Wadati would -- you could imagine --
- he did a plot like this, where this is distance -- distance --
- So if you have an earthquake someplace, you aren't always sitting right on top of the epicenter
- where you measure it.
- You might be sitting over here. You're actually measure --
- your measuring stations might be some distance away.
- So he looks at how far the measuring station was and then he looks at
- the ground motion at the measuring station. So that would be some earthquake over there.
- A relatively -- let's say that's a relatively medium earthquake.
- This right over here would be a weak earthquake
- because you're close to the earthquake
- and it still didn't move the ground much. So I mean this is the magnitude,
- this axis is the magnitude.
- How much the ground is moving.
- And then for example, this would be a very strong earthquake.
- And then Charles Richter said in the interview:
- "I tried a similar procedure for our stations,
- but the range between the largest and smallest magnitudes seemed
- unmanageably large."
- So what he's saying is when he tried to plot it like Professor Wadati,
- he found that: Ok you can put -- you get some earthquakes that you can plot around here,
- but no matter how you create a linear scale, no matter how you do a linear scale over here,
- if you want any resolution down here,
- the stronger earthquakes go off the charts, or maybe off the page.
- So the stronger earthquakes you might have to start plotting here, or here,
- or maybe they don't even fit on the page.
- And so he says "Dr. Bino Gutenburg --" And they were all working at CalTech when
- they came up with the Richter Scale. "Dr. Bino Gutenburg then made the natural suggestion
- to plot the amplitudes logarithmically. I was -- I was lucky because logarithmic plots are a device of the devil."
- And I'm not really sure what he means when he says they were "a device of the devil,"
- I'm assuming he means that they're kind of magical, that all of a sudden you can take these things,
- that you want your resolution down here
- or you want to be able to tell the difference between these weak earthquakes,
- but at the same time you want to be able to compare them to the large earthquakes.
- And he thought -- I guess he viewed them as a bit of a magical instrument.
- And we say that they are logarithmic -- or he plotted them on a logarithmic scale --
- what essentially it is he's saying -- is essentially taking the logarithm of the
- magnitude of every one of those earthquakes.
- So if you're measuring the earthquake, maybe on the
- seismograph, so this is before the earthquake, then the earthquake hits,
- and then the earthquake stops and then you measure the amplitude of this earthquake.
- If you just plotted them linearly, you'd have the problem that he saw
- or if you tried to plot them the way that Professor Wadati did you'd have that problem,
- but what he did is that he measures this now and he plots the logarithm --
- the logarithm of that, and so what happens is that you get a scale that is plotted -- or that you
- get a logarithmic scale, for lack of a better word.
- But what I want to do in this video is think about what implication that has
- for the magnitude of earthquakes, especially some of the earthquakes that we have seen lately.
- So this right here is the earthquake that occured August 23rd on the East Coast of the United States
- and it wasn't that strong of an earthquake, it was a 5.8,
- that's not a small earthquake, you would definitely feel it, it's a good bit of shaking
- it could even cause some minor damage.
- But the reason why it's notable is because it happened in a part of the world
- that does not see earthquakes too frequently.
- So let's just take that on our scale. I'm going to go down way over here.
- So I'm going to do our scale over here.
- So let's just put that as a 5.8.
- I'm going to call this a 5.8.
- So if you shake your seat fairly fairly vigorously, it might help you
- know what it felt like on top of that earthquake,
- so this is 2011 East Coast Earthquake.
- And then probably the most famous earthquake in the United States is the one that occurred
- at Loma Prieta over here about 40 or 50 miles south of
- San Francisco -- and this is damage caused in San Francisco,
- a freeway collapsed right over here, and this whole area actually became very nice after they removed
- this freeway.
- But you can imagine how powerful this was, that it was able to cause this type of damage this far away
- And actually I live right over here, so I'm glad I wasn't around
- or I wasn't in the Bay Area during that earthquake.
- But that earthquake, I've -- depending on how you measure it -- is a 7.0. So that earthquake measured
- at a 7.0,
- so let's call this this over here is 7.
- Let's do that in a color you're going to see. So that earthquake
- was a 7.
- Loma Prietta. That's in the San Francisco Bay area, and that earthquake was in
- 1989, it happened actually right before the World Series.
- And then in 2011 an very unfortunate
- earthquake in japan, the tohoku earthquake,
- Right over here, this circle shows the magnitude of the earthquake,
- it was off the coast of Japan
- All of these were the after shocks,
- and the damage it caused was actually the tsunami it caused
- and the damage it did to the Fukushima Nuclear Power Plant
- well sometimes it's called 8.9 or 9.0,
- let's just call that a 9.0 for simplicity.
- So this is almost 6 and this would be 7 and at 8 would get us almost over there and
- so 9.0 is right over there, so this is 2011 Japan -- the earthquake in Japan.
- And the greatest earthquake ever recorded was the Chilean earthquake in
- 1960, that was a 9.5, so 9.5
- would stick us right over here.
- And this is the 1960 earthquake in Chile.
- And to just give us a sense, you know
- when you look at this, if this was a linear scale,
- you'd say that the Chilean earthquake was
- a little bit than twice as bad as the East Coast earthquake, and that doesn't seem as bad
- until you realize that it isn't a linear scale, it's a logarithmic scale
- and the way that you interpret it is thinking about how many powers of ten one of these earthquakes
- is from another.
- So you can view these as powers of 10.
- So if you take -- go from 5.8 to 7.0, that was 1.2 difference, but remember this is a logarithmic scale
- and I encourage you to watch the videos we made
- on the logarithmic scale.
- On a logarithmic scale, a fixed distance is not a fixed amount of movement
- or change on that scale
- it's not kinda a fixed linear distance,
- it's actually a scaling factor.
- And you're not scaling by 1.2 right over here.
- You're scaling by 10 to the 1.2 power.
- So this is times 10 to the 1.2 power.
- Let me get my calculator right over here and let's figure
- what that is.
- So you can imagine what it's going to be:
- 10 to the first power is 10. An then you have .2.
- So it's gonna be, let's do it.
- 10 to the 1.2 power. It's 15.8, so it's roughly 16 times stronger.
- So whatever shaking there was just felt on the east cost
- and maybe some of you watching this might have felt it.
- Loma Prieta earthquake was 16 times stronger.
- Let me write this: it is 16 times stronger than the one
- we've just had in the east cost.
- So that's a dramatic difference.
- Even though this caused some damage
- and this kind of shaking on, you know, on a pretty good scale
- imagine 16 times as much shaking and how much damage would that cause.
- I've actually just met a reporter who told me that
- she was in her backyard in the Loma Prieta earthquake
- not too far from where I live now
- and she says "all the cars were like jumping up and down"
- so it was a massive earthquake.
- Now let's think about the japanese earthquake.
- We could think about how much stronger was it than Loma Prieta?
- So remember: you don't just think of this as:
- "oh, it's just you know - this is just 2 times stronger".
- It's 10 to the second times stronger
- and we know how to figure that out.
- 10 to the second power is a 100.
- So this right over here, so cars were jumping up and down at Loma Prieta earthquake.
- The japanese earthquake was 100 times stronger than Loma Prieta.
- And if you compare to the East Cost earthquake
- it'd be 16 00 times the East Cost earthquake that occured
- in August of 2011.
- So massive earthquake.
- And just to get a sense of how much stronger
- the chilean earthquake was at 1960...
- and there are some fascinating outcomes of the japanese earthquake.
- It was estimated that Japan over the course of earthquake
- got 13 feet wider.
- So this is doing something to the actual shape of a huge island
- and of top of that it's estimated that because of the shaking
- and the distortions in Earth caused by that shaking
- That the day on Earth got one milionth of a second shorter.
- Little over milionth of the second shorter.
- So you might say: "hey it's only milionth of a second".
- But I say, hey look! It actually changed the day of the Earth,
- the very fundamental thing and it actually matter
- when people send thing to space and probes into Mars
- that they're able to know that our day just got milionth of a second shorter.
- So this was already a massive quake
- and the chilean earthquake is going to be 10 to the 0.5 times stronger
- than that. So let's get out calculator out.
- So you can really view it as a square root of 10.
- So 10 to the 0.5 is the same thing as 10 to the one half.
- Which is the same thing as square root of 10.
- Which is 3.16.
- So the strongest earthquake on record was 3.16 times stronger
- than the japanese earthquake
- the one that shortened the day of the planet
- the one that made Japan 13 feet wider.
- And so this was, if you want to compare it to the East Cost earthquake
- this would be almost or about 5000 times stronger,
- so massive earthquake.
- So one: hopefuly that gives you a sense of what Richter scale
- is all about and also gives you sense of how massive
- some of these supermassive earthquakes are.
- And you can also appreciate what Charles Richter first problem was.
- If you want to plot all of these on the same linear plot
- you'd have to stick this one - 5000 further along an axis
- than you would have to stick this one.
- And this one itself it's still a pretty big earthquake
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