Richter Scale The basics of the logarithmic Richter and Moment Magnitude Scales to measure earthquakes
⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.
- 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
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
Have something that's not a question about this content?
This discussion area is not meant for answering homework questions.
Share a tip
When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
- disrespectful or offensive
- an advertisement
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site