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Current time:0:00Total duration:11:19

Video transcript

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 that 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 but 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 earthquakes 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 kind of gives the rationale for how he came up with the Richter scale I found a paper by Professor K wa da T of Japan in which he compared large earthquakes by plotting the maximum ground motion against the distance to the epicenter so this professor kala Dottie 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 state you're 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 he would that would be some earthquake over there 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 hua Dottie he found that okay you could put you get some earthquakes that you could 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 just 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. Beno Gutenberg and they were all working at Cal Tech when they came up with the Richter scale dr. Beno Gutenberg then made the natural suggestion to plot the amplitudes logarithmic ly 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 that they were a device of the devil I'm assuming he means that they're kind of magical that all of a sudden you could take these things that you want your resolution down here you want to be able to tell the difference between those we cue 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're logarithmic or he plotted on a logarithmic scale what essentially is he's saying is he's essentially taking the logarithm of the magnitude of every one of those earthquakes so if you're measuring the earthquake maybe on a seismograph so this is before they'll quickly and the earthquake hits and then the earthquake stops and then you measure the amplitude of this earthquake if you just plotted them linearly you would have the problem that he saw or if you tried to plot him the way doc professor what daddy did it you would have that problem but what he does is 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 you get a logarithmic scale for lack of a better word but what I want to do in this video is think about how what implication that has for the magnitude of earthquakes especially some of the earthquakes that we have seen recently so this right here is the earthquake that occurred August 23rd on the East Coast 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's a good bit of shaking it can even cause some minor damage but the reason why it's notable is it happened in a part of the world that does not see earthquakes too frequently so let's just protect that on our scale I'm gonna go down all the way over here so I'm gonna do our scale here so this is let's just put that as a 5.8 and if you shake your seat fairly fairly vigorously that'll give you a good idea of what it might feel like on the top of that earthquake so this is 2011 East Coast earthquake East Coast earthquake and then probably the most famous earthquake in the United States in recent memory was the one that occurred at Loma Prieta this is Loma Prieta right over here about 40 or 50 miles south of San Francisco and this is damage that was caused in San Francisco an actual freeway collapsed right over here and this whole areas actually now become very nice after they removed this freeway but you could imagine how powerful it was that it was able to cause this type of damage this far away and actually I live I live right over here so I'm glad I wasn't around when I wasn't in the Bay Area during that earthquake but that earthquake they're depending on you measured but we'll just call it a 7.0 so that earthquake measured at a 7.0 so let's call this so this right over here is seven let me do the color you're more likely to see so that earthquake was a 7.0 Loma Prieta Loma Prieta that was in the San Francisco Bay Area and this was in 1989 it happened right actually before the World Series and then of course 2011 a very unfortunate earthquake in Japan the Tohoku earthquake right over here this circle shows the magnitude of that earthquake it was off the coast of Japan all of these were the aftershocks and the real damage it caused was really the tsunami and the damage it did to the Fukushima nuclear power plant but that was an 8-point well sometimes it's called 8.9 sometimes a 9.0 depending on how you measure it let's just call that a 9.0 for simplicity so this let's say this is almost 6 and this would be 7 then an 8 would get us right over there so a 9.0 was right over there so this is 2011 the earthquake in Japan the Tohoku earthquake and then the largest earthquake ever recorded was the great Chilean earthquake in 1960 and that was a 9.5 so a 9.5 would stick us right over let's say right over the year and this is the 1960 quake in Chile and just to give a sense you know when you look at this well if you thought that this was a linear scale you'd say okay the Chilean earthquake maybe that was a little bit a little bit less than twice as bad as the East Coast earthquake and it doesn't too bad until you realize that it is not a linear scale it is a logarithmic scale and the way that you interpret it the way that you interpret it is it's thinking about how many powers of 10 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 one point to a 1.0 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 on that scale or a change on that scale it's not kind of a fixed a fixed linear distance it is actually a scaling factor and you're not scaling by 1.2 over here you're scaling by 10 to the 1.2 power so this is times 10 to the 1.2 power so I'll get my calculator out right over here let's figure out what that is so you could imagine what it's going to be 10 to the first power is 10 and then you have point to 2 so it's gonna be it's gonna be let's just do it 10 10 to the 1.2 power it's 15 point eight so it's roughly 16 times stronger so whatever shaking that was just felt on the East Coast and maybe some of y'all watching this might be might have felt it Loma Prieta earthquake was 16 times stronger than the earthquake then the so let me write this is 16 times stronger stronger than the one that we just had in the East Coast so that's a dramatic difference even though this caused some damage and this is kind of shaking this is shaking on you know on a pretty good scale imagine 16 times as much shaking and how much damage that would cause I actually just met a reporter who told me that you know she was in her backyard during 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 massive earthquake now let's think about the Japanese earthquake we could think about how much stronger was that a louver Prieta so remember this isn't you don't just think of this as oh it's just you know this is this isn't just 2 times stronger it is 10 to the second time stronger and we know how to figure that out 10 to the second power is a hundred so this right over here so cars were jumping up and down at the Loma Prieta earthquake the Japanese earthquake was 100 times stronger 100 times stronger than Loma Prieta and if you compared to the East Coast earthquake it would be 1,600 times 1,600 times the East Coast the East Coast earthquake that occurred in August of 2011 so massive massive massive earthquake and just to get a sense of how much stronger the Chilean earthquake was in 1960 and just to and there's some fascinating outcomes of the Japanese earthquake it was estimated that Japan over the course of the just over the course of the earthquake got 13 feet wider so this is you know this is happen this is doing something to the actual shape of of a huge island and on top of that it's estimated that that because of the shaking and the distortions in earth caused by that shaking that the day on earth got one millionth of a second shorter a little over a millionth of a second shorter so you might say hey that's only a millionth of a second but I'd say hey look it actually changed the the day of the earth a very fundamental thing it actually matters when people send things into space and and and probes it to Mars is that they are today able to know that our day just got a millionth of a second shorter so this was already a massive quake and the Chilean earthquake is going to be ten to the point five times stronger than that so let's get our calculator out so you really could view this as a square root of ten so ten to the point five is the same thing as ten to the 1/2 which is the same thing as the square root of ten which is three point one six so the strongest earthquake on record was three point one six times stronger than the Japanese earthquake the one that's shortened the day of the planet the one that made the mage Japan 13 feet wider and so this was if you wanted to compare it if you want to compare it to the East Coast earthquake this would be almost or about five thousand times stronger so massive massive earthquake so one hopefully that gives you a sense of of what the Richter scale is all about it also gives you a sense of how massive some of these super massive earthquakes are and you can also appreciate what Charles Richter's first problem was if you wanted to plot all of these on the same linear plot you would have to stick this one you would have to stick this one five thousand times further along an axis than you would have to stick this one and this one itself is still a pretty big pretty big earthquake so this would have to be five thousand times further than some of the earthquakes at the low end of the of the Richter scale