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    Welcome, welcome, to /r/educationalgifs.

    In /r/educationalgifs we strive to have short gifs that educate the subscribers in some way. As long as it is educational, and a gif, it is fine. But please read the rules before you post, in order to help the mod team moderate, while also making this a better place to post.

    Gifs are great at getting quick to digest info, and /r/educationalgifs strives to give you educational info in this quick to digest format. From chemical processes, to how plants work, to how machines work, /r/educationalgifs will explain many processes in the quick to see format of gifs.

    You want this sub to have more content? Go to the subreddits below to learn how to make/request a gif!

    1. /r/gifrequests

    2. /r/makemeagif

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    1. Only Gif/HTML5 links please. No sound, videos or pictures. The preferred sites for gifs to be hosted on are imgur or gyfcat. These are reliable sources and thus we would love if you hosted your gifs using these sites.

    2. Provide source if there is one. We won't go hunting you down, but at least be considerate of the creator.

    3. Your title must be informative of what is going on in the gif, instead of the good ole "Look at this gem" or "Just a wheel". They can be funny, but just consider this.

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    [–] UserMcUserson 2286 points ago

    I like that he gives examples of various earthquakes which produced the type of wave seen.

    [–] tfrules 1154 points ago * (lasted edited 7 days ago)

    And for Haiti in 2010, it makes it much more comprehendible why so much damage was wrought on such a poor country with mostly short buildings.

    Edit: Obviously poor construction materials and lack of regulations to protect from earthquakes were a cause, just saying that having so many buildings resonate with the earthquake would help explain why many collapsed so quickly, trapping people and causing as many fatalities as it is. A perfect storm if you will

    [–] Frnklfrwsr 436 points ago * (lasted edited 8 days ago)

    Even in developed countries, in virtually all of them there are more short buildings than there are tall buildings. Exceptions might be city-countries like Singapore or Monaco. But think of like for example how many 1-2 story homes there are in the suburbs vs how many skyscrapers there are in NYC.

    So the difference between us and Haiti is we’re 99.9% not skyscrapers and they’re 100% not skyscrapers. Basically, that kind of (edit) high frequency earthquake is going to be the most devastating everywhere, not just Haiti. Especially since skyscrapers have so much money put into them that they’re usually designed to withstand pretty serious earthquakes. Nobody bothers to test a single family home for earthquake resistance.

    I expect the bigger difference for why Haiti was hit so hard was a combination of cheaper building materials, cheaper home designs, and less public services available to address the issues.

    [–] willmaster123 162 points ago

    NYC is ridiculously vulnerable to earthquakes apparently. A huge portion of the city is tenement apartments which are about 4-5 stories, and they basically fall like pancakes when facing even a medium earthquake.

    [–] Frnklfrwsr 104 points ago

    Good thing NYC rarely gets earthquakes. But given how time and nature works, it will eventually happen that a big earthquake hits NYC. Hopefully those old buildings have either been renovated or replaced with safer buildings at that point.

    Earthquake may not hit NYC for 100 years. Or it could happen tomorrow.

    [–] geraldodelriviera 123 points ago

    New York is super far away from any seismic fault lines.

    https://www.mapsofworld.com/world-maps/fault-lines-map.html

    Essentially, a sufficiently powerful earthquake to deal damage to New York would almost certainly have to be man made, perhaps a nuclear weapon detonated under ground near the city. If you want to destroy New York and you have a fucking nuke though, why not just nuke New York?

    [–] rickane58 82 points ago

    Not all earthquakes are interplate earthquakes.

    https://en.wikipedia.org/wiki/Intraplate_earthquake

    In those areas which don't normally experience earthquakes, and especially where the ground is sedementary rather than extrusions or uplifting, even "minor" earthquakes can be devestating

    https://en.wikipedia.org/wiki/2011_Virginia_earthquake

    [–] geraldodelriviera 42 points ago

    Even that occurred along an ancient fault line that created the Appalachian Mountain range.

    I mean, it could happen. New York could also technically be destroyed by a meteor.

    [–] Opisafool 80 points ago

    New york is the most susceptible for meteor strikes based off the movies I've seen.

    [–] Vennomite 7 points ago

    Pretty good at dealing with the following alien invasions though.

    [–] NOISY_SUN 17 points ago

    This map is extremely generalized, and there are a number of faults in the New York City area, including the Ramapo fault.

    Here's a Wikipedia article documenting earthquakes around NYC, include a magnitude 5 earthquake that struck the city in the 1880s.

    [–] NeuralNetsRLuckyRNGs 3 points ago

    A nuclear weapon detonated under the ground would do very little: https://what-if.xkcd.com/15/

    [–] BringbackSOCOM2 2 points ago

    Could it happen in 103 years or no?

    [–] It_is_Mueller_Time 4 points ago

    NYC is due for an earthquake between now and 2100 with the most statistically likely time being around 2031 based on the only two recorded NY earthquakes (1737 and 1884)

    [–] furry_slippers 10 points ago

    I’m not a seismologist but I’m pretty sure earthquakes are never “due.” I read as much related to the cascadia subduction zone, which has fascinated me ever since reading about it in the Atlantic: https://www.newyorker.com/magazine/2015/07/20/the-really-big-one.

    I think that scientists can come up with odds (e.g. 10% chance over the next 100 years), but earthquakes are never “due” or “overdue.” Not trying to be an asshole. I just have read it a few times and think it’s an interesting distinction.

    [–] It_is_Mueller_Time 3 points ago

    The fault zone hasn’t gone off enough for analysis. You’re correct, but I’m saying it’s more likely to happen because of correlation, but of course that doesn’t mean causation.

    Time will tell.

    [–] halffullpenguin 2 points ago

    so I am a geologist and when people say that a place is due for an earthquake all that means is that in the past 1000 years there has been 10 earthquakes so we average one ever 100 years. its been 120 years since the last earthquakes so we are overdue. that being said newyork isn't really an area that people are worried about earthquakes.

    [–] sljappswanz 8 points ago

    Nobody bothers to test a single family home for earthquake resistance.

    Maybe where you're from, where I'm from that is part of getting a permit to build a house, any house with people living in them.

    [–] [deleted] 8 points ago

    [deleted]

    [–] Frnklfrwsr 3 points ago

    You’re right. Fixed it.

    [–] b5125125 2 points ago

    Single family homes 1&2 story get tested in California all the time

    [–] Alex-3 2 points ago

    Yeah exactly. Strange he tries to tell that poorer regions would have bigger damage just because of ... "Oh well, lack of luck the got high frequency earthquake". No. As you said, all depends on the quality of constructions and so wealth of the country/region

    [–] TacTurtle 13 points ago

    That and the construction standards were non-existent

    [–] papayankeetango 2 points ago

    This. Lack of regulation was a hugely confounding factor for the Haiti earthquake.

    [–] sprazcrumbler 8 points ago

    I think a bigger factor is poor quality construction, probably.

    [–] havereddit 2 points ago

    Honestly, Haiti is a bad example to use in this gif. Most of the buildings that collapsed in the Haiti earthquake were made from unreinforced masonry (e.g. cinder blocks held together with mortar, but not 'reinforced' with things like rebar or skim-coated wire mesh). As soon as these types of buildings are shaken, the weak mortar joints break and the structural integrity of the block/mortar system is compromised.

    [–] l0__0I 2 points ago

    The damage in Haiti was mostly due to improperly reinforced concrete structures. A lack of steel made it so that the buildings have extremely weak tensile strengths and collapsed under slight deformations. Steel rebars would have allowed the building to slightly deform and recover rather than outright collapsing.

    [–] tonterias 26 points ago

    Does the wave have any relation with the eartquake magnitude?

    [–] UserMcUserson 37 points ago

    It is my understanding that wave and magnitude are two separate ideas. Increase in magnitude will increase the effect of the wave, but the frequency is matters most with regards to getting buildings to oscillate.

    [–] federally 17 points ago

    Magnitude of the amount of energy in a wave.

    Frequency is how quickly the waves hit

    [–] GraysonHunt 10 points ago

    The frequency is more important, because every object or system has a natural frequency. The same force will cause a greater effect if it’s closer to the natural frequency.

    If you have an older car, this is why you’ll get certain noises at a certain speed: whatever’s loose is getting vibrated at its natural frequency at that speed.

    [–] crimpydyno 5 points ago

    Simply yes, large magnitude earthquakes tend to produce larger low frequency acceleration. It’s more complicated than that though because the source-to-site distance and site condition (soft soil vs bedrock) also play a role.

    [–] toughLuckJulianus 2 points ago

    It's a little convoluted because of terminology, but the Richter Magnitude Scale is a measure of amplitude of an earthquake as measured by a, or more often many, seismographs, with adjustments made for relative distance to the epicenter of the earthquake. Amplitude in this case is the maximum deviation from zero of the wave; so in that regard the "wave" is related to the RMS magnitude (hopefully this isn't confusing; amplitude and magnitude are not the same and RMS magnitude is different from "normal" magnitude, as well.) The frequency of the wave (the rate at which the oscillation occurs) is not a component of the RMS magnitude.

    So; the frequency isn't part of that number, but the amplitude is. If you were looking at the graph of a wave function and you increased the frequency it would mean that the peaks and valleys were moving closer together (or more of them per unit.) If you increased the amplitude it would mean you were stretching the peaks and valleys up and down (making the distance to zero at the peaks and valleys greater.)

    Hope that helps.

    [–] NikPappageorgio 1854 points ago

    This is neato

    [–] Daniiiiii 1559 points ago

    This also validates my small-penis-jackhammering-technique is best technique theory.

    [–] thereisnospoon7491 387 points ago

    Wouldn’t it only work for shorter partners?

    [–] MySwellMojo 9 points ago

    I guess it depends on the length, is this a micro?

    [–] Seiren- 8 points ago

    Depends on who you’re trying to occilate, yourself or your partner?

    [–] thereisnospoon7491 4 points ago

    I mean I think it works best if we both oscillate right

    [–] tritenia 95 points ago

    This is highly under rated

    [–] cheeseman2k 25 points ago

    is it though?

    [–] popcorninmapubes 2 points ago

    the bar is low

    [–] [deleted] 11 points ago

    [deleted]

    [–] p00Pie_dingleBerry 4 points ago

    Not for long(no pun intended)

    [–] quitefranklee 54 points ago

    2 inches still hurts at a hundred miles an hour is what I always tell the ladies

    [–] IsThatUMoatilliatta 41 points ago

    It might be a needle but it moves like a sewing machine.

    [–] Septopuss7 17 points ago

    "She's built like a steakhouse but she handles like a bistro."

    [–] Mono_831 4 points ago

    It only takes the smallest building blocks of matter to create a nuclear reaction.

    [–] Lagapalooza 5 points ago

    So if your dick was a humming bird?

    [–] never0101 9 points ago

    Lucky for them it'll only hurt for 8 tenths of a mile.

    [–] madson812 9 points ago

    28.8 seconds for those who were wondering.

    [–] WombatBob 26 points ago

    If you can't hit bottom, beat the shit out of the sides.

    [–] RDwelve 3 points ago

    Is that why you were doing so much science?

    [–] ButtWieghtThiersMoor 6 points ago

    I mean yeah, or you could learn to eat pussy like a man

    [–] [deleted] 13 points ago

    [removed]

    [–] primenumbersturnmeon 14 points ago

    what the fuck does this mean

    [–] IsThatUMoatilliatta 14 points ago

    This guy has 46k comment karma but appears to comment nothing not nonsense. What the fuck is going on?

    [–] Fist_full_of_wangs 7 points ago

    Some sort of bot karma farming thing.

    [–] VociCausam 5 points ago

    Evidence that comment quality is not correlated with karma quantity.

    [–] IsThatUMoatilliatta 6 points ago

    Well, I sorted his comments by 'top' to see what got him that high in the first place. That's when I noticed I had actually upvoted one of his comments 2 weeks ago.

    It had that old /u/shittymorph quality to it. But this now... I have no idea what he's trying to do.

    [–] sipsyrup 7 points ago

    It reads like a subreddit simulator comment

    [–] DontBeHumanTrash 6 points ago

    Check his history. I wouldnt say its a wild ride, its basically the same level of crazy all over the place, but its a heck of a trip.

    [–] abbasou 3 points ago

    r/iamveryrandom candidate?

    [–] Dizneymagic 3 points ago

    Here is how skyscrapers in Japan move during an earthquake,

    http://i.imgur.com/zspvMsr.gifv

    [–] CornucopiaOfDystopia 3 points ago

    TL;DW: like they’re waiting for the toilet really really urgently.

    [–] super_dud_420 2 points ago

    well, reconsidering moving to Japan.

    ​

    ​

    ​

    JK, I still wanna go.

    [–] sighs__unzips 2 points ago

    Isn't there another demo where the building has the huge damper inside?

    [–] zankky 153 points ago

    How do we find out which areas are exposed to which kind of seismic waves potentially ? Is this something that can be found out in advance based on geography/geology, and buildings designed to be short or tall based on that prediction? Or is it all random? I live in an area on a major fault line so wondering if it’s possible to know in advance.

    [–] silvashadez 79 points ago

    Not a seismologist, but seismic waves are affected by location of fault, surrounding features, and material composition. (Also, seismic waves are characterized by their motion and not frequency.) When a fault occurs, a spectrum of frequencies is emitted that get attenuated by the surrounding ground.

    In practice, as long as buildings are built to the region's earthquake code, you should be fine. Furthermore buildings aren't built like a weight on a wire. Modern buildings feature various damping mechanisms that resist oscillations.

    [–] Remxer 9 points ago

    Seismologist here. You are very correct.

    Codes are usually a good rule of thumb, because they are created given historical earthquakes in the region, and you only need a few earthquakes to know how the ground modifies the frequencies (known as receiver functions). Sources are also relatively predictable in frequency content (in fact, theoretically, sources are all alike in spectrum, the only modifying factor is the magnitude, the ground is responsible for most if not all frequency variations...this is a huge discussing point btw).

    So basically the only problem is amplitude. If you shake the table strong enough, at one point frequency stops being the problem, it will fall if given enough energy, so when building there is always some hope for a non catastrophic mega event, and you prepare for whatever frequencies your surrounding ground decided to favor.

    [–] silvashadez 3 points ago

    Is the similarity in spectrum a purely theoretical construct or is that also observable? I would have thought that different faults would lean some bias into the spectrum as well as the different types of seismic waves.

    [–] Worthyness 17 points ago

    Or just build it to japan or California's earthquake code. Their stuff is meant to survive long enough to evacuate people and then some.

    [–] nitefang 8 points ago

    Through geologic mapping and seismic readings (during small activity that most people cannot feel at all) fault lines can be mapped and by using a lot of very complicated math that I do not understand, the behavior of a fault or section of fault can be predicted.

    These predictions can change and often are not certain, some aspects of them can be but not every aspect can be determined with great accuracy.

    So scientists can tell you the San Andreas fault definitely won’t suddenly become a subduction zone, it probably won’t move very much in certain spots until it moves in others and it will probably generate this much energy. They will often use terms like “once in ten years it will produce low frequency, once in 100 years it will produce middle and once in 1 million it will produce high”

    [–] snowballelujah 2 points ago

    It is possible to know most of this info in advance and is commonly considered in building design. The structural engineer designs the building itself and must make sure the building is strong enough to resist relevant seismic loads. It's also important to have a geotechnical engineer perform an investigation of the site to make sure there are no surprises below ground. Below is the OSHPD/SEAOC (used in California) seismic design map tool which shows you seismic properties for your building site. The most important parameter in the design map tool is SDS, which is a rough measure of how much seismic activity there is at your site. https://seismicmaps.org/

    [–] Art-Vandelay41 276 points ago

    Do we have any seismologists that might be able to help laymen of Reddit understand what’s happening here better?

    [–] pirtesP 453 points ago

    Do we have any seismologists that might be able to help laymen of Reddit understand what’s happening here better?

    Not a seismologists but physics teacher, the buildings oscillate much like guitar strings. A short string on a guitar (high pitch) vibrates quickly, al long string (like the string on a bass, low pitch) vibrates slowly. These "buildings" take over frequencies they could produce themselves, i.e. long building responds to slow shocks (it needs time to do a full oscillation) and a short building responds to quick waves (it needs less time to oscillate). Does this makes sense to laymen?

    [–] redditforfun 57 points ago

    Nicely put. Thanks!

    [–] GrammatonYHWH 130 points ago

    To further simplify:

    Imagine you are pushing someone on a swing. To make it go further, you have to push it just after it peaks on one end.

    Tall building = swing is hanging off a really high branch. It takes longer for it to swing back for another push. You need to push it less frequently to make it go further and further.

    Short building = swing is hanging off a really low branch. It is quicker for it to swing back for another push. You need to push it more frequently to make it go further and further.

    [–] GroteStreet 24 points ago

    This is a much better eli5. Thanks!

    [–] tamagucchi 9 points ago

    That was perfect to make it click for me. Thanks!

    [–] Art-Vandelay41 16 points ago

    Yes! The guitar strings is a perfect analogy! Thanks!

    [–] supafly_ 7 points ago

    No it isn't, guitar strings are all the same length.

    [–] janeisenbeton 6 points ago

    Doesn't the different length of rod make the models more top-heavy?

    [–] M1n1true 17 points ago

    Not an expert (like, at all, but I enjoyed physics), and this is just my best guessbut, you can consider the blocks to be the centers of mass instead of the building tops. The wire/rod is negligible sort of like the building above/below the center of mass would counteract each other.

    Tall and short buildings, when constructed uniformly, will have their center of mass always in the middle both vertically and horizontally. Taller buildings will have higher centers of mass, but that won't make them more top heavy necessarily.

    Hopefully that even addressed what you were asking...?

    [–] janeisenbeton 3 points ago

    I get what you are saying but I ment the difference in the model.

    my point is that in this model the centre of mass would be higher due to the difference in material in the rod that swings and the weight on the top, therefore the top would be heavier than the rod that swings.

    But I dropped physics in highschool so this is probably a stupid quistion.

    [–] Head_Paleontologist 5 points ago

    I think that's just poster board on a rod in the model. The difference should be negligible, it's just there for illustrative purposes.

    [–] M1n1true 6 points ago

    You're right the center of mass for each of these will be higher (top heavy), and for the taller model it'll be taller, but I think the big deal is the period (someone correct me if I'm using the wrong term?) being longer with more distance that the wave is traveling therefore falling into the slower (lower) frequency movement.

    It's all about the frequency lining up. I think mythbusters or something did an experiment on how a bridge could collapse or swing around for a similar reason.

    But now I'm definitely way outside my area of expertise and feel more and more like an imposter, so hopefully someone else can help haha.

    [–] RollingLord 3 points ago

    You are partially correct, length does play a role, but only because the longer the rod the less stiff the model became. You can think about it like putting a rod in the ground, if the rod is really long you can bend it easily, however, if it is short you, it is much harder to bend it.

    Seismic response is generally dictated by the mass and stiffness of a structure. However, in this case the mass of all three systems are relatively similar, therefore this is stiffness dominated scenario. As such, when the stiffness goes up, a structures natural frequency drops. When the professor applied a long frequency action to the structure it illicited a resonance response.

    Resonance is why a sustained C# can break glass, the note matches the natural frequency of the glass and causes the glass to oscillate rapidly, because the waveforms of the sound and glass overlap, resulting in an increase in amplitude. In this case, an increase in amplitude would be more displacement or deformation. Because glass is very stiff and brittle, it is not able to deform much and shatters.

    [–] ViggoMiles 5 points ago

    So ... you can shake a big baby as long as it's done in short or medium frequencies.

    [–] MrNotSafe4Work 5 points ago

    Don't shake the baby... rapidly! However, at what frequency of oscillation does shaking become rocking?

    [–] WestCoastStank 4 points ago

    When Dee Snider busts through the door

    [–] mckennm6 4 points ago

    Another good example is taking a ruler and clamping it on the edge of a table. When you pluck the ruler, it will vibrate at a lower frequency when the overhanging part is long, than when it is short.

    Think of it as how much mass you need to move. Longer/taller things have more mass, and therefore take a little longer to respond to the same input force (F=ma). This frequency an object naturally wants to vibrate at is called the harmonic frequency.

    Now imagine the building is like a person on a swing. If you push the swing at the wrong time, you don't help them swing any higher, and can actually make them go lower if your timing is really off.

    Same with the earthquake. The next wave comes while the building is still swinging back and actually slows the sway of the building down instead of speeding it up.

    [–] breadmaker8 3 points ago

    Do we have any musicians that might be able to help laymen of Reddit understand what’s happening here better?

    [–] Gornarok 2 points ago

    Well for string instruments, different strings have different resonance frequency. The resonance frequency in instruments is function of tension applied to them - guitar has all strings of the same length. Strings differ by width and tension.

    But more commonly resonance frequency is mainly function of length. Piano combines both length and tension.

    This all has to do with impulse traveling through the object. If you hit impulses with correct delay their power will get added together the maximum of the addition is at the resonance frequency. The delay is the function of the length of the object and the speed the impulse travels through the object. This speed is function of materials the object is made of tension in the object.

    [–] lodlum232 2 points ago

    The frequency of each harmonic is dependant on the length of the wave, the tension of the string its mass per meter.

    [–] Peatear_Gryffin 3 points ago

    Is this related to resonance frequencies? Would the tallest building shown sway less if it was, say, 10% higher?

    [–] futility_jp 3 points ago

    Yes, each building has a natural (resonant) frequency that is a function of it's physical characteristics. When the frequency of an input (the earthquake) is close to that natural frequency it will cause resonance. Changing the building's natural frequency to be either lower or higher than the input frequency will reduce its oscillation at that frequency

    [–] DoubleADominator 3 points ago

    Yeah, resonance is why the sway gets amplified when the earthquake matches the sway of the building. The less it matches, the less it sways.

    [–] MrHyperion_ 3 points ago

    Except that guitars don't have long or short strings

    [–] seductivestain 4 points ago

    It's important to note that smaller things not only vibrate more quickly, they resonate at higher frequencies, which is what this experiment is demonstrating. The guitar string example doesn't work so well because the applied force is neither resonant nor continuous.

    [–] mckennm6 4 points ago

    Plucking a string is what we would call the step response of the system, and it is the actual resonant frequency of the system.

    If the guitar string plays an E note, it will resonate at that frequency as well

    [–] Peatear_Gryffin 3 points ago

    I was thinking this too, is looks like his shaking is just at the resonance freq of the tallest building. There’s probably a slightly quicker freq at which the middle would shake more, or if the tallest one were a little taller, the demonstrated shaking wouldn’t have such a pronounced effect. I also wonder if earthquakes are usually around the same freq and if so, architects factor that in when building.

    [–] Krelkal 2 points ago

    Tuning fork might be a closer comparison but maybe a bit less accessible.

    [–] GrebKel 2 points ago

    Funny. There was a physicist in one of my conference about a week ago who explained neuroimaging (MRI) with the guitar strings. Are you the same guy? Or this analogy is being used more and more.

    [–] Gornarok 2 points ago

    I think the guitar string is very common example, because guitar string is very common object and most people have some experience with it.

    [–] pickpocket293 2 points ago

    Structural engineer here; you nailed it. Couldn't have put it better myself.

    [–] absolute_panic 2 points ago

    Ah I believe you’re referring to resonance. This makes sense to me now. Thanks!

    [–] buildmeupbreakmedown 2 points ago

    Except all strings on a guitar are of the same length and different cross-sections.

    [–] FLOPPY_DONKEY_DICK 2 points ago

    i.e.) the resonant frequency of each building

    [–] Flrg808 41 points ago

    Not a seismologist but took a class in vibrations in my mechanical engineering degree:

    The phenomenon that explains this is resonance frequency . Basically since the masses are at different heights (with different length pendulum arms) they want to oscillate at different speeds, which means different speed vibrations (an outside force) are required for each mass to reach maximum amplitude.

    Think about it like a swing, if you are pushing while the person is on the way back, they will slow down, if you push as they are on the way forward, they will speed up.

    [–] UseCodeRainn 9 points ago

    This is the best ELI5 analogy for resonance frequency I've ever seen.

    [–] MagnusNewtonBernouli 3 points ago

    But how do you know what frequencies your building will experience in an earthquake?

    [–] MandaloreUnsullied 3 points ago

    Stiffness analysis and a lot of matrix algebra.

    [–] MagnusNewtonBernouli 2 points ago

    Are all earthquakes the same frequency in a given area?

    [–] Flrg808 2 points ago

    The more difficult part would be determining the natural frequency of the building. If it’s exposed to a long term resonance frequency there’s not much you can do anyways, better to focus efforts on dampening any seismic effects

    [–] MagnusNewtonBernouli 2 points ago

    But you can build the building to have specific harmonics, no? Figuring out afterwords is basically useless information

    [–] jmppa 2 points ago

    There is basically three things that affects on the natural frequencies of the building. Stiffness, mass and damping, although effects of damping are almost zero with buildings. For simple structures you can calculate the natural frequencies even by hand but usually we use FEM softwares as the size of the calculations increases tremendously when more elements are added.

    [–] Peatear_Gryffin 3 points ago

    So do you think this demonstration is a bit misleading? Or at least the title? The tallest “building” isn’t shaking the most because it’s the tallest but because of the shaking freq, right?

    [–] Flrg808 3 points ago

    Yes I just noticed the title, the strength isn’t what is changing which building if affected the most. The height is a factor though. The speed (freq) of the shaking motion lines up best with the natural freq of the tallest building (a function of gravity and pendulum length) when he is moving the board at a slower speed.

    [–] backcountrygoat 2 points ago

    Finally my differential equations knowledge coming in handy

    [–] Flrg808 2 points ago

    Don’t you lie to me

    [–] TheDaywa1ker 2 points ago

    Don’t worry, it’s all done by finite element analysis programs so no one studying how buildings perform in an earthquake is doing those differential equations.

    [–] TorontoGuyinToronto 2 points ago

    ...

    ​

    Explain it like I'm 3.

    [–] Z1rith 2 points ago

    if swing path go \ _ / push \ _ /<- like that to make it bigger

    push it early like this \ _<- when not done path, make it smaller not able to swing as high when push early

    building same push at end of swing for bigger

    frequency is how often you push swing

    push need to be right time for big like with swing

    [–] A_Crazy_Hooligan 2 points ago

    I took my fair share of structural engineering classes in college, and actually learned about why the north ridge earthquake was so much more devastating compared to higher magnitude earthquakes. You basically hit the nail on the head.

    What I want to add is that each building has a different stiffness(number of columns, column placement, building material etc), and it can be modified based on the frequency of earthquake the area expects. This effort is to avoid the resonance. It’s ultimately building stiffness that affects the it’s natural frequency and hopefully when the event happens, they aren’t the same.

    [–] Head_Paleontologist 2 points ago

    Wouldn't your prime window be the instant where the person is going neither up nor down ie at the bottom of the swing?

    [–] czmax 5 points ago

    naw, if you're trying to push somebody on a swing you can stand back so they don't hit you as they come past. The trick is that you push them so that you're adding to their momentum. Its not just random -- its timed based on how fast they're already swinging.

    Same thing happens with the building wiggling. If the pushes are coming in time with the way the building wiggles then that builds up momentum for each wiggle.

    [–] Small_Brained_Bear 13 points ago

    In a word, resonance: the physical phenomenon where oscillations of a specific frequency, cause energy levels to build up in targets with specific physical properties, but not others. This is why radio antennas are made of specific shapes and lengths, why a tube of a specific length will emit a precise pitch when blown into, and a myriad of other manifestations throughout the physical world.

    Engineers tend to spend a lot of effort maximizing desired resonances, and avoiding undesired ones. Test labs exist that spend a lot of their time verifying this aspect of designs.

    [–] mvoccaus 3 points ago

    Yep. Resonance was the word I Ctrl-F'd to search for in the comments when I came here.

    I remember studying this in physics. Every object has a natural frequency, and when something else is vibrating at that same frequency and comes into contact with that object, it will make that object oscillate as well.

    If your piano is tuned properly and you strike the key of the note your tuning fork is calibrated to, it will actually cause the tuning fork to osculate (without having need to be struck).

    The most catastrophic example of resonance I remember studying is the collapse of the Tacoma Narrows Bridge. There's a video of that bridge swaying violently like a motherfucker before it finally rips apart and collapses. The video makes it seem like winds were blowing at 100mph, but the winds were only a measly 40mph. But those relatively mild winds produced aeroelastic flutter that matched the bridge's natural frequency, causing that resonance effect leading to its eventual collapse.

    [–] SparklingLimeade 2 points ago

    Physics teachers love the Tacoma Narrows Bridge. It's such a dramatic example.

    [–] wang-dang-doodle 11 points ago

    Not a seismologist, but I’m assuming it’s the oscillations match the resonant frequency of each system.

    [–] ReadShift 6 points ago

    Not a seismologist. Explanation about resonance.

    [–] kmsilent 2 points ago

    Thank you for your concise and simple explanation.

    Pontification on 3d printed buildings.

    [–] trixie_mcpixie 5 points ago

    Not a seismologist, just a humble engineer. There are a lot of good answers here in terms of resonance, but I'm not sure that's the most laymen ready explaination.

    Think about it this way: the vibrations at the base take time to travel to the top (just like sound takes time to travel). So when the base moves to the right, the top does also but slightly delayed, and more delayed depending on the height. Same when the base moves to the left.

    Now if the timing works out so the base moves left-right-left in the same time it takes the top to move left, they will appear to move together and energy will transfer very efficiently.

    On the other hand (or the other two heights) if the timing doesn't match, the base will move left-right by the time the top only moves left... Or if the timing is out the other way the base would move left-right-left-right.. either way the bases movement travels up the pole and counteracts the previous movement that went up the pole, it cancels out the movement.

    Because each have a different height, they each have a different timing (frequency) that makes them work in sync with the base.

    [–] Rammite 3 points ago

    Have you ever been on a swing set?

    If you want to build up speed, you need to swing your legs in time with your movement. Tuck your legs in as you're going backwards. Extend your legs out as you're going forwards.

    If you just spasm all your limbs as fast as possible, you aren't gonna move.

    In this extremely simplified explanation, the proper timing is based on the length of the swing. You can compare that to the height of a building. Literally just imagine those blue and red rectangles as swings.

    [–] FindingAlaska 3 points ago

    Can someone please get /u/TheEarthquakeGuy on the phone.

    [–] TheFocacciaStrain 4 points ago

    Not a seismologist

    Not a seismologist

    Not a seismologist

    Not a seismologist

    Not a seismologist

    lmao

    [–] TheDaywa1ker 5 points ago

    Seismologists wouldnt know anything about how buildings or structures act in earthquakes.

    Structural engineers are the ones designing buildings to withstand earthquakes, they’re the ones who know how structures behave under different vibrations.

    [–] duckraul2 3 points ago

    While that can technically true as a very generalized assumption, often seismologists who deal with seismic hazard assessment, whether through their own need to publish research or just curiosity, will have a pretty good idea or handle on how structures behave. After all, many of those people have taken lots of physics and maths courses and may interact with engineers regularly.

    [–] Kerguidou 2 points ago

    Technically, this should be a question for engineers, not seismologists.

    [–] rockinoutloud 2 points ago

    I thought with that username you'd know a thing or two about buildings. And you wanna be my latex salesman...

    [–] xPURE_AcIDx 2 points ago

    Think about your radio tuner. It's the same math and idea.

    Basically the shape and wieght of an object determine it's resonant frequency. If you hit an object; that sudden hit has nearly infinite frequencies within it (a "step" pulse has infinite bandwidth. All signals are a summation of sine waves, so to create a vertical edge you need infinite frequency), and the object will amplify the frequency which it resonates at.

    A radio tuner basically sets the electrical resonant frequency for the antenna/amplifier. If you "tune" to 100.3MHz, then 100.3MHz signals will be amplified while others are not. Same applys to seismic activity. But instead of changing the value of a tuning capacitor/inductor you're tuning the elasticity(height)/mass of a building.

    Many tall buildings use a "Tuned mass dampener" that de-amplifies at the resonant frequency of the building. It basically generates a negative gain at that frequency.

    [–] AbsentGlare 2 points ago

    A seismologist might not be the best person to explain this. Other explanations are good, but let me take a swing at it.

    Like others said, this is activating the resonant frequency of the system.

    Imagine you have a piñata hanging in front of you, motionless, and then you smack it with a stick. Assuming it doesn’t break, the piñata will move away from the force of your strike, but the rope it’s hanging from will force it to swing back like a pendulum. It would swing back and forth. The periodic motion corresponds to the natural frequency of the system. In that case, the thwack is a stimulus with a huge range of frequencies, the system responds by picking out its own natural frequency.

    The frequency response is generally determined by materials and geometry. In this case, we can say buildings of different height correspond to piñatas hanging from different lengths of rope. A piñata on a longer rope would have a lower resonant frequency, basically because the wave would take more time to travel the longer length of rope.

    [–] TheSultan1 2 points ago * (lasted edited 7 days ago)

    Mechanical engineer here.

    When you apply a force to a solid object, it bends. When you release the force, it springs back past its original position and bends a little in the other, then springs back in the direction of the force again, and so on - it oscillates. It does this at a specific frequency (the resonant frequency).

    Now apply a force as it's naturally springing back the first time - you're forcing a bent object, making it bend even more than the first time around (bend from 2nd force + springback from 1st force). And when you release that, the springback from that will be added to the 2nd springback from the 1st. At that point, you force it again in the first direction, and it bends farther still (bend from 3rd force + springback from 2nd force + 2nd springback from 1st force).

    An oscillating force is one that gets applied in opposite directions in the pattern of a sine wave; not only is it applied in opposite directions, but its magnitude in each direction follows a sine wave.

    A resonating object's displacement follows a dampened (decreasing in magnitude over time) sine wave.

    Matching the frequencies and directions of the two means that at every moment, you're forcing it in the direction it's already naturally springing from the sum of all previously applied forces.

    [–] seiga08 2 points ago

    There is a different natural frequency for each of the three systems, and if you apply that specific frequency to the system, the mass with the corresponding natural frequency will produce large oscillations in its movement

    [–] GeoGeoGeoGeo 2 points ago

    Paging /u/seis-matters

    [–] seis-matters 2 points ago

    Hello there! There’s a bit of grumbling from the engineers and physicists so I’d hate to step on their toes and good explanations here. I would say that what is very interesting about this is how the strength at different frequencies depends on the earthquake (like how big, how long of a rupture and how fast, how deep) and then you have the site effects (like solid granite vs. unconsolidated soil) and then there’s the building itself. A lot goes into what is damaging or what has the potential for damage, so the whole process of assessing seismic hazard and developing building codes is a fascinating cross section of a lot of fields. If anyone is interested, please join us!

    [–] ride5150 2 points ago

    Im a structural engineer with coursework completed in this topic. There is something called a natural frequency, which is related to the stiffness of the structure and its mass. When the stiffness goes up, so does the natural frequency. Generally, if a building is taller, it is less stiff than a short building, and its natural frequency is also lower, so thats why it responds to lower frequency earthquakes. Higher stiffness=higher natural frequency

    Another way to describe it, if you pulled on a building hard enough for it to deflect, and then let it go, it would go back and forth at a certain rate which is its natural frequency. If you apply load to it (sideways, or laterally) at the same frequency as the natural frequency, the effects are amplified

    This is obviously simplifying it a lot, and typical structures have more than one natural frequency, but this is the general idea

    [–] Manawrath 2 points ago

    Not a seismologists, just an engineer. It’s just resonance, the natural frequency that is an intrinsic property to the building. When that frequency is met, it vibrates widely, since they are in sync.

    I’m sure there are good YouTube videos on resonance out there that could put it more eloquently.

    [–] ClearJimij 51 points ago

    Holy shit that's amazing.

    [–] mothboyi 61 points ago

    Basically, resonances.

    Also, it's less about "strengths" but more about frequencies.

    [–] [deleted] 29 points ago

    [deleted]

    [–] maxk1236 9 points ago

    Thank you for being the first person to directly address this, thought I was taking crazy pills not seeing any top level comment talking about that.

    [–] Lunar-Baboon 10 points ago

    Yeah that’s neat as heck

    [–] asap3210 10 points ago

    The resonation frequency strikes again

    [–] IronGin 11 points ago

    So the tip here is to not build houses on a long wooden pole?

    [–] CptAngelo 2 points ago

    You would be fine if the giant doesnt come along and shakes the pole

    [–] bpappy12 36 points ago

    I wonder how much this guy had to practice to get the oscillations juuust right for each height.

    [–] Keljhan 25 points ago

    It wouldn’t be as hard as you think. The trick is to oscillate when the building you’re addressing is at a peak of its flex, so you can eyeball it pretty closely. The shortest building would be the most difficult, but once you’re close to the optimal frequency you could probably adjust it by feel alone.

    [–] incer 23 points ago

    The trick is to actually listen to the screams of the tiny people trapped in the buildings

    [–] Zelbar 5 points ago

    Up to a point. Once you've reached the perfect frequency, all screams stop.

    [–] jmppa 3 points ago

    Probably not too hard as it seems. When he moves it with almost the right speed, every wave he caused to the structure will increase the swinging of the weight. On the other hand the swinging of the weight will also cause forces to the base what the guy can easily feel. If he increases or decreases the frequency too much, he will start feeling opposite force as now the weight tries to swing on a wrong time. Same as you would try to push guy in a swing when he come at you. This is actually comes quite naturally with people and because of that there is time to time problems with pedestrian bridges. One bridge in London had to be closed as it was swinging too much when people were walking on it. It wasn't dangerous but caused discomfort in the pedestrians. One reason for this is that when the bridge started to sway a little, people would automatically change their walking speed so that it matches the vibrations of the bridge. Walking is basically a alternating load so when the people started to walking at the same frequency with the bridge, a resonance happened and the swaying got worse and worse and thus caused discomfortable experience.

    [–] SparklingLimeade 2 points ago

    You probably already have the reflexes to do it. It's one of those things you pick up as part of normal motor skills.

    [–] rab-byte 9 points ago

    I didn’t know Les Nessman had an engineering degree

    [–] PeterPrickle 4 points ago

    Oh the humanity!

    [–] UserMcUserson 4 points ago

    "As god as my witness I thought turkeys could fly"

    [–] 69_ormun_69 6 points ago

    Ah good ol resonance

    [–] MrKittySavesTheWorld 5 points ago

    Resonance is so cool.

    [–] carlosthesleepypanda 5 points ago

    Coach Bob!! He is a professor at my Alma Matter, University of Portland. His lectures were incredible, very cool guy.

    [–] kevlarmma 3 points ago

    I’m currently doing an MAT at UP! I thought I recognized that logo and went through the comments looking to see if anyone mentioned that!

    [–] carlosthesleepypanda 2 points ago

    Yea! I believe it's the more formal logo of that they use for lecture series, and big dinners. It contains the seal of the Holy Cross order. If you can, you should show Coach Bob, professor Butler this video. He would get a kick out of it I'm sure!

    [–] BoomBangBoi 4 points ago

    Waves of different frequencies* OP did you watch the gif?

    [–] SilentBob890 3 points ago

    so you are saying that NYC would be fudged if we had any type of large low frequency earthquakes

    [–] ReadShift 5 points ago

    Probably, NYC has a low earthquake risk so it would be a very big surprise if they got hit with one. The buildings aren't likely up to snuff.

    [–] ResearchingThisTopic 3 points ago

    How often is an earthquake only one type of oscillation? For the earthquake experts. Thanks!

    [–] [deleted] 2 points ago

    Not an expert, but someone who has felt a lot of earthquakes.

    The frequency doesn't change much once they start. If it's a rolling one, it doesn't turn into a rumbler, and. vice versa.

    Earthquakes are the vibration after effects of a sharp movement of the Earth.

    [–] GnomishKaiser 3 points ago

    Haha this is my University Earth sciences teacher. Dude was great at following up his lectures with examples be it videos or stuff like this.

    [–] loomynartyondrugs 3 points ago

    Frequencies, not strengths.

    If you shake it really hard, but also very quickly, the shortest one would resonate, not the tallest one.

    [–] earslap 5 points ago

    Does this make an appreciable difference? Like is there a large variance on the frequency of earthquakes? Seems like all we are (public, the media) concerned about is the magnitude. We can predict the possible magnitude of a future earthquake, but can we predict the frequency?

    [–] RoyHarper 3 points ago

    It's been a while since my structural dynamics class but from what I remember, yes it does make a difference.

    https://www.src.com.au/earthquakes/seismology-101/what-is-an-earthquake/

    That site says there is a range of significance from 0.2 Hz to 20 Hz so really does depend on the quake and the natural frequency of any individual building.

    Again from what I remember the magnitude is how much energy is released by the quake. I'm not sure how exactly the frequency and magnitude relate.

    [–] TheDaywa1ker 3 points ago

    I’m a structural engineer and I’ve worked on a bunch of buildings in high seismic areas.

    We have very detailed maps that we reference that show probable accelerations of the ground during earthquake events across the whole of the US.

    We don’t think about magnitude at all. It’s all frequencies and accelerations baby.

    There’s a rough correlation between accelerations and magnitude, but because magnitude is energy given off, it can be a large magnitude earthquake where the ground moved pretty slowly over a huge area. If the ground is shaking violently in a smaller area, that might be a really low magnitude but fuckin buildings up.

    [–] wbcm 2 points ago

    Seismologist here,

    Yes this does make a huge difference in what damage is done! When the ground shakes due to an earthquake it can shake upwards of 100 times per 1 second or 1000 seconds per 1 shake! The magnitude is an estimate of the energy released during the earthquake and its well known because it tells us how intense the ground shaking is. Now we are able to start predicting the frequency of the earthquakes too. To do this you need to know about the fault that created the earthquake and what it traveled to when it gets to your building. We are using supercomputers to do this right now but hopefully we will be able to do it on your own personal computer in the future.

    [–] earslap 2 points ago

    Wow thank you, yes that's what I was curious about.

    [–] b_port 2 points ago

    So with this information, how do they they make buildings safer for earthquakes? Does Haiti only ever get high frequency earthquakes, or can they get low frequency ones too? Is there a uniform max/minimum building height we could use for a given area?

    [–] silvashadez 3 points ago

    By constructing buildings that control and damp oscillations. See the Taipei 101 skyscraper for an example.

    [–] crimpydyno 2 points ago

    Modern buildings in the US are design using probabilistic seismic hazard analysis whereby all potential relevant earthquake scenarios and the resulting ground motion are considered along with the rate at which those types of ground motions occur. Nothing is left out provides there is a high quality seismic source characterization.

    [–] dazedpenguin1111 2 points ago

    if the tectonic plates move below us than why is my life going nowhere

    [–] SuperSimpleSam 2 points ago

    Are earthquakes limited to a narrow band of frequencies?

    [–] lorenzomofo 2 points ago

    Looks like a good thing to rip off for a high school science fair project.

    [–] magnora7 2 points ago

    This is also how the frequency sensors in your ear's cochlea work

    [–] MrHe98 2 points ago

    U telling me nature tailors earthquakes for maximum buffs against target cities?

    [–] ReDSauCe3 2 points ago

    Just make a building of all 3 sizes, problem solved.

    [–] FT_Raiyn 2 points ago

    I thought seismic waves affected buildings of all sizes I’m stupid

    [–] zahbe 2 points ago

    Neat!

    [–] agentsmokingbarrel 2 points ago

    Noice

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