Earthquakes, Circles and Spheres - Numberphile

Tadashi is back with a discussion of how we know where earthquakes occur. A second video is at: • Balls and Cones - Numb...
More links & stuff in full description below ↓↓↓
More Tadashi Tokieda at: bit.ly/tadashi_vids
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Videos by Brady Haran
Art and animation in this video by Pete McPartlan
Archive footage courtesy of the AP Archive.
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[@numberphile]

A second video is at: kzbin.info/www/bejne/oqbFeKGhZbqNqpI The new Objectivity video out today is also worth a look: kzbin.info/www/bejne/iZfclWBmqb10qMU

[@Jcpo23]

This video language is set to german so we can't have right automatic subtitles :/

[@KevinTwiner]

Awesomeness

[@sachingiyer]

Numberphile Is this how GPS triangulation works?

[@petros_adamopoulos]

The question is why would I NOT want to check out the other video.

[@aeyet8184]

@Numberphile - Could you please tell me of anything in reality that is 2 dimensional?

[@KryssAA]

Professor Tadashi should have his own channel, he explains things so well !

[@numberphile]

He has his own playlist here on Numberphile... bit.ly/tadashi_vids

[@brian554xx]

And that voice! He sounds like the universe explaining itself.

[@Tympan]

@@numberphile ok I’ve watched them all. So now make more!!

[@pullt]

He's well-spoken.

[@fahrenheit2101]

Legitimately the best maths teacher I've ever witnessed.

[@HeavyboxesDIYMaster]

I'm a simple man. I see a Tadashi video, I click on it. Actually, I'm a complicated man. I have thoughts, feelings, and ideas.

[@jamieg2427]

Lol this meme.

[@damienjones1487]

Heavyboxes DIY Master why is your profile pic just your ir someone else's chin?

[@HeavyboxesDIYMaster]

alien the harold ... It's me. I just wanted to make it different.

[@damienjones1487]

Heavyboxes DIY Master its weel spooky i can not know i can handle it

[@nipunajayatunge8924]

None of us are just "one dimensional" like that! XD

[@OrSomeSayKosm]

Foolish seismologist: "The earthquake originated from about 30km below the surface." Enlightened pure mathematician: "Or 30km above the surface."

[@vunop3078]

How is that "pure" mathematic when it doesnt account for the fact that not every output is right, that only heights below surface are the answere. It could as well be: Artist: Thats a Line. Mathematican: No thats a triangle with two angles of 0° and one 180° angle.

[@anlumo1]

Japan actually has had two earthquakes with an epicenter above the surface. However, the reason is not really funny.

[@Sakkura1]

The epicenter is always at the surface. It's the projection of the center onto the surface.

[@kurtu5]

Yeah the US used seismometers, and still does, to detect the hypocenter of atmospheric NUDETs. That job is where I learned my seismology.

[@WiseSquash]

projection of the hypocenter*

[@Script-MD]

MY BOI TADASHI IS BACK

[@DrKaii]

He need to come back again

[@Daniel_Rodrigues_89]

I would love to ask Professor Tadashi if he ever considered writing a book about mathematics and physics of our daily lives. I see that he clearly is one of the greatest science communicators of our time (maybe beyond that) and getting to know a little more on his personnal experiences and philosophy towards education, knowledge and such would be a treat. Of course, I hope the partnership with this channel will go on forever! P.S. Congratulations to the animation/edition guys. Superb job making an already didactic explanation even more understandable.

[@QuasiELVIS]

What would you want him to communicate? I think his genius is in how he speaks which you wouldn't get from a book.

[@Kokurorokuko]

@@QuasiELVIS what do you mean "how he speaks"? I'm sure it isn't the accent that delivers the point

[@QuasiELVIS]

@@Kokurorokuko he's just funny.

[@Kokurorokuko]

@@QuasiELVIS no only, he delivers information in a very approachable way

[@want-diversecontent3887]

@@Kokurorokuko Maybe the pacing?

[@RicoCordova]

I love his voice. It's very soothing. No morning classes from this guy.

[@guitarBoyJunior]

It's funny that the p in p-wave stands for both "primary" and "pressure", while the s in s-wave stands for both "secondary" and "shear". The two polarization components of electromagnetic waves are termed p and s as well. In that case however, p means "parallel" (same in German), while s is German for "senkrecht" (since "perpendicular" also starts with p). Thanks for the great video, btw!

[@MonkeySuperGamer]

Good job to the animator on this video! Wow!

[@expressrobkill]

Kelvin Lee i know i could watch a show with this style of animation.

[@Superphilipp]

Zilch is a rigorous mathematical term.

[@MilesQuickster]

Really now?

[@kisaragiayami]

Miles Quickster r/woooosh

[@MilesQuickster]

WTH...

[@pablogriswold421]

Miles Quickster I believe he meant to provide sound for the following situation: ------The Joke----> *WHOOOSH* -----Your head-----

[@MilesQuickster]

Oh. They think I'm serious 😒

[@JBLewis]

I love this video, I studied Surveying in college, and this theorem is right my alley. GPS positioning works on the same basis: you have multiple spheres, each emanating from the one of the GPS satellites, each meeting you GPS receiver's antenna. We can, generally speaking, determine the time it takes for each of them to reach you. With the first sphere, we can place you somewhere in space, on the surface of that sphere. When we add a second sphere, the two intersect to form a circle in space where you might be. Add a third sphere intersecting, and now we have you on either of two points. And just as we don't generally get earthquakes from above, only in exceptionally rare cases are we going to be way out in space. Instead, we can intuit that we are in fact at the one point of the intersection of three spheres... that intersects with a fourth spheroid, namely the earth! Now, since there are lots of variables involved with the measuring the time is takes for each of those radio signals (spheres) to reach you, we can use the redundant data from the spheres of additional GPS satellites to refine our calculated position. So too, 4 or 5 or more seismometers are used to pin point the epicenter of an earthquake!

[@Indian_Ravioli]

Tadashi always amazes me.

[@numberphile]

Us too!

[@jackren295]

I actually observed this property of three intersecting circles and tried to proof it myself, and failed. Tadashi's explanation just blew my mind! I always loved space with different dimensions, and this video encapsulates my feeling.

[@alameachan]

I dare say if your epicenter is above ground you shouldn't calculate but run for the nearest fallout shelter.

[@christianbarnay2499]

Also your distance measurement is all wrong because waves travelling through the air and through the earth have different shapes and speeds.

[@Sakkura1]

*Center. The epicenter is always at the surface, because it's the projection of the earthquake's center onto the surface.

[@kurtu5]

Hypocenter is the word you are looking for, and yes its also used for atmospheric nuclear detonations.

[@kurtu5]

@@uku4171 I think that for an atmospheric nuclear detonation, the epiccenter is the point on the earth's surface closest to the hypocenter(the center of the detonation). So in this case its above.

[@petros_adamopoulos]

"Usually we don't get earthquakes from above" he said very matter-of-factly.

[@stlCkofdOom]

Great as always, but I really enjoyed the low-tec visuals!

[@hanniffydinn6019]

stlCkofdOom they are called sweed

[@IDoNotLikeHandlesOnYT]

Really? I thought they were some of the least helpful visual aids I've ever seen, and I already had some knowledge of the stuff being discussed.

[@SavageMontreal]

12:51 "What does it have to do with this theorem? Everything has to do with this theorem."

[@myuu22]

I live in northern California, near the Hayward Fault. Before that, I lived closer to the San Andreas Fault. And in my experience living in earthquake zones, the P-wave is more up/down and the S-wave is more side/side. Tadashi's illustration makes sense, but I have a theory that the reason it's reversed in the illustration is because it fails to take depth into account. The closer to the epicenter you are, the more you feel the waves coming from below you, the more vertical the P-wave will be, and the more up/down motion it will cause.

[@shanematthews1985]

Now if i had teachers like Tadashi i might actually have learned something in school lol

[@rtt1961]

Yes, this guy intermediately impressed me as very clear.

[@flappy7373]

was that a yoke m8?

[@MsBombastik]

no you would not, dont blame your/your parents incompetence on teachers

[@meinbuch9458]

Cypherous Blaming your teachers doesn't solve the problem,you ever heard of self-learning?

[@shanematthews1985]

Self learning the age before technology when you had no means of long distance transportation, back then all we really had were schools and the library, but without any kind of "reference" how would i have even been aware that something was seriously wrong, i mean we're not talking recent times here we're talking 2 decades :P

[@princechisanga7717]

I would love to have a lecturer who teaches like professor Tadashi. He is excellent at explaining things

[@dLichti]

The epicenter is, by definition, always on the surface (of the earth). The point below the surface, where the earthquake happens, is called hypocenter.

[@CrizTaylor]

no but, it is up above ground, in the air.

[@algotkristoffersson15]

But if they are above and below the center respectively, where is the center?

[@bandarubidda8039]

'Usually we don't have earth quakes from above', this made my day :) this guy is my new favorite on Numberphile

[@topilinkala1594]

There is a ban on athmospheric atomic bomb tests, so if we assume everyone holds the ban the "quake" must have been underground. Seismographs are easy way to detect atomic (or hydrogenic) bomb tests.

[@GratefulNachos]

As a geologist this is a wonderful explanation. Love it!

[@westerp]

I'm a 42 year old man and I just love the playfulness of Tadashi's videos. There can never be too many Tadashi videos so make more :-)

[@0xBADFECE5]

small error in terminology: epicenter refers to the point on the earth's surface directly above the source of the earthquake, itself called the hypocenter. so if a line is constructed between the 2 meeting points of the spheres, the bottom point will be the hypocenter and the point at which the line intersects the surface of the earth will be the epicenter. edit: more trivia: for mid-air explosions, it's the opposite; hypocenter on surface, epicenter is explosion source. the math works out the same except sometimes instead of counting the seconds between the flash and the rumble, you start counting when you go blind and stop counting when your organs rupture. or you don't have time to count.

[@Sakkura1]

You can also just call it the center or focus, hypocenter is an unnecessary backformation.

[@kurtu5]

hypocenter is nicer because any nuclear scientist or geologists will know immediately what you mean. If you say focus or center, it could be anything.

[@deejuggle]

r77xxl thanks! This is exactly the sort of semantic trivia that I love. Will definitely use.

[@ELFanatic]

I'm pretty sure that's what he's explaining at the very end

[@JackFlashTech]

The hypocenter is at the intersection of the spheres, but the epicenter is at the intersection of the chords of the circles, so I’m not sure he’s as off as all that.

[@Kaesekuchen002]

The explanations of Tadashi are always so amazing. Great video!

[@justcarcrazy]

Tadashi-sensei is a great explainer. I could never interpret the difference between pressure waves and shear waves.

[@LycroF]

This was the very first time watching one of your videos. I've been subscribed to it for a little while, but never got around to it. Absolutely fascinating.

[@mateuszolszewski1314]

Lovely animation, it's great to see this channel improving.

[@bencardwell5545]

Wow. This is one of my favorite Numberphile videos. I am getting the tingles, because the connections he is able to make and explain so clearly are elegant and insightful

[@ScottTilYouDrop]

Love the editing and visuals 😍😍 Thank you xoxo

[@tiberiu_nicolae]

I love how professor Tadashi explain things and the animations were awesome

[@14m600l]

Man, the animation here is so brilliant. I'm always impressed by the animation for the Tadashi videos. Keep up the great work!!

[@t4g3d]

I love the recent increase in Numberphile's animation production value! 💕👌

[@ABCD-bl5rw]

I really enjoyed this video and the creative visualisations too.

[@BKITU]

This was so beautifully executed. His teaching method is so clear, so *graspable*, that I sincerely just want to sit at his feet for a few years and take it all in.

[@GothicKin]

Absolutely brilliant, I love prof. Tadahi's videos and great work with the animations.

[@ramata1962]

I know it's been over a year since this was made but this professor is so much fun. He's very clear and easy to understand.

[@will4not]

The animations are amazing. Just add perfectly to the great content.

[@FinetalPies]

Tadashi is so gifted, they can teach me things I don't understand and, (as is the case today), keep me entertained and interested even when explaining something I already understand.

[@Sam_but_not_really]

This one has great animations. Well done!

[@andreas_arvidsson]

Great video and easy to follow. The animations are superb. The tectonic plate spazzing around had me laughing out loud.

[@nab-rk4ob]

I love his illustrations and animations. I think I say that on every video you put out with him in it.

[@PhillipJohnsonphiljo]

Fantastic! Thank you Professor Tadashi!

[@DutchMaster6]

one of the best numberphile videos of all time

[@flappy7373]

understood this *completely* this man is a wonderful, wonderful teacher. Tadashi.

[@darikdatta]

Pretty sure I heard a Wilhelm scream.

[@BeCurieUs]

Visuals of this make me feel like I am back in Beakman's world, basically, I loved them!

[@Endureromex]

Every single school and university should have someone like professor Tadashi

[@silasfrench2719]

I couldn't stop laughing at the spasmodic ring of fire

[@pbjandahighfive]

Tadashi is straight-up my favorite Numberphile guest. He always brings something interesting to the table. I wish he was one of the "regulars".

[@TheGreatDefective]

Great video and especially great production

[@alisonsheep]

Brady, you have just the coolest job ever.

[@EchosTackyTiki]

That idea of measuring the seconds between two waves or between the lightning and the thunder actually has an interesting application in military combat scenarios. Due to the fact that most sniper rifle bullets move at well in excess of the speed of sound, you actually use the elapsed time between the supersonic crack of a bullet going past you and the thump of the rifle that fired it going off in the distance, and you can actually estimate the distance that the enemy sniper fired at you from. If you take that most rounds that might be fired at you from long range have a muzzle velocity of between 700 and 800 m/s (we'll call it at the average of 750 m/s), and the speed of sound is about 343 m/s, and then you account for all the things that slow a bullet down after it leaves the muzzle, like air resistance, wind, gravity, etc., then you get a delay of somewhere just over 300 meters for every second between the crack of the bullet whizzing past you and the thump of the rifle going off. When you hear a crack, start counting (as you take cover, of course). 2 second elapsed means the enemy sniper is approximately just beyond 600 meters from your position. Snipers call the technique "Crack-Thump", and it's extremely useful in helping to find the enemy sniper who's shooting at you so you can engage him and win the fight. Most of you will never need that information, but for what it's worth there's actually a lot of really cool applications for math, mainly for geometry and trigonometry, in long range shooting.

[@wbwarren57]

Fantastic video! Thank you.

[@ritan5643]

The animations are sick..🔥🔥🔥

[@jjfoerch]

Love the graphics in this one.

[@spmcdade901]

Great subject matter, great video. Thanks

[@Porglit]

His drawing with him and his baby is absolutely adorable.

[@pegy6384]

Really lovely animation, and a very nice explanation for a Californian who should have known this by now.

[@7177YT]

ah wow, this is another brilliant one, and despite the simple exposition equisitely intellectually stimulating. well done!

[@letMeSayThatInIrish]

This was beautiful.

[@FEYSCONTROL]

Super interesting! I am not sure how exactly I got to this channel but definitely I am subscribing now!

[@jms547]

Ah! The animations!

[@UK_Bollington]

Thank you for sharing this great video!

[@ryanbrunette3870]

Loving the editing in this one.

[@BlessedForever888]

The animator behind these videos is also brilliant. Your hard work is much appreciated!

[@wvvwkx]

I love Tadashi's explanations

[@StephenRoderick-td4nb]

Earthquake so strong that it makes Japanese women scream like Wilhelm..

[@camillagreer9028]

Love the new visualization style!

[@MrJayPuff]

That was extremely fascinating great video!

[@prestonferry]

I love the beginning!

[@OcteractSG]

Nice. That gives both the epicenter and focus of a quake.

[@feliciabarker9210]

The animations in this one were fantastic

[@flamencoprof]

Thanks for an excellent presentation.

[@MartinIDavies]

this is fantastic.. a maths teacher with passion and ability to explain complexity with ease.. considering the copiousness amount dross on KZbin this is quality.. thanks for posting. am looking forward to more :-)

[@Yobleck]

love the animations!

[@oplemath]

Both the math and the earthquake calculation were stunning!!

[@nicholasdunn999]

I have learned SO much about earthquakes, thank you!

[@Morrvard]

Beautiful animations and stop motion!

[@gamechep]

That was so beautiful and informative!

[@Algebrodadio]

Beautiful. And very well explained.

[@rDnhey]

Beautiful video!

[@vulkandrache1928]

I first learned about this kind of spherical triangulation while playing Eve online. Was really helpful in visualizing the scanning probes functionality.

[@MichaelBerthelsen]

Currently living in Japan, this was quite interesting!😊

[@johnhammer8668]

he draws with words. Its so clear

[@PalestinianLad]

Just experienced an earthquake and used his method to check how far the earthquake was, and what do u know, it was spot on 😂

[@Missi1981]

this guy is a gift.. Thank you

[@CADable]

Excellent demonstration Professor!

[@janus2059]

Tadashi is always great

[@PetraKann]

He never disappoints - yet another very interesting mathematical theorem and its application

[@dle511]

aww, we have baby Tadashi now will this channel still be around when he/she is able to grasp these ideas..

[@sourandbitter3062]

What a great explanation!

[@claycon]

Beautiful video! Thx

[@b1aflatoxin]

I'm surprised at how fast this made sense to me! :) Thanks!

[@19darius92]

The animations look very good!

[@jtveg]

I love this professor and his awesome stories. 😎👍

[@buzhichun]

Tadashi's little drawing is adorable!

[@owlsseeyou]

I didn't know i needed to know this it's also kinda cool!

[@deepsheep9102]

Great video, I accept to wait for the next video that shows that we can reject the point from above using 4-dimensional spheres.

[@ideallyyours]

As described in the video, 3 spheres intersecting forms a singular line of contact. To determine a singular *point*, you just need to use the intersection of a 4th sphere across that line. No 4th dimension is necessary.

[@66fee99]

awesome explanation!

[@mallowthecloud]

Tadashi has always been my favorite, and now I know he felt the same earthquake as I did last October. :P