In a matter of seconds, an earthquake can release more energy than thousands of nuclear bombs, level entire cities, and hurl walls of water across whole oceans. Earthquakes and the tsunamis they spawn are among the deadliest natural disasters humans face — and understanding them is the first step to surviving them. This course explores their raw power, their human cost, and how to stay alive when the ground moves. (It complements our course on plate tectonics, which explains why the Earth's plates move; this one focuses on the quakes and tsunamis themselves, and on people.)You'll begin with the sheer scale of earthquakes — just how big can they get? — using a famous thought experiment about a magnitude-15 quake. You'll see why buildings collapse, through the lens of the devastating 2023 Turkey-Syria earthquake, then learn the cruel physics of tsunamis: how an undersea quake becomes a wall of water. Finally, you'll learn what actually keeps people alive when a tsunami strikes. Honest note: the science here is well-established. The opening magnitude-15 scenario is a deliberate thought experiment — no real earthquake comes close — used to make the magnitude scale intuitive. The 2023 Turkey-Syria earthquake killed an estimated 60,000 people, a real and recent tragedy. The survival lesson is genuinely useful but is no substitute for the official guidance of your local authorities.
this is a question from Alex who asks what if a RoR magnitude 15 earthquake were to hit America at let's say New York City what about a RoR Zer or 25 well given that a magnitude 25 Quake would destroy the sun if one happened there it would certainly destroy New York City but we're getting ahead of ourselves the RoR scale which has technically been replaced by the moment magnitude scale measures the strength of an earthquake since we usually hear about earthquakes with ratings somewhere between 3 and 9 a lot of people probably think of 10 as the top of the scale and Z is the bottom in fact there is no top or bottom to the scale but even if 10 isn't the top of the scale it might as well be a magnitude 9 earthquake already measurably Alters the rotation of the earth the two magnitude 9 plus earthquakes this Century both altered the length of the day by a tiny but measurable fraction of a second in order to get to magnitude 10 you'd need a ruptured fault line 32,000 km long and a magnitude 11 Quake would require a fault that went Halfway Around the World a magnitude 15 earthquake would be a million times more powerful than that and involve the release of enough energy to evaporate all the water on Earth though if that happened we could rest easy knowing the earthquake couldn't cause any tsunamis going a few steps further a magnitude 18 earthquake would release nearly 10 to the 32 Jew of energy which is roughly the gravitational binding energy of the earth to put it another way the Death Star caused a magnitude 18 earthquake on alderon you could in theory talk about a more powerful earthquake on Earth but in practice all it would mean is that the expanding cloud of space debris would be faster and hotter the sun with its higher gravitational binding energy could have up to a magnitude 24 Quake this is about the energy release you would get if you packed the entire volume of Jupiter with hydrogen bombs and detonated them all at once the most powerful Quakes in the known universe which occur in superheavy neutron stars are about this magnitude a magnitude 25 Quake would explode the sun hold on we're spending a lot of time thinking about things that are large and violent what about the bottom end of the scale is there such a thing as a magnitude zero earthquake yes in fact the scale goes all the way down past zero let's take a look at some low magnitude earthquakes with a description of what they would be like if they hit your house a magnitude one Quake releases the same energy as dropping a partially loaded cement truck from 10 m onto the street in front of your house a magnitude zero earthquake is equivalent to the Dallas Cowboys American football team running at Full Tilt into the side of your neighbor's garage a magnitude negative 1 Quake is like a single American football player running into a tree in your yard a cat falling off a dresser would have a magnitude of -2 a cat knocking your cell phone off your nightstand would have a magnitude neg3 magnitude -4 is like a penny falling off of a dog magnitude-5 is a key press on an IBM modelm mechanical keyboard -6 is a key press on a lightweight keyboard -7 is a single feather fluttering to the ground A fine grain of sand falling onto the pile at the bottom of a tiny hourglass would be a magnitude 8 quake and let's jump all the way down to magnitude -15 a drifting mode of dust coming to rest gently on a table sometimes it's nice not to destroy the world for a change [Music]
Tsunami waves that form in the open ocean travel at high speeds but are barely noticeable. Now the wave is approaching the shore where the water depth decreases. Surprisingly, the wave that initially seemed harmless suddenly gains a huge amplitude. A devastating tsunami. The slowmoving ocean beds sometimes interact like this. One tectonic plate sliding under another. Notice the bulging upper layer. How long will this motion continue? These stuck wooden pieces demonstrate what happens. Let's keep on tightening them. But after some point of time, boom. Similar to the experiment, the ocean beds release all the accumulated energy in a short period of time. This is how tsunami waves are formed. If by magic you could drain the entire ocean, you would clearly see different pieces of the Earth's surface. They are called tectonic plates. The Earth's surface is made up of different tectonic plates moving relative to each other. Precisely seven major tectonic plates. The molten lava in the Earth's core circulates continuously due to convective heat transfer. The tectonic plates float on the molten core like ice floats on water. Due to the continuous motion of lava, the tectonic plates are constantly moving. For example, in this animation, two tectonic plates are diverging away and a rift valley is being formed. The East African rift valley is a great example of this kind of motion. Now look at this tectonic plate movement. Here the plates are converging. This kind of interaction can result in the formation of mountains, trenches and sometimes active volcanoes. The best example of this kind of converging motion is Cascade Range Northwestern USA. The movement of tectonic plates is very slow, just a few inches per year. Now an interesting observation. Mark dots on all the earthquakeprone areas of the globe. You will find that they all lie in regions where two tectonic plates meet. Yes, the relative motion between two tectonic plates and associated energy release results in earthquakes. When an earthquake happens deep in the ocean, it may lead to a tsunami. The tectonic plate movement that causes the tsunami is very interesting. It's called subduction zone movement. We've already seen this kind of converging movement, but this time it happens underwater. In this movement, strain energy accumulates in the top tectonic plate over time. Here the continental crust bulges upward and the oceanic plate sinks beneath it. This happens because the oceanic plate is much denser than the continental crust. You may observe one interesting feature of the continental crust. It bends inward resulting in the formation of huge trenches along the tectonic plate boundary. Look at the beautiful trenches formed on the ocean floor of the Pacific Ocean. But how long does this energy accumulation continue? Some subduction zones store energy for centuries. In other subduction zones, the strain energy is released gradually over time. This slow slip event does not result in a tsunami. However, in some regions like the Japan trench and the Chile Peru trench, the energy is released in a fraction of a second. Such earthquakes definitely result in a tsunami wave. The waves so generated will have a speed of more than 200 kmh, but it's barely noticeable due to its low amplitude. Tsunami waves typically have an amplitude of less than half a meter, but a wavelength measuring hundreds of kilome. However, when the wave approaches the shoreline, the story changes. What's the impact of the decreasing water depth on the wave? Let's generate a wave to find out answer for this question. Note on the time taken by the wave to reach the other end of the tank is 1.9 seconds. But when the water depth is half, the wave takes more time to reach the other end. [Music] Let's compare it together. This means when the water depreces, the whale speed decreases. Similar to the experiment, as the wave approaches the shore, its speed decreases significantly. The frequency of the wave remains constant throughout this process. This means the wave has to decrease its wavelength in the shallow region. However, since the overall energy remains constant, the only option to maintain the constant energy is to increase the amplitude of the wave. This phenomenon is called wave sholing. This is the reason why the tsunami wave becomes so huge near the shore. A slowmoving wave with an unbelievably high amplitude. Finally, this wave crashes onto the shore wreking destruction. [Music] It should be noted that in a wave there is no horizontal movement of matter. If you place some balls along the wave path, they will just oscillate in their own positions. The formation of a tsunami is truly the cruelty of physics. No water particle is moving forward, but due to the circumstances, the wave amplitude becomes so high that it crashes onto the shore. There is a popular belief that if you see the shoreline receding dramatically at a beach, you can expect a tsunami soon. There is truth in this belief. Sometimes the trough of a tsunami reaches the shore first. This means you will suddenly see the shoreline receding. After a few seconds, the crest of the tsunami will reach the shore. However, it should be noted that not every tsunami is preceded by a receding shoreline. Sometimes the crest of the tsunami arrives first. The Indian Ocean tsunami of 2004 was the most devastating tsunami mankind has ever witnessed. It rose more than 30 m and killed over 340,000 people. The tsunami was caused by a massive undersea earthquake near Sumatra, Indonesia. This earthquake was extremely strong, measuring about 9.1 to 9.3 on the RTER scale. In Sumatra alone, more than 100,000 people were killed. The earthquake occurred because the Indian plate was forced underneath the Burma plate which suddenly moved and pushed the seafloor upward. It lasted almost 10 minutes, making it one of the longest earthquakes ever recorded. The energy released was equivalent to 23,000 Hiroshima atomic bombs. This sudden movement displaced a huge amount of water, creating enormous waves that spread across the ocean. In some places, the waves were as high as 30 m. These waves moved very fast, traveling up to 800 km hour. Coastal areas near the epicenter, like Indonesia, were hit within minutes, while places farther away, like India and Africa, were struck hours later. A size comparison animation of all the major tsunamis mankind has ever witnessed is shown here. [Music] Underwater earthquakes are the major cause of tsunamis. However, it should be noted that there are three other causes that can initiate tsunamis. Volcanic eruptions under the sea are another major cause that can initiate a tsunami. When an underwater volcano erupts, it can blow apart or collapse, pushing water outward and forming large waves, eventually creating a tsunami. Sometimes landslides under the ocean or near the coast can also cause tsunamis. If a large amount of rock, mud, or ice suddenly falls into the sea, it pushes the water and creates waves. These waves can be dangerous if they reach land. Although very rare, when a large mass falls into the ocean, it can also cause a tsunami. For example, a meteorite. The tsunami in the Vajot dam was formed in a similar way. A huge mass from a landslide hit the water body. When a big mass hits the water, it creates a splash that can turn into huge waves. Luckily, this kind of tsunami doesn't happen often. Back in 2004, there was no tsunami early warning system in the Indian Ocean. The 2004 tragedy was a wake-up call for all nations. They launched buoys to detect deep ocean changes as early as possible. Pressure sensors on the ocean floor detect any change in water level height. This pressure data is sent to the buoy which is fitted with an antenna and then relayed to a satellite. Remember in the 2004 tsunami the wave took approximately 20 minutes to reach Sumatra, 1 to 2 hours to reach Thailand and 2 to 3 hours to reach Sri Lanka and India. If the dart buoys can transmit information faster than the tsunami wave travels, authorities would be able to evacuate people in tsunami prone areas. Here comes the big question. Is it possible to prevent tsunamis? Japan thinks so. After the devastating earthquake and tsunami of 2011, Japan decided to build a seaw wall 400 km long with a maximum height of 15 m to reduce tsunami impact. Before 2011, the height of this wall varied from 5 to 10 m. And the tsunami, which had a height of 15 m, easily overwhelmed it. The 2011 tsunami also destroyed many seaw walls along Japan's northeastern coast, including the famous double seaw walls in the Taro district. It should be noted that Japan's early warning tsunami system initially predicted a wave of just 3 m in height and people assumed that it wouldn't cross a sea wall. This raises a valid question. If a technologically advanced country like Japan can miss a tsunami height, what about the early warning systems installed in the other part of the world? I hope this video about tsunami was quite informative to you. To support my educational activities, please check out our Patreon page and pledge your support today. Take care.
[Music] you're on a beach not a worry in the world the Sun bronzing your skin sand trickling between your toes the sound of waves wait what where did all the water go did you see it going out better act quickly in a matter of minutes you may be underwater here's how to survive a tsunami according to science tsunamis are triggered by intense underwater activity usually an earthquake or an underwater volcanic eruption these events displace huge volumes of water pushing it up from the oceans floor to its surface but when gravity pulls it back down all this built-up energy is released outwards forming deadly waves that grow stronger as they ripple across the ocean a tsunamis waves can be 100 kilometres long and sometimes taller than 30 metres they can travel across whole oceans moving at the speed of a jet airplane so with such speed strength and stamina how does anyone stand a chance even in a tsunami hazard zone you can still survive if you know what to do the first step to survival is to be able to identify the early signs of a tsunami the Pacific Ocean is home to volatile tectonic activity which explains why 75% of the world's volcanic eruptions and 90% of the world's earthquakes occur in the Pacific these geological disturbances are the reason why 85% of all tsunamis happen in the Pacific Ocean in most cases an earthquake comes before a tsunami so if you're near the coast and you experienced an earthquake protect yourself from that first but once the shaking stops move to higher ground as quickly as possible the beach will grow bigger run the other way an early sign of an impending tsunami is that the water along the coast will recede it pulls back and exposes the sea floor do not go to the beach to investigate you'll only be putting yourself at risk for when the water surges back instead head in the opposite direction try to get as far as three and a half kilometers from the ocean or thirty meters above sea level to an sure your safety get to the highest elevation possible tsunamis travel quickly and you may not have enough time to clear the hazard zone in this case look for a tall building with a sturdy concrete foundation if you see one nearby run inside and get to the roof as quickly as possible if you can't make it to a building in time your best bet is to grab on to something and hold on though that might not sound very practical hold the eye roll for a moment in the 2004 Indian Ocean tsunami an Indonesian woman was finally rescued after holding onto a palm tree for five days straight while it isn't ideal if you can't get to higher ground in time you need to find something to hold on to as the tsunami moves inland it will sweep tons of debris along with it this can be very dangerous as the accumulation of debris traveling at high speeds become fatal obstacles for anyone who's caught in the current however many tsunami victims have been saved by climbing on two detached roofs or holding on tightly to floating cars or other large objects of course if you've made it this far your troubles aren't over yet a tsunami isn't one wave but a series of waves known as a tsunami wave train waves may be anywhere from five minutes apart to an hour apart and be aware that the first wave that hits isn't always the strongest so even when you think it's over stay where you're safe until you hear from local officials it goes without saying tsunamis are terrifying and when a 30 meter wave is hurtling towards you at 800 kilometres per hour you're probably feeling pretty helpless but have faith in science trust empirical research and you'll see there's always a way out we'll keep showing you one episode at a time on according to science