Intro Quiz: How can we measure and predict earthquakes?

Video: How can we measure and predict earthquakes?

﻿Hi, everyone, my name is Miss Earthrowl. Welcome to lesson eight in the Key-Stage-3 unit of work on Plate Tectonics. Today we're going to be looking at earthquakes. We're going to look at how they work and how they can be measured and predicted. For today's lesson, you'll need a piece of paper and an exercise book to write in. You'll also need to find yourself a pen or a pencil. If you can find a quiet space away from any distractions that will really help you focus on your learning. So gather those items, get yourself ready, and press play when you're all set to go. The big question for today's lesson is how can we measure and predict an earthquake? But before we work that out, we need to look at what causes an earthquake. So an earthquake is a sudden or violent movement within the Earth's crust followed by a series of shocks. Earthquakes can cause a lot of damage, as you can see in this image here, a car has been entirely crushed by falling building and the reason that building fell down was because of the shaking of the earth, an earthquake. So what are the stages of an earthquake occurring? So let's go through the step by step process of how an earthquake happens. I want you to imagine two of the Earth's tectonic plates pushing towards or past each other. I'm demonstrating this using the diagram at the bottom of the screen, you can see that two squares are being pushed into each other at great force. Strain energy builds up where they meet. You can see this on the diagram with the pink oval, but in real life, we cannot see it but we know it's there, is a bit like when you go to click your fingers, if you put your thumb and your finger together, you can feel the pressure building up, this is strain energy. With tectonic plates, the edges of the place are rough and so friction keeps the plates stuck together. The strain energy builds up increasing the pressure. Again back to our clicking fingers. If we're pushing them together, we can kind of feel the friction between our finger and thumb. Essentially, there's a sudden release of pressure and energy and the plate jolts forward a bit like our fingers suddenly clicking. You can see this on the diagram here. It's a sudden movement and that is an earthquake. You can see this on the diagram represented by the red circles. These red circles also show the seismic waves. Now seismic waves come out in all directions and they can cause a lot of damage. Your main task is to put the following statements in the correct order to explain the process of an earthquake. Now, this is really challenging, so I want you to not only use what you've learned today, but try and think through the logic as well. The first one is correct, and has been highlighted in pink. So pause the video to complete your task. Don't forget to press resume when you're done. Excellent, Well done for having a go. Let's see if you've managed to get them in the correct order. So the first one was done for you. Two tectonic plates push into or past each other. Strain energy builds up where they meet. In real life, we cannot see it but we know it's there. Remember, it's a bit like clicking your fingers, you can feel the pressure and the strain energy building up as you're pushing your finger and thumb into each other. Friction keeps the plates stuck together and the strain energy builds up increasing the pressure, I can still feel the pressure increasing between my finger and thumb. Eventually, there's a sudden release of pressure and energy and the plate jolts forward. Just like the sudden release of energy when you click your fingers. This sudden movement when it's in the Earth's crust, is an earthquake. An earthquake sends out seismic waves in all direction. I hope you managed to get those right. Give yourself a tick for everyone in the correct order. If you want to, you can pause the video here and double check your answers and make sure you write down the correct sequence of events if you need to. There're a lot of key words involved in earthquakes. So let's learn some of them. The focus is the source of the earthquake beneath Earth's the surface, this is shown on the diagram the arrow and it's the middle of those red circles or seismic waves. The epicentre is the point directly above the focus. Here you can see it represented on the diagram by the line. And the seismic waves, the fast waves of energy generated at the focus of the earthquake, and they move outwards in all directions, and they're the ones that cause the damage. So these are all key terms, and I've got a more sophisticated diagram here to help you. You also have listed on the diagram, a fault. Fault lines or breaks or fractures in the Earth's crust. What I'd like you to do is pause the video, you need to make sure you've got those key terms written down because we're going to be using them throughout today's lesson. You can also draw the diagram if you would like to. I find diagrams really useful to help me imagine what's going on in the real world. So pause the video to complete this task, and press resume when you finished. Excellent, well done. Let's see how many times we use those keywords in today's lesson. Let's see what you've learned. The epicentre is... one of these definitions is the epicentre. Let's see if you can work out which one it is. Is it, breaks or fractures within the Earth's crust? Fast waves of energy coming out from the focus in all directions? The source of the earthquake beneath the Earth's crust or the point on the Earth's surface directly above the focus? The epicentre is, option for the point on the Earth's surface directly above the focus. Option one, a foot lines, face breaks and fractures within the Earth's crust. Option two are the seismic waves that come out of all directions. And option three is the source of the earthquake beneath the Earth's surface is the focus. Well done if you managed to get that right and give yourself a pat on the back. How are earthquakes measured? A seismometer is an instrument used to detect any sudden movement or vibrations in the Earth's crust. A seismometer is the cylindrical item here, the black instrument that you can see in the foreground of this image. This instrument is buried underneath the ground in different places, normally along those plate margins where earthquakes are known to occur. It detects any movement or vibrations in Earth's crust. This seismometer that's out buried in the ground send signals back to a seismograph and a seismograph records the information from a seismometer, a seismograph can also be seen in this image behind the seismometer. Watch this quick video clip that explains how it works. This video shows us the seismograph in action. As you can see, the ink feeds down the needle and through onto the paper, recording all of the seismic tremors in the Earth's crust. So these are really important instruments that help us measure earthquakes. Pause the video and write down the two key definitions. Excellent, well done. We're now going to look at the Richter scale. The Richter scale measures the magnitude of an earthquake. The magnitude is how powerful those seismic waves are, so measuring this tells us the power of an earthquake. You can see in this diagram here, it goes from number one, which is a relatively small tremor, or seismic waves and not very powerful up to 10, which is very powerful, less frequent, but cause a massive amount of destruction, as shown by the pictures where you've got cars falling off bridges. This is the Richter scale, and it measures the magnitude on what we call a logarithmic scale. Which means that for every equal increase in number, the power is 10 times as strong. So an earthquake that measures five on the Richter scale. If it goes up to six, it becomes 10 times more powerful than an earthquake that measures five, that's pretty strong and it's really important because it allows seismologists and scientists to measure earthquakes that are very small and very big, all on the same scale. Which two statements are true? the Richter scale, one, shows the magnitude or power of an earthquake on a scale of one to 10. Two, is an instrument which detects movement within the Earth's crust. Three, is the record created by seismograph, or four, is logarithmic, meaning each number is 10 times more powerful than the last. Hopefully, you managed to get that it's option one, it's measured on a scale of one to 10 and it's logarithmic, meaning each number is 10 times more powerful than the last. Option two is actually the definition for a seismometer, whereas option three is a seismograph. These are the instruments that helped measure the power and the magnitude of the earthquake, which tell us how strong it is but it's the Richter scale measured on a scale of one to 10 that helps us to understand what those measurements mean. We also have the Mercalli scale, the Mercalli scale measures how people feel and react to an earthquake, and the damage it causes. This is measured on a scale of one to 12. So for example, if three on the Mercalli scale, you might feel some shaking, your glass of water might get knocked over, or you're fast as you can see in the picture, but you're not really affected that much by the earthquake and there isn't much damage that's caused. If we go for five on the Mercalli scale, you can see that this can really feel the earth shaking. Flowerpots might get knocked over, and small bits of furniture might get knocked over as well. You might also have some broken windows, you can see that as you move up the scale, the damage becomes greater. If we go for 11 on the Mercalli scale, you can see that the damage becomes much greater. You've got broken buildings, you've got big cracks in the earth and you can also see that you've got fallen roofs. This scale is a lot easier for people to understand that aren't necessarily seismologists or scientists studying volcanoes. It really allows people to understand and put into context, the strength of the earthquake. The largest earthquake ever recorded and I need to disappear for this because it's right at the top of that diagram, with 9.6 on the Richter scale. That's incredibly disruptive. It was in Valvida in Chile in 1960. So it was quite a long time ago but it's still remembered because it's the largest earthquake that has ever been recorded. Approximately 1,655 people were killed, and 2 million people were left homeless. That's because it was so high on the Richter scale and it would have been high up on the Mercalli scale as well because you'd have seen a lot of damage to buildings and property, as well as unfortunately people being killed. So let's see which two statements are true. One, the Mercalli scale goes from one to 10. Two, the Richter scale goes from one to 12. Three, the Mercalli scale measures how people feel and react to an earthquake and the damage it causes, or four, the world strongest earthquake ever recorded was 9.6 on the Richter scale. Option three is correct. The Mercalli scale measures how people feel and react to an earthquake and the damage it causes. Remember these pitches going up the scale, it really helps people to understand and put into context, what it's like to be in an earthquake of different strengths. The world's strongest ever recorded earthquake was 9.6 on the Richter scale, and it was in Chile in 1960. Option one and two are incorrect. The Mercalli scale actually goes from one to 12 and the Richter scale goes from one to 10. So those two numbers are swapped round. Well done if you manage to get those rights. So the big question is can earthquakes be predicted? We know that most earthquakes mostly occur at plate boundaries where two plates meet. That's because they're pushing past each other, causing that friction and the strain energy to build until you get a sudden release or jolts, so we know where they're likely to occur, but it's very difficult to predict or forecast when an earthquake will strike. This is because there are no clear or reliable warning signs. There are some warning signs though, seismographs can be monitored for irregular tremors. You can see these two pictures here, the needle feeding through to draw the graph on a seismograph. You also get seismographs being electronically recorded, as you can see here in the second picture. This shows us and highlights different colours for different types of tremors. So some people find that a computerised version is a lot easier to read. Now, seismologists study this, you often get Earth movement. But when there is an increase in tremors, and those lines become wider, that's when it could indicate that earthquake is likely to occur. Also, when the movement of the Earth's crust, rocks get pushed together, when the rocks are pushed together, it leads to an increase in pressure within the rock, just like the cause of an earthquake with the pressure between our thumb and finger, it's the same thing that's occurring, but the rocks get squashed. This can cause radon gas to be released, and it can be measured, so therefore, if it's measured and we start to notice an increase in that particular gas, we could say that the pressure underneath the earth between the two tectonic plates is becoming greater. It can also cause groundwater levels to rise or fall. In particular, we think about those rocks being squashed together. Inside those rocks, you've got tiny bits of water, believe it or not, and sometimes they can get pushed up and that can indicate that the pressure is becoming much greater. The last warning sign that could potentially indicate an earthquake is, animal behaviour. So you can see here in this picture, you've got loads of bats suddenly escaping out of the tree, you also get lots of erratic behaviour from dogs, whether they're big dogs or small dogs. There's lots of barking and lots of running around. It's almost as if the animals have a sixth sense to changes in our Earth. So let's do a very quick summary of those warning signs. Complete the following paragraph. You can see the words at the bottom that you need to fill it in with, so pause the video now to complete your task. Excellent, well done. Let's see what you've got right? Did you get it? There are thought to be some warning signs that an earthquake will strike, seismographs can show irregular tremors when rocks are pushed together. The pressure on the rocks means that radon gas can be released and the water levels can change. Animals can also behave very erratically. If you manage to get those right well done and give yourself some big ticks. Even though there are some warning signs, it is very difficult to predict when earthquakes will happen, because the warning signs are unreliable. So we know that they might happen along plate boundaries but we don't know when they're going to strike and it's very hard for us to predict. Although earthquakes and very hard for us to predict in advance. There is one warning sign but it is very last minute. If you look at this diagram and just remind yourself of what those key words mean, seismic waves, are the first waves of energy that come out of the focus and there's actually two types of seismic waves that we're going to look at to explain this last minute warning sign. These are primary waves or p-waves. They're the fastest wave and so they arrive at the epicentre first, these waves are not very destructive. Then we have the secondary waves or s-waves. These take a little bit longer to arrive at the epicentre second, these are the ways that cause the most damage. Therefore, the p-waves arrive just before the disruptive s-waves. If scientists can detect p-waves, they have about a minute to warn people to take cover. This means that people can get themselves in a safe position such as underneath the table. So although it is a warning sign, and helps us to predict that earthquake that really destructive secondary wave of the earthquake is about to arrive, it's so last minute although it is a prediction, it doesn't really allow people to leave the area. That brings us to the end of today's lesson. Well done for all of your hard work. Today we've learned about earthquakes and how they work. We've also answered this question, how can we measure and predict an earthquake? We found out that earthquakes are actually very hard to predict in advance. Next lesson, we're going to look at how we can prepare and protect against the impact of earthquakes, so I hope to see you then. If you'd like to please ask your parent or carer to share your work on Instagram, Facebook or Twitter tagging @planetearthrowl. @OakNational and #learnwithOak

Exit Quiz: How can we measure and predict earthquakes?

Completed: How can we measure and predict earthquakes?

This lesson will look at how we can measure and predict earthquakes to help save lives.

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How can we measure and predict earthquakes?

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