Hello, my name is Ruth Amy. I'm a PhD student at the University of Leeds and I use satellites to watch how the Earth deforms from space.

Today we're going to talk about forces that are literally ripping the Earth apart and the sudden releases of energy that they cause. That's right, we're going to talk about earthquakes. Have you ever wondered why earthquakes happen where they do? Well, earthquakes happen on fractures or breaks in the Earth's surface.

These are known as faults and when movement happens really quickly on these faults and it releases a lot of energy then this is what we know as an earthquake. The reason this movement happens is because rocks are under stress. They're being pushed and they're being pulled around and eventually the stress gets too much and they break and move quickly and cause this energy which we know as an earthquake.

Now faults crisscross the entire Earth's surface and some are being stressed and are capable of causing earthquakes. So you can see why it's really important to know where faults are and what they might do if an earthquake did happen. Now we're going to take a few minutes to go over some key concepts with your teacher to make sure you understand these for the rest of the lesson.

I've written them on the board so you need to go over the Earth's interior, plate tectonics and plate boundaries. As well as going over these key concepts you should also take a minute to think about some other questions about earthquakes. So do you live near an active fault? If so, do you know its name and when an earthquake last happened on it?

Or if you don't know, do you know where you might go to find out and what you might do if you did find out you lived near an active fault? So take a few minutes to talk about that in your class and we'll meet back soon.

Welcome back. You'll have just discussed some key concepts and talked about what you know about active faults in your region. Now if any of you are lucky enough to live near mountains then these are made by repeated earthquakes happening on faults at their base. Over time and over repeated earthquake cycles gradually great mountains have grown.

There are many mountains that don't have earthquakes happen on them anymore. The faults don't host earthquakes but there are other regions where they do have a lot of earthquakes such as central Italy or the Himalayas. If you do live in a region that's prone to earthquakes make sure that you have emergency supplies in your house and that you know what to do in the case of an earthquake.

We have other videos in this series that can help you find out what to do. Do you remember that I told you that rocks are under a lot of stress? Well we're going to learn about the three different kinds. The first one is called compression. So this is what happens when things are squeezed together. The second is called tension and this is what happens when things are pulled apart.

The third is called shear and this is what happens when the same body is being pulled in different directions. So now what you're going to do in your class is use some dough to try out these different kinds of stress. So I want you to try compression, squeezing it together, tension, pulling it apart and shearing it.

Whilst you're doing so I want you to think about the shape of the dough. Is it getting thicker or thinner? So have a go at that and we'll meet back soon.

Hi, welcome back. I hope you enjoyed playing with the dough. So now we're going to go through the different things that you might have seen as you were playing with it. So first, if you're trying out compression, this is what happens when you squeeze the dough. And can you see that as I push it in from the left and right it gets thicker in the middle?

Well imagine if this happened on the earth. This is how mountains are made. The crust is getting thicker and great mountains are being built up. We call this compression and this is what happens at convergent plate boundaries. So this is a picture of me in the French Alps and you can see behind me there's a great mountain range.

And so this entire mountain range was built because of compression. The earth's crust is being compressed and gradually over time this mountain range was built up. So next you will have pulled the dough. So did you notice that as you pulled it out on the left and right it's getting thinner in the middle? Now this is called tension and this is what happens at divergent plate boundaries.

So a really exciting example of where this is happening is the East African Rift. Here is a Google Earth image of Africa and if we zoom in a little bit on the East African Rift, you can see I've added some arrows and this is showing where the crust is being pulled apart. And gradually as it's being pulled, water is infilling where the crust has gotten thinner.

And if this tension continues, if the crust keeps pulling, then eventually a new ocean will open up. So next you will have sheared the dough like this. So can you see from the side that as you did this, it didn't get thicker or thinner? The blocks just moved past each other.

So this stress is known as shear and this happens at transform plate boundaries. At transform plate boundaries, blocks of the earth are just moving past each other. Here's an example that my colleague Christoph took in Central Asia. Now it's not immediately obvious to see, but can you get your eyes in along the top of the hills?

You'll notice that they're actually offset. So I've put some arrows so you can see that the top of this hilltop was originally aligned with this one, but gradually because of shear, they've been offset. One thing that you'll notice is that the dough we've been using is soft. It's really easy to change shape. It flows really easily as we compress and stretch it.

But if you think about the Earth's crust, now rocks aren't really like this. Rocks are hard. Instead of being soft and easy to move around, they break. So imagine if you start compressing a rock. At first it might crumble into folds. Here's a picture of some folded sediments that I took in the French Alps.

So you can see that compression will have happened from the left and right and it's formed this fold. But if the stress is too great and the rocks can't fold, then they will break and fracture. And then if movement happens on this fracture, this is what we know as a fault, and this is what earthquakes can happen on. During earthquakes, the ground will only move a little bit depending on the size of the earthquake.

We'll see some images of offsets that happened in earthquake later. So now you're going to do some drawings. You're going to be dividing into three groups and each group is going to be given a piece of cardboard like this. Then group one, what I want you to do is draw a picture as though you're looking down at the Earth from above.

Here's an example I've done. So this is a bird's eye view of the Earth and you can see I've drawn a road and a fence. Next what I want you to do is draw a line at right angles to the road like this. And then with a pair of scissors, I want you to cut along that line.

Groups two and three, what I want you to do is to draw some horizontal layers. These represent layers of rock underneath the ground. This is like slicing through a cake and seeing the internal layers.

So here's an example. I've got my horizontal layers of rock and you can see the surface and I've drawn a house. So what I want you to do then is draw a line at 45 degrees like this. And then you two take a pair of scissors and cut along this line.

So if you do that, we'll meet back soon to talk about what you should do next. Welcome back. I hope you enjoyed doing some drawing.

So group one, you'll have made a model that looks something like this. So a bird's eye view of the Earth from above. Groups two and three, you'll have drawn something that looks like this, where you can see the horizontal layers of rock. So what you've actually made are some models of faults.

Group one, you've made a strike-slip fault. So I've drawn it here on the board and you can move the blocks past each other like how the arrows show. Group two, you made a normal fault. So I want you to move the blocks like I've shown here. Group three, you made a reverse fault. So move the blocks like I've shown here. So I have a question. Where do you think the fault is?

Remember that the movement is the line on which movement happens. So you might have guessed by now. The fault is where you made the cut because this is where you're moving your model. So as you're moving these models, I want you to fill in this handout which your teacher will give you. The first column shows the pictures that you've drawn, the models that you've made.

In the second column, I want you to write down whether you think the crust has shortened, lengthened or neither. In the third column, think about the stress, whether it's shear, compression or tension. The fourth column is filled in for you. And in the fifth column, write down if this were a plate boundary, would it be convergent, divergent or transformed.

So fill in your form and move your models and we'll meet back soon to talk about what you found.

Hi, welcome back. So now we're going to go through the results that you've put in your handout about your different fault models. So before we go through that, I want you all to run your finger along the cut that you made in your models. Does it feel rough or bumpy? I've heard that it does. And this is actually quite like in real life.

Imagine that fault lines are made of lots of rough rocks and because it's rough, as the fault moves it might get locked and movement might not be able to happen. But as the stress continues to build and build upon a fault, then eventually the stress is too much and they'll break and move suddenly and this is an earthquake. So group one, you made a strike-slip fault.

Your model will have looked something like this. And you will have moved it like this. So you can see that the features in your model, the road, has now become offset. So the type of stress that's associated with this type of fault is shear.

And you'll notice that if this is looking down at the earth from above, the crust is neither lengthened nor shortened, it stayed the same. And the type of plate boundary that's associated with this type of stress is known as a transformed plate boundary. A really exciting example of a transformed plate boundary is the San Andreas Fault.

The earthquake that I study is called the Napa Valley earthquake and it happened in 2014 in San Francisco in America. Here is a picture that my colleague Austin took during this earthquake. You can see that it's someone's drive and there's some damage. Where do you think the fault line is? If I draw it on here and show you the arrows, you can see that the

fault has cut straight through their drive and the curve is now offset from each other. Because of this shear, because of this strike-slip fault. Group two, you made a normal fault and it will have looked something like this. So the rock that's on top of the fault has moved down and you can see that the layers have been offset.

The type of stress that's associated with normal faults is tension and it's caused lengthening of the crust. You can see that your model has gotten longer. The type of plate boundary that's associated with this are divergent. Here is a picture of a normal fault in the field that my colleague Christoph took.

So it's like looking at a little cliff. Like in your model, you can see the horizontal layers of rock. And if you look closely, and I'll draw some arrows on, you can see how the horizontal layers have been offset. This is a normal fault, just like your model. Group three, you made a reverse fault and your model looks something like this too.

But in your case, the rock above the fault moved up the slope like this. And again, you can see that the horizontal layers have been offset from each other. The type of stress associated with a reverse fault is compression and this causes shortening.

The type of plate boundary associated with this kind of fault is convergent and this is what causes mountains. Here is a picture of my colleague Jeff that he took in Pembrokeshire in Wales. And you can see, like in your model, there are horizontal layers of rock. And like in your model, the rock above the fault has moved up the slope.

So you can see this is a reverse fault, just like the one you've made. So in this lesson, we've learned about the different kinds of faults upon which earthquakes can happen. And we've learned about the different types of stress associated with these faults. So you've learned about compression, tension and shear. And then you've made models of strike-slip, normal and reverse faults.

So remember that every model is just an analogue. It's just a simple representation of what we see in the earth. And with every model, there are strengths and weaknesses. So at the end of this video, take the time to discuss the following questions. What are the strengths and weaknesses of your model and how could they be made better?

I also encourage you to find out about faults in your community and whether you live near an active fault. And if you do live near an active fault, make sure you have a plan in place and you know what to do if there were to be an earthquake. Thank you very much for listening and goodbye.

Hello, my name is Ruth Amy. I'm a PhD student at the University of Leeds. Thank you for using this video. In this section, I'm going to give you some information about the background and the activities that you'll be doing in this lesson. This video is designed to be played during the lesson and then paused with breaks for discussion and activities.

This is designed to teach about the different types of stresses and their relationship to faults and earthquakes. The key learning points in this lesson are that there are different stresses acting on the crust. The Earth's crust is covered in fractures called faults and it's these that earthquakes happen on. During an earthquake, the ground moves quickly along these faults.

And there are three different kinds of fault. Normal faults, strike-slip faults and reverse faults. And the prior knowledge needed for this video are information about the Earth's interior, plate boundaries and plate tectonics. It's important to understand these when we start talking about the crust. If you need any help on these concepts, please see other videos in this series.

So all of the resources that you need for the video are shown here. So in one activity, you'll need dough. You may want some per group or in pairs. Whatever you do will be a bit messy, so make sure that you have newspaper and flour to put on the people's hands so it doesn't get so sticky.

So then later you'll divide your class into three groups and each group will need a big piece of cardboard. Then you'll need some colouring pencils so that the pupils can draw things on the cardboard and some scissors to cut a fault in this model. You'll also need a handout which is given in the resources for this lecture

that they'll fill in as they make their fault models. It's always useful to have photographs of sort of real faults in the field and so feel free to use the ones that we've used in the video here and also try and find out if there are any examples from places local to you because it makes it more engaging for the pupils. In the first section of this lesson, we invite you to think about active faults in your neighbourhood.

So make sure that you've looked up and found out if there are active faults near you. Some pupils might never have thought about this so it's really important that you've looked up beforehand the answer to these kind of questions. One thing you might like to do as an extension activity is to make a more three-dimensional model of a fault. So I have an example here.

What I've got here are some simple sponges and I've taken the scouring pads off the top of all of them apart from the top one to represent grass at the surface and then just glued them together. So this is useful because it's showing the horizontal layers of rock. So this is my strike-slip fault. So in this case, this would be the surface.

Here are the rocks under the ground and the fault would move like this. I've done the same for normal and reverse faults. So here I've got my three layers of rock and the grass at the surface and here I've actually drawn arrows on. So in this case, on the front I've drawn a reverse fault so it would move like this

and then on the back I've drawn a normal fault so it would move like this. And this is quite a nice analogue because there's actually a lot of friction when you're moving these apart so this is quite like what you'd see in the earth. It's quite realistic. This wraps up the teacher's guide for this lesson. If you have any questions or improvements

please do get in touch with us. We'd love to hear. Thank you and good luck on implementing your video.