1 00:00:00,000 --> 00:00:04,000 Ready, R.J.? 2 00:00:04,000 --> 00:00:08,000 Hey, guys. I'm here at the San Andreas Fault, 3 00:00:08,000 --> 00:00:12,000 near where the epicenter of the 1906 San Francisco earthquake occurred. 4 00:00:12,000 --> 00:00:15,000 Hi, guys. You must be the treehouse detectives. How can I help you? 5 00:00:15,000 --> 00:00:18,000 Our friends in Virginia felt a vibration the other day, 6 00:00:18,000 --> 00:00:20,000 and they wanted to find out if it was an earthquake. 7 00:00:20,000 --> 00:00:22,000 They said we needed to learn more about faults. 8 00:00:22,000 --> 00:00:24,000 Well, a fault is a weak zone in the Earth's crust 9 00:00:24,000 --> 00:00:27,000 where the rock layers have broken and slipped apart. 10 00:00:27,000 --> 00:00:29,000 Would you like to see the San Andreas Fault? 11 00:00:29,000 --> 00:00:31,000 R.J., be sure and get me on camera. 12 00:00:31,000 --> 00:00:33,000 Okay. 13 00:00:38,000 --> 00:00:40,000 So where's the fault line? 14 00:00:40,000 --> 00:00:42,000 You can see it here. 15 00:00:42,000 --> 00:00:47,000 See the line that goes up the wall? 16 00:00:47,000 --> 00:00:49,000 Are there different kinds of faults? 17 00:00:49,000 --> 00:00:51,000 Yes, there's three kinds of faults. 18 00:00:51,000 --> 00:00:54,000 One is called a normal fault, and that's when the fault is at an angle, 19 00:00:54,000 --> 00:00:57,000 and the top block is called the hanging wall, 20 00:00:57,000 --> 00:01:00,000 and that moves down relative to the lower block called the foot wall. 21 00:01:00,000 --> 00:01:03,000 And this happens where there's extension in the crust and it pulls apart. 22 00:01:03,000 --> 00:01:05,000 Is there an abnormal fault? 23 00:01:05,000 --> 00:01:07,000 Well, it's not really an abnormal fault, 24 00:01:07,000 --> 00:01:09,000 but there is a fault that's opposite of a normal fault, 25 00:01:09,000 --> 00:01:13,000 and that's when the hanging wall block moves up relative to the foot wall block. 26 00:01:13,000 --> 00:01:16,000 And this happens where there's crustal compression, 27 00:01:16,000 --> 00:01:19,000 and those faults are called reverse faults or thrust faults. 28 00:01:19,000 --> 00:01:20,000 What's the last type of fault? 29 00:01:20,000 --> 00:01:22,000 Well, the last kind of fault is called a strike-slip fault, 30 00:01:22,000 --> 00:01:25,000 and that's like where we are now on the San Andreas Fault. 31 00:01:25,000 --> 00:01:28,000 We learned that the Earth's lithosphere is broken up into plates, 32 00:01:28,000 --> 00:01:30,000 and the plates' movement is what causes earthquakes. 33 00:01:30,000 --> 00:01:33,000 But I don't get it. Are plates and faults the same thing? 34 00:01:33,000 --> 00:01:37,000 Well, moving plates grind and scrape against each other at their edges, 35 00:01:37,000 --> 00:01:39,000 and those edges we call plate boundaries, 36 00:01:39,000 --> 00:01:42,000 and plate boundaries are usually made up of many faults. 37 00:01:42,000 --> 00:01:46,000 Are there different kinds of plate boundaries like there are different kinds of faults? 38 00:01:46,000 --> 00:01:48,000 Yes, there's also three of those. 39 00:01:48,000 --> 00:01:51,000 Divergent boundaries are where the crust is being pulled apart. 40 00:01:51,000 --> 00:01:55,000 These can form new crusts or cause rift valleys and even make volcanoes. 41 00:01:55,000 --> 00:01:58,000 The pulling apart can happen at about two centimeters a year. 42 00:01:58,000 --> 00:02:01,000 That's not very much. It must move really slowly. 43 00:02:01,000 --> 00:02:02,000 Yeah, they do. 44 00:02:02,000 --> 00:02:05,000 And a convergent boundary is where the plates crash head-on. 45 00:02:05,000 --> 00:02:07,000 Oh, those boundaries move slowly too. 46 00:02:07,000 --> 00:02:10,000 Yeah, they do. They only move a few centimeters a year, 47 00:02:10,000 --> 00:02:13,000 and because it's slow, it can take millions of years for them to form. 48 00:02:13,000 --> 00:02:18,000 And when the plates collide, sometimes you can get large mountain chains like the Himalayas. 49 00:02:18,000 --> 00:02:22,000 Wow, now I'm starting to understand why the Earth is shaped the way it is. 50 00:02:22,000 --> 00:02:24,000 The last boundary is called a transform boundary. 51 00:02:24,000 --> 00:02:28,000 It's when plates slide past each other, like the San Andreas Fault here. 52 00:02:28,000 --> 00:02:31,000 Does that mean California is not going to break off and fall into the ocean? 53 00:02:31,000 --> 00:02:33,000 No, that's a common misconception. 54 00:02:33,000 --> 00:02:36,000 Actually, Los Angeles may someday be next to San Francisco, 55 00:02:36,000 --> 00:02:38,000 but that will probably take 10 million years. 56 00:02:38,000 --> 00:02:40,000 That's a long time. 57 00:02:40,000 --> 00:02:42,000 I don't think we have any boundaries in Virginia. 58 00:02:42,000 --> 00:02:44,000 Do earthquakes occur anywhere else? 59 00:02:44,000 --> 00:02:48,000 Yeah, a few earthquakes occur in the middle of plates, called interplate earthquakes. 60 00:02:48,000 --> 00:02:52,000 And in 1886, there was a large earthquake in Charleston, South Carolina. 61 00:02:52,000 --> 00:02:54,000 South Carolina is near Virginia. 62 00:02:54,000 --> 00:02:56,000 Maybe they did have an earthquake. 63 00:02:56,000 --> 00:02:58,000 Do you want to try making your own earthquake? 64 00:02:58,000 --> 00:02:59,000 Will it knock houses down? 65 00:02:59,000 --> 00:03:03,000 No, it won't be a real earthquake. It'll just be a simulation of a very small one. 66 00:03:03,000 --> 00:03:04,000 Let's go. 67 00:03:04,000 --> 00:03:08,000 I have a setup here that we're going to pretend is like the Earth's plates moving. 68 00:03:08,000 --> 00:03:11,000 So you're going to turn the crank and apply stress to these blocks. 69 00:03:11,000 --> 00:03:13,000 You're going to cause a force to be pulling them, 70 00:03:13,000 --> 00:03:15,000 and this is going to be the equivalent of one plate, 71 00:03:15,000 --> 00:03:18,000 and this is going to be the equivalent of another crustal plate. 72 00:03:18,000 --> 00:03:23,000 And watch as you add more and more stress and see if you can get an earthquake. 73 00:03:23,000 --> 00:03:24,000 RJ? 74 00:03:29,000 --> 00:03:31,000 Wow, was that an earthquake? 75 00:03:31,000 --> 00:03:32,000 Yeah. 76 00:03:32,000 --> 00:03:34,000 Now that's my kind of earthquake. 77 00:03:34,000 --> 00:03:36,000 This has really been helpful. Thank you. 78 00:03:36,000 --> 00:03:39,000 Sure. Well, email me if you have any more questions. 79 00:03:39,000 --> 00:03:40,000 Okay.