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Hey there, I'm Johnny Alonzo.

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You may recognize me from my role as Jimmy on Dawson's Creek.

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Now on today's episode of NASA Sci-Files, there's going to be a whole lot of shaking going on

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when the Treehouse Detectives use science, math, and technology to reveal the secrets of earthquakes.

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So stay tuned and hold on for this exciting episode of NASA Sci-Files, The Case of the Shaky Quake.

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Music

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On this segment of The Case of the Shaky Quake, you'll be asked the following questions.

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What is a seismologist?

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Describe the layers of the Earth.

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What are two types of clues that help us learn about the Earth's history?

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And when you see this icon, you will know that the answer is near.

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Music

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I think this bone goes right here. I think it's part of the tail.

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Wrong, it's actually part of the head.

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I guess so. But this is the closest that we're going to get to a dinosaur, Dave.

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Jacob is going to have so much fun looking for dino bones.

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Excuse me? They're called fossils.

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Did you feel that?

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I did. What could it be?

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I felt that one.

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Now that you're with us, what do you think it is?

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It's an earthquake. Don't jump to conclusions.

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Go to the NASA Sci-Files website to see if they have any information on earthquakes.

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Visit the research rack on the NASA Sci-Files website for resources on earthquakes.

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I found two places in Virginia where seismologists record earthquakes.

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A size what?

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A seismologist is someone who studies and measures earthquakes.

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Look, I found a seismogram located near us at Tidewater Community College.

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Let's call seismologist Michael Lyle.

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Michael Lyle, Tidewater Community College, Seismology Lab.

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Hello, Mr. Lyle. Tony D'Angelo, Treehouse Detective.

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I would like to inquire if your instrument picked up a tremor a few minutes ago.

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Yes, our seismograph did detect something.

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Was it an earthquake?

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Maybe, but it's not clear from my reading here.

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Okay, we'll check back with you.

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Mr. Lyle says there's a very good possibility there's been an earthquake.

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Maybe I exaggerated a little bit.

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We all know it's going to take a lot more research to solve this problem.

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Look, here's an update from KSNN.

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I'm Ted Toon with the Kid Science News Network special report.

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Strange vibrations in the area have local residents concerned.

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We've sent our reporter the usually unshakable I Am Listening outside to look around.

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I Am?

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Well, Ted, I'm outside. I don't see anything.

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Well, I Am, don't get shaken up. Why don't you look around a little?

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Mostly because it's starting to rain, Ted. I'm coming back in.

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I Am? I Am!

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And she calls herself an investigative journalist.

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Anyway, that was I Am Listening with a live...

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I'm glad we're not the only ones who felt the vibration.

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I think there's sufficient evidence to show that we need to launch an official investigation.

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In simple words, let's go to the problem board.

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We know we felt the shake.

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TCC recorded something, and KSNN reported a mysterious vibration.

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Since we're pretty sure it's an earthquake, I think we need to...

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Wait a minute. We need to do a lot more research before we come to that conclusion.

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Okay, so we need to do more research on earthquakes.

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They'll say I'm correct.

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I think we need to know what else causes vibrations.

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I'm sorry, what did you say?

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I was calculating the cost of remodeling a treehouse to make it earthquake-proof.

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Tony, we don't even know if it was an earthquake.

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And we sure don't have enough information to know how to make a treehouse earthquake-proof.

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I estimate that it would cost about $20,000.

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And if we took out a loan with an interest rate of 6.5% for 30 years,

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then our payment would be $128 a month for principal and interest.

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Okay, okay, let's get back to the problem.

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Dr. D's from California. I'm sure he's been in a few earthquakes.

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Hi, Dr. D.

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Hi, guys. What's up?

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We felt our treehouse shake this morning and wanted to know what happened.

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Yeah, I felt something too.

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We think that it might have been an earthquake, but we can't prove it yet.

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Have you ever been in an earthquake?

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Yes, I have. But it didn't feel the same as what I felt this morning.

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See, I told you it wasn't an earthquake.

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Wait a minute. All earthquakes don't feel the same.

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To begin understanding earthquakes, you have to know something about the structure of the Earth.

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That makes sense. What can you tell us?

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Come on, let me show you.

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Let me cut this peach in half.

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Okay, be careful.

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I will, thanks.

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This will be our Earth.

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Only, it's a lot smaller.

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It's called a scale model.

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The pit is like the core of the Earth.

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The Earth's core is about half of its diameter.

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What's it made of?

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We've never been there, but we think it's made of iron and nickel.

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The inner part of the core is solid, and the outer part is liquid.

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It is so dense, if we had a gallon jug full of the Earth's core material, it would weigh over 100 pounds.

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Wait, Dr. D, you lost me.

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How do we know how big the core is and what it's made of if we've never been there?

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Well, it's just a guess.

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You're kidding.

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Well, actually, it's a pretty good guess, based upon a lot of evidence.

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One of the biggest clues we have to the structure of the Earth comes from our study of earthquakes.

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So we're using earthquakes to help us understand earthquakes?

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That's right.

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The part of the peach that you eat is called the Earth's mantle.

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It's not as dense as the core, but it's more dense than what's on the outside.

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What's the outside called?

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It's called the crust.

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Just like the crust of a bread.

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Very good.

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Like the skin of a peach, the Earth's crust is very thin.

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The crust under the oceans is typically between 5 and 10 kilometers thick.

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It's made of a dark, dense rock called basalt.

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The continental crust is between 30 and 70 kilometers thick.

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It's made of a lighter, less dense rock, like this granite.

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Is there a reason why the Earth is layered like this?

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It's because of density.

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Watch us experiment over here.

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We're going to put this green-tinted water and this salad oil into this graduated cylinder and shake them up.

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Let's see what happens.

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The salad oil is on top, and then the water.

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Let's put in some motor oil.

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It turns out, the least dense, which is motor oil, floats on the top.

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And the most dense, water, sinks to the bottom.

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It's just like the early history of the Earth, when it was all liquid.

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Earth? Liquid? Strange.

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But what does this have to do with earthquakes?

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When the Earth cooled, the crust's upper mantle became rigid and brittle.

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They broke into about 12 segments, which we call plates.

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Kind of like this cracked, boiled egg.

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These plates float on the more dense but flexible mantle below.

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Kind of like this egg white.

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These plates are in continual movement.

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Wow, this is too weird.

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Why don't we feel them moving?

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They move about as fast as your fingernails grow, which is only a few centimeters.

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They move about as fast as your fingernails grow, which is only a few centimeters per year.

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But we have fossil evidence of this movement, which we call plate tectonics.

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Are fossils also clues to understanding earthquakes?

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Yes.

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But Dr. D, aren't there other things that could cause vibrations?

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Well yes, that's a good question.

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Anything that makes a very loud sound can make things shake a little.

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I watched fireworks on the 4th, and some were so big, I did feel a vibration.

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Oh no, I'm late for an appointment.

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Why don't you take a walk and discuss this amongst yourselves.

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Okay, bye Dr. D.

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Let's go over there and discuss this.

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What about a sonic boom?

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We learned from the case of the barking dog that a sonic boom is created when a plane travels faster than the speed of sound.

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That's it, it's our hypothesis.

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If there are airplanes flying faster than the speed of sound, then it will cause the ground to vibrate.

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I don't think a sonic boom is our hypothesis.

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I forgot, my dad says that the military never flies faster than the speed of sound over land anymore.

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Oh, I thought we had it.

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I'm glad RJ and Jacob are going to California for the science fair.

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Maybe they can research earthquakes for us.

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Wait a minute, Jacob is in Utah looking for fossils.

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Dr. D said there's fossil evidence of plate tectonics.

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I wonder if that's the same thing as the continental drift theory my teacher talked about.

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Maybe, but I don't understand what fossils have to do with plate tectonics or earthquakes.

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Let's email Jacob and see if he can find the answers for us.

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Okay, I'll do it.

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We need to do some research on our own.

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Let's go back to the tree house and find out if anyone else has felt the vibrations.

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Wow, this is amazing.

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This is so cool.

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I can't believe I'm touching a dinosaur bone.

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Is this real?

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Yes, it is.

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Hi, I'm David Wittman.

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I'm a park ranger here, and these bones are 150 million years old.

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Wow.

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Want to see something really neat?

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Yes.

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Follow me.

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Amazing.

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I've never seen anything like this.

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Did you just put these bones in the wall?

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No, we didn't.

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Excavation started here in 1909 and ended in 1990.

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We're doing excavations elsewhere.

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But during that period of time, we uncovered over 1,000 dinosaur bones.

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How did they all get here?

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A lot of them died of natural causes, and some of them died when the river dried up and they didn't have enough water.

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Oh, I almost forgot.

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My friends wanted to find out for sure if fossils are clues towards plate tectonics and earthquakes.

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Oh, I can help you with that.

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I have lots of questions.

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What was the environment like?

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Well, this was the bottom of a river, and the area was flat, arid.

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There were a lot of plants growing along the rivers, and, of course, that's where the dinosaurs congregated.

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Another question.

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How warm was the climate?

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It was hot year-round.

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And the reason for that was that this area was a lot closer to the equator 150 million years ago.

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So over the last 150 million years, because of plate tectonics or continental drift, this area has moved northward 400 miles.

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It's hard to believe that land can actually move that far.

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I read in a book once that no one believed Alfred Wagner in the early 1900s when he proposed the idea known as continental drift.

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What is continental drift?

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It was a theory that stated that the continents were once one large land mass called Pangaea.

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Clues indicate that in the last 200 million years, the continents have moved or drifted horizontally to their current locations.

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A revised theory called plate tectonics explains why continents drift.

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Continents are part of large plates that move across the Earth's surface and bang into one another, causing earthquakes and pushing up mountain ranges.

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You mean fossil clues?

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Yes. Fossils can be clues to continental drift.

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For example, fossils of the reptile Messosaurus have been found in South America and Africa.

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These reptiles live in freshwater and on land, so how could they be found on different continents unless the continents had at one time been together?

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Well, another clue could be found in rocks.

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Strange. How do you know that a rock found here is the same as another rock found in the Colorado Plateau?

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Why don't you come with me? We'll take a walk and find out.

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Great!

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Well, Jacob, this is the Green River.

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Wow. I know I'd never seen anything like this before.

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As you can see, there's lots of different kinds of rocks here.

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Rocks can be clues to continental drift, but that's not the case here.

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They all look the same to me. How can you tell the difference between rock structures?

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Well, it's like a detective story.

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If we look over at this sandstone over here, it looks like six other types of sandstone that we have in the monument.

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So how do we tell the difference?

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We have to look at the rocks that are associated with it.

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If we look at the rock that's just below that sandstone, we can tell it's the Chinle Formation.

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Chinle looks the same all across the Colorado Plateau.

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So now we know the rock above it, this sandstone, is the Glen Canyon Sandstone.

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Do you have earthquakes here?

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Here, earthquakes are caused by mountain building forces.

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So 65 million years ago, as these flat rocks were being pushed up into an arch, earthquakes occurred.

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If you've ever seen a cake in an oven, it'll rise and rise and rise, but at some point, what happens to the cake?

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It rises too much.

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It has to sink back down eventually.

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It'll collapse. Well, the same thing happens with rocks.

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They'll be bent, but they can only bend so far, and at some point, they'll eventually break.

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And when the rocks break, is that what causes an earthquake?

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That's correct.

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That break is the fault line, and when the rocks move along the fault line, it creates an earthquake.

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Well, have I answered all your questions?

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Yeah, I can't wait to go email the treehouse detectives.

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Well, do you have some time to go look for some fossils?

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Sure.

237
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All right, let's go.

238
00:14:34,000 --> 00:14:38,000
So what's up? Will fossils help the treehouse detectives solve the mystery?

239
00:14:38,000 --> 00:14:42,000
Do you think the treehouse detectives experienced an earthquake?

240
00:14:42,000 --> 00:14:44,000
What else could have caused the vibration?

241
00:14:44,000 --> 00:14:48,000
Stay tuned for the next exciting chapter of The Case of the Shaky Quake.

242
00:14:53,000 --> 00:14:58,000
Try to answer these questions for the next episode of The Case of the Shaky Quake.

243
00:14:58,000 --> 00:15:00,000
What are three types of faults?

244
00:15:02,000 --> 00:15:04,000
What are three types of plate boundaries?

245
00:15:06,000 --> 00:15:08,000
How does a seismograph measure the shaking of the Earth?

246
00:15:15,000 --> 00:15:17,000
That was my last call.

247
00:15:17,000 --> 00:15:20,000
A lot of people on my list said they felt a vibration.

248
00:15:20,000 --> 00:15:24,000
We received a lot of emails. Some people say it felt like an explosion.

249
00:15:24,000 --> 00:15:28,000
Let's email KSNN and ask if there are any reports of an explosion in the area.

250
00:15:32,000 --> 00:15:34,000
Maybe this is our new hypothesis.

251
00:15:34,000 --> 00:15:37,000
If there was an explosion, then it will cause the ground to vibrate.

252
00:15:37,000 --> 00:15:41,000
I was talking to one person who said it felt like a heavy truck driving by.

253
00:15:41,000 --> 00:15:43,000
There was also an email describing it as a sonic boom.

254
00:15:43,000 --> 00:15:45,000
But we know it's not a sonic boom.

255
00:15:45,000 --> 00:15:49,000
Here comes an update from KSNN. I wonder if they received our email.

256
00:15:49,000 --> 00:15:51,000
This just in.

257
00:15:51,000 --> 00:15:54,000
Ah, the treehouse detectives have raised this question.

258
00:15:54,000 --> 00:15:59,000
Were there any explosions that could account for the vibrations detected yesterday around noon?

259
00:15:59,000 --> 00:16:02,000
For the answer, we go to I Am Listening on the scene.

260
00:16:03,000 --> 00:16:06,000
Ted, we're here at the site of the new Mega Bulk Mart.

261
00:16:06,000 --> 00:16:13,000
Yesterday at exactly 12 noon, the original This Little Piggy BBQ restaurant was demolished to make way for construction.

262
00:16:13,000 --> 00:16:18,000
We have this exclusive videotape sent to us by Mr. Flange Lugnut.

263
00:16:23,000 --> 00:16:24,000
There you have it, folks.

264
00:16:24,000 --> 00:16:28,000
The tremors felt yesterday were simply gigantic explosions.

265
00:16:28,000 --> 00:16:30,000
Nothing to worry about.

266
00:16:30,000 --> 00:16:31,000
Back to you, Ted.

267
00:16:32,000 --> 00:16:34,000
I Am is obviously not a scientist.

268
00:16:34,000 --> 00:16:37,000
Doesn't she know you just can't jump to conclusions?

269
00:16:37,000 --> 00:16:38,000
You must do research.

270
00:16:38,000 --> 00:16:41,000
Cool. That confirms my hypothesis.

271
00:16:41,000 --> 00:16:43,000
Look at our clock. It stopped at noon.

272
00:16:43,000 --> 00:16:45,000
So they must be the same explosions.

273
00:16:45,000 --> 00:16:48,000
That's what I call using my observation skills.

274
00:16:48,000 --> 00:16:51,000
Observation is an important part of the scientific process.

275
00:16:51,000 --> 00:16:53,000
You're like I Am, jumping to conclusions.

276
00:16:53,000 --> 00:16:57,000
I still think it could be an earthquake, and I don't want to take any chances.

277
00:16:57,000 --> 00:16:58,000
Maybe Tony is right.

278
00:16:58,000 --> 00:17:01,000
Jacob sent us an email from the Dinosaur National Monument

279
00:17:01,000 --> 00:17:06,000
that the movement of the Earth's crust and upper mantle, called plate tectonics, causes earthquakes.

280
00:17:06,000 --> 00:17:09,000
I'm reading more about plate tectonics in my Earth Science book.

281
00:17:09,000 --> 00:17:12,000
It says the crustal movement occurs along fault lines.

282
00:17:12,000 --> 00:17:14,000
Maybe we should learn more about faults.

283
00:17:14,000 --> 00:17:16,000
Let's do an internet search.

284
00:17:16,000 --> 00:17:21,000
I'll go to a search engine and type in the words earthquake, faults, and Virginia.

285
00:17:25,000 --> 00:17:26,000
Finding anything?

286
00:17:26,000 --> 00:17:31,000
The search shows several websites for the United States Geological Survey, or USGS.

287
00:17:31,000 --> 00:17:33,000
Let's go to their home page.

288
00:17:33,000 --> 00:17:36,000
I heard they monitor earthquakes all over the U.S.

289
00:17:36,000 --> 00:17:38,000
It sounds like they'd be able to help us.

290
00:17:38,000 --> 00:17:42,000
I clicked on California on the map, and they have an office in San Francisco.

291
00:17:42,000 --> 00:17:46,000
Let's email Jacob and RJ and ask them to talk to the USGS.

292
00:17:48,000 --> 00:17:49,000
Ready, RJ?

293
00:17:52,000 --> 00:17:54,000
Hey guys, I'm here at the San Andreas Fault.

294
00:17:56,000 --> 00:18:00,000
Near where the epicenter of the 1906 San Francisco earthquake occurred.

295
00:18:00,000 --> 00:18:03,000
Hi guys, you must be the treehouse detectives. How can I help you?

296
00:18:03,000 --> 00:18:08,000
Our friends in Virginia felt a vibration the other day, and they wanted to find out if it was an earthquake.

297
00:18:08,000 --> 00:18:10,000
They said we needed to learn more about faults.

298
00:18:10,000 --> 00:18:15,000
Well, a fault is a weak zone in the Earth's crust where the rock layers have broken and slipped apart.

299
00:18:15,000 --> 00:18:17,000
Would you like to see the San Andreas Fault?

300
00:18:17,000 --> 00:18:19,000
RJ, be sure and get me on camera.

301
00:18:19,000 --> 00:18:20,000
Okay.

302
00:18:27,000 --> 00:18:28,000
So where's the fault line?

303
00:18:28,000 --> 00:18:30,000
You can see it here.

304
00:18:30,000 --> 00:18:35,000
See the line that goes up the wall?

305
00:18:35,000 --> 00:18:37,000
Are there different kinds of faults?

306
00:18:37,000 --> 00:18:39,000
Yes, there's three kinds of faults.

307
00:18:39,000 --> 00:18:45,000
One is called a normal fault, and that's when the fault is at an angle, and the top block is called the hanging wall.

308
00:18:45,000 --> 00:18:48,000
And that moves down relative to the lower block, called the foot wall.

309
00:18:48,000 --> 00:18:51,000
And this happens where there's extension in the crust, and it pulls apart.

310
00:18:51,000 --> 00:18:53,000
Is there an abnormal fault?

311
00:18:53,000 --> 00:18:57,000
Well, it's not really an abnormal fault, but there is a fault that's opposite of a normal fault,

312
00:18:57,000 --> 00:19:01,000
and that's when the hanging wall block moves up relative to the foot wall block.

313
00:19:01,000 --> 00:19:04,000
And this happens where there's crustal compression.

314
00:19:04,000 --> 00:19:07,000
Those faults are called reverse faults or thrust faults.

315
00:19:07,000 --> 00:19:08,000
What's the last type of fault?

316
00:19:08,000 --> 00:19:13,000
Well, the last kind of fault is called a strike-slip fault, and that's like where we are now on the San Andreas Fault.

317
00:19:13,000 --> 00:19:18,000
We learned that the Earth's lithosphere is broken up into plates, and the plates' movement is what causes earthquakes.

318
00:19:18,000 --> 00:19:21,000
But I don't get it. Are plates and faults the same thing?

319
00:19:21,000 --> 00:19:27,000
Well, moving plates grind and scrape against each other at their edges, and those edges we call plate boundaries.

320
00:19:27,000 --> 00:19:30,000
And plate boundaries are usually made up of many faults.

321
00:19:30,000 --> 00:19:33,000
Are there different kinds of plate boundaries, like there are different kinds of faults?

322
00:19:33,000 --> 00:19:35,000
Yes, there's also three of those.

323
00:19:35,000 --> 00:19:39,000
Divergent boundaries are where the crust is being pulled apart.

324
00:19:39,000 --> 00:19:43,000
This can form new crusts or cause rift valleys and even make volcanoes.

325
00:19:43,000 --> 00:19:46,000
The pulling apart can happen at about 2 centimeters a year.

326
00:19:46,000 --> 00:19:49,000
That's not very much. It must move really slowly.

327
00:19:49,000 --> 00:19:53,000
Yeah, they do. And a convergent boundary is where the plates crash head-on.

328
00:19:53,000 --> 00:19:55,000
Oh, those boundaries move slowly, too.

329
00:19:55,000 --> 00:19:58,000
Yeah, they do. They only move a few centimeters a year.

330
00:19:58,000 --> 00:20:01,000
And because it's slow, it can take millions of years for them to form.

331
00:20:01,000 --> 00:20:06,000
And when the plates collide, sometimes you can get large mountain chains like the Himalayas.

332
00:20:06,000 --> 00:20:10,000
Wow, now I'm starting to understand why the Earth is shaped the way it is.

333
00:20:10,000 --> 00:20:12,000
The last boundary is called a transform boundary.

334
00:20:12,000 --> 00:20:16,000
It's when plates slide past each other, like the San Andreas Fault here.

335
00:20:16,000 --> 00:20:19,000
Does that mean California is not going to break off and fall into the ocean?

336
00:20:19,000 --> 00:20:21,000
No, that's a common misconception.

337
00:20:21,000 --> 00:20:26,000
Actually, Los Angeles may someday be next to San Francisco, but that will probably take 10 million years.

338
00:20:26,000 --> 00:20:28,000
That's a long time.

339
00:20:28,000 --> 00:20:32,000
I don't think we have any boundaries in Virginia. Do earthquakes occur anywhere else?

340
00:20:32,000 --> 00:20:36,000
Yeah, a few earthquakes occur in the middle of plates, called interplate earthquakes.

341
00:20:36,000 --> 00:20:40,000
And in 1886, there was a large earthquake in Charleston, South Carolina.

342
00:20:40,000 --> 00:20:44,000
South Carolina is near Virginia. Maybe they did have an earthquake.

343
00:20:44,000 --> 00:20:46,000
Do you want to try making your own earthquake?

344
00:20:46,000 --> 00:20:47,000
Will it knock houses down?

345
00:20:47,000 --> 00:20:51,000
No, it won't be a real earthquake. It will just be a simulation of a very small one.

346
00:20:51,000 --> 00:20:52,000
Let's go.

347
00:20:52,000 --> 00:20:56,000
I have a setup here that we're going to pretend is like the Earth's plates moving.

348
00:20:56,000 --> 00:20:59,000
So you're going to turn the crank and apply stress to these blocks.

349
00:20:59,000 --> 00:21:02,000
You're going to cause a force to be pulling them.

350
00:21:02,000 --> 00:21:04,000
And this is going to be the equivalent of one plate.

351
00:21:04,000 --> 00:21:07,000
And this is going to be the equivalent of another crustal plate.

352
00:21:07,000 --> 00:21:11,000
And watch as you add more and more stress and see if you can get an earthquake.

353
00:21:11,000 --> 00:21:12,000
RJ?

354
00:21:15,000 --> 00:21:17,000
Wow. Was that an earthquake?

355
00:21:17,000 --> 00:21:18,000
Yeah.

356
00:21:18,000 --> 00:21:21,000
Now that's my kind of earthquake.

357
00:21:21,000 --> 00:21:23,000
This has really been helpful. Thank you.

358
00:21:23,000 --> 00:21:25,000
Sure. Well, email me if you have any more questions.

359
00:21:25,000 --> 00:21:26,000
Okay.

360
00:21:32,000 --> 00:21:33,000
Done.

361
00:21:33,000 --> 00:21:35,000
Do you know what kind of dinosaur this is?

362
00:21:35,000 --> 00:21:37,000
Yeah, it's a Tyrannosaurus Rex.

363
00:21:37,000 --> 00:21:38,000
Not bad.

364
00:21:39,000 --> 00:21:40,000
What's going on?

365
00:21:40,000 --> 00:21:42,000
I don't know, but I don't like it.

366
00:21:42,000 --> 00:21:43,000
Now that was an earthquake.

367
00:21:43,000 --> 00:21:44,000
How do you know?

368
00:21:44,000 --> 00:21:45,000
Just felt like one.

369
00:21:45,000 --> 00:21:49,000
Maybe it was another construction blast. I'll call KSNN.

370
00:21:50,000 --> 00:21:52,000
Do you think an earthquake could affect the stock market?

371
00:21:52,000 --> 00:21:56,000
Listen, right now, we have bigger problems.

372
00:21:57,000 --> 00:22:01,000
KSNN just confirmed that there were no reports of a construction blast.

373
00:22:01,000 --> 00:22:03,000
I don't know, but we need to organize our thoughts.

374
00:22:03,000 --> 00:22:05,000
Let's go to the problem board.

375
00:22:05,000 --> 00:22:07,000
We know we've had a few tremors.

376
00:22:07,000 --> 00:22:11,000
We know that KSNN said the first set of tremors was from a construction blast.

377
00:22:11,000 --> 00:22:12,000
And the second was not.

378
00:22:12,000 --> 00:22:15,000
We know that the structure of the Earth is divided into layers.

379
00:22:16,000 --> 00:22:19,000
We also know the Earth's crust is divided into plates.

380
00:22:19,000 --> 00:22:21,000
And these plates can move and cause earthquakes.

381
00:22:21,000 --> 00:22:24,000
Oh, yeah. Remember that email from Jacob and RJ?

382
00:22:24,000 --> 00:22:26,000
They talked to Ms. Heidi Stenner,

383
00:22:26,000 --> 00:22:29,000
who confirmed that there are a lot of faults in the Earth's crust.

384
00:22:29,000 --> 00:22:32,000
Now we need to know if there are any faults in the area that could cause tremors.

385
00:22:32,000 --> 00:22:35,000
I think we need to visit the seismologist at TCC

386
00:22:35,000 --> 00:22:37,000
to find out if there are any faults in our area.

387
00:22:37,000 --> 00:22:40,000
We can also see if they reported another tremor this time.

388
00:22:40,000 --> 00:22:41,000
Let's get up and go.

389
00:22:42,000 --> 00:22:46,000
I think we're closer to figuring out that this vibration was an earthquake.

390
00:22:49,000 --> 00:22:51,000
This must be a seismograph.

391
00:22:51,000 --> 00:22:53,000
I recognize it from TV.

392
00:22:53,000 --> 00:22:55,000
I wonder if Mr. Lyle is here.

393
00:22:55,000 --> 00:22:57,000
Oh, hi, Mr. Lyle.

394
00:22:57,000 --> 00:22:58,000
Hi, girls.

395
00:22:58,000 --> 00:22:59,000
We're the Treehouse Detectives.

396
00:22:59,000 --> 00:23:01,000
We called you about an earlier tremor.

397
00:23:01,000 --> 00:23:04,000
Now we need to know if you've reported anything on your seismograph today.

398
00:23:04,000 --> 00:23:07,000
As a matter of fact, we did, and here it is right here.

399
00:23:07,000 --> 00:23:09,000
Wow! Was that an earthquake?

400
00:23:09,000 --> 00:23:11,000
Can you really tell from that reading?

401
00:23:11,000 --> 00:23:13,000
We're not sure at this time.

402
00:23:13,000 --> 00:23:17,000
We're analyzing the data because not all detected tremors are related to earthquakes.

403
00:23:17,000 --> 00:23:21,000
Analyzing your data is very important in the scientific process.

404
00:23:21,000 --> 00:23:24,000
In this area, most of the tremors we detect are relatively small,

405
00:23:24,000 --> 00:23:28,000
travel a short distance, and generally occur between 8 a.m. and 5 p.m.

406
00:23:28,000 --> 00:23:31,000
This suggests that they're caused by human conditions.

407
00:23:31,000 --> 00:23:34,000
We learned that there are earthquakes because there are breaks in the Earth's crust

408
00:23:34,000 --> 00:23:35,000
that are moving along fault lines.

409
00:23:35,000 --> 00:23:37,000
Are there faults in Virginia?

410
00:23:37,000 --> 00:23:41,000
Yes, there are numerous faults in Virginia, but not all of them are active faults.

411
00:23:41,000 --> 00:23:44,000
Wow! Does Virginia have a lot of earthquakes?

412
00:23:44,000 --> 00:23:45,000
Not really.

413
00:23:45,000 --> 00:23:49,000
In the last 30 years, there have been more than 150 earthquakes in Virginia.

414
00:23:49,000 --> 00:23:53,000
But these are low-intensity events seldom felt by people.

415
00:23:53,000 --> 00:23:55,000
Where do most Virginia earthquakes occur?

416
00:23:55,000 --> 00:23:58,000
Most seem to occur in the central and western part of the state.

417
00:23:58,000 --> 00:24:00,000
We don't live near that part of the state.

418
00:24:00,000 --> 00:24:04,000
Hmm. What other things could cause a reading on your seismograph?

419
00:24:04,000 --> 00:24:06,000
Anything that shakes the ground can be recorded.

420
00:24:06,000 --> 00:24:10,000
Here's a seismogram or paper recording of that construction blast from the other day.

421
00:24:10,000 --> 00:24:13,000
It looks so small, but it created such a big boom.

422
00:24:13,000 --> 00:24:16,000
Our seismometer measuring instrument is very sensitive.

423
00:24:16,000 --> 00:24:20,000
This is what automobile traffic and even storm waves from the beach look like.

424
00:24:20,000 --> 00:24:22,000
That's pretty neat.

425
00:24:22,000 --> 00:24:25,000
The seismometer is buried 70 meters below us.

426
00:24:25,000 --> 00:24:28,000
It is so sensitive that we had to put it in a very quiet place.

427
00:24:28,000 --> 00:24:30,000
That's way down there.

428
00:24:30,000 --> 00:24:33,000
Would you like to see a seismogram of a confirmed earthquake?

429
00:24:33,000 --> 00:24:34,000
Yes.

430
00:24:34,000 --> 00:24:36,000
What are the little square marks?

431
00:24:36,000 --> 00:24:38,000
How can you figure anything out?

432
00:24:38,000 --> 00:24:41,000
You guys have lots of questions.

433
00:24:41,000 --> 00:24:44,000
Well, every square ticks off a minute.

434
00:24:44,000 --> 00:24:48,000
Oh, so you can tell when an earthquake happens and how long it lasts.

435
00:24:48,000 --> 00:24:49,000
That's correct.

436
00:24:49,000 --> 00:24:53,000
To most people, these look like squiggly lines, but when I look at them, I see S and P waves.

437
00:24:53,000 --> 00:24:55,000
Like sound waves.

438
00:24:55,000 --> 00:24:57,000
They are somewhat like sound waves.

439
00:24:57,000 --> 00:24:59,000
These are vibrations in the earth.

440
00:24:59,000 --> 00:25:02,000
That doesn't look at all like the tremor we felt.

441
00:25:02,000 --> 00:25:04,000
Does that mean it wasn't an earthquake?

442
00:25:04,000 --> 00:25:05,000
Not necessarily.

443
00:25:05,000 --> 00:25:08,000
A local earthquake could look very different from this.

444
00:25:08,000 --> 00:25:09,000
We need one of these in our treehouse.

445
00:25:09,000 --> 00:25:11,000
Then we can measure the next tremor.

446
00:25:11,000 --> 00:25:14,000
I think Dr. D is down the hall building a seismograph.

447
00:25:14,000 --> 00:25:16,000
Dr. D? A seismograph?

448
00:25:16,000 --> 00:25:18,000
We're there.

449
00:25:20,000 --> 00:25:21,000
Hi, Dr. D.

450
00:25:21,000 --> 00:25:22,000
Hi, kids.

451
00:25:22,000 --> 00:25:24,000
Is this the seismograph you're building?

452
00:25:24,000 --> 00:25:25,000
That's right.

453
00:25:25,000 --> 00:25:27,000
Almost finished.

454
00:25:27,000 --> 00:25:31,000
This seismograph is not very sensitive, but it does work.

455
00:25:31,000 --> 00:25:33,000
It measures horizontal motion.

456
00:25:33,000 --> 00:25:36,000
So you actually use a peanut can and an old brick?

457
00:25:36,000 --> 00:25:37,000
Yeah, sure.

458
00:25:37,000 --> 00:25:38,000
Let me start from the beginning.

459
00:25:38,000 --> 00:25:40,000
The seismograph measures the shaking of the earth.

460
00:25:40,000 --> 00:25:44,000
To measure the shaking, we take advantage of Newton's first law.

461
00:25:44,000 --> 00:25:45,000
I think I remember.

462
00:25:45,000 --> 00:25:47,000
Isn't it also called inertia?

463
00:25:47,000 --> 00:25:48,000
I'm impressed.

464
00:25:48,000 --> 00:25:50,000
So what is inertia?

465
00:25:50,000 --> 00:25:53,000
It means that when an object is at rest, it stays at rest.

466
00:25:53,000 --> 00:25:55,000
And when an object is in motion, it remains in motion.

467
00:25:55,000 --> 00:25:56,000
That's right.

468
00:25:56,000 --> 00:25:59,000
This brick has a lot of inertia, so it's hard to get moving.

469
00:25:59,000 --> 00:26:03,000
When the earth shakes, the base of the seismograph will also shake.

470
00:26:03,000 --> 00:26:07,000
But the brick, which is not tied to the base, will not.

471
00:26:07,000 --> 00:26:09,000
The pen over there records the vibration.

472
00:26:09,000 --> 00:26:10,000
Can we try it?

473
00:26:10,000 --> 00:26:11,000
Sure.

474
00:26:11,000 --> 00:26:13,000
Let's make an earthquake by shaking the table.

475
00:26:14,000 --> 00:26:15,000
It really works.

476
00:26:15,000 --> 00:26:16,000
Look at the waves.

477
00:26:16,000 --> 00:26:18,000
Did we do that?

478
00:26:18,000 --> 00:26:19,000
You sure did.

479
00:26:20,000 --> 00:26:22,000
Here's a different kind of seismograph.

480
00:26:22,000 --> 00:26:24,000
It measures vertical motion.

481
00:26:25,000 --> 00:26:27,000
It looks really different.

482
00:26:27,000 --> 00:26:32,000
Because it has inertia, this magnet hanging on the spring tends to stand still

483
00:26:32,000 --> 00:26:34,000
when the table moves up and down.

484
00:26:34,000 --> 00:26:38,000
A magnet moving through a coil of wire produces electricity, which this meter records.

485
00:26:38,000 --> 00:26:40,000
Can we try this one too?

486
00:26:40,000 --> 00:26:41,000
Sure.

487
00:26:42,000 --> 00:26:43,000
All right.

488
00:26:43,000 --> 00:26:47,000
But here's a sensitive seismometer that hooked up to this computer.

489
00:26:47,000 --> 00:26:50,000
That graph looks a lot like the seismogram that Mr. Lau showed us.

490
00:26:58,000 --> 00:27:02,000
The harder I hit the table, the larger the signal.

491
00:27:02,000 --> 00:27:03,000
This is really cool.

492
00:27:03,000 --> 00:27:06,000
And look at how it vibrates up and down.

493
00:27:06,000 --> 00:27:09,000
Because it produces an electric signal, it is easy to amplify.

494
00:27:09,000 --> 00:27:12,000
Even a small vibration can be shown on the computer.

495
00:27:12,000 --> 00:27:14,000
Now, I can't loan you this device.

496
00:27:14,000 --> 00:27:18,000
But why don't you take my wooden seismograph back to the treehouse

497
00:27:18,000 --> 00:27:21,000
and see if you can record another tremor?

498
00:27:21,000 --> 00:27:25,000
I have a friend at NASA's Jet Propulsion Laboratory in Pasadena, California.

499
00:27:25,000 --> 00:27:28,000
He uses satellites to measure the motion of the Earth's crust.

500
00:27:28,000 --> 00:27:32,000
You might want to talk to him in your quest to become earthquake experts.

501
00:27:36,000 --> 00:27:37,000
So what's up?

502
00:27:37,000 --> 00:27:41,000
Will the seismograph help the treehouse detectives solve the mystery?

503
00:27:41,000 --> 00:27:43,000
Will satellites provide the answer?

504
00:27:43,000 --> 00:27:48,000
Stay with us for the next exciting chapter of The Case of the Shaky Quake.

505
00:27:48,000 --> 00:27:52,000
NASA Jet Propulsion Laboratory, California Institute of Technology

506
00:27:54,000 --> 00:27:56,000
Can you answer these questions?

507
00:27:56,000 --> 00:27:59,000
What is GPS and how is it used?

508
00:28:01,000 --> 00:28:04,000
What are SMP waves and how do they differ?

509
00:28:06,000 --> 00:28:09,000
What are two types of scales used to measure earthquakes?

510
00:28:12,000 --> 00:28:13,000
I'm not so bad.

511
00:28:13,000 --> 00:28:14,000
What?

512
00:28:14,000 --> 00:28:15,000
I'm looking at my soccer journal.

513
00:28:15,000 --> 00:28:20,000
And so far in my soccer career, I've scored 282 goals and attempted 670.

514
00:28:20,000 --> 00:28:24,000
That means that my shooting percentage is 42.1%.

515
00:28:24,000 --> 00:28:27,000
That means I score a goal about half the time.

516
00:28:27,000 --> 00:28:29,000
See, you do use math in sports.

517
00:28:29,000 --> 00:28:33,000
Okay, getting back to business, this is a homemade seismograph from Dr. D.

518
00:28:33,000 --> 00:28:36,000
Now I'll be prepared in case there's another tremor.

519
00:28:36,000 --> 00:28:38,000
I don't know if I would depend on that machine.

520
00:28:38,000 --> 00:28:39,000
It looks rather weak.

521
00:28:39,000 --> 00:28:43,000
But maybe this instrument isn't the only way to detect earthquakes.

522
00:28:43,000 --> 00:28:48,000
Remember Dr. D. told us about JPL and how they monitor crustal movement using satellites.

523
00:28:48,000 --> 00:28:50,000
He gave me the name of his friend, Andrea Donnellan.

524
00:28:50,000 --> 00:28:51,000
Let's dial her up.

525
00:28:52,000 --> 00:28:54,000
Hi, we're the Treehouse Detectives.

526
00:28:54,000 --> 00:28:58,000
Dr. D. said that you might be able to help us learn about how crustal movement is monitored.

527
00:28:58,000 --> 00:29:01,000
I sure can. I use GPS to measure crustal movements.

528
00:29:01,000 --> 00:29:05,000
I've heard of GPS, but I'm not sure what it is or how it works.

529
00:29:05,000 --> 00:29:08,000
GPS stands for Global Positioning System.

530
00:29:08,000 --> 00:29:11,000
It's a satellite navigation system consisting of 24 satellites.

531
00:29:12,000 --> 00:29:14,000
Pilots and boaters use it to plot their course.

532
00:29:14,000 --> 00:29:18,000
Geologists use it to accurately measure the position of monitoring stations.

533
00:29:18,000 --> 00:29:23,000
Here in Southern California, we have a network of 250 GPS stations.

534
00:29:23,000 --> 00:29:27,000
How does knowing the position of these stations help you to understand earthquakes?

535
00:29:27,000 --> 00:29:31,000
It shows us the stretching, warping, and movement of the crust that's not really noticeable.

536
00:29:31,000 --> 00:29:33,000
How accurate is it?

537
00:29:33,000 --> 00:29:38,000
We can measure the positions of points on the Earth to 3 millimeters horizontally and 7 millimeters vertically.

538
00:29:38,000 --> 00:29:42,000
That's small. How does that differ from what a seismograph does?

539
00:29:42,000 --> 00:29:45,000
A seismograph measures earthquakes when they happen.

540
00:29:45,000 --> 00:29:48,000
With GPS, we can actually measure the quiet motions of the Earth.

541
00:29:48,000 --> 00:29:52,000
That means we can measure the strain buildup as well as the earthquakes themselves.

542
00:29:52,000 --> 00:29:55,000
It is particularly useful in identifying active blind faults.

543
00:29:55,000 --> 00:29:57,000
What's a blind fault?

544
00:29:57,000 --> 00:30:01,000
A blind fault is a break in the crust that doesn't break through the surface anywhere.

545
00:30:01,000 --> 00:30:06,000
Naturally, these faults are not easy to locate or study and might go unnoticed without GPS technology.

546
00:30:06,000 --> 00:30:10,000
That's pretty impressive. I'm glad we have the ability to see these faults.

547
00:30:10,000 --> 00:30:13,000
Would this technology help us to predict earthquakes?

548
00:30:13,000 --> 00:30:17,000
We are integrating data from a lot of different sources into computer simulations.

549
00:30:17,000 --> 00:30:20,000
These simulations should help us understand the earthquake process.

550
00:30:20,000 --> 00:30:23,000
We hope to eventually be able to do short-term forecasting.

551
00:30:23,000 --> 00:30:25,000
Can you give us an example?

552
00:30:25,000 --> 00:30:29,000
By monitoring all the stations, we can find out which faults have the greatest slip rate.

553
00:30:29,000 --> 00:30:35,000
The slip rate, typically measured in millimeters per year, is how fast the two sides of a fault are moving past each other.

554
00:30:35,000 --> 00:30:39,000
These faults that have the greatest slip rates may be the locations of future earthquakes.

555
00:30:39,000 --> 00:30:42,000
I wish you were able to make a prediction now.

556
00:30:42,000 --> 00:30:45,000
Can GPS help us to know if we experience an earthquake in Virginia?

557
00:30:45,000 --> 00:30:50,000
We can use GPS to measure displacements from earthquakes, but we don't measure the shaking part from an earthquake.

558
00:30:50,000 --> 00:30:54,000
A seismometer is used to measure this and it will be better able to answer your question.

559
00:30:54,000 --> 00:30:56,000
Thank you very much, Dr. Donilon.

560
00:30:56,000 --> 00:31:00,000
You're welcome. Email me if you have any questions and say hello to Dr. D for me.

561
00:31:01,000 --> 00:31:06,000
Cool. I can't believe that the GPS can detect three millimeters of movement from space.

562
00:31:06,000 --> 00:31:08,000
Check this out. Come closer.

563
00:31:08,000 --> 00:31:11,000
Three millimeters is only this much.

564
00:31:11,000 --> 00:31:16,000
Hi, Tony. We're talking about GPS. In the future, it might help us to predict earthquakes.

565
00:31:16,000 --> 00:31:20,000
Yeah, that's great, but what about the problem right now?

566
00:31:20,000 --> 00:31:25,000
Dr. Donilon said that if there was an earthquake in Virginia, seismographs would pick it up.

567
00:31:25,000 --> 00:31:28,000
Well, we looked at a few seismograms and we still don't have a definite answer.

568
00:31:28,000 --> 00:31:30,000
Let's do some problem solving.

569
00:31:30,000 --> 00:31:32,000
I have an idea. Why don't we call RJ and Jacob?

570
00:31:32,000 --> 00:31:36,000
Tell them hi. I've got to go. I've got soccer practice today.

571
00:31:36,000 --> 00:31:37,000
Bye. See ya.

572
00:31:37,000 --> 00:31:39,000
Hi, guys. How's California?

573
00:31:39,000 --> 00:31:42,000
It's great. Look at the Golden Gate Bridge behind us.

574
00:31:42,000 --> 00:31:45,000
And we're learning a lot at the Science Fair.

575
00:31:45,000 --> 00:31:47,000
So, are you still trying to solve the tremor problem?

576
00:31:47,000 --> 00:31:50,000
Yes, but we need your help with the problem board.

577
00:31:50,000 --> 00:31:51,000
Okay, let's go to it.

578
00:31:51,000 --> 00:31:55,000
Well, we know the first set of tremors was not related to the second.

579
00:31:55,000 --> 00:31:59,000
We know the place movements can cause earthquakes and that there are a lot of faults.

580
00:31:59,000 --> 00:32:01,000
We know there are faults in Virginia.

581
00:32:01,000 --> 00:32:04,000
And we also know that other things can cause movement on the seismograph.

582
00:32:04,000 --> 00:32:05,000
Like what?

583
00:32:05,000 --> 00:32:11,000
The seismologist told us that quarry blasts, sonic booms, and thunderstorms can often be mistaken for earthquakes.

584
00:32:11,000 --> 00:32:14,000
Thunderstorms? Did we have storms that day?

585
00:32:14,000 --> 00:32:17,000
It was cloudy and stormy that day, but I don't remember seeing any lightning.

586
00:32:17,000 --> 00:32:22,000
But it did sound like a clap of thunder, and that will register on the seismograms.

587
00:32:22,000 --> 00:32:25,000
And earthquakes don't make noise, so it must be thunder.

588
00:32:25,000 --> 00:32:27,000
Maybe this is our new hypothesis.

589
00:32:27,000 --> 00:32:30,000
If there was thunder, then it would cause vibrations on Earth.

590
00:32:30,000 --> 00:32:33,000
Don't throw away your earthquake hypothesis too quickly.

591
00:32:33,000 --> 00:32:36,000
During my vacation, I've been doing a lot of research on earthquakes.

592
00:32:36,000 --> 00:32:40,000
And look, I just happened to find this account of an earthquake in Oklahoma.

593
00:32:40,000 --> 00:32:41,000
And here it is.

594
00:32:41,000 --> 00:32:45,000
I heard something like a loud clap of thunder or something exploding.

595
00:32:45,000 --> 00:32:49,000
Great job, guys. Our competing earthquake hypothesis still survives.

596
00:32:49,000 --> 00:32:52,000
I still think that we need to know if there was thunder and lightning that day.

597
00:32:52,000 --> 00:32:56,000
We never checked out what the seismologist said about S&P waves.

598
00:32:56,000 --> 00:32:58,000
And I think we should. It might be a clue.

599
00:32:58,000 --> 00:33:00,000
See you guys. Have fun with Dr. D.

600
00:33:03,000 --> 00:33:04,000
Hey, Dr. D.

601
00:33:04,000 --> 00:33:07,000
Hi, guys. Good to see you here in San Francisco, California.

602
00:33:07,000 --> 00:33:10,000
I understand from the email that you want to know more about earthquake waves.

603
00:33:10,000 --> 00:33:11,000
Yes.

604
00:33:11,000 --> 00:33:13,000
I've put together some demonstrations for you.

605
00:33:13,000 --> 00:33:14,000
Great!

606
00:33:14,000 --> 00:33:16,000
Let's talk about three different kinds of waves.

607
00:33:16,000 --> 00:33:18,000
The first two are S&P waves.

608
00:33:18,000 --> 00:33:21,000
They're called body waves because they travel through the body of the Earth.

609
00:33:21,000 --> 00:33:25,000
Mr. Lyle showed the other treehouse detectives those on the seismogram.

610
00:33:25,000 --> 00:33:28,000
P stands for primary or compressional waves.

611
00:33:28,000 --> 00:33:31,000
And S is for secondary or shear waves.

612
00:33:31,000 --> 00:33:35,000
P waves make the Earth vibrate back and forth along the direction of motion.

613
00:33:35,000 --> 00:33:37,000
Let me show you with this slinky over here.

614
00:33:38,000 --> 00:33:42,000
Those don't look like the waves I'm used to seeing, like ocean waves.

615
00:33:42,000 --> 00:33:45,000
The wave you're used to seeing has up and down or side to side motion.

616
00:33:45,000 --> 00:33:47,000
This is like the shear wave or S wave.

617
00:33:47,000 --> 00:33:48,000
It looks like this.

618
00:33:51,000 --> 00:33:56,000
Another important difference between S&P waves is that P waves travel faster than S waves.

619
00:33:56,000 --> 00:33:58,000
Almost twice as fast.

620
00:33:58,000 --> 00:34:01,000
I guess that means that P waves will always arrive first.

621
00:34:01,000 --> 00:34:02,000
That's right.

622
00:34:03,000 --> 00:34:04,000
That's right.

623
00:34:04,000 --> 00:34:07,000
And the difference in time between the arrival of the S and P waves

624
00:34:07,000 --> 00:34:09,000
help us find the epicenter of the earthquake.

625
00:34:09,000 --> 00:34:10,000
What's an epicenter?

626
00:34:10,000 --> 00:34:14,000
It's the point on the Earth directly above the focus or the point where the earthquake originates.

627
00:34:14,000 --> 00:34:19,000
Have you ever heard about counting the seconds between seeing the lightning and hearing the thunder?

628
00:34:19,000 --> 00:34:21,000
I have, but I've never done it.

629
00:34:21,000 --> 00:34:24,000
Well, it works because light and sound travel at different speeds.

630
00:34:24,000 --> 00:34:27,000
For example, when you see the lightning, start counting.

631
00:34:28,000 --> 00:34:32,000
1,001, 1,002, 1,003.

632
00:34:32,000 --> 00:34:35,000
The sound arrived about three seconds after the lightning.

633
00:34:35,000 --> 00:34:38,000
That means the lightning is about one kilometer away.

634
00:34:38,000 --> 00:34:43,000
For earthquakes, first you feel a P wave, and then seconds later you'll feel a more powerful S wave.

635
00:34:43,000 --> 00:34:49,000
For local earthquakes, every second that you count means you're about eight kilometers further away from the epicenter.

636
00:34:49,000 --> 00:34:52,000
I don't think I'd be counting the seconds if I was in an earthquake.

637
00:34:52,000 --> 00:34:54,000
I don't think I would either.

638
00:34:54,000 --> 00:34:59,000
The third and slowest of these waves, the surface wave, is the most destructive of them all.

639
00:34:59,000 --> 00:35:03,000
Here in California, they have to build structures to withstand these dangerous waves.

640
00:35:03,000 --> 00:35:05,000
How do they know how to do that?

641
00:35:05,000 --> 00:35:10,000
One way is for engineers to use shaky tables like these, only much bigger, to test their designs.

642
00:35:10,000 --> 00:35:11,000
Let's try it out.

643
00:35:11,000 --> 00:35:14,000
I'll bet my structure can't withstand the greatest earthquake.

644
00:35:14,000 --> 00:35:16,000
We'll see who's the best engineer.

645
00:35:24,000 --> 00:35:42,000
Yes!

646
00:35:42,000 --> 00:35:45,000
I guess we have a little bit more to learn about the power of earthquakes.

647
00:35:45,000 --> 00:35:49,000
Dr. D, didn't you say we could experience an earthquake here at the museum?

648
00:35:49,000 --> 00:35:51,000
You need to go see my friend, Dr. Tang.

649
00:35:55,000 --> 00:35:57,000
That must be the earthquake theater.

650
00:35:57,000 --> 00:36:00,000
I hope it's not like the hurricane room that Bianca and Catherine went to.

651
00:36:00,000 --> 00:36:01,000
Yeah.

652
00:36:01,000 --> 00:36:02,000
Treehouse detectives?

653
00:36:02,000 --> 00:36:03,000
That's us.

654
00:36:03,000 --> 00:36:04,000
Nice to meet you, Dr. Tang.

655
00:36:04,000 --> 00:36:07,000
I hear you're interested in experiencing an earthquake.

656
00:36:07,000 --> 00:36:12,000
Well, I don't know about that, but we do need to learn more about how experts measure the power of earthquakes.

657
00:36:12,000 --> 00:36:14,000
One such scale is called the Richter scale.

658
00:36:14,000 --> 00:36:16,000
It tells us the strength of an earthquake.

659
00:36:16,000 --> 00:36:18,000
Are there other scales that scientists use?

660
00:36:19,000 --> 00:36:23,000
Now scientists prefer a more precise scale called the moment magnitude scale.

661
00:36:23,000 --> 00:36:27,000
It's a number that tells us about the energy released from an earthquake.

662
00:36:27,000 --> 00:36:28,000
What's the number of our earthquake?

663
00:36:28,000 --> 00:36:32,000
Well, if it was a quake that people could feel, it must be at least a 2.

664
00:36:32,000 --> 00:36:35,000
A moderate earthquake is about a 5.

665
00:36:35,000 --> 00:36:38,000
Wasn't there a major earthquake here in San Francisco in 1906?

666
00:36:38,000 --> 00:36:39,000
What was its number?

667
00:36:39,000 --> 00:36:41,000
It was a 7.7.

668
00:36:41,000 --> 00:36:44,000
But to understand what that means, you really ought to experience the earthquake.

669
00:36:44,000 --> 00:36:46,000
I'm not sure I want to do that.

670
00:36:46,000 --> 00:36:48,000
Don't worry, it's quite safe.

671
00:36:48,000 --> 00:36:52,000
We're going to be doing it here in the Earthquake Theater at the California Academy of Sciences.

672
00:36:52,000 --> 00:36:54,000
Don't forget to bring the camera.

673
00:36:54,000 --> 00:36:55,000
I got it.

674
00:36:55,000 --> 00:36:56,000
Don't forget to bring the camera.

675
00:36:56,000 --> 00:36:57,000
I got it.

676
00:36:57,000 --> 00:37:26,000
At 5.40 on October 17, 1989,

677
00:37:26,000 --> 00:37:30,000
the San Francisco Pantheon experienced a powerful earthquake.

678
00:37:30,000 --> 00:37:33,000
Cool, it seems so real.

679
00:37:33,000 --> 00:37:35,000
How do scientists know so much?

680
00:37:35,000 --> 00:37:37,000
Well, we looked at people's diaries,

681
00:37:37,000 --> 00:37:41,000
and also had houses and churches that were damaged during the earthquake,

682
00:37:41,000 --> 00:37:45,000
and also how the earthquake ruptured the ground around San Francisco during the time period.

683
00:37:45,000 --> 00:37:47,000
I guess observations are important.

684
00:37:47,000 --> 00:37:50,000
Your science journal might be valuable evidence one day.

685
00:37:50,000 --> 00:37:53,000
Yes, well take a look at this earthquake questionnaire.

686
00:37:53,000 --> 00:37:56,000
You'll see that even today, even with sophisticated instruments,

687
00:37:56,000 --> 00:38:00,000
scientists still depend on people's experiences to understand earthquakes.

688
00:38:00,000 --> 00:38:02,000
Wow, look at this.

689
00:38:02,000 --> 00:38:04,000
They want to know if it was difficult to stand or walk.

690
00:38:04,000 --> 00:38:07,000
And did objects rattle or fall off the shelf?

691
00:38:07,000 --> 00:38:09,000
Here's a simple question.

692
00:38:09,000 --> 00:38:11,000
What's your zip code?

693
00:38:11,000 --> 00:38:13,000
Does it make a difference where you live?

694
00:38:13,000 --> 00:38:18,000
Yes, the effects of an earthquake vary greatly depending on how far away from the source you are.

695
00:38:18,000 --> 00:38:21,000
You mean the farther away you are, the less shaking you feel from a quake?

696
00:38:21,000 --> 00:38:24,000
Yes, but it also depends on what the ground is like.

697
00:38:24,000 --> 00:38:26,000
What does the ground have to do with it?

698
00:38:26,000 --> 00:38:28,000
Well, let's take a look at this gelatin.

699
00:38:28,000 --> 00:38:31,000
If I push on it even a little bit, it jiggles a lot.

700
00:38:31,000 --> 00:38:37,000
And yet, if I take a rock, no matter how hard I push on it, it's not going to jiggle at all.

701
00:38:37,000 --> 00:38:40,000
I know where I would want to stand during an earthquake.

702
00:38:40,000 --> 00:38:41,000
Solid rock.

703
00:38:41,000 --> 00:38:42,000
That's right.

704
00:38:42,000 --> 00:38:46,000
Houses built on mud and sand don't do so well during an earthquake.

705
00:38:46,000 --> 00:38:47,000
Thanks, Dr. Tang.

706
00:38:47,000 --> 00:38:48,000
You're welcome.

707
00:38:51,000 --> 00:38:52,000
So what's up?

708
00:38:52,000 --> 00:38:54,000
Could a thunderstorm have caused the tremor?

709
00:38:54,000 --> 00:38:57,000
Will S&P waves help solve the mystery?

710
00:38:57,000 --> 00:39:00,000
What should the Treehouse Detectives investigate next?

711
00:39:00,000 --> 00:39:04,000
Don't miss the exciting conclusion of The Case of the Shaky Quake.

712
00:39:08,000 --> 00:39:13,000
In the conclusion of The Case of the Shaky Quake, see if you can answer these questions.

713
00:39:13,000 --> 00:39:17,000
How many earthquakes occur each year?

714
00:39:17,000 --> 00:39:22,000
How many seismic stations are necessary to pinpoint the epicenter of an earthquake?

715
00:39:24,000 --> 00:39:28,000
What are the differences between meteors, meteorites, and meteoroids?

716
00:39:32,000 --> 00:39:33,000
Why are you so down?

717
00:39:33,000 --> 00:39:39,000
I called the Weather Service, and they said they didn't record any lightning strikes in our area on the day we felt the last tremor.

718
00:39:39,000 --> 00:39:44,000
Maybe I shouldn't mention that I called another seismologist at Virginia Tech, which is about 300 kilometers away,

719
00:39:44,000 --> 00:39:47,000
and their seismograph picked up something around the same time that we felt the tremor.

720
00:39:47,000 --> 00:39:50,000
So that doesn't mean my thunder hypothesis is wrong.

721
00:39:50,000 --> 00:39:52,000
It might. Think about it.

722
00:39:52,000 --> 00:39:54,000
The seismologist said it was clear that day.

723
00:39:54,000 --> 00:39:56,000
No thunderstorms in sight.

724
00:39:56,000 --> 00:39:59,000
Well, Mr. Lau said his seismograph only detects local thunder.

725
00:39:59,000 --> 00:40:01,000
Well, maybe you're right.

726
00:40:01,000 --> 00:40:06,000
The seismologist also said that eyewitnesses reported seeing a fireball in the sky, and they heard a loud noise.

727
00:40:06,000 --> 00:40:08,000
I don't remember seeing a fireball that day.

728
00:40:08,000 --> 00:40:10,000
Here comes Dr. Textbook.

729
00:40:10,000 --> 00:40:15,000
Hello! Dr. Textbook here with some earth-shattering facts.

730
00:40:19,000 --> 00:40:23,000
You'll never guess how many detectable earthquakes there are in the world each year.

731
00:40:23,000 --> 00:40:27,000
Try 500,000. That's half a million earthquakes a year.

732
00:40:27,000 --> 00:40:29,000
Californians, listen up.

733
00:40:29,000 --> 00:40:35,000
Every year, the southern part of California has 10,000 earthquakes, but most of them are not felt.

734
00:40:35,000 --> 00:40:37,000
Yee-haw!

735
00:40:37,000 --> 00:40:40,000
Now, which state is the most earthquake-prone?

736
00:40:40,000 --> 00:40:44,000
Not California. Try Alaska.

737
00:40:44,000 --> 00:40:47,000
It has a magnitude 7 earthquake every year.

738
00:40:47,000 --> 00:40:49,000
And here is a trick question.

739
00:40:49,000 --> 00:40:53,000
Is there such a thing as earthquake weather?

740
00:40:53,000 --> 00:41:00,000
No! Earthquakes happen in the cold, in the rain, and in the heat.

741
00:41:00,000 --> 00:41:05,000
Now, let's see if we can feel one of those 500,000 earthquakes.

742
00:41:06,000 --> 00:41:10,000
Not a very good idea.

743
00:41:10,000 --> 00:41:12,000
Earthquakes are like hurricanes.

744
00:41:12,000 --> 00:41:15,000
They're so powerful and can be so deadly.

745
00:41:15,000 --> 00:41:18,000
Look, we have an email from Jacob and RJ.

746
00:41:18,000 --> 00:41:23,000
They say Dr. D told them about how to use PNS waves to find the center of an earthquake.

747
00:41:23,000 --> 00:41:26,000
Dr. D says you must have three seismic stations to locate the epicenter.

748
00:41:26,000 --> 00:41:28,000
We have two. Maybe that's enough.

749
00:41:28,000 --> 00:41:30,000
I doubt it, but I have an idea.

750
00:41:30,000 --> 00:41:32,000
Let's write this off as kids class.

751
00:41:32,000 --> 00:41:34,000
I doubt it, but I have an idea.

752
00:41:34,000 --> 00:41:36,000
Let's write this off as kids class.

753
00:41:36,000 --> 00:41:40,000
And ask them if they know how to use S&P waves to map an epicenter.

754
00:41:40,000 --> 00:41:46,000
Hey, we have a response from Roberts Park Elementary School in Norfolk, Virginia.

755
00:41:46,000 --> 00:41:55,000
Hi, we're from Mr. Darrell Ransom's third grade class at Roberts Park Elementary School in Norfolk, Virginia.

756
00:41:55,000 --> 00:42:00,000
Hi, we're the Treehouse Detectives, and we see you're doing an activity to find out where an earthquake occurred.

757
00:42:00,000 --> 00:42:02,000
Could you tell us something about it?

758
00:42:02,000 --> 00:42:09,000
Sure. Our mentors from the Society of Women Engineers helped us with the activity called triangulation.

759
00:42:09,000 --> 00:42:12,000
It must have something to do with threes.

760
00:42:12,000 --> 00:42:17,000
Yes, we learned that in order to find the origin or epicenter of an earthquake,

761
00:42:17,000 --> 00:42:21,000
we needed data from three different seismic stations.

762
00:42:21,000 --> 00:42:23,000
Did you need any special materials?

763
00:42:23,000 --> 00:42:29,000
No, just a world map, a seismogram, a graph, and a drawing compass.

764
00:42:29,000 --> 00:42:31,000
What did you do next?

765
00:42:31,000 --> 00:42:40,000
First, we looked at the seismic recordings and determined when the S&P waves each arrived at the seismic station.

766
00:42:40,000 --> 00:42:43,000
How could you tell which one was which?

767
00:42:43,000 --> 00:42:47,000
We know the P waves travel faster and arrive first.

768
00:42:47,000 --> 00:42:51,000
We then found the difference between the two times in seconds.

769
00:42:51,000 --> 00:42:58,000
For example, at the Denver, Colorado station, the P waves arrived at 10 hours and 16 minutes,

770
00:42:58,000 --> 00:43:02,000
and the S waves arrived at 10 hours, 18 minutes, and 30 seconds.

771
00:43:02,000 --> 00:43:05,000
I know. The difference was 2 minutes and 30 seconds.

772
00:43:05,000 --> 00:43:13,000
That's correct. We then used the graph to mark off 2 minutes and 30 seconds along the edge of the piece of paper.

773
00:43:13,000 --> 00:43:21,000
We slid the paper along the graph between the S waves and the P waves to find the distance in kilometers that the waves had traveled.

774
00:43:21,000 --> 00:43:23,000
How far did the waves travel?

775
00:43:23,000 --> 00:43:26,000
About 1,600 kilometers.

776
00:43:26,000 --> 00:43:32,000
After finding the distance the waves traveled, we located the city on the map.

777
00:43:32,000 --> 00:43:37,000
We used the map scale and our drawing compass to measure that distance.

778
00:43:37,000 --> 00:43:42,000
We placed the point of our compass on the city and drew a circle.

779
00:43:42,000 --> 00:43:43,000
Why a circle?

780
00:43:43,000 --> 00:43:52,000
We know that the earthquake occurred 1,600 kilometers from Denver, but that could be 1,600 kilometers in any direction.

781
00:43:52,000 --> 00:44:00,000
So we used 1,600 kilometers as our radius, and the earthquake occurred somewhere along the circle.

782
00:44:00,000 --> 00:44:03,000
How do you pinpoint the location?

783
00:44:03,000 --> 00:44:08,000
We repeated the steps with the next seismic recording for Terre Haute, Indiana.

784
00:44:08,000 --> 00:44:13,000
But the two circles intersect at two different points. How can you tell which one is the epicenter?

785
00:44:13,000 --> 00:44:16,000
That's why you need a third seismic station.

786
00:44:16,000 --> 00:44:22,000
Once all three stations are plotted on the map, you find where the three circles intersect.

787
00:44:22,000 --> 00:44:27,000
The intersection is the approximate epicenter of the earthquake.

788
00:44:27,000 --> 00:44:33,000
Well, they answered one question for us. We really do need three seismic stations, not two, to map out the epicenter.

789
00:44:33,000 --> 00:44:35,000
Is the earthquake our only hypothesis?

790
00:44:35,000 --> 00:44:37,000
It is for me.

791
00:44:38,000 --> 00:44:43,000
Just joking. I think we need more conclusive evidence to show that it was an earthquake.

792
00:44:43,000 --> 00:44:44,000
Will this help?

793
00:44:44,000 --> 00:44:46,000
Arte, you're back.

794
00:44:46,000 --> 00:44:49,000
I have this DVD of Jacob and me in an earthquake.

795
00:44:49,000 --> 00:44:51,000
You were in an earthquake?

796
00:44:51,000 --> 00:44:55,000
Well, sort of, but really it was an earthquake room.

797
00:45:07,000 --> 00:45:10,000
That doesn't look like what we saw at our treehouse.

798
00:45:10,000 --> 00:45:13,000
This case isn't as easy to solve as the others.

799
00:45:13,000 --> 00:45:17,000
No one will confirm that it's an earthquake, not even a seismologist.

800
00:45:17,000 --> 00:45:21,000
Let's call another seismic station to see if they picked up a tremor on their instruments.

801
00:45:21,000 --> 00:45:23,000
Maybe that will help confirm it.

802
00:45:23,000 --> 00:45:25,000
I don't know why, but I think it's something else.

803
00:45:25,000 --> 00:45:29,000
Here comes KSNN. Maybe they have some more information.

804
00:45:29,000 --> 00:45:33,000
Ladies and gentlemen, we are continuing to investigate the recent tremors.

805
00:45:33,000 --> 00:45:36,000
It seems that the quakes felt by our viewers may have had different sources.

806
00:45:36,000 --> 00:45:39,000
For more, we go live to I Am Listening.

807
00:45:39,000 --> 00:45:43,000
Ted, I'm here with esteemed scientist Dr. Liz Ard.

808
00:45:43,000 --> 00:45:47,000
Dr. Ard, what can you tell us about the events of yesterday?

809
00:45:47,000 --> 00:45:52,000
Well, I Am, we have received vibration reports from cities all along the East Coast.

810
00:45:52,000 --> 00:45:57,000
Many people also saw a fireball, which we now believe was a meteor entering Earth's atmosphere.

811
00:45:57,000 --> 00:46:03,000
Our tracking cameras were able to record this image before the meteor flew out of sight.

812
00:46:03,000 --> 00:46:07,000
Amazing! Thank you, doctor. Back to you, Ted.

813
00:46:07,000 --> 00:46:12,000
Well, folks, those vibrations were merely giant explosions and huge meteors falling from space.

814
00:46:12,000 --> 00:46:15,000
Nothing to worry about.

815
00:46:15,000 --> 00:46:18,000
Nothing at all.

816
00:46:18,000 --> 00:46:20,000
Mommy?

817
00:46:20,000 --> 00:46:21,000
What's a meteor?

818
00:46:21,000 --> 00:46:24,000
I can tell you. I have my I Am Encyclopedia.

819
00:46:24,000 --> 00:46:27,000
Of course.

820
00:46:27,000 --> 00:46:34,000
Let's see. A meteor is a small piece of rock that enters the Earth's atmosphere and burns up as it falls.

821
00:46:34,000 --> 00:46:37,000
Could this meteor be our new hypothesis?

822
00:46:37,000 --> 00:46:41,000
No, I don't think so. We had a tremor, but not a fireball.

823
00:46:41,000 --> 00:46:46,000
Maybe we just didn't see it.

824
00:46:46,000 --> 00:46:50,000
It says in my notes that it was a cloudy day here.

825
00:46:50,000 --> 00:46:55,000
That's right. Regina Tech reported seeing a fireball, but they also said it was a clear day.

826
00:46:55,000 --> 00:46:58,000
I wonder if a meteor could travel faster than the speed of sound.

827
00:46:58,000 --> 00:47:02,000
If it did, then it could cause a sonic boom, just like an airplane.

828
00:47:02,000 --> 00:47:06,000
And we learned that sonic booms can cause tremors. That might work.

829
00:47:06,000 --> 00:47:08,000
Let's write the hypothesis like this.

830
00:47:08,000 --> 00:47:16,000
If a meteor or a fireball is moving faster than the speed of sound, then maybe it can form a sonic boom that causes the tremor.

831
00:47:16,000 --> 00:47:20,000
I think we really need to look into the meteor as the possible cause.

832
00:47:20,000 --> 00:47:22,000
We just talked to JPL. Let's call them again.

833
00:47:22,000 --> 00:47:24,000
Okay.

834
00:47:24,000 --> 00:47:26,000
Hi, Mr. Vahlke.

835
00:47:26,000 --> 00:47:29,000
It's neat that you actually have a meteorite named after you.

836
00:47:29,000 --> 00:47:33,000
Yeah, we're a little confused on what a meteor actually is.

837
00:47:33,000 --> 00:47:36,000
Isn't it the same thing as a meteoroid and a meteorite?

838
00:47:36,000 --> 00:47:38,000
I'm glad to help you.

839
00:47:38,000 --> 00:47:40,000
Actually, I had an asteroid named after me.

840
00:47:40,000 --> 00:47:42,000
It's easy to get them confused.

841
00:47:42,000 --> 00:47:48,000
Meteoroids are small pieces of rock from an asteroid or comet drifting in outer space.

842
00:47:48,000 --> 00:47:53,000
When a meteorite enters into the Earth's atmosphere and burns up, it's called a meteor.

843
00:47:53,000 --> 00:47:57,000
People often see these meteors and call them shooting stars.

844
00:47:57,000 --> 00:47:59,000
People near us have reported seeing a fireball.

845
00:47:59,000 --> 00:48:01,000
Is a fireball like a shooting star?

846
00:48:01,000 --> 00:48:05,000
Yes, a fireball is a name given to a particularly bright meteor.

847
00:48:05,000 --> 00:48:08,000
They are sometimes so bright they can be seen in the daytime.

848
00:48:08,000 --> 00:48:11,000
What's a meteorite?

849
00:48:11,000 --> 00:48:15,000
Most meteorites burn up completely when they enter into Earth's atmosphere.

850
00:48:15,000 --> 00:48:21,000
But if it's large enough and survives and impacts the Earth, it's called a meteorite, such as the one I'm holding here.

851
00:48:21,000 --> 00:48:25,000
Some meteorites can cause craters, such as the one in Meteor Crater in Arizona.

852
00:48:25,000 --> 00:48:30,000
We understand that a fireball was sighted near our town and that it may have caused a sonic boom.

853
00:48:30,000 --> 00:48:32,000
Is this possible?

854
00:48:32,000 --> 00:48:33,000
Yes, if it's large enough.

855
00:48:33,000 --> 00:48:38,000
The larger size will allow it to last longer and penetrate deeper into the atmosphere.

856
00:48:38,000 --> 00:48:43,000
The sonic boom is caused because the meteor is traveling faster than the speed of sound.

857
00:48:43,000 --> 00:48:47,000
Would a sonic boom from a meteor be powerful enough to cause a seismic reading?

858
00:48:47,000 --> 00:48:51,000
Yes, a seismometer will detect a sonic boom from a large meteor.

859
00:48:51,000 --> 00:48:57,000
However, to hear the sonic boom, you have to be relatively close, typically within 50 miles or so.

860
00:48:57,000 --> 00:49:01,000
And the fireball is visible as far away as 500 miles away.

861
00:49:01,000 --> 00:49:03,000
I would love to see one.

862
00:49:03,000 --> 00:49:09,000
Both fireballs are not observed because 75% of the Earth is ocean and there aren't too many people in the middle of the ocean.

863
00:49:09,000 --> 00:49:15,000
In July of 2001, there was a fireball that was seen from Virginia to Ontario, Canada.

864
00:49:15,000 --> 00:49:19,000
The sonic booms were reported by people stretched over an area of more than 100 miles.

865
00:49:19,000 --> 00:49:22,000
This has been a lot of help, Mr. Balki.

866
00:49:22,000 --> 00:49:24,000
I think we found the answer to our mystery.

867
00:49:24,000 --> 00:49:29,000
Dr. Peter Brown at the University of Western Ontario is an expert on fireballs.

868
00:49:29,000 --> 00:49:32,000
You might want to send him an email and ask him some more questions.

869
00:49:32,000 --> 00:49:34,000
Thanks so much.

870
00:49:34,000 --> 00:49:36,000
I'll send Dr. Brown an email.

871
00:49:36,000 --> 00:49:39,000
Wow, I didn't know there could be sonic booms from meteors.

872
00:49:39,000 --> 00:49:41,000
We talked about sonic booms being the answer.

873
00:49:41,000 --> 00:49:44,000
But not sonic booms from a meteor.

874
00:49:44,000 --> 00:49:47,000
Hey you guys, I just got an email from Dr. Peter Brown.

875
00:49:47,000 --> 00:49:52,000
He said it would take a meteor of several hundred kilograms, or the size of a small chair,

876
00:49:52,000 --> 00:49:56,000
to equal a sonic boom large enough to be recorded on a seismograph.

877
00:49:56,000 --> 00:49:57,000
Look at this.

878
00:49:57,000 --> 00:50:02,000
He also says that if a meteoroid is large enough, has enough energy, and travels deep enough into the atmosphere,

879
00:50:02,000 --> 00:50:05,000
then it can cause substantial shaking of the ground and windows.

880
00:50:05,000 --> 00:50:08,000
I think this is it. We might have the answer.

881
00:50:08,000 --> 00:50:10,000
I wonder what Dr. D thinks about this.

882
00:50:10,000 --> 00:50:12,000
Let's go see him.

883
00:50:12,000 --> 00:50:13,000
Okay.

884
00:50:15,000 --> 00:50:17,000
Hi Dr. D.

885
00:50:17,000 --> 00:50:19,000
Hi guys.

886
00:50:19,000 --> 00:50:22,000
We think we solved our problem.

887
00:50:22,000 --> 00:50:24,000
Great. Was it an earthquake?

888
00:50:24,000 --> 00:50:26,000
We're pretty sure that wasn't an earthquake.

889
00:50:26,000 --> 00:50:29,000
We think that we have proof that it was a sonic boom produced by a meteor.

890
00:50:29,000 --> 00:50:32,000
A meteor? How did you come to that conclusion?

891
00:50:32,000 --> 00:50:34,000
It wasn't easy.

892
00:50:34,000 --> 00:50:39,000
Tony kept insisting that it was an earthquake, but I knew the whole time that it was a sonic boom.

893
00:50:39,000 --> 00:50:40,000
Not really.

894
00:50:40,000 --> 00:50:42,000
We dismissed the sonic boom hypothesis in the beginning,

895
00:50:42,000 --> 00:50:45,000
because generally, planes don't fly that fast over land anymore.

896
00:50:45,000 --> 00:50:50,000
In the end, we came back to the idea of a sonic boom when KCN reported that a fireball had been seen

897
00:50:50,000 --> 00:50:52,000
around the same time the vibrations were felt.

898
00:50:52,000 --> 00:50:56,000
When we heard that the people at Virginia Tech saw a fireball, heard a sonic boom,

899
00:50:56,000 --> 00:50:59,000
and recorded seismic readings just moments before we did,

900
00:50:59,000 --> 00:51:01,000
it just didn't register that a meteor could be the answer.

901
00:51:01,000 --> 00:51:04,000
That's because it was overcast that day, and we didn't see a fireball.

902
00:51:04,000 --> 00:51:07,000
Who would have thought it would be a fast-moving chunk of rock?

903
00:51:07,000 --> 00:51:08,000
Would you think?

904
00:51:08,000 --> 00:51:11,000
Then we talked with some experts who told us that meteors can cause sonic booms.

905
00:51:11,000 --> 00:51:14,000
Well, it sounds like you've learned several important things.

906
00:51:14,000 --> 00:51:18,000
You've learned not to dismiss a hypothesis too quickly like you did with the sonic boom hypothesis.

907
00:51:18,000 --> 00:51:23,000
Yes, and Virginia Tech practically gave us the answer, but we didn't even consider it.

908
00:51:23,000 --> 00:51:27,000
Sometimes the answer is right in front of you, but you just can't see it.

909
00:51:27,000 --> 00:51:30,000
The problem is you haven't completely solved your mystery.

910
00:51:30,000 --> 00:51:32,000
We haven't? Well, what do you mean?

911
00:51:32,000 --> 00:51:34,000
We have lots of evidence.

912
00:51:34,000 --> 00:51:36,000
We knew it wasn't a construction blast,

913
00:51:36,000 --> 00:51:38,000
and we ruled out earthquakes for a number of reasons.

914
00:51:38,000 --> 00:51:41,000
We also eliminated thunder because there weren't any lightning strikes that day.

915
00:51:41,000 --> 00:51:45,000
So Dr. D, isn't our fireball explanation the best one?

916
00:51:45,000 --> 00:51:49,000
Quote the greatest detective of all time, Sherlock Holmes.

917
00:51:49,000 --> 00:51:53,000
Eliminate all other factors, and the one that remains must be the truth.

918
00:51:53,000 --> 00:51:55,000
Isn't that what we did?

919
00:51:55,000 --> 00:51:58,000
Well, I guess we didn't completely rule out earthquakes.

920
00:51:58,000 --> 00:52:01,000
You have shown that a fireball can cause a sonic boom,

921
00:52:01,000 --> 00:52:03,000
that a fireball was seen elsewhere,

922
00:52:04,000 --> 00:52:06,000
but you don't yet have enough evidence to really prove

923
00:52:06,000 --> 00:52:09,000
that the fireball caused the vibration you felt.

924
00:52:09,000 --> 00:52:12,000
In science, you quite often go with the best explanation,

925
00:52:12,000 --> 00:52:14,000
even though it's not proven beyond question.

926
00:52:14,000 --> 00:52:17,000
All who agree that this is the best explanation, say aye.

927
00:52:17,000 --> 00:52:19,000
Aye.

928
00:52:19,000 --> 00:52:21,000
You might have hit a lot of dead ends,

929
00:52:21,000 --> 00:52:23,000
but along the way you've learned a lot about earthquakes.

930
00:52:23,000 --> 00:52:26,000
Sometimes a journey is just as important as the destination.

931
00:52:26,000 --> 00:52:31,000
So you mean what we learned along the way is as important as reaching a conclusion?

932
00:52:31,000 --> 00:52:33,000
Something like that. Congratulations.

933
00:52:34,000 --> 00:52:36,000
Oh no, it's happening again.

934
00:52:36,000 --> 00:52:37,000
Can you guys feel that?

935
00:52:37,000 --> 00:52:38,000
Yes.

936
00:52:42,000 --> 00:52:44,000
We're off the wrong sonic boom.

937
00:52:44,000 --> 00:52:46,000
Watch the boom, Kathy.

938
00:52:47,000 --> 00:52:48,000
Ready, Mr. Franklin?

939
00:52:48,000 --> 00:52:49,000
Ready.

940
00:53:01,000 --> 00:53:03,000
Boom.

941
00:53:31,000 --> 00:53:32,000
Boom.

942
00:54:01,000 --> 00:54:03,000
Now, if you have any questions,

943
00:54:03,000 --> 00:54:06,000
please feel free to leave them in the comments below.

944
00:54:06,000 --> 00:54:07,000
Thank you for tuning in.

945
00:54:07,000 --> 00:54:10,000
And I'm going to leave you to play a little bit of Sonic Boom.

946
00:54:10,000 --> 00:54:12,000
So, thanks for tuning in.

947
00:54:12,000 --> 00:54:14,000
And thank you for watching.

948
00:54:14,000 --> 00:54:17,000
And we'll see you in the next video.

949
00:54:17,000 --> 00:54:18,000
Bye.

950
00:54:18,000 --> 00:54:19,000
Bye.

951
00:54:19,000 --> 00:54:20,000
Bye.

952
00:54:20,000 --> 00:54:21,000
Bye.

953
00:54:21,000 --> 00:54:22,000
Bye.

954
00:54:22,000 --> 00:54:23,000
Bye.

955
00:54:23,000 --> 00:54:24,000
Bye.

956
00:54:24,000 --> 00:54:25,000
Bye.

957
00:54:25,000 --> 00:54:26,000
Bye.

958
00:54:26,000 --> 00:54:27,000
Bye.

959
00:54:27,000 --> 00:54:28,000
Bye.

960
00:54:28,000 --> 00:54:29,000
Bye.

961
00:54:29,000 --> 00:54:30,000
Bye.

962
00:54:30,000 --> 00:54:31,000
Bye.

963
00:54:31,000 --> 00:54:32,000
Bye.

964
00:54:32,000 --> 00:54:37,000
Bye.

965
00:55:01,000 --> 00:55:06,000
Bye.

966
00:55:06,000 --> 00:55:11,000
Bye.

967
00:55:30,000 --> 00:55:35,000
Bye.

968
00:55:35,000 --> 00:55:40,000
Bye.

969
00:55:40,000 --> 00:55:45,000
Bye.

970
00:55:45,000 --> 00:55:50,000
Bye.

971
00:55:50,000 --> 00:55:55,000
Bye.

972
00:55:55,000 --> 00:56:02,000
Bye.

973
00:56:02,000 --> 00:56:09,000
Bye.