1
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That must be the earthquake theater.

2
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I hope it's not like the hurricane room that Bianca and Catherine went to.

3
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Treehouse detectives?

4
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That's us.

5
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Nice to meet you, Dr. Tang.

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I hear you're interested in experiencing an earthquake.

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Well, I don't know about that, but we do need to learn more about how experts measure the

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power of earthquakes.

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One such scale is called the Richter scale.

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It tells us the strength of an earthquake.

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Are there other scales that scientists use?

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Now scientists prefer a more precise scale called the moment magnitude scale.

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It's a number that tells us about the energy released from an earthquake.

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What's the number of our earthquake?

15
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Well, if it was a quake that people could feel, it must be at least a 2.

16
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A moderate earthquake is about a 5.

17
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Wasn't there a major earthquake here in San Francisco in 1906?

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What was its number?

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It was a 7.7, but to understand what that means, you really ought to experience the

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earthquake.

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I'm not sure I want to do that.

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Don't worry.

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It's quite safe.

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We're doing it here in the Earthquake Theater at the California Academy of Sciences.

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Don't forget to bring the camera.

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I got it.

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At 5.40 on October 17, 1989, the San Francisco Wind Area experienced a powerful earthquake.

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Cool.

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It seems so real.

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How do scientists know so much?

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Well, we looked at people's diaries and also had houses and churches that were damaged

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during the earthquake and also how the earthquake ruptured the ground around San Francisco during

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the time period.

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I guess observations are important.

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Your science journal might be valuable evidence one day.

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Yes.

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Well, take a look at this earthquake questionnaire.

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You'll see that even today, even with sophisticated instruments, scientists still depend on people's

39
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experiences to understand earthquakes.

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Wow.

41
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Look at this.

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They want to know if it was difficult to stand or walk.

43
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And did objects rattle or fall off the shelf?

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Here's a simple question.

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What's your zip code?

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Does it make a difference where you live?

47
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Yes.

48
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The effects of an earthquake vary greatly depending on how far away from the source you are.

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You mean the farther away you are, the less shaking you feel from a quake?

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Yes, but it also depends on what the ground is like.

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What does the ground have to do with it?

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Well, let's take a look at this gelatin.

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If I push on it even a little bit, it jiggles a lot.

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And yet, if I take a rock, no matter how hard I push on it, it's not going to jiggle at

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all.

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I know where I would want to stand during an earthquake.

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Solid rock.

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That's right.

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Houses built on mud and sand don't do so well during an earthquake.

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Thanks, Dr. Tang.

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You're welcome.