# Warm Up – December 17 What kind of stress occurs at a divergent boundary? What type of fault is it? What landform is created? Tension Normal Fault Fault.

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Warm Up – December 17 What kind of stress occurs at a divergent boundary? What type of fault is it? What landform is created? Tension Normal Fault Fault Block Mountains

MYP Unit Question: How does land change? Area of Interaction: Environment Learner Profile: Thinker Standard: Investigate the scientific process of how the Earth's surface is made. Learning Target: Today I’m learning about seismic waves because earthquakes create seismic waves and change earth’s surface.

What are Earthquakes? The shaking and trembling that results from the movement of rock beneath Earth's surface.

Where Do Earthquakes Occur? Earthquakes occur along fault lines near tectonic plate edges. Near earth’s surface or deep inside.

The Three Types of Faults Plate MotionFault NameFault Movement Transform Boundary (shearing) Strike Slip Fault Convergent Boundary (compression) Reverse Fault Divergent Boundary (tension) Normal Fault Type of Stress?

What Causes Earthquakes? Stress builds on a rock, the rock shatters, releasing energy, creating an earthquake. What are the three types of stress? Tension, Compression, Shearing

How do scientists know which fault broke and triggered the earthquake? They use seismic waves to locate the focus.

Focus The point beneath Earth’s surface where rock breaks under stress and causes an earthquake

Epicenter The point on Earth’s surface directly above an earthquake’s focus

Seismic Waves

A vibration that travels through Earth carrying the energy released during an earthquake

There are three types of seismic waves: 1. Primary Waves: P-Waves 2. Secondary Waves: S-Waves 3. Surface Waves

Primary Waves (P-Waves) Begins at focus Arrives first Moves the fastest Move in back and forth in a straight line Move through solids and liquids; slows down in liquids.

Secondary Waves (S-Waves) Begins at focus 2 nd fastest to P-waves Vibrates side to side and up and down Can only move through solids; stops at liquids.

S-Wave Animation

Surface Waves Begins at epicenter Result of P-waves and S-waves when they reach the surface Slowest Slowest seismic waves roll Make the ground roll like ocean waves Responsible for surface damage and falling buildings.

How are P waves different from S Waves? P waves move back and forth P waves travel through solids and liquids Fastest from the focus S waves vibrate from side to side S waves can not move through liquids Second fastest from focus

Closing: Earthquake in Japan Homework: Fault Worksheet

Detecting Seismic Waves

Seismograph A device that records ground movements caused by seismic waves as they move through Earth

Describe how a mechanical seismograph records ground movement. A heavy weight attaches to a frame by spring or wire A pen connected to the weight rests its point on a rotating drum During an earthquake the seismic waves cause the drum to shake while the pen stays in place The pen records lines on the paper around the drum

Measuring Earthquakes

The Mercalli Scale

Mercalli Scale A scale that rates earthquakes according to their intensity and how much damage they cause Developed in the early twentieth century

Figure 14: How would you rate the damage to the Foligno city hall on the Mercalli scale? The damage would probably rate VII - VIII

The Richter Scale

Richter Scale A scale that rates seismic waves as measured by a particular type of mechanical seismograph

How does the Richter scale measure an earthquake? The Richter scale measures seismic waves using a seismograph Over time, mechanical seismographs were replaced by electronic seismographs

What is a strength of the Richter scale when measuring earthquakes? What is a weakness? Strength: Provides accurate measurements for small, nearby earthquakes Weakness: Does not measure larger and more distant earthquakes well

How are the Mercalli scale and the Richter scale similar? How are they different? Both measure the strength of an earthquake The Mercalli scale measures the strength in terms of extent people notice the earthquake and the amount of damage caused The Richter scale measures the size of seismic waves

The Moment Magnitude Scale

Moment Magnitude Scale A scale that rates earthquakes by estimating the total energy released by an earthquake

Why is the moment magnitude scale used today by geologists to measure earthquakes? The moment magnitude scale determines the total energy released by an earthquake This scale uses a electronic seismograph that can measure earthquakes that are big or small, and near or far Geologist examine movement along the fault and the strength of broken rock These two measurements give a more accurate measurement of an earthquake

On which scale would an earthquake’s strength vary from one place to another? Explain. The Mercalli scale because the amount of shaking that people would feel and the damage to objects would be greater in a place closer to the earthquake’s epicenter

Checkpoint (Page 68):What are three scales for measuring earthquakes? Explain what each one measures. Mercalli Scale Measures earthquakes on how much damage they cause Richter Scale Measures seismic waves using a seismograph Measures small and nearby earthquakes Moment Magnitude Scale Looks at the total energy released Measures large and distant earthquakes Helps scientists predict how much fault movement their was

Locating the Epicenter

How do scientists calculate how far a location is from the epicenter of an earthquake? Scientists calculate the difference between arrival times of the P waves and S waves The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

Figure 17: Use the map scale to determine the distances from Savannah and Houston to the epicenter. Which one is closer? Houston 800 Km Savannah 900 km

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