Seismic Waves

Lesson 4.1.2: Earthquakes and Seismic Waves Part 2

Multiple Choice

The Shaking and trembling that results from the movement of rock beneath the Earth's Surface is called an Earthquake

• True

• False

Multiple Choice

The _________ of an Earthquake is the point where two plates meet and rock is placed under stress until it begins to break or move

• Focus

• Epicenter

• Fault

• P-Wave

Multiple Choice

The Epicenter of an Earthquake is below the focus

• True

• False

Multiple Choice

The energy released by an earthquake move out from the Earthquake's _______ in the form of Seismic Waves

• Focus

• Epicenter

• Fault

• P-Wave

Multiple Choice

True or False: Seismic Waves only travel in one direction

• True

• False

Match

Match the following

• P waves

• S waves

• Surface Waves

Compress and expand the ground

Vibrate from side to side

can make the ground roll like Ocean Waves

• Compress and expand the ground

• Vibrate from side to side

• can make the ground roll like Ocean Waves

How are earthquakes measured?

• Two main methods are used to measure earthquakes

  • The amount of damage is measured using the Modified Mercalli Scale

  • ​The size of an Earthquake is measured using the Richter Scale

• Seismograph: An Instrument that records & measures an Earthquake's seismic waves

Grade 8 Ohio| Lesson 4.1

The Modified Mercalli Scale

• Measures the amount of shaking

  • Rated by peoples observations w/o any scientific instruments

    • Useful in areas that don't have the ability to build or store those machines

• Has twelve stages shown in Roman Numerals​

Grade 8 Ohio| Lesson 4.1

The Richter Scale

• Magnitude: a single number geologists assign to an Earthquake based on it's size

• The Richter Scale is the earliest magnitude scale

  • Rates earthquakes based on the size of waves recorded by seismographs

  • Uses multiple seismographs since waves energy decreases the farther out from the epicenter

• Moment Magnitude Scale: rates the total energy released by an earthquake

  • This is the number used in news reports

Grade 8 Ohio| Lesson 4.1

Comparing Magnitudes

• Moment Magnitude tells how much energy is released

  • Each one point on the scale is 32x larger than the point before

    • Magnitude 6 is 32x larger than Magnitude 5

  • Most Earthquakes are below Magnitude 5 and cause little damage

  • Only three Earthquakes have ever gone above magnitude 9

    • December 2004: Magnitude 9.2 in Sumatra

Grade 8 Ohio| Lesson 4.1

How is an Epicenter Located?

• Seismic Waves help identify an epicenter

• Thousands of Seismographs all over the world record the effects of different waves

  • Comparing where the most energy is recoded helps to find which ares is closest to the epicenter

  • Data from at least 3 Seismographs are needed

• Graphs of P and S Waves can get even more specific

  • The closer P and S waves are on a graph, the closer that spot is to the epicenter ​

Grade 8 Ohio| Lesson 4.1

How is an Epicenter Located?

Grade 8 Ohio| Lesson 4.1

Multiple Choice

Which Scale uses only people observations to describe an Earthquake

• The Modified Mercalli Scale

• The Richter Scale

• The Shake Rattle n'Roll Scale

• The Magnitude of Movement Sc

Multiple Choice

True or False: P waves can become surface waves when they reach the Earth's Surface

• True

• False

Multiple Choice

True or False: Geologists can pinpoint the epicenter of an Earthquake from Just two seismographs

• True

• False