Earthquakes Guided Notes (Answer Key)
Section 1
What Are Earthquakes?
Write your answer in your science journal.
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Explain where earthquakes take place.
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Explain what causes earthquakes.
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Identify three different types of faults that occur at plate boundaries.
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Describe how energy from earthquakes travels through the Earth.
Where Do Earthquakes Occur?
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Tectonic Plates Most earthquakes take place near the edges of tectonic plates.
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Faults As a result of tectonic plate movements, numerous features called faults exist in
the Earth’s crust. A fault is a break in the Earth’s crust along which blocks of the crust
slide relative to one another. Earthquakes occur along faults because of this sliding.
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Deformation Elastic deformation leads to earthquakes.
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Elastic Rebound The sudden return of elastically deformed rock to its original shape is
called elastic rebound. Elastic rebound is illustrated on the next slide.
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P Waves Waves that travel through solids, liquids, and gases are called P waves
(pressure waves).
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S Waves After being deformed from side to side, the rock springs back to its original
position and S waves are created. S waves, or shear waves, are the second-fastest
seismic waves.
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Surface Waves Surface waves move along the Earth’s surface and produce motion
mostly in the upper few kilometers of Earth’s surface.
Section 2
Earthquake Measurement
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Explain how earthquakes are detected.
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Describe how to locate an earthquake’s epicenter.
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Explain how the strength of an earthquake is measured.
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Explain how the intensity of an earthquake is measured
Locating Earthquakes
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Determining Time and Location of Earthquakes Seismologists use seismograms to
calculate when an earthquake began. Seismologists also use seismograms to find an
earthquake’s epicenter.
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The S-P Time Method Perhaps the simplest method by which seismologists find an
earthquake’s epicenter is the S-P time method. The next slide illustrates how the S-P
time method can be used to find an earthquake’s epicenter.
Measuring Earthquake Strength and Intensity
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The Richter Magnitude Scale Throughout much of the 20th century, seismologists used
the Richter magnitude scale, commonly called the Richter scale, to measure the
strength of earthquakes.
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Earthquake Ground Motion The Richter scale measures the ground motion from an
earthquake and adjusts for distance to find its strength.
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Modified Mercalli Intensity Scale Currently, seismologists in the United States use the
Modified Mercalli Intensity Scale to measure earthquake intensity.
Section 3
Objectives
Earthquakes and Society
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Explain how earthquake-hazard level is determined.
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Compare methods of earthquake forecasting.
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Describe five ways to safeguard buildings against earthquakes.
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Outline earthquake safety procedures.
Earthquake Hazard
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What Is Earthquake Hazard? Earthquake hazard is a measurement of how likely an area
is to have damaging earthquakes in the future.
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Area with a High Hazard The West Coast of the United States has a very high
earthquake-hazard level because it has a lot of seismic activity.
Earthquake Forecasting
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Strength and Frequency The strength of earthquakes is related to how often they occur.
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The Gap Hypothesis The gap hypothesis is a hypothesis that states that sections of
active faults that have had relatively few earthquakes are likely to be the sites of strong
earthquakes in the future.
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Using the Gap Hypothesis Some seismologists think the gap hypothesis helped forecast
the approximate location and strength of the 1989 Loma Prieta earthquake.
Earthquakes and Buildings
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Retrofitting The process of making older structures more earthquake resistant is called
retrofitting.
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Earthquake Resistant Buildings Architects and engineers use the newest technology to
design and construct buildings and bridges to better withstand earthquakes.
Are You Prepared for an Earthquake?
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Before the Shaking Starts The first thing you should do is safeguard your home against
earthquakes. Next, you should find safe places within each room of your home and
outside of your home.
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When the Shaking Starts The best thing to do if you are indoors when an earthquake
begins is to crouch or lie face down under a table or desk in the center of a room.
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After the Shaking Stops Remove yourself from immediate danger, such as downed
power lines and broken glass. Be aware that there may be aftershocks.
Concept Map
Use the following terms to complete the concept map on the next slide: seismograph,
seismic waves, earthquakes, surface waves, body waves, S waves.