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Locating Quakes
Chapter 4 Lesson 3
Objectives
• Define focus and epicenter, and describe how to locate an earthquake’s epicenter.
• Describe features of earthquake-resistant structures.
Main Idea
• Scientists can locate _______________ and _______________ their strength. Earthquakes
damage_______________ and_______________ habitats.
Vocabulary
• _________________________ – (noun), the point on the surface directly above the focus.
• _________________________ – (noun), the point underground where an earthquake begins.
• _________________________ – (noun), a measure of how much ground shaking an
earthquake produces.
• _________________________ – (noun), the amount of energy and earthquake releases.
• _________________________ – (noun), a huge sea wave produced by an earthquake, a
landslide, or volcanic eruption on the ocean floor.
Building Background
Earthquakes are the result of movement of rock at_______________. This movement produces
several types of seismic waves that caused the ground motion that result in____________________
damage.
At the Faults
• ____________________ in Earth’s crust are usually so small and slow you can’t even feel
them. But at times, these movements can be quick and_______________, causing sudden
and unexpected changes to Earth’s surface. Such movements typically happen
at_______________.
Types of Faults
• _______________ _______________ occur at or near divergent boundaries, places where the
Earth’s crust is being stretched apart. Eventually, the rock breaks. A fault forms when one
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block moves down the edge of a sloping_______________. Most normal faults
are_______________, with blocks of rock moving down by just a meter or so.
• _______________ _______________ usually occur at convergent plate boundaries, where
rock is being squeezed. As the rock breaks, one block is pushed_______________ along a
sloping crack. This type of fault often occurs in regions where one plate_______________
below the other.
• ____________________ _______________ occur where tectonic plates slide past each other
and transform-fault boundaries. In contrast to the other two types of faults, the movement
is____________________, is one block grinds past the other. California’s_______________
_______________ _______________ is a strike-slip fault.
Seismic Waves
• Remember that tectonic plates move very_______________. Sometimes rocks move along
easily with the plates, but they can also jam up against a plate or between
two_______________. Over time, stress builds up within the rock at the
plates_______________ against each other.
• Eventually, the stress becomes so great that the rocks_______________. The plates
shoulder and_______________ into a new position. This causes an_______________.
• The released energy during an earthquake travels and waves in all directions, including up to
the_______________. These waves are called_______________ _______________. They
cause the_______________ that is felt as an earthquake.
• Seismic waves that travel through Earth’s interior are called_______________
_______________. There are two kinds of body waves: _______________ and
_______________. P-waves or _______________ _______________, are an example of
longitudinal waves. Rocks move back and forth in the same direction the wave
_______________. P-waves are the fastest kind of seismic wave traveling at about
____________________ through the rock.
• During an earthquake, the first jolt or bad you feel is the arrival of the_______________.
The P-waves _______________ and _______________ on rock along their path. As P-waves
reach the surface, the ground cracks and crumples. P-waves can travel through solids and
liquids, including Earth’s liquid_______________ _______________.
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• The second type of body waves is the S-wave or _______________ _______________. Swaves are_______________ waves. Rocks move up and down or____________________ at
right angles to the direction the wave travels. S-waves are_______________than P-waves.
When S-waves it, you might feel a strong____________________ motion. S-waves can only
travel through solid_______________.
Surface Waves
• Surface waves travel only across Earth’s surface. The L-wave or_______________ wave is the
slowest. L-waves arrive just after both P-waves and S-waves. _______________
_______________ do not travel as far from an earthquake’s origin as body waves. They cause
a rolling motion on the surface that can cause great damage to_______________. L-waves
are often the most_______________.
• Although each type of wave differs in_______________, all seismic waves travel very fast.
• Compare the surface movements caused by P-waves and S-waves.
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Recording Seismic Waves
• When an earthquake strikes, sciences can quickly locate its_______________ and measure
its_______________. ____________________ are the main tools for measuring the strength
and duration of an earthquake. A_______________ detects and measures the amount of
ground motion during a quake. Scientists interpret these data to measure the strength of an
earthquake, also called its_______________.
• A seismograph produces a written trace of seismic waves called a_______________. Data
are recorded as lines on a drum or by a computer. One type of seismograph
measures_______________ motion. It consists of a rotating drum attached firmly to the
bedrock_______________. A weighted pen is suspended over the drum like
a_______________. The pen marks the paper wrapped around the_______________
_______________.
• When an earthquake strikes, the drum attached to the bedrock moves with
Earth’s_______________. The_______________ pen does not move. So it traces the
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movement of the drum beneath it. Seismographs also record aftershocks, which are
smaller_______________ that follow the first one. Aftershocks can occur for several days
after an earthquake.
• In what order do waves appear on a seismogram?
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