Page 423 - Laboratory Manual in Physical Geology

BIG IDEAS PRE-LAB VIDEO

Earthquakes are vibrations of Earth that occur naturally
when magma moves beneath volcanoes, volcanoes
erupt, or rocks suddently rupture along faults. The
vibrations radiate outward as seismic waves, which
are detected at seismic stations and recorded as
seismograms. The seismograms can be used to calculate
distance from the earthquake, and seismograms from
three or more seismic stations can be used to determine
where the earthquake occurred. Geologists use models
to study the effects of earthquakes on natural materials
and human structures and mitigate earthquake hazards.

FOCUS YOUR INQUIRY

|
THINK How do bedrock and sediment behave during
About It earthquakes and how does this affect human-
made structures?

ACTIVITY 16.1 Earthquake Hazards Inquiry (p. 392 )

THINK | How can seismic wave data be used to locate the
About It epicenter of an earthquake?

ACTIVITY 16.2 How Seismic Waves Travel through Earth
(p. 392 )
ACTIVITY 16.3 Locate the Epicenter of an Earthquake
(p. 393 )
LA B O RA T O R Y 16 THINK | How do geologists use remote sensing, geologic

maps, seismograms, and first motion studies to
About It
analyze fault motions?

ACTIVITY 16.4 San Andreas Fault Analysis at Wallace
Creek (p. 394 )
Earthquake ACTIVITY 16.5 New Madrid Blind Fault Zone (p. 394 )

Hazards and Introduction

Human Risks Earthquakes are shaking motions and vibrations of
Earth caused by large releases of energy that accompany
volcanic eruptions, explosions, and movements of Earth’s
bedrock along fault lines. News reports usually describe an
C ONTRIBUTING A UTHORS
earthquake’s epicenter , which is the point on Earth’s surface
Thomas H. Anderson • University of Pittsburgh
(location on a map) directly above the focus (underground
David N. Lumsden • University of Memphis
origin of the earthquake, in bedrock) ( FIGURE 16.1 ).The
Pamela J.W. Gore • Georgia Perimeter College
episodic releases of energy that occur along fault lines strain
the bedrock like a person jumping on a diving board.
This strain produces waves of vibration and shaking called
An earthquake in Sichuan, China pulled this road apart, damaged seismic waves (earthquake waves). Seismic waves originate
this home, and caused boulders to fall from adjacent hillsides.
(USGS image by Sarah C. Behan) at the earthquake’s focus ( FIGURES 16.1 ) and travel in all
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