Earthquakes and Volcanoes Week 2 Reading
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Geology
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Dec 6, 2023
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Week 2 Reading / Questions (50 points)
In
Essentials of Geology
(13
th
Edition), read Chapters 9 and 10 and answer the following questions:
1.
What is an earthquake? Under what circumstances do most large earthquakes occur?
An earthquake is a ground tremor brought on by abrupt and quick motion along faults in the
Earth. The majority of significant earthquakes happen when enormous quantities of energy that
have been trapped in the rocks suddenly release.
2.
How are faults, hypocenters (foci) and epicenters related?
Slippage of rocks that generate earthquakes occur along faults. The hypocenter is the place
slippage occurs between the rocks and the epicenter is the location on Earth’s surface directly
above the hypocenter.
3.
Describe how a seismograph works.
The inertia of the suspended weight keeps it motionless while the recording drum is secured to
solid ground. The magnitude of the seismic waves determines how much the recording drum
vibrates.
4.
List the major differences between P, S, and surface waves.
P waves are body waves that travel through materials compressed. S waves are shaking waves
that oscillate at right angles to the wave motion. Surface waves are the slowest wave type and
can cause the surface of Earth to shake laterally or vertically.
5.
What does the Modified Mercalli Intensity scale tell us about an earthquake?
It tells us the intensity of the ground shaking.
6.
How much more energy does a magnitude 7.0 earthquake release than a magnitude 6.0
earthquake?
It releases 32 times more energy.
7.
What is a tsunami? How are tsunamis generated?
A tsunami is a large ocean wave that spans the depth of the water column. Tsunamis are
generated when a large slab of seafloor is displaced along a fault which displaces the water
above it.
8.
What zone on Earth has the greatest amount of seismic activity?
The circum-Pacific belt.
9.
Explain why an earthquake east of the Rockies may produce damage over a larger area than one
of similar magnitude in California.
It’s because the underlying bedrock in the central and eastern United States is older and more
rigid.
10.
How do seismic waves help scientists describe Earth’s interior?
Because the scientists measure the arrival of seismic waves at stations around the world.
11.
How do continental crust and oceanic crust differ?
Continental crust is thicker, less dense, and more buoyant while oceanic crust is thinner and
denser.
12.
What are the three major topographic provinces of the ocean floor?
Ocean ridges, continental margins, and deep-ocean basins.
13.
Describe the differences between active and passive continental margins and give a geographic
example of each.
Passive margins are where flooded extensions of the continent merge into oceanic crust, and
there is active deposition. Active margins are too tectonically active with subduction for
sediments to accumulate, they form the Ring of Fire with active volcanism.
14.
Explain how deep-ocean trenches are related to plate boundaries.
Mid-ocean ridges are spreading centers, they are divergent plate boundaries where magma
wells up from below, creating new oceanic crust. Ocean trenches form where crustal plates
plunge back into the mantle. Thus, these long, narrow depressions are associated with
convergent plate boundaries.
15.
Briefly describe the oceanic ridge system.
A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate
tectonics. This uplifting of the ocean floor occurs when convection currents rise in the mantle
beneath the oceanic crust and create magma where two tectonic plates meet at a divergent
boundary.
16.
Name a modern example of a continental rift.
East African Rift, Rhine Valley.
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