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Guide
to Reading 
The topic of this chapter, earthquakes, is often
a favorite of readers. After all, quakes are dramatic events, potentially
dangerous, and many people live in or visit areas where a quake might
happen at any moment. Those who’ve experienced major quakes
aren’t always so fond of them. Many testify it’s profoundly
disturbing when the good old solid dependable Earth shakes and crashes
around you.
Nevertheless, with such widespread interest, everybody
kind of knows what an earthquake is. But there’s more to defining
an earthquake than most people realize, and the chapter begins with
more to say about the essentials (the what, why, how, where, and
when of quakes) than you’d expect. There’s seismicity,
focus, epicenter, foreshocks, aftershocks, and stick-slip behavior.
Most significant quakes are caused by movement along faults, so you’ll
read about hanging walls, foot walls, normal faults, reverse faults,
thrust faults, strike-slip faults, displacement, active faults, inactive
faults, and fault scarps and traces.
Keeping track of seismic activity is a worldwide
concern. You read about the instrument that detects and records quakes
(the seismograph) and how to interpret the seismograms it produces
(using arrival times and travel-time curves). Earthquakes come in
all sizes, from too small to be detected by humans to real monsters.
This chapter deals with three commonly used scales that rate quake
size more precisely: the Mercalli, Richter, and seismic-moment magnitude
scales.
When the question arises “Why do quakes occur
where they do,” guess what the answer is? By now you shouldn’t
be surprised: plate tectonics. The information in this section isn’t
new; it’s just presented in a way to point out the seismic
connections.
The last part of the chapter deals with how quakes
affect society. Types of damage from earthquakes vary. Naturally
there’s ground shaking and displacement, and depending on the
location, there can also be landslides, avalanches, liquefaction,
fire, tsunamis, and even widespread disease.
What can people do about earthquakes? We can’t
stop them. We’ve had limited success in predicting them (short-term
and long-term prediction, recurrence intervals, and seismic gaps).
Earthquake zoning and engineering seem to be the best ways to protect
human life and property.The chapter ends with a discussion of what
society as a whole can do and what you as an individual can do to
protect against quake dangers. It also reminds us that no matter
what we do, plate tectonics will continue to shift the world and
earthquakes will continue to shake it.
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Key Terms
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