Geology Reference
In-Depth Information
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earthquakes. They think that this would relieve the
pressure on the fault and prevent a major earthquake from
occurring.
Although this plan is intriguing, it also has many po-
tential problems. For instance, there is no guarantee that
only a small earthquake might result. Instead, a major
earthquake might occur, causing tremendous property
damage and loss of life. Who would be responsible? Cer-
tainly, a great deal more research is needed before such an
experiment is performed, even in an area of low population
density.
What Would You Do
Some geologists think that by pumping liquids into locked
segments of active faults, they can generate small- to
moderate-sized earthquakes. These earthquakes would
relieve the buildup of pressure along a fault and thus prevent
very large earthquakes from taking place. What do you think
of this proposal? What kind of social, political, and economic
consequences would there be? Do you think such an effort
will ever actually reduce the threat of earthquakes?
During most of historic time, Earth's interior was perceived
as an underground world of vast caverns, heat, and sulfur
gases, populated by demons. By the 1860s, scientists knew
what the average density of Earth was and that pressure and
temperature increase with depth. And even though Earth's
interior is hidden from direct observation, scientists now
have a reasonably good idea of its internal structure and
composition.
Earth is generally depicted as consisting of concentric
layers that differ in composition and density separated from
adjacent layers by rather distinct boundaries (
Recall that the outermost layer, or
crust
, is Earth's thin skin.
Below the crust and extending about halfway to Earth's center
is the
mantle
, which comprises more than 80% of Earth's
volume. The central part of Earth consists of a
core
, which
is divided into a solid inner portion and a liquid outer part
(Figure 8.21).
The behavior and travel times of P- and S-waves pro-
vide geologists with information about Earth's internal
structure. Seismic waves travel outward as wave fronts from
their source areas, although it is most convenient to depict
them as
wave rays
, which are lines showing the direction
of movement of small parts of wave fronts (Figure 8.3).
◗
Figure 8.21).
TABLE 8.5
What You Can Do to Prepare for an Earthquake
Anyone who lives in an area that is subject to earthquakes
or who will be visiting or moving to such an area can take certain
precautions to reduce the risks and losses resulting from an
earthquake.
Before an earthquake:
2. If you are indoors, get under a desk or table if possible, or
stand in an interior doorway or room corner as these are the
structurally strongest parts of a room; avoid windows and
falling debris.
3. In a tall building, do not rush for the stairwells or elevators.
1. Become familiar with the geologic hazards of the area where you
live and work.
4. In an unreinforced or other hazardous building, it may be
better to get out of the building rather than to stay in it.
Be on the alert for fallen power lines and the possibility of
falling debris.
2. Make sure your house is securely attached to the foundation
by anchor bolts and that the walls, fl oors, and roof are all fi rmly
connected together.
5. If you are outside, get to an open area away from buildings
if possible.
3. Heavy furniture such as bookcases should be bolted to the walls;
semifl exible natural gas lines should be used so that they can
give without breaking; water heaters and furnaces should be
strapped and the straps bolted to wall studs to prevent gas-line
rupture and fi re. Brick chimneys should have a bracket or brace
that can be anchored to the roof.
6. If you are in an automobile, stay in the car, and avoid tall
buildings, overpasses, and bridges if possible.
After an earthquake:
1. If you are uninjured, remain calm and assess the situation.
4. Maintain a several-day supply of freshwater and canned foods,
and keep a fresh supply of fl ashlight and radio batteries, as well
as a fi re extinguisher.
2. Help anyone who is injured.
3. Make sure there are no fi res or fi re hazards.
5. Maintain a basic fi rst-aid kit and have a working knowledge of
fi rst-aid procedures.
4. Check for damage to utilities and turn off gas valves if you
smell gas.
6. Learn how to turn off the various utilities at your house.
5. Use your telephone only for emergencies.
7. Above all, have a planned course of action for when an
earthquake strikes.
6. Do not go sightseeing or move around the streets
unnecessarily.
During an earthquake:
7. Avoid landslide and beach areas.
1. Remain calm and avoid panic.
8. Be prepared for aftershocks.
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