Download Earthquakes By Steven and Amanda

Amanda Embrey and Steven Bomar
Chapter 8
EARTHQUAKES
WHAT ARE EARTHQUAKES?
Even though we believe that earthquakes are
just ground tremors, they are way more
complex than that. In order to understand them
more, we use seismology (the study of
earthquakes).
WHERE DO EARTHQUAKES OCCUR?
Earthquakes happen along tectonic plates. In
order for an earthquake to happen, though, the
plates must slide against and past each other.
Due to this movement, faults (breaks in the
Earth’s crust) may occur.
WHAT CAUSES EARTHQUAKES?
As tectonic plates move against each other,
stress builds up along the faults. Rocks may
change, which is a process called deformation
(the change in the shape of rock in response to
stress). In some circumstances, elastic
rebound (the sudden return of elastically
formed rock) may happen. This is when a rock
stretches out but doesn’t break. Deformed rock
also returns to it’s original state.
DIAGRAM OF ROCK DEFORMATION AND
ELASTIC REBOUND
TRANSFORMING
Transforming occurs where two plates slip past
each other. During this motion, strike-slip faults
may form. These faults cause moderate and
shallow earthquakes.
CONVERGING
Converging occurs where two plates push
together. This movement creates reverse faults.
Along these faults, strong and deep
earthquakes occur.
DIVERGING
Diverging occurs where two plates pull away
from each other. This motion causes normal
faults. Earthquakes that are weak and shallow
form along these faults.
HOW DO EARTHQUAKES TRAVEL?
After rock releases energy, the energy travels in
waves called seismic waves (waves of energy
that travel through the Earth). The two types of
waves are P waves (travel through solids,
liquids, and gases, and are the fastest) and S
waves (second-fastest seismic wave that move
rock back and forth).
LOCATING EARTHQUAKES
To locate earthquakes, instruments called
seismographs (located at for near the surface
of the Earth that record seismic waves)
measure the waves. A seismogram (another
instrument that measures waves) traces the
motion of the earthquake.
WHERE IN THE EARTH DO THEY HAPPEN?
The epicenter (the point on the Earth’s surface
directly above an earthquake’s starting point) is
where scientists measure the power of the
earthquake. The focus is where the earthquake
begins.
MEASURING EARTHQUAKE STRENGTH
Richter Scales are used to measure the
intensity of an earthquake. This scale ranges
from 2.0 to 10.0. When the measurement is
high, the power of the earthquake is high.
EARTHQUAKE HAZARD
Certain areas are more prone to earthquakes.
In the U.S., the west coast is more prone than
the east. This is because California etc. sits
near the tectonic plates. California experiences
an earthquake every day.
EARTHQUAKE HAZARD (CONTINUED)
The Gulf Coast and Midwest have a low
vulnerability to earthquakes. Areas that are not
near the tectonic plates do not experience
many.
EARTHQUAKE FORECASTING
Predicting earthquakes is difficult to do.
Scientists must monitor active faults regularly
in order to predict them. The strength of
earthquake is related to how often they occur.
THE GAP HYPOTHESIS
The gap hypothesis is another way of predicting
earthquakes. This hypothesis states that active
faults that have recently had an earthquake are
likely to have one again and will be strong. An
area of a fault that has very few earthquakes is
called a seismic gap.
EARTHQUAKES AND BUILDINGS
The damage done to a building during an
earthquakes varies with its strength. Some
buildings are modified to resist a certain
amount of damage from earthquakes. Even
though, the most strong buildings may crumble
if the strength is too high.
DISCOVERIES IN EARTH’S INTERIOR
A point in the Earth called a Moho has been
discovered. This point is where the speed of
seismic waves increase. A shadow zone is a
point on the Earth where seismic waves cannot
be detected when an earthquake occurs.
QUAKES AND SHAKES ON OTHER COSMIC
BODIES
Earthquakes are known to occur on the sun
and moon. On the moon, asteroid impacts can
cause moonquakes. On the sun, solar flares
cause sunquakes. Sunquakes are stronger
than earthquakes and moonquakes.
ARE YOU PREPARED FOR AN EARTHQUAKE?
If an earthquake is about to occur, it is advised
to put heavier objects on a lower shelf so that
nothing falls on your head. Also, it is best to
find shelter immediately under a table or in a
doorway.
VOCABULARY USED
Seismology
 Fault
 Deformation
 Elastic Rebound
 Seismic Waves
 P Waves
 S Waves
 Seismograph

Seismogram
 Epicenter
 Focus
 Gap Hypothesis
 Seismic Gap
 Moho
 Shadow Zone
