Chapter 11 Section 3 Outline
People and Earthquakes
I.
Earthquake Activity: Earthquakes are natural geological events that provide
information about Earth. They cause billions of dollars in property
damage and kill approximately 10,000 people per year.
A. Studying and Measuring Earthquakes: Seismologists are scientists
who study earthquakes. They use seismographs and printed
seismograms to locate earthquake epicenters.
1. The Richter magnitude scale is used to describe the strength of
the earthquake and is based on the height of the lines on a
seismogram. The lines on the seismogram are a measure of the
energy released during an earthquake. This is called the
magnitude of an earthquake, which uses Arabic numbers.
2. The Richter scale has no maximum limit; however, scientists
believe a 9.5 would be the maximum strength of an earthquake.
3. For each 1.0 increase on the Richter scale, the height of the line is
10 times greater. However, for each 1.0 increase on the scale, 32
times more energy is released.
B. Past Earthquakes: Most earthquakes have magnitudes too low to be
felt by most humans; however scientists record thousands of
earthquakes every day. About 55,000 earthquakes occur each year,
but most have magnitudes between 3.0 and 4.9, which cause little or
no damage.
C. The Modified Mercalli Intensity Scale: This scale measures the
intensity of an earthquake based on the amount of structural and
geological damage caused by the earthquake. The Mercalli scale uses
Roman numerals instead of Arabic numerals.
1. Roman numerals I – IV would be mild earthquakes that cause little
or no damage and are only felt by a few people indoors.
2. Roman numeral IX would cause considerable damage and would
be felt by everyone.
3. Roman numeral XII would cause total destruction to buildings and
objects.
D. Liquefaction: This is when wet soil is shaken during an earthquake,
which causes the soil to act more like a liquid than a solid. When
liquefaction occurs, buildings can sink into the soil and collapse.
E. Tsunamis: An earthquake under the ocean pushes against the water,
sending energy through it. This energy creates a powerful, sea wave
called a tsunami.
1. Tsunamis can travel thousands of kilometers in all directions and
can reach a crest 30m high.
2. Just before a tsunami crashes onto shore, the water along a
shoreline can move rapidly toward the sea. This is a warning sign
that the tsunami is about to hit.
II. Earthquake Safety: Earthquakes cannot be predicted reliably, but action can
be taken to reduce damage and loss of life.
A. Quake-resistant Structures: Most deaths from earthquakes occur
when people are trapped in or under these crumbling structures.
1. Seismic-safe structures are being built to stand up to earthquake
vibrations.
2. New buildings are being built with supports called moorings.
Moorings are circular supports that are made of steel plates filled
with alternating layers of rubber and steel. These are placed
under buildings to act like cushions to absorb earthquake waves.
3. Older buildings are often supported with steel rods.
B. What to do before, during, and after an earthquake:
1. Before an Earthquake: Move heavy objects to lower shelves.
Learn how to turn off gas, water, and electricity. Secure and
support water heaters and gas appliances. New sensors are being
put on gas lines that automatically shut off the gas when
earthquake vibrations are felt.
2. During an Earthquake: If indoors, stay away from windows and
falling objects. Seek shelter under a table or doorway. If outdoors,
stay out in the open, away from power lines and parts of buildings
that can fall on you.
3. After an Earthquake: Evacuate any area that smells like gas. Stay
away from damaged buildings. Wear boots or sturdy shoes, and
beware of broken glass and rubble. Stay away from beaches, due
to the possibility of tsunamais.