Earth Science 8.3 Earthquake Hazards
Earthquake Hazards
Causes of Earthquake Damage
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The Prince William Sound
earthquake struck Alaska in 1964
and was the most violent
earthquake to hit North America
in the 20th century.
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It had a moment magnitude of
9.2 and lasted 3 to 4 minutes. It
left 131 people dead and
thousands homeless damaging
the major ports and towns of
Alaska.
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Had this earthquake happened in
more populated areas, it’s affect
would have been devastating.
Causes of Earthquake Damage
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An earthquake as powerful as
the 1964 earthquake in Alaska
can cause catastrophic damage.
But even less powerful
earthquakes still pose a severe
danger.
Earthquake related hazards
include seismic shaking,
liquefaction, landslides,
mudflows and tsunamis.
Causes of Earthquake Damage

Seismic Shaking:
 The ground vibrations caused by an
earthquake, called seismic shaking,
are the most obvious hazard of an
earthquake.
 Seismic waves interact to jolt and
twist structures. Buildings made of
unreinforced brick may collapse.
 Wood frame buildings may remain
intact but can be knocked clear off
their foundations.
Causes of Earthquake Damage

Seismic Shaking:
 Seismic shaking is generally
strongest closest to the epicenter.
 Strong seismic shaking can occur in
areas of loose soil or filled in land
far from an epicenter.
 The filled soil magnifies the
effects of the seismic waves.
 Structures in such an area can
experience severe damage though
far from the epicenter.
Causes of Earthquake Damage

Liquefication:
 Where sediment layers
and rock are saturated
with water, earthquakes
can cause a process
called liquefaction.
 When liquefaction
occurs, what had been
stable soil suddenly
turns into liquid.
Causes of Earthquake Damage

Liquefication:
 The liquid cannot
support buildings or
other structures.
Buildings and bridges
may settle and collapse.
 Underground storage
tanks or sewer lines may
float to the surface.
Causes of Earthquake Damage

Landslides and
Mudflows:
 Earthquakes can trigger
different types of mass
movements. These mass
movements can often do
more destruction and loss
of life than the initial
quake.
 Earthquakes often cause
loose rock and soil on
slopes to move. These
movements are called
landslides.
Causes of Earthquake Damage

Landslides and
Mudflows:
 In areas where the water
content of the soil is high,
an earthquake can start a
mudflow. During a
mudflow, a mixture of soil
and water slides downhill
rapidly burying everything
beneath.
Causes of Earthquake Damage

Tsunamis:
 A tsunamis is a wave
formed when the ocean
floor shifts suddenly
during an earthquake.
 In 2004, a magnitude 9.4
earthquake west of the
island of Sumatra in the
Indian ocean produced
devastating tsunamis.
Causes of Earthquake Damage

Tsunamis:
 Without warning, the
huge waves struck
coastal areas of
Indonesia, Sri Lanka,
Thailand and several
other countries killing
nearly 300,000 people.
Causes of Earthquake Damage
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Tsunami’s form when an
earthquake pushes up a
slab of ocean floor along a
fault.
An underwater landslide or
volcanic eruption can also
trigger a tsunami.
Once formed, a tsunami
resembles the ripples
created when you drop a
stone in the water.
Causes of Earthquake Damage
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A tsunami wave in open ocean
is only a meter high but
moves very fast; at hundreds
of miles per hour.
As the wave enters shallower
water near a shore, the
water slows down and the
waves begin to pile up.
When the waves do hit shore,
they are much bigger due to
the compression and hit with
devastating force sweeping
inland for miles.
Reducing Earthquake Damage
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Earthquake damage depends
on several factors.
Two very important factors
are the strength and
duration of the seismic
shaking and the materials and
design of structures.
Earthquake damage and loss
of life can be reduced by
determining the earthquake
risk for an area, building
earthquake resistant
structures, and following
earthquake safety
procedures.
Reducing Earthquake Damage
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The first step to reduce
earthquake risk is to asses
the danger or probability of
an earthquake in an area.
Earthquakes are most
common along the boundaries
of Earth’s tectonic plates.
Scientists use several
methods to determine
earthquake risk.
One way is to study historical
records of earthquakes and
look at where they have
occurred in the past.
Reducing Earthquake Damage
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Scientists also use devices to
measure the uplift,
subsidence, and strain on
rocks in the fault areas.
They also study seismic gaps.
A seismic gap is an area along
a fault where there has not
been any earthquake activity
for a long period of time.
Scientists hypothesize that
the buildup of strain along a
seismic gap will eventually
lead to an earthquake.
Reducing Earthquake Damage
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Scientists also look for
small warning signs that an
earthquake may be about
to strike. They may
measure water levels and
pressure in wells, radon
gas emissions, small
changes in the
electromagnetic properties
of rocks even.
Efforts at short term
prediction of earthquakes
are at present far from
adequate to allow timely
warning.
Reducing Earthquake Damage
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Seismic Design safety:
 Many modern cities in
earthquake prone areas,
such as San Francisco
and Los Angeles, have
modern building codes
that take earthquakes
into account.
Reducing Earthquake Damage

Seismic Design safety:
several examples
 Steel building frames are often
reinforced with cross-braces.
 Buildings are sometimes
mounted on large rubber and
steel pads called base-isolators
that absorb shock.
 Wooden frame houses are
often reinforced and bolted to
their foundations more
securely.
 Flexible pipes and automatic
shutoff valves prevent rupture
of gas and water lines and
leakage of gas or fluids.
Computer Lab:

After completing worksheet 8.3; use the internet to
research and find information on the following topic. Write
a short mini-report of three paragraphs minimum on the
following: DO NOT COPY, CUT OR PASTE: USE YOUR
OWN WORDS

In recent years, earthquake proofing has become an
important legal mandate in many cities around the world.
Research earthquake proofing and find at least 5 different
design techniques that are used to help earthquake proof
a building.