Earthquakes and
Society
Section 3
Chapter 7
Key Concept
 Studying seismic activity can help scientists
forecast earthquakes and reduce the damage
that earthquakes cause.
Earthquake Hazard
 Earthquake hazard is
a measurement of
how likely an area is
to have damaging
earthquakes in the
future.
Earthquake hazard in the U.S.
Earthquake hazard in the
world.
Earthquake Forecasting
Strength and Frequency
 Strong earthquakes
are more rare than
weak earthquakes.
 The weak
earthquakes release
small amounts of
energy over a long
period of time.
 The strong
earthquakes release
a huge amount of
energy all at once.
The Gap Hypothesis
 The Gap Hypothesis says that sections
of active faults that have had relatively
few recent earthquakes are likely to be
the sites of strong earthquakes
sometime in the future.
 These sections are called SEISMIC
GAPS.
 Stress builds in these gaps for long
periods of time and when it is suddenly
released it causes large-magnitude
(strong) earthquakes.
This web site will show you how
many earthquakes have
happened TODAY in California.
 http://earthquake.usgs.gov/eqcenter/recenteqsww/Maps/region/N_America.php
Using the Gap Hypothesis
 Earthquakes are very
difficult to predict.
 Not all scientists
think that the Gap
Hypothesis is a good
way to predicts
earthquakes,
although it has
worked in some
cases.
Reducing Earthquake Damage
 Much of the loss of human
life during earthquakes is
caused by buildings that
collapse.
 Retrofitting, making buildings
more earthquake resistant, is
being done to older
buildings.
 Architects and engineers use
the newest technologies to
design and construct building
and bridges to better
withstand earthquakes.
Click on this site and then click
‘animations’. There are movies
available instantly (some 45 minutes
long) showing earthquake
information. Take a look!
 http://earthquake.usgs.gov/learning/kids/
Earthquake resistant?
Earthquake resistant building
technology
 Mass damper–
 Active tendon system
 Base isolators cross braces
 Flexible pipes
 STUDY THE ILLUSTRATION ON PAGE
247 OF YOUR TEXTBOOK.
Are You Prepared for an
Earthquake?
Before the shaking starts
 Put heavy objects on low shelves
 Talk to a parent about having your home
strengthened
 Find places that are safe within each room of
your home and outside.
 Make a plan to meet with others in a safe place
after the earthquake
 Store water, nonperishable food, fire
extinguisher, flashlight with batteries, portable
radio, medicines and a first-aid kit in a place
that you can get to after the earthquake.
When the shaking starts
 Stay indoors until the shaking
stops.
 Crouch or lie down under a table
or desk in the center of a room.
 If you are outside, stay outside,
and lie face down away from
buildings, powerlines, and trees.
Cover your head with you hands.
 If you are in a car, stop the car
and remain inside.
After the shaking stops
 Identify immediate dangers, such as downed
power lines, broken, glass, and fire hazards.
 Stay out of damaged buildings
 There may be aftershocks, which may cause
more damage.
Tsunamis
 When earthquakes happen on the ocean floor,
they can cause tsunamis.
 A Tsunami is an extremely long wave that can
travel across the ocean at speeds of up to
800km/h.
 They are caused when an earthquake causes a
vertical movement of the sea floor.
 They can also be caused by underwater
volcanic eruptions, landslides, and meteorite
impacts.
Hyperlink to tsunami animation
 http://cais.cu.edu.eg/e/flash/TsunamiEn.swf
 In the open ocean, tsunami waves seem
very small.
 As waves enter shallow water along a
coastline, the energy of the waves is
compressed.
 The waves get taller. Sometimes taller
than 30 meters.
Destructive Tsunamis
 Tsunamis can cause large amounts of
damage and loss of life by smashing and
washing away anything in their paths.
 One reason tsunamis cause so many
deaths is that the ocean may recede far
from the shoreline as the waves
approach.
 When people go to see the exposed
ocean floor, they get caught as the
waves suddenly rush onto the shore.
After the tsunami
Monitoring Tsunamis
 Tsunamis are monitored by most of the nations
that border the Pacific Ocean.
 These countries provide seismic data to the
Pacific Tsunami Warning Center (PTWC)
 If a tsunami has been generated, a watch
bulletin is issued for the Pacific Ocean area.
 If the bulletin is upgraded to a warning,
agencies my order residents to evacuate.
Summary
 Earthquakes and tsunamis can affect human





societies
Earthquake hazard is a measure of how likely
an area is to have earthquakes in the future.
Scientists use their knowledge of the
relationship between earthquake strength and
frequency and of the gap hypothesis to forecast
earthquakes.
Homes, buildings, and bridges can be
strengthened to decrease earthquake damage.
People who live in earthquake zones should
safeguard their homes against earthquakes and
have an earthquake emergency plan
Tsunamis are giant ocean waves that may be
caused by earthquakes on the sea floor.