Download Introductory Presentation on Earthquakes

What should I know about
earthquake?
• What is an
earthquake?
•Earthquake is the Earth’s
natural means of releasing
stress.
•After applying enough force to
both ends of the pencil, the
pencil would break in the
middle, releasing the stress
you have put on it.
• Earth’s crust acts in the same way. As the
earth’s plates move side to side, up and
down and also interact head on, they put
forces on themselves and each other
breaking the crust.
• When this break occurs, the stress is
released as energy which moves through
the Earth in the form of waves, which we
feel and call an earthquake.
• Most often earthquakes that occur across
one plate due to movement on preexisting
faults.
What are faults?
• The outer part of the Earth is relatively
cold and so breaks if pushed quickly.
These breaks, across which slip has
occurred are called faults.
• Faults can be classified on the basis of the
direction of displacement relative to the
orientation of the fault plane at the time of
displacement.
• Three major types of faults are strike-slip,
normal, and reverse.
The relative displacement is parallel to the strike of the
fault.
Fundamental Mechanisms of
Faults
• September 2, 1999
• Fault Rupture from Izmit Earthquake
• Topographic humps offset by the fault reveal
stratigraphy. Bridge in background was knocked
down during earthquake.
How Do I locate earthquake’s
epicenter?
•Seismograms are used to determine
relative distances to earthquake
epicenters.
•Seismic travel time curves are used to
determine the actual distance to
epicenters.
•Triangulation is used to locate
epicenters.
How are earthquakes measured?
•Magnitude is the most common way of describing
an earthquake’s size.
•Magnitude is the number that represents the size
of an earthquake source as determined from
seismographic observations.
•The original earthquake magnitude scale was the
Richter scale (ML).
•The moment magnitude (MW) is the preferred
magnitude scale, as it provides the most reliable
estimate of the size of the largest quakes.
What is the intensity of an
earthquake describe?
• Intensity is a measure of
ground shaking describing the
local severity of an earthquake
in terms of its effects on the
earth’s surface and on humans
and their structures.
What’s the difference between
magnitude and intensity?
• Magnitude is a measurement of the
energy produced by an earthquake.
• Intensity is a measure of ground
shaking describing the local severity
of an earthquake in terms of effects
on the earth's surface and on humans
and their structures.
What should you do before the
next large earthquake?
• Earthquakes are inevitable, but the
damage from earthquakes is not.
• Earthquake damage and loss can
be limited by taking various
precautions during and after
earthquakes.
Seismic Waves
• Two different waves are
generated by the sudden
movement on a fault; Pwaves and S-waves.
• P-waves travel fastest and
consist of successive
contractions and
expansions, just like sound
waves in air.
• S-waves are transverse
waves and slower than Pwaves.
• On a seismogram from an earthquake, the
P-wave is the first signal to arrive, followed
by the slower S-wave, then the surface
waves. The arrival times of the P- and Swaves at different seismographs are used
to determine the location of the
earthquake. Given that we know the
relative speed of P- and S-waves, the time
difference between the arrivals of the Pand S-waves determines the distance the
earthquake is from the seismograph.
By looking at the seismograms from different recording stations we can
find out the epicenter of the earthquake. The signals arrive first at the
closest station and last at the one furthest away. The time difference
between the P- and S-waves tells us the distance the earthquake is from
the seismograph. By measuring this at three stations we can work out
where the epicenter is.
We need measurements from at least three stations to find the epicenter.
The intersection of the circles whose radius is equivalent to the distance
from the earthquake gives the epicenter.
•6.6
Magnitude
Earthquake
off the coast
of Japan, on
July 16,
2007.
•Landslide at
the
Oumigawa
train station.
Permanent lateral deformatiion of train tracks at the
arahama station, the result of compression due to
surface waves.
The Bhuj, India Earthquake of
January 26, 2001
Ground
subsidenc
e due to
reactivatio
n of Kutch
mainland
fault Zone.
A sand blow in the Rann of Kutch, a
manifestation of liquefaction.
Total crushing of ground floors due to failure of load bearing columns in well- built
new constructions at Manfera village.
2004 Parkfield Earthquake, CA.
Northwestern Turkey Earthquake of Magnitude 7.2,
on November 12, 1999.
Earthquake rocks Peru
A strong earthquake lasting more than a
minute has hit southern Peru, killing at
least 47 people and injuring hundreds.
A magnitude 6.2 earthquake
shook southern Peru on
Tuesday Killing at least one
person and damaging several
homes.
Offsets along the length of the
surface rupture
• Right lateral offset in
upper jack creek,
near the point of
maximum
displacement during
the November 3
earthqake.
• The surface rupture of
the Denali fault M7.9
earthquake,
November 3, 2002.
At least 500 people have
been killed and 1,500
injured after a powerful
earthquake struck off the
coast of Peru
Peru earthquake , August 19. 2007
Members of a church inspect the ruins with
a firefighter in Pisco, Peru, August 19,
2007.
8.0 magnitude earthquake in Peru
7 steps to earthquake safety
Identify potential hazards in your
home and begin to fix them.
• Secure your space by strapping
top heavy furniture and appliances
to walls.
• Add latches to kitchen cabinets
and secure TVs and other heavy
objects that can topple and cause
serious injuries.
#2 create a disaster preparedness
plan
• Plan now to be safe during earthquake. Identify
safe spots in every room, practice ‘drop,cover ,
and hold on”.
• Plan now how to respond after an earthquake.
• Plan now to communicate and recover after an
earthquake. Keep copies of essential
documents, provide all family members with a
list of important contact phone numbers.
#3 Create disaster supplies Kits
• Everyone should have personal disaster
supplies kit. Keep one kit in your home,
another in your car, and a third kit at work.
• Store a household disaster supplies kit in
an easily accessible location, with a threeday to one-week supply of essential items
like, sleeping bags, cooking utensils,
canned and packaged foods.
#4 Identify your building’s potential
weaknesses and begin to fix them
• Common building problems include
inadequate foundations, unbraced cripple
walls, unreinforced masonry.
#5 Protect yourself during
earthquake shaking… drop, cover
and hold on
• If your indoors, drop to the floor against
the interior wall and protect your head and
neck with your arms.
• You are less likely to be injured staying
where you are.
#6 After the earthquake, check for
injuries and damage.
• Check for injuries and get medical help.
Look for detailed instructions on first aid
measures.
• Check for gas leaks, damaged electrical
wiring, broken lights and appliances and
damaged masonry.
#7 When safe, continue to follow
your distaster plan.
• After the earthquake, use the information
you have put togerther in your disaster
plan and the supplies you organized in
your disaster kits.