Transcript My Presentation on Earthquakes

What is an earthquake?
An earthquake is a shaking of the ground caused by the
sudden breaking and movement of large sections (tectonic
plates) of the earth rocky outmost crust. The edge of the
tectonic plates are marked by faults (or fractures ). Most
earthquake occur along the fault line when the plates slide
past each other or collide against each other. The shifting
masses send out shock waves that may be powerful enough
to alter the surface of the earth, thrusting up cliffs and
opening cracks in the ground. They also cause great damage,
collapse of man made structures, break power and gas lines,
landslides, snow avalanches, tsunamis and volcanic
eruptions.
Epicenter of an Earthquake
Images of an Earthquake
Types of Seismic Waves
 Seismology is the study of earthquakes and seismic waves that move
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through and around the earth. Seismic waves are the wave energy
caused by the sudden breaking of rocks within the earth or an explosion.
Earthquakes generate three types of seismic waves. These arrive at
seismic recording stations one after another.
P (Primary) waves: This is the fastest kind of wave and is the first to
arrive at a seismic station. This can move through solid rocks and fluids
like water layers of the earth.
S (Secondary) waves: These are the second waves you feel in an
earthquake. This is slower than the P wave and can only move through
solid rocks.
Surface waves: These travel only through the crust and are of a lower
frequency and easily distinguished on a seismogram as a result. Though
they arrive after the body wave, these waves are almost entirely
responsible for the damage and destructions associated with
earthquakes.
How are earthquakes measured
The first widely used method, the Richter scale, developed by Charles F.
Richter in 1934, and was specific to California earthquakes. This did not
provide accurate estimates for large magnitude earthquakes hence, the
development of the preferred Moment Magnitude scale which works
over a wider range of earthquake sizes and is applicable globally.
Moment Magnitude estimates are about the same as Richter magnitudes
for small to large earthquakes. But only the moment magnitude scale is
capable of measuring M8 (magnitude 8) and greater events accurately.
The moment magnitude scale is based on the total moment release of
the earthquake. Moment is a product of the distance a fault moved and
the force required to move it. Magnitudes are based on a logarithmic
scale. These scales can be used to describe earthquakes so small that
they are expressed in negative numbers.
Safety tips for earthquakes
 Have an earthquake readiness plan
 Consult a professional to learn how to make your home sturdier, e.g.
bolting bookcases to wall.
 Locate a safe place in the home that you can go to in case of an
earthquake. This area should be free of falling objects.
 Turn off gas and water mains.
 Keep a supply of canned food, first aid kit, water, dust masks and
goggles and a working battery operated radio and flashlights.
If shaking begins
 Drop down, take cover under a desk or table and hold on.
 Stay inside until shaking stops and you’re sure it’s safe to exit.
 Stay away from objects that can fall on you.
 If you’re in bed, stay there and hold on, protecting your head with a
pillow.
 Stay away from windows.
 If you are outdoors, find a clear spot away from buildings, trees and
power lines. Drop to the ground.
 If you are in a car, slow down and drive to a clear place. Stay in the car
until the shaking stops.