Download How are seismic waves generated-Elastic rebound theory Describe

EARTHQUAKES
Tommy Her , Ben Lee , James Edwards , Chandler Collier, Brent Dorn,
and April Bartholomew (photographer)
Introduction to Physical Science, EMPACTS Project
C. Dianne Phillips, Instructor, NWACC, Bentonville, AR 72712
How are Seismic waves generated?
Seismic waves are tremors or vibrations in the Earth's crust that are caused by the
build up or accumulation of pressure (more correctly termed stress).
This accumulation of stress causes the rocks that make up the crust to deform
elastically. This is very similar to what happens when you squash or stretch a spring
and cause a form of energy to be stored in the rocks of the crust - technically
described as elastic potential energy. Strain energy increases and eventually
exceeds the ability of the rock to accommodate the stress applied.
When this stress gets too large, it exceeds the strength of the rocks in the crust and
causes a brittle failure. Brittle failures are failures where fractures form through the
material.
https://www.youtube.com/watch?v=yOGoKCK17a4
Elastic Rebound Theory
The elastic rebound theory is an explanation for how energy is spread
during earthquakes. As rocks on opposite sides of a fault are subjected to
force and shift, they accumulate energy and slowly deform until their internal
strength is exceeded. At that time, a sudden movement occurs along the
fault, releasing the accumulated energy, and the rocks snap back to their
original undeformed shape.
https://www.youtube.com/watch?v=zGcnUUaYXv4
Different types of Seismic Waves
 P waves- P-waves, also known as primary waves or pressure waves, travel at
the greatest velocity through the Earth. When they travel through air, they
take the form of sound waves.
 S waves- S-waves, also known as secondary waves, shear waves or shaking
waves, are transverse waves that travel slower than P-waves. In this
case, particle motion is perpendicular to the direction of wave
propagation. Again, imagine a slinky partially stretched, except this time, lift
a section and then release it, a transverse wave will travel along the length
of the slinky. S-waves cannot travel through air or water but are more
destructive than P-waves because of their larger amplitudes.
Seismogram
A seismogram is a graph output by a seismograph. It is a record of the ground
motion Seismograms typically record motions in three cartesian axes (x, y, and
z), with the z axis perpendicular to the Earth's surface and the x- and y- axes
parallel to the surface.
https://www.youtube.com/watch?v=Gbd1FcuLJLQ
Surface waves are similar in nature to water waves and travel just under the
Earth’s surface. They are typically generated when the source of the
earthquake is close to the Earth’s surface. Although surface waves travel more
slowly than S-waves, they can be much larger in amplitude and can be the
most destructive type of seismic wave. There are two basic kinds of surface
waves:
 Rayleigh waves- these waves travel as ripples like water.
 Love waves- they cause horizontal sheering of the ground. They are a bit faster
than Rayleigh waves.
What can seismic waves tell us?
Studies of the different types of seismic waves can tell us much about
the nature of the Earth’s structure.
For example, seismologists can use the direction and the difference in
the arrival times between P-waves and S-waves to determine the
distance to the source of an earthquake. If the seismographs are too far
away from the event to record S-waves, several recordings of P-waves
can be crunched in a computer program to give an approximate
location of the source.
Different kinds of Earthquakes
Earthquakes can come in three main forms, depending on the plate
movements that occur beneath the earth's surface. They could occur on a
Convergent Boundary, Divergent Boundary or a Transform Fault.
Convergent boundary: one plate is forced over another plate during movement creating a
thrust fault
Divergent boundary: plates are force apart each other, using forming a Rift Zone. This kind is
coming in ocean floors where new floors are created.
Transform fault: The plates slip by each other this is also called Strike-Slip.
Faulting?
Faulting is a break in the rocks that make up the Earth’s crust, along which
rocks on either side have moved past each other.
Difference between a fault and
a tectonic boundary.
Fault
 A fault is a break in the rock,
where each side of the rock
moves in opposite directions
Tectonic boundary
 A tectonic plate boundary is
simply where 2 plates meet
Links
 http://earthquakestoday.info/
 http://earthquake.usgs.gov/
 http://www.world-earthquakes.com/
 http://environment.nationalgeographic.com/environment/naturaldisasters/earthquake-profile/
 http://ds.iris.edu/seismon/
 http://quakes.globalincidentmap.com/
 http://www.emsc-csem.org/#2