Download P and S waves moving through the Earth`s Interior

P and S waves moving through
the Earth’s Interior
• S and P waves are shock waves that are sent
out as a result of an earthquake.
• These waves are similar to water waves
• Shock waves are created by a disturbance in
an object and the shock of the disturbance
creates waves, that also have wavelengths,
amplitude, and frequencies.
• The waves depend greatly on the
composition that they are trying to pass
through, which gives scientists a great deal
of information about the interior of the
Earth.
• P waves travel fastest and are the first to
arrive from the earthquake. In S or shear
waves, rock oscillates perpendicular to the
direction of wave propagation. In rock, S
waves generally travel about 60% the speed
of P waves, and the S wave always arrives
after the P wave.
• P waves, or primary waves, are the first type
of waves to be felt at a considerable
distance, and they travel very fast, more
than 13,000 miles per hour.
• Animation of P and S waves
We can use P and S waves and
their characteristics to map the
interior of the earth.
Scientists deduced the structure of Earth's
interior and how waves move through it by
analyzing thousands of earthquakes recorded at
Earth's surface.
• Seismic waves have helped scientists learn
the various densities of the Earth's many
layers because the speed of P waves moving
through the earth generally increases with
depth. This is because as density increases,
seismic wave velocity increases.
P waves
• travel through the Earth's crust at an average
of about four miles per second
• they reach an average of seven miles per
second at the center of the Earth.
• When the waves suddenly shift in direction
and speed, scientists are able to determine
the depths at which Earth's various layers
are located.
P waves
• Can travel through solid rock and fluids
• their speed will vary depending on the
density of the rock through which they
travel
• increased speed will indicate increased
density, thus providing information about
the density and possible mineralogy of
Earth's various layers.
• The seismologists record the travel time it takes
from the time the waves are released to the time it
penetrates the other side. By triangulating these
measurements, the seismologists can get a better
understanding of the composition of what the
waves are traveling through. The waves travel at a
higher velocity when going through denser
materials. By noting where the waves have
considerable velocity changes, the seismologists
can infer where the composition boundaries are,
giving them the ability to map the interior of the
Earth.
S waves
• cannot travel through fluids
• thus when an S-wave encounters the outer core of
the Earth (liquid iron and nickel), it is disrupted
• This indicates the boundary between the mantle
and outer core and the boundary between the
inner core and outer core. The effect observed
from the motion of S-waves reveals a 'shadow
zone', opposite to where they originate.
Animation of P and S
video
• P and S waves and shadow zones in earths
interior
• http://www.youtube.com/watch?v=yOGoK
CK17a4&feature=related
Crust:
• A very thin, solid outer layer. The oceanic
crust is about 3 miles thick. The continental
crust is from 18–24 miles thick.
Moho:
• The boundary between the crust and the
mantle.
Mantle:
• The layer beneath the crust. The mantle is
about 1790 miles thick.
Upper mantle:
• Includes a solid layer fused to the crust.
This layer combined with the crust is called
the lithosphere. Beneath this is the
asthenosphere, which is a partly molten
layer. The asthenosphere is thought to be the
layer upon which tectonic plates ride. The
upper mantle is about 420 miles thick.
Lower mantle:
• Is composed of solid rock under conditions
of extremely high temperature and pressure.
This layer is about 1,370 miles thick.
Outer Core:
• A layer about 1,400 miles thick, having the
properties of a metallic liquid.
Inner Core:
• A solid, metallic, spherical layer about 755
miles thick.
• Earth Scientist at University discussing interior
and P and S waves……first few min and skip to
21:53 to 23:10 min.
http://www.youtube.com/watch?v=ve7N25R2h4c
&feature=fvw
• http://www.youtube.com/watch?v=4nS10xNBfVE
&feature=related shows seismic wave animation
seismographs
• http://www.youtube.com/watch?v=eE54rBa
k8vA
iPhone App seismograph
• http://www.youtube.com/watch?v=YjutFgj0
tLY
• Constructive and destructive processes