Ms. Scott
 Scientific
study of earthquakes (the seismic
waves they generate)
 It
is through this study that we have an
understanding of what the interior of the
Earth is comprised of.
 When
an earthquake occurs, the energy
releases seismic waves that move outward
from its focus(center) in all direction
 Using

a seismographs
Sensitive instruments positioned hundreds and
and even thousands of kilometers from an
earthquake
 There



are three main kinds of seismic waves
P or Primary Waves
S or Secondary Waves
L or Long( Love) Waves
P
waves are the fastest of the waves
 Penetrate the earth’s interior.
 Compressional waves since they alternatively
push (compress) and pull (dilate) the rocks
through which they pass
 Can pass through both solid and liquid
 Can be detected far away from the focus

Which leads scientist to believe that the core is
in a liquid (or semi-liquid state)
S
waves are slower, transverse waves that
travel through the rock by moving it from
side to side (shearing the rock)

Due to this action this wave can only travel
through solid formations
 On

page 62 (figure 4.11)
Shows how seismic waves are bent, or refracted
as the move across the boundaries between the
layers with differing density

This bending creates two shadow zones where there
are no P or S waves detected.
 Travel
on the surface of the earth and shake
the rocks sideways as they progress across
the surface
 The
distance from the seismic station to the
earthquake’s epicenter (the point on the
earth’s surface directly above the focus) can
be determined
 The actual location of the earthquake can be
plotted on a map using distance calculation
from at least 3 different seismic stations.
 Scientists use the seismic information to
determine the nature of the interior of earth

The speed of the seismic eaves gives an
indication of the density (the denser the material
the faster the waves can travel)