Earth'S Interior: By: Mumtaz Ali Khan
Earth'S Interior: By: Mumtaz Ali Khan
Earth'S Interior: By: Mumtaz Ali Khan
1) Seismic Waves
2) Gravity
3) Magnetic Field
SEISMIC WAVES
Two types of waves travel away from the focus of a seismic
event. These waves travel at different speeds. In addition to
surface waves, the waves that are providing evidence about
the interior of the Earth are 'P' waves (P standing for
primary or pressure), and 'S' waves (S for secondary or
shear). P-waves are faster than S waves.
P-waves can travel through solid rock and fluids, and 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.
SEISMIC WAVES
Gravity is a fundamental
force of nature. A
constant force in every
system on Earth.
Isostasy is gravitational
adjustment of the crust. 21
HOW DO WE KNOW ABOUT THE
EARTH INTERIOR IS LIKE ?
1) Drilling
2) Volcanic activity
3) Samples of the solar system (meteorites)
4) Study of seismic waves generated by earthquakes
and nuclear explosions
22
Seismograph Seismogram
DIFFERENCE BETWEEN SEISMOGRAM &
SEISMOGRAPH
• SEISMOGRAPH
Is an instrument that records movements within the earth.
• SEISMOGRAM
Is a graph output by a seismograph. It is a record of the ground
motion at a measuring station as a function of time.
SEISMOGRAM PRINTOUT
EARTH’S INTERNAL STRUCTURE
Earth
• Temperature 37000 C.
INNER CORE
• They can form in air, in water, and within the earth itself. Basically,
if a portion of the fluid is heated, it will become less dense than the
surrounding fluid and will eventually rise; if it is cooled, it will sink.
CONVECTION CURRENTS
The middle mantle
"flows" because of
convection currents.
Convection currents
caused by the very hot
material at the deepest
part of the mantle rising,
then cooling and sinking
again repeating this
cycle over and over.
CONVECTION CURRENTS
P waves S waves
SEISMIC SHADOW ZONES
• P-wave shadow zone (103°-142° from epicenter)
explained by refraction of waves encountering
core-mantle boundary.
• S-wave shadow zone (≥103° from epicenter)
suggests outer core is a liquid.
P waves S waves
P waves
THE INNER CORE
S waves
• Inge Lehmann discovered that the inner core was solid in 1936
by careful observations of P-wave refraction patterns through
the inner core.
THE CORE
• Core composition inferred from its
calculated density, electro-magnetic
properties, and composition of
meteorites.
Iron metal (liquid in outer core and solid in
inner core) best fits observed properties.
Iron is the only metal common in
meteorites.
• D layer or Gutenberg Discontinuity is
the core-mantle boundary, it is marked
by great changes in seismic velocity,
density and temperature.
Hot core may melt lowermost mantle or
react chemically to form iron silicates in this
zone and is called as ultralow-velocity zone
(ULVZ).
EARTH’S MAGNETIC FIELD
• A Magnetic Field (region of
magnetic force) surrounds the
Earth.
Field has north and south
Magnetic Poles.
Earth’s magnetic field is
what a compass detects.
Recorded by magnetic
minerals (e.g., magnetite)
in igneous rocks as they
cool.
EARTH’S MAGNETIC FIELD