Chapter 4: The Earth’s Interior
Geophysics – application of physical laws and principles to a study of the Earth (includes study of
seismic waves and Earth’s magnetic field, gravity, and heat)
WHAT CAN WE LEARN FROM THE STUDY OF SEISMIC WAVES?
Seismic Reflection – return of some energy of seismic waves to the Earth’s surface after waves bounce
off a rock boundary
Seismic Refraction – bending of seismic waves as they pass from one material to another (similar to how
light waves bend when passing through lenses of eyeglasses.
Diagram 4.3 pg. 107 (Station 1 and Station 2)
WHAT IS INSIDE THE EARTH?
Crust – outer layer of rock, which forms thin skin on Earth’s surface
Mantle – lies below crust, thick shell of rock that separates crust above from core below
Core – central zone of Earth, probably metallic and source of Earth’s magnetic field
•Seismic waves travel faster in oceanic crust than in continental crust
•Seismic P waves travel through oceanic crust at about 7 km/sec and through continental crust at
about 6 km/sec
•Average thickness of oceanic crust is 7 km varying from 5-8 km. Avg. thickness of continental
crust 30-50 km varying from 10-70 km.
•Felsic – rocks high in feldspar, Silicon – for continental crust, Mafic – rocks high in magnesium
and iron (ferric) – for oceanic crust
•Continental crust less dense the oceanic crust
•Mohorovičić discontinuity (Moho) – boundary separating crust from mantle beneath
•Geoscientists interpret it to be made of solid rock
•P waves travel at about 8 km/sec in upper mantle
•Mantle different type of rock from oceanic or continental crust, hypothesis of geoscientists say it
is made up of Ultramafic rock
•Ultramafic Rock – dense igneous rock compose mainly of ferromagnesian minerals such as
olivine and pyroxene