Unit 4 – Earth’s Interior
Chapter 11 – Earthquakes
11.1
Forces Inside Earth
Causes of Earthquakes
- movement of Earth’s plates and faults due to potential and kinetic energy
- rocks bend and stretch due to elastic deformation
o pressure and movement causes the rocks to bend to a point and then they break
- rocks break along surfaces called faults
- the breaking causes vibrations that are earthquakes
Types of faults
- Types of forces:
o Compression
o Tension
o Shear
 Compression – force or stress that squeezes and compresses
 Tension – stress that causes rocks to stretch and become longer
 Shear – force that causes rocks on either side of fault to move past each
other
- Normal faults
o from tension forces
o rocks pull apart and one side sinks or drops
- Reverse faults
o From compression forces
o Rocks push together and one is raised over the other
- Strike-slip faults
o From shear forces
o Rocks slide past each other on the same plane
o Causes earthquakes
11.2
Earthquake Information
Types of Seismic Waves
- made by an earthquake
- Focus
o the point where the energy is released from Earth to cause the earthquake
 Primary Waves
 Waves that cause particles in rock to move back and forth in the
same direction
 Particles of rock squeeze together then stretch apart

-
-
-
 fastest
Secondary Waves
 Causes particles in rocks to vibrate at right angles to the direction
of the wave
 second
Epicenter
o The point on Earth’s surface directly above an earthquakes focus
 Surface waves
 Waves that travel along the surface of the Earth outward
 Cause most of the destruction of an earthquake
 Motion is up and down and side to side
 slowest
locating the epicenter
o all three types of waves do not travel at the same speed
o primary is fastest, and surface is slowest
o different speeds help find the epicenter
o Farther apart the waves, the further the distance from the epicenter
o At least 3 seismograph stations need readings
 Draw circles with their station as the center
 The radius is the distance of the wave from the station
 Three stations drawing circles – intersection is where the epicenter is
mapping the Earth’s interior
o different densities in Earth makes waves travel at different speeds
o allows scientists to decipher what the interior is composed of due to those
different speeds
o four basic parts:
 inner core – solid
 mostly iron, and some oxygen, silicon, sulfur, or nickel
 outer core – liquid
 mostly iron
 mantle – solid and liquid
 silicon, oxygen, magnesium, and iron
 crust – solid
 thinnest, outermost
Moho Discontinuity
- waves speed up when they reach the crust
- boundary between the crust and the mantle
o speed up because they are passing through a denser layer of Earth
o upper mantle
Plasticlike Layer
- primary and secondary waves slow down
- less dense
Shadow zone
- area where no seismic waves are detected
o secondary waves don’t pass through liquid
o primary waves get bent
o leaves and area blank
Mantle Samples
- magma contains some pieces of mantle that allows scientists to study the composition
- volcanic or lava eruptions from vents, fissures, or volcanoes can bring up pieces of the
mantle to study
Meteorites
- formed about the same time as Earth
- can help us learn more about our composition
- contain some of the same elements and minerals found in specimens on Earth