Earthquakes
• Many basic properties of earthquakes are
described in the Virtual Earthquake website.
• We will NOT review these properties in detail.
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seismograms
P waves
S waves
S-P interval
Determining epicenters
Magnitude
Richter Magnitude Scale
Earthquakes
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What is an earthquake?
How does the earth quake?
What makes the earth quake?
Where do earthquakes happen?
How do we describe the strength and energy of
earthquakes?
•  Can we predict earthquakes
•  How are Tsunamis related to earthquakes?
Seismograph Operation
•  Seismographs work on the principle of inertia.
•  The large mass of the seismograph tries to
remain at rest while the paper moves under it.
•  The paper moving with the earth causes wave
patterns to be recorded.
Seismograph
Seismograph
Seismograph
P and S Body Waves
L Waves - long period surface waves Richter Scale
•  The Richter Scale is a measurement of the
size of the earth quake.
•  The scale ranges from 0 to 12 and is
logarithmic.
•  The logarithmic scale means that Richter
measurement increase of one give 10 times
the intensity and 30 times the energy.
•  An increase of two gives 100 times the
intensity and 900 (30 squared) times the
energy.
Epicenter and Focus
•  The epicenter of the earthquake is determined
by measuring the difference in time for the P
and S waves from different locations like in
your internet exercise.
•  The epicenter of the earthquake is on the
surface directly above the focus of the quake.
•  Foci is the plural form of focus.
Epicenter, Focus, Fault
Fault
•  A fault is the crack in the bedrock that is
caused during an earthquake. •  The rock breaks and then slides along the
fault.
Faults
Hanging Wall
Foot Wall
Normal Faults
•  Normal faults form when the hanging wall
drops down. •  The forces that create normal faults are
pulling the sides apart, or extensional.
Reverse Faults
•  Reverse faults form when the hanging wall
moves up. •  The forces creating reverse faults are
compressional, pushing the sides together.
•  Together, normal and reverse faults are
called dip-slip faults, because the movement
on them occurs along the dip direction;
either down or up, respectively.
Strike-Slip Faults
•  Strike-slip faults have walls that move sideways, not up
or down. •  The slip occurs along the strike, not up or down the
dip. •  In these faults the fault plane is usually vertical, so
there is no hanging wall or footwall. •  Strike-slip faults are either right lateral or left lateral. •  That means someone standing near the fault line and
looking across it would see the far side move to the
right for right lateral and left for left lateral.
Earthquakes of the World
Earthquake Regions
Seismic Activity
West Coast Plates
Earthquake Causes
•  Earthquakes happen when two plates (think
plate tectonics) rub against each other.
•  Three types of boundaries happen between
plates - transform, divergent and convergent.
Plate Boundaries
Benioff Zone
Plate Movements
Benioff Zone
Subduction Zones
Subduction Zones
Tsunami
•  A Tsunami is a large wave produced
because of the uplift in the ocean floor
caused by an earthquake.
•  The wave often travels very quickly with
much kinetic energy in deep water and then
becomes very large (high) as the water gets
more shallow.
•  Life of a Tsunami
•  December 26, 2004 Tsunami
Tsunami Movie
December 26, 2004