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Earthquakes
Earthquakes
An earthquake is…
• The shaking of the earth’s crust caused by a release of energy.
• Earthquakes can be caused by:
– 1. Eruption of a volcano
– 2. Collapse of a cavern
• Earthquakes can be caused by:
– 3. Impact of a meteorite
– 4. Strain built up along boundaries between plates
A fault is…
• A break in the lithosphere along which
movement has occurred. Most
earthquakes occur in this way.
– Friction between plates prevents them from
moving, so strain builds up. The rock
deforms. Eventually, the strain becomes
great enough that the rock moves, and
returns to normal shape. This causes an
earthquake (elastic rebound theory).
–Friction between plates prevents
them from moving, so strain builds
up. The rock deforms. Eventually,
the strain becomes great enough
that the rock moves, and returns to
normal shape. This causes an
earthquake (elastic rebound
theory).
• Focus: the point at which the rock first
breaks and moves in an earthquake.
Below the surface.
.
• Epicenter: the point on the earth’s surface
directly above the focus.
Seismic Waves
• The energy released in an earthquake travels
in waves. There are three types:
–Primary waves (P waves)
–Secondary waves (S waves)
–Surface waves (Love and Rayleigh)
Primary Waves• Called P waves
• Compression waves- squeeze and
stretch rock (Push and Pull)
• Can travel through any material- solid,
liquids, and gases
• Travel the fastest
Secondary Waves• S waves
• Side to Side movement.
• Can travel only through solid
material, not liquids or gases
• Travel a little more than half the speed
of P waves
Surface Waves
• Seismic waves that travel along Earth’s
Surface
• When P and S waves reach the surface,
they make Surface waves
• There are two types, Love waves and
Rayleigh waves
• Cause lots of damage
Measuring Earthquakes• Seismograph:
Instrument used to measure an Earthquake
• Seismogram:
The paper record of the Earthquake data (shaking) is called a seismogram
The S-P Time
Interval is the
time between
the start of the
p wave and the
s wave.
Locating Earthquakes
• Because P waves and S waves travel at
different speeds, the difference in their
arrival times can be used to determine the
DISTANCE away an earthquake occurred.
Locating Earthquakes
• If you know the distance an earthquake
occurred from at least three different
seismic stations, you can determine the
location of the epicenter.
• Triangulation:
Using the S-P
time interval
data from 3
stations to
determine the
epicenter
Earthquake Magnitude: strength
measured by the amount of released energy
•Richter Scale by Charles Richter
•Each increase in number represents 10x an increase in power.
•Example: a 4.0 is ten times stronger than a 3.0
Earthquake Hazards
• Fire: Causes the most damage in an Earthquake, some utility lines and roads get damaged
• Liquefaction: When the ground turns to quicksand due to the shaking
• Tsunamis: Are caused by underwater earthquakes that make a big wave.
