Chapter 10
Earthquakes
10.1 – How and Where Earthquakes Occur
Vocabulary:
Earthquake: The shaking of Earth’s crust caused by a release of energy.
The cause of most earthquakes is the strain (pressure) that builds up along
faults at or near boundaries between lithospheric plates.
Fault: A break in the lithosphere along which movement has occurred.
Focus: The point at which the first movement occurs during an earthquake
Epicenter: The point on Earth’s surface directly above the focus
Body waves: Waves that travel from the focus of an earthquake through
Earth
P waves: Primary/compressional waves that squeeze and stretch rock
material as they pass through Earth. P waves can travel through any
material – solid rock, magma, ocean water, even air
S waves: Shear waves/secondary waves cause particles of rock to material to
move at right angles to the direction in which the waves are traveling. S
waves can travel through solid material but not liquids or gases
Surface waves: Earthquake waves that travel along Earth’s surface. Love
Waves and Rayleigh waves are two types of surface waves
Key Idea: Most earthquakes result from the release of stress that has built up
at plate boundaries.
Stress builds at faults
↓
Plates shift/earthquake occurs
↓
Body Waves
Surface Waves
↓
↓
↓
↓
S waves
P waves
Love waves
Rayleigh Waves
S waves and Love waves are the waves that cause particles of materials to
move at right angles to the direction of the waves.
http://www.discoverourearth.org/student/earthquakes/index.html
http://earthquakes.usgs.gov/learning/animations/
10.2- Locating and Measuring Earthquakes
Vocabulary:
Seismograph: An instrument that detects and records waves produced by
earthquakes
Seismogram: The recording of an earthquake made by a seismograph
Magnitude: The measure of the amount of energy released in an earthquake
Key Idea: A seismograph is used to determine the magnitude of an
earthquake and the location of the epicenter.
Sesimograph
The instrument consists
of weight, pen, and
drum
Things both have in
common
Both the seismograph
and the seismogram are
used to detect
earthquakes
Seismogram
The record sheet,
indicates arrival time of
each type of wave
Why do we need seismograms from several locations in order to locate an
earthquake’s epicenter?
A seismogram indicates only the distance from a station to the epicenter;
therefore, the epicenter could be any point on a circle with that distance as a
radius. By picking three (3) or more stations, and drawing a circle around
each, scientists can locate the epicenter at the point where the three circles
meet.
The time at
which a seismic wave arrives at a seismometer. The image to the right shows a
seismogram with the P wave and S wave arrival times marked. According to this
example, the P wave arrived at the recording device shortly after 11:43 AM and
the S wave arrived shortly before 11:45 AM.
10.3 – Earthquake Hazards
Vocabulary:
Liquefaction: A temporary state in which loose soil and rock materials take
on the property of liquid, often as the result of severe ground shaking.
Aftershock: A smaller earthquake that follows a larger earthquake
Tsunami: A large ocean wave that results from an underwater earthquake,
landslide, or volcanic eruption
Seismic gap: An area along a seismically active fault where no earthquake
activity has occurred over a long period of time.
Key Idea: The amount of damage an earthquake causes depends on its
magnitude and where it occurs. Safe building practices can limit loss of life
and damage to property.
1.Type of earthquake damage
2. Preventing earthquake damage
a. Liquefaction more common on
a. determining what factors make
bogs and soft landfill
structures resist earthquake
b. Liquefaction can lead to
damage
foundation failure
b. revising building codes as in
c. There can be up to 1000
Japan
aftershocks a day after a major
earthquake
d. Aftershocks can lead to
ruptured gas lines and fires
e. Tsunamis can cause massive
destruction
3. Areas of earthquake risk
4. Predicting earthquakes
a. regions lying at plate
a. predicting when, where, and
boundaries, such as California,
what magnitude.
Alaska.
b. Plotting earthquake activity
b. Places where many faults are
along faults
buried beneath rock, such as
c. Identifying seismic gaps
New Madrid, Mississippi
http://www.geology.siu.edu/quakes/images/tsunami2.gif
Animation of tsunami caused by earthquake
10.4 – Studying Earth’s Interior
Key Idea: Scientists use data from seismic waves to learn about the
structure of Earth’s interior.
Difference between S waves and P waves:
S waves cannot travel through liquid Since S waves cannot pass through the
outer core, scientists believe that the outer core is liquid.
P waves can travel through any matter which includes: solid rock, magma,
ocean water, even air.
Shadow Zone:
This is the area where P waves are refracted and S waves cannot pass
through the liquid outer core.
University of Colorado / AP
A scientist studies the New Madrid seismic zone in Lake County, Tenn., in this
undated photo. A new study of the area found that the faults in the zone have
moved much less than expected -- a sign that the area may not generate any
more earthquakes.