Download Notes on Earthquakes

Ch 15 Earthquakes

I. Earthquake – the shaking of Earth’s crust
caused by a release of energy; vibrations
made from rocks breaking
II. Forces Inside the
Earth
Elastic Rebound Theory
1. friction prevents movement
2. stress deforms plates
3. stress overcomes friction & plates move
suddenly because rocks have bent &
stretched until they have broken

Results : plates snap back to shape but at
new locations; Earthquake
B. Fault


Surface along which
rocks break
Rocks move in
different directions on
either side of a fault
http://www.thirteen.org/savageearth/earthqua
kes/html/sidebar1.html
C. Focus – place inside the Earth
where the quake actually occurs
D. Epicenter - pt.
on Earth’s
surface directly
above the focus
of the quake
E. 3 Forces Rocks Experience
1.
2.
3.
Compression – stress that squeezes
compacts
Tension – stress that causes
stretching & elongation
Shear – force that causes slippage &
the rocks on either side to move past
each other
III. Earthquake Information
A.
B.
Seismic waves - energy waves that
move outward from the earthquake
focus & make the ground quake
3 Types of Seismic Waves
1. Primary wave (P-wave)
2. Secondary wave (S-wave)
3. Surface wave (L-wave)
a. Love
b. Rayleigh
C. Primary waves
Compressional, travel through any
material: solid rock, magma, ocean
water, & air
 Compaction & stretching of rock
 Fastest wave 2 x speed of S waves

D. Secondary wave

Shear, travel through solids, not through
liquids or gases
E. Surface waves (Longitudinal waves)
- Waves that travel like ripples on a pond
across Earth's surface
 Travel out from the epicenter
 Particles move in an elliptical motion,
as well as back & forth
 Cause the most destruction
 Slowest waves
 Two types: Rayleigh & Love waves
Surface Waves
Rayleigh Waves
III. Locating an Earthquake

Seismograph - instrument that detects &
records earthquakes

Readings from 3 seismograph stations are
needed to locate the epicenter
 P-waves travel the fastest

The more time between the P & S waves,
the farther away the epicenter is

Damaged area increases as focus depth
increases
The difference in arrival times
between the P & S waves (from 3
different stations) is used to find
the distance to that earthquake.
The difference in arrival times is ___
A.
Richter Scale - the measure of the
amount of energy (magnitude)
released by a quake, each # is 32 x
greater in energy
B.
Moho Discontinuity - boundary
between the crust & the mantle

seismic waves speed up because they are
passing through a denser region
Moho Discontinuity
Seismology
– the study of earthquakes
– person who studies
earthquakes & seismic waves
Seismologist

Seismograph –
instrument used to
record seismic waves

Tsunami – ocean
waves generated by
earthquakes
Cove where Tsunami Hit in 1964
Height of Tsunami Wave
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