Download Earth Quakes

Chapter 19
 Most
Earthquakes are the result of
movement in the Earth’s crust at the
tectonic plates.
 Rocks in the crust resist movement and
build up stress overtime.
 Stress is the total force acting on crustal
rocks per unit of area. When stress is
greater than the strength of the rocks,
they slip resulting in an earthquake.
 Compression: decreases
volume of
material
 Tension: pulls material apart
 Shear: twists material
 When material is subject to stress it can
become deformed; strain.
 When rocks break due to stress and
strain, it releases massive amounts of
energy this usually happens at Faults.
PRIMARY WAVES




Aka P waves
Behave like a compression
wave
P waves squeeze and push
rocks in the direction the
wave is travelling.
Travel fast!
SECONDARY WAVES




Aka S waves
Behave like a transverse
wave
S waves move
perpendicular to the
direction of the wave
Travel slower.
 Surface
waves: the slowest type of waves
which only travel along the Earth’s
surface, not the interior like the S and P
body waves.
 Surface waves usually cause the most
destruction because they move the
ground and take the longest time to pass.
 The point where the waves originate is
where the rock fails; the focus. The point
on the crust above this is the epicenter.
RICHTER SCALE



A scale that measures the
energy of the largest
seismic waves (in
magnitude) that are
produced during an
earthquake.
The numbers are
determined by the height
or amplitude of the waves.
A wave that measures 8 on
the Richter scale is 10 times
more energy than a 7.
MERCALLI SCALE


Measures Earthquakes by
how much damage they
cause.
See table 19.2 p. 540 in the
text.
A
large ocean wave generated by
vertical motions of the seafloor during an
earthquake.
 Wave spreads from the epicenter much
like the seismic waves.