Chapter 19.1 EARTHQUAKES
Earthquakes
Natural vibrations
of the ground
caused by
movement along
fractures in the
crust or volcanic
eruptions
 Fractures form
when stress
exceeds the
strength of the rock

Types of Stress
 Tension-
pull
 Compressionpush
 Shear- twist
 Strain-
deformation
caused by stress
Ductile Deformation
Elastic deformation
occurs as a result
of low stress
 Ductile deformation
occurs when stress
is high
 When does
fracture occur?

Faults
 Fractures
in the Earth’s crust along
which movement occurs
Types of Faults
 Normal-
tension
 Reverse- compression
 Strike-slip- shear
Seismic Waves
(Primary) P-wavessqueeze and pull
rocks in the same
direction of the waves
 (Secondary) S-wavescause rock to move at
right angles to the
direction of the waves
 Surface waves- cause
rock to move up &
down

Focus- point where an earthquake originates
 Epicenter- point on surface directly above the
focus

Chapter 19.2 EARTHQUAKES
Seismology
Study of earthquake waves
 Seismograph/seismometer- register the vibrations
 Seismogram- the record of vibrations

Travel- time
 Travel
time for P and
S waves differ
 Can you tell which
ones reach a location
first?
 Where is the biggest
difference in the time
one wave arrives
before the other?
Clues to Earth’s Interior
P waves are
refracted in the
core
 S waves can not
travel through
liquids
 Behavior of
waves provide
details of Earth’s
interior structure
and composition

Chapter 19.3 EARTHQUAKES
Earthquake Magnitude and
Intensity
Magnitude- the
amount of energy
released during an
earthquake
 Richter scaleearthquake rating
based on the size of
the largest seismic
waves
 Increases by power of
10 for each magnitude

Moment Magnitude Scale
 Most
used today
 Based on the
size of the fault
rupture, amount
of movement
along the fault,
and the rocks’
stiffness
Modified Mercalli Scale
 Based
on the
amount of
damage done to
structures
 Measure of
intensity
Intensity Relates to
Magnitude
Locating an Earthquake
Distance from
epicenter is calculated
by comparing the
separation time
between P and S
waves
 3 locations are needed
to accurately
determine the
epicenter of the
earthquake
 Why?

Seismic Belts


80% occur in the Circum-Pacific Belt
15% occur in the Mediterranean-Asian Belt
Chapter 19.4 EARTHQUAKES
Earthquake Hazards
 Structural
Failure
 Pancaking
 Collapse
2010 Pichilemu earthquake in Chile
1999 Izmit earthquake in Turkey
Earthquake Hazards

Land and Soil Failure
 Liquifaction
 Seismic wave amplification
Liquifaction in Christchurch, NZ
Earthquake Hazards
 Fault
Scarps
 Vertical offset
Earthquake Hazards

Tsunamis
Seismic Risk
Earthquake Prediction
History
 Strain
Accumulation
