Transcript Chapter 19: Earthquakes - Richmond County Schools

Chapter 19: Earthquakes
What are Earthquakes?
• Natural vibrations of
the ground caused by
movement in fractures
in Earth’s crust or
sometimes volcanic
eruptions
• Most occur because of
movements along faults
• Irregular surfaces in
rocks snag and lock
causing stress to build
in the rocks
• When rocks meet their
elastic limit they break
causing an Earthquake
What is Stress and Strain
• Fractures form when stress
exceeds the strength of the
rock involved
• Strain occurs in response to
stress and causes the
material to deform
Three types of stress
• Compression – squeezes
• Tension – pulls apart
• Shear – Causes twisting
What Is a Fault
• A fracture or system of fractures along which
movement occurs
• 3 types of faults
– Reverse fault
– Normal fault
– Strike slip fault
What are seismic waves?
Vibrations of the ground
during an earthquake
P and S waves are called body
waves because they pass
through Earths interior
3 types of seismic waves
– Primary (P) – squeeze
and pull rocks along the
same direction the wave
travels
– Secondary (S) – cause
rocks to move at right
angels to the direction of
the waves
– Surface - cause up-anddown and side –to-side
as they pass through
rocks
What is the focus and epicenter of an
earthquake
• The focus of an earthquake
is the point of failure of
rocks at the depth where an
earthquake originates
• The epicenter of an
earthquake is the point on
earth directly above the
focus
Seismology is the study of earthquake
waves
• Seismometers or
seismographs are sensitive
instruments that detect and
record the vibrations of an
earthquake
• A seismogram is the record
produced by the
seismometer
• The different speeds of the
P and S waves are used to
determine the epicenter of
an earthquake
Clues to Earths Interior
• Seismic waves are
reflected and refracted
as they strike different
materials
– P waves travel through
the mantel fairly straight
– P waves are refracted or
bent at Earths core
– S waves do not enter
Earths core because they
do not travel through
liquid
Clues to Earths Interior
• Analysis of these waves
has enables scientist to
determine the structure
and composition of
Earths interior
– Disappearance of S
waves leads scientist to
believe Earth’s outer
core must be liquid
– Refraction of P waves
indicates the inner core
is solid
Seismology and Earths Interior
Measuring and locating Earthquakes
• Magnitude is a measure
of the energy released
during a earthquake
and can be measured
on the Richter Scale.
• Intensity is a measure
of damage caused by a
quake and is measured
by the Modified
Mercalli Scale
– Uses roman numerals
– Higher the number the
greater the damage
Measuring and locating Earthquakes
• Data from at least 3
• Most Earthquakes occur
seismic stations are
in areas associated with
needed to determine an
plate boundaries called
earthquakes epicenter
seismic belts
Earthquakes and Society
• Earthquakes can cause
structural damage,
landslides, soil
liquefaction, fissures,
fault scarps, uplift or
subsidence and
tsunamis
• Tsunamis is a large
destructive ocean wave
caused by an
underwater
earthquake.
Tsunami 2004
Probability of an Earthquake
• The probability that an area will have an earthquake
is based on the history of a region and the rate of
strain that builds on rocks