Earthquakes and Landscapes
Objectives
• Describe how earthquakes are produced by fault
movement and how their strength is measured
• Discuss the cause and behavior of tsunamis
• Consider the types of damage that earthquakes
produce
• Relate the spatial pattern of earthquakes to plate
tectonics
• Introduce the landscapes and landforms that
bear the signature of fault movement and
earthquakes
What Produces Earthquakes?
• Faults
– A fracture in crustal
rock where one side
is displaced with
respect to the other
side
Earthquakes
• Stress is applied to a body
of rock
• Rocks deform while
storing energy
• Eventually stress becomes
greater than the strength
of the rock and the rock
breaks
• Energy is released in the
form of seismic waves
• Seismic waves radiate in
all directions
Earthquakes
• Focus
– The location where
earthquakes originate
• Epicenter
– The point directly above
the focus on the Earth’s
surface
Measuring Earthquake Strength
• Magnitude
– Measures the amount of
energy released
• Seismograph
– Instrument used to
detect and record earth’s
motion
Base anchored to the surface of the Earth and
suspended weight records earth’s motion. © USGS
Measuring Earthquake Strength
• Intensity
– Measures the amount of shaking that has occurred
– Determined by humans and property damage
– The amount of shaking decreases with increasing
distance from the focus – attenuation
– Amplification occurs when the amount of shaking
increases with distance because of loose sediment
Descriptive table of Modified Mercalli Intensity scale. © USGS
Tsunami
• Giant sea wave
• Commonly referred to a
seismic sea wave
• Produced by a sudden
displacement of ocean
water
Earthquake Damage
• Damage not proportional
to magnitude
• Damage proportional to
population density
• Alaska (1964)
– 9.2M resulted in 131 deaths
• Haiti (2010)
– 7.0M resulted in 300,000
deaths
Earthquake Distribution
• Majority of earthquake occur along plate boundaries
• Greatest concentration along Circum-Pacific belt
Great Subduction Zone Earthquakes
9.0M+ and tsunami
• Japan (2011)
– 4th strongest quake
– Tsunami reached almost
30m (100 ft.)
• Strongest earthquakes
occur along subduction
zones
– Alaska (1964)
– Chile (1960)
– Sumatra (2004)
Intraplate Earthquakes
• Earthquakes that do
not occur along a
plate boundary
• Can potentially
cause more damage
because buildings
are not built to
withstand shaking
Earthquakes and Landscapes
• Fault scarp
– Exposed clifflike face
• Fault plane
– Contact surface along
which blocks move on
either side of a fault
• Fault trace
– Lower edge of a fault
scarp