EARTHQUAKES AND
EARTH’S INTERIOR
Objectives
• Explain the connection between earthquakes and plate
tectonics.
• Identify several earthquake-related hazards.
• Define body waves and surface waves.
• Explain how the materials in Earth’s interior affect
seismic waves.
• Define and describe the composition of Earth’s crust,
mantle and core.
Megathrust earthquakes
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Earthquakes and earthquake
hazards
• Seismology
– The scientific study of
earthquakes and seismic
waves
• Seismic waves
– An elastic shock wave
that travels outward in all
directions from an
earthquake’s source
• Seismic creep
Earthquakes and plate motion
• The elastic rebound
theory
– Continuing stress along a
fault
– Results in buildup of
elastic energy in the
rocks
– Energy abruptly released
when an earthquake
occurs
Earthquakes and plate motion
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Earthquake Hazards and
Predictions
• Primary hazards
– Collapsing buildings, bridges and other structures
– Aftershock
• Secondary hazards
– Landslides, fires, ground liquefaction, tsunamis
Earthquake hazards
Landslide, Huascaran, Peru
Open fissure, Golcuk, Turkey
Earthquake hazards
Fire, San Francisco, California
Ground liquification, Niigata, Japan
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Tsunami (Seismic Sea Wave)
The Sumatra-Andaman Tsunami
(2004)
Earthquake prediction
• Short-term prediction and early warning
– Precursor phenomena
– Foreshocks
• Long-term forecasting
• Paleoseismology
– The study of prehistoric earthquakes
– Seismic gaps
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When did the last
earthquake
occur?
Earthquake Readiness
• Preparation and
readiness to
earthquakes key to
reducing fatalities
– Reinforced structures
– Bolting wood-framed
buildings to foundation
– Protecting utility lines from
movement
– Education
The Science of Seismology
• Seismograph
– An instrument that detects
and measures vibrations of
Earth’s surface
– Advanced seismographs
detect vibrations 10-8 of a
centimeter
• Seismogram
– The record made by a
seismograph
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The Science of Seismology
Seismic waves
• Body wave
– Travels through Earth’s
interior
• Surface wave
– Travels along Earth’s surface
• Focus
– Where rupture commences
and an earthquake’s energy is
first released
• Epicenter– surface point above focus
Locating earthquakes
• Compressional wave:
– Wave consisting of alternating pulses of compression and
expansion
– Can pass through any medium (solids, liquids, gases)
– P (or primary) wave
• Shear wave:
– Rock is subjected to side to side or up and down forces,
perpendicular to wave’s direction of travel
– S (secondary) wave
– Not transmitted through water
– Travel slower than P waves
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Locating earthquakes
Locating earthquakes
Locating earthquakes
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Locating earthquakes
• Epicenter
– The point on Earth’s
surface directly above an
earthquake’s focus
Three measuring
stations are
necessary to locate
an epicenter
Measuring Earthquakes
• The Richter Magnitude Scale
– A scale of earthquake intensity based on the recorded
heights, or amplitudes, of the seismic waves recorded on a
seismograph
– A logarithmic scale—a 10 fold increase in amplitude for
each unit
• Moment Magnitude Scale
– A measure of earthquake strength that is based on the
rupture size, rock properties, and amount of displacement on
the fault surface
Measuring Earthquakes
Richter magnitude 6
Richter magnitude 7
Richter magnitude 8
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Studying Earth’s Interior
• Seismic discontinuity
– A boundary inside Earth
where the velocities of
seismic waves change
abruptly
S waves cannot pass
through the outer core
because it is liquid.
A Multilayered Planet
• Crust
– The outermost compositional layer of the solid Earth, part of the
Lithosphere
– Thickness ranges between 8 kilometers (oceanic) and 45 km
(continental)
• Mantle
– The middle compositional layer of Earth, between the core and the
crust
– Comprised primarily of olivine and pyroxene
– Asthenosphere: mantle where rock is near melting
– Mantle-core boundary: mesosphere
• Core
– Iron-nickel alloy
– Outer core is molten, inner core is solid
A Multilayered Planet
Compositional layers
Different rock
properties
and behavior
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A Multilayered Planet
• Core
– Innermost layer,
where the
magnetic field is
generated and
much geothermal
energy resides
– Separated into
outer core (liquid)
and inner core
(solid)
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