Download Earthquakes PPT - Van Buren Public Schools

Earthquakes

Vibration of Earth
produced by the rapid
release of energy.
 Caused by slippage
along a fault.

Fault is a fracture in
the Earth where
movement has
occurred.
Earthquakes

Focus
 Point within Earth
where the
earthquake starts.
 Located along a
fault

Epicenter
 Location on the
surface directly
above the focus.
Earthquakes

Slippage along a fault
Cause of Earthquakes

Elastic Rebound
Hypothesis
 Most earthquakes are
produced by the rapid
release of elastic
energy stored in rock
that has been subjected
to great forces.
 When the strength of
the rock is exceeded, it
suddenly breaks,
causing the vibrations
of an earthquake.
Cause of Earthquakes
 Aftershocks
and Foreshocks
 An aftershock is a small
earthquake that follows the main
earthquake.
 A foreshock is a small earthquake
that often precedes a major
earthquake.
Measuring Earthquakes

Earthquake waves
 Study of earthquake waves is called seismology

2 Types of earthquake waves produced:
 Body waves
○ P-waves
○ S-waves
 Surface waves
○ Slowest velocity of all waves
○ Move up-and-down as well as side-to-side
○ Larger than body waves, most destructive of all
waves
Measuring Earthquakes

Earthquake recording
instrument
(seismograph)
 Records movement of
Earth
 Record is called a
seismogram
○ shows all three types of
seismic waves—surface
waves, P waves, and S
waves.
Seismograph
Measuring Earthquakes
 Historically,
scientists have used two
different types of measurements to describe
the size of an earthquake:
 Intensity
○ Measure of the amount of earthquake shaking at a
given location based on amount of damage.
○ Modified Mercalli scale
 Magnitude “M”
○ Measure of the size of seismic waves or the amount of
energy released at the source.
○ Richter & Moment Magnitude Scale
Measuring Earthquakes

Richter Scale
 Based on the amplitude (height) of the largest seismic
wave
 Does not estimate adequately the size of very large
earthquakes

Momentum Magnitude
 Derived from the amount of displacement that occurs
along the fault zone
 Measures very large earthquakes
 The most widely used measurement for earthquakes
○ it is the only magnitude scale that estimates the energy
released by earthquakes.
Measuring Earthquakes
Measuring Earthquakes

Locating an Earthquake
 Earthquake Distance
○ The epicenter is located using the difference
in the arrival times between P and S wave
recordings, which are related to distance.
 Earthquake Direction
○ Travel-time graphs from three or more
seismographs can be used to find the exact
location of an earthquake epicenter.
Measuring Earthquakes
Earthquake Hazards

Seismic Shaking
 Ground vibrations
caused by seismic
waves
 Jolt and twist
structures
 Strongest close to an
epicenter
Earthquake Hazards

Liquefaction
 Rocks and soils are
saturated with water
○ Stable soil turns into
liquid
○ Liquid can’t support
buildings & structures
○ Structures may
settle and collapse
○ Underground objects
may float to surface
Earthquake Hazards
 Landslides
 Loose rock & soil on
slopes move due to
earthquakes

Mudflows
 Water content of soil is
high
 Causes mixture of soil
and water to slide rapidly
downhill.
Earthquake Hazards

Tsunamis
 A tsunami triggered by an earthquake
occurs where a slab of the ocean floor is
displaced vertically along a fault.
 A tsunami also can occur when the vibration
of a quake sets an underwater landslide
into motion or a volcanic eruption.
 Tsunami is the Japanese word for “seismic
sea wave.”
Earthquake Hazards
Earthquake Hazards

Tsunami Warning System
 Large earthquakes are reported to Hawaii
from Pacific seismic stations.
 Although tsunamis travel quickly, there is
sufficient time to evacuate all but the area
closest to the epicenter.
Reducing Earthquake Damage

Distribution of earthquakes forms a pattern.
 Most frequent along the boundaries of Earth’s
tectonic plates

Short-Range Predictions
 So far, methods for short-range predictions of
earthquakes have not been successful.

Long-Range Forecasts
 Scientists don’t yet understand enough about how
and where earthquakes will occur to make accurate
long-term predictions.
 A seismic gap is an area along a fault where there
has not been any earthquake activity for a long
period of time.