Transcript how do tectonic plates cause earthquakes?

ESSENTIAL QUESTION:
HOW HAS EARTHQUAKES SHAPED OUR EARTH?
HOW DO TECTONIC PLATES CAUSE EARTHQUAKES?
Whose Fault is it?
 Faults are fractures in Earth where movement has
occurred
 Because earthquakes occur when two plates rub
together, they are often said to occur on fault lines.
 Faults occur because
forces inside the
Earth cause Earth’s
plates to move
placing stress on or
near the plate edge
What are the types of Faults?
 To relieve this stress, the rocks tend to bend,
compress, or stretch
 If the force is great enough the rocks will break.
 This breaking produces an earthquake.
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An earthquake is when abrupt shakings of the Earth are
caused by the release of built up pressure on the Earth’s
surface
What are the 3 types of Faults?
 3 types of forces act
on rocks: tension,
compression, and
shear
 Normal Faultcaused by rock above
the fault moving
downward in
relation to the rock
below the fault
What are the 3 types of Faults?
• Reverse faults result
from compression
forces that squeeze
rock.
• If rock breaks from
forces pushing from
opposite directions,
rock above a reverse
fault surface is forced
up and over the rock
below the fault
surface.
What are the 3 types of Faults?
 At a strike-slip fault,
rocks on either side of
the fault are moving past
each other without much
upward or downward
movement
 The San Andreas Fault is
the boundary between
two of Earth’s plates that
are moving sideways past
each other.
What are the features of an Earthquake?
 Seismic Waves- waves generated by an earthquake,
can move the ground forward and backward, up and
down, and side to side
 Focus- an earthquake’s
point of energy release
 This is the point within
Earth where the
earthquake starts
 Epicenter- is the point
on the earth’s surface
directly above the
earthquake focus
What are the types of Seismic Waves that are
produced?
 Primary Waves (P-Waves)- cause particles in rocks
to move back and forth in the same direction that the
wave is traveling
 Secondary Waves (S-waves)- move through Earth by
causing particles in rocks to move at right angles to
the direction of wave travel.
 Surface Waves- are seismic waves that travel along
Earth’s outer layer

These waves cause most of the destruction resulting from
earthquakes
How do we locate an Earthquake?
 The different speeds of seismic waves allow scientist
to determine the epicenter
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Primary waves move fastest
Secondary waves follow
Surface waves move slowest and arrive at the seismograph
station last
 The difference in arrival
times is used to calculate
the distance from the
seismograph station to the
earthquake epicenter
How do we locate an Earthquake?
 Seismic waves from
earthquakes are
measured with an
instrument known
as a seismograph
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Consists of a rotating
drum of paper and a
pendulum with an
attached pen
The paper record of a
seismic event is called
a seismogram
How do we measure an earthquake?
 We can measure earthquakes by its:
Intensity – a measure of the effects on an earthquake
at a particular location
OR
 Magnitude: a measure of the strength or amount of
energy released during an earthquake

How do we measure an earthquake?
 The Richter
scale is used to
describe the
strength of an
earthquake and
is based on the
height of the
lines on the
seismograph
How do we measure an earthquake?
 The Mercalli Scale is based on actual observations
of damage
Earthquake dangers…
 Most earthquake damage occurs when surface waves
cause building, bridge, and roads to collapse
 However, an earthquake under the ocean causes a
sudden movement of the ocean floor
 The movement pushes against the water, causing a
powerful wave that can travel thousands of
kilometers in all directions
 These ocean waves caused by earthquakes are called
seismic sea waves, or tsunamis