Download Earthquakes

Lab # 6 – Pg. 121
Earthquakes and the
Earth’s Interior
Layers of the Earth
• Lithosphere – outermost layer, contains
both types of crust (Continental and
Oceanic) ; 100 km thick
• All earthquakes occur in the area.
• Asthenosphere - Not solid, capable of
flow or movement.
• Area nearest to lithosphere is molten; this
allows the plates to move.
• 600 km thick.
Geothermal Gradient
• As the depth of the Earth increases the
Temperature Increases.
• For every Km of depth the temperature
increases by 14oC
• Thus if we are 3km below the surface then
we have a temperature of 42oC or 105oF
Geothermal Gradient #2
• If we are at a distance of 100km below the
surface then we have a temp 1400oC
• Why is 100 km important?
• This is the bottom of the Lithosphere
• At this depth, the rock that makes up this
layer (Basalt) melts
• If the Basalt travels any lower it will melt.
Earthquakes
• Must occur in solid material.
• They are vibrations of Earth that occur
when the lithosphere is strained.
• Focus is the exact source underground
where the earthquake occurred.
• Epicenter is the same location on the
Earth’s surface.
• They can be 100 km or less.
Types of Earthquakes
• Shallow focus – occur at mid ocean ridges,
divergent boundaries.
• Deep focus – occur at deep ocean trenches
convergent boundaries.
• The depth of the quake has nothing to do with
its strength.
• Wave velocity increases as density of the
material it travels through increases.
• Energy is released (waves) in all directions
from focus.
Wave Types
• P (Primary) waves 14mi/sec, they can travel
through any media; solid rock, plastic like
(Asthenosphere), fluid (outer core)
• S (Secondary) waves 8 mi/sec; they can
travel through all except fluid. (not through
outer core)
• L (Tertiary) waves (Long or Love) wave
travel on the surface.
• They cause the most damage
Location of Earthquakes
• The global distribution of earthquakes
follows a narrow belt that winds around the
Earth.
• Pacific belt (Ring of Fire)
• Alpine belt (Mediterranean belt) through
Italy, around Mediterranean sea Iran, Iraq,
around Himalayan mountains into Indonesia.
• Mid oceanic ridge system
Plate Boundaries
Terminology
• Seismologist - a person who reads
seismographs.
• Seismographs - a machine that records
earthquakes.
• Seismograms – this is the paper report of
the Earth’s Vibrations.
Seismogram pg 122
• Each vertical line represents 1 minute.
• How much time elapsed from when the
first p wave was recorded to the when the
first s wave was recorded?
• 5 minutes
Use the chart on pg 124 to determine
the distance to the Epicenter.
• Distance between waves is 5 minutes.
(from last slide)
• Find the point between the two graphs
where the time difference is 5 minutes.
• This is accomplished by counting the
number of white lines between the red and
blue graphs; each white line = 1 minute.
• Once this point is located on the graph;
follow the graph downward to determine the
distance in miles to the epicenter.
Chart page 124
Difference in time
equals 5 minutes
Follow the graph downward
to determine the distance
in miles to the epicenter.
Distance to Epicenter
• When the time difference is 5 minutes the
distance to the epicenter is approximately 2000
miles.
• Remember: the greater the time difference
the farther the distance to the epicenter.
• Also all three waves initiate at the same
time; they just travel at different speeds.
Pg 124 3 Seismograms
• (1) What is difference in time of the two waves?
• (2) What is difference in time of the two waves?
• (3) What is the difference in time of the two
waves?
• Use a compass and the scale on the bottom of
the page to determine the location of the quake.
Chap Summary Pg 131
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Questions 1-11 Ignore # 8
# 4 Hint where can earthquakes occur?
# 7 Upper mantle - crust Lithosphere and
Asthenosphere see pg 126.
Crust 0- 70 Km
Mantle base of crust 70 km - to bottom of
Mantle 2885 km solid to a plastic layer.
Outer core 2885km - 5100km
Inner Core 5100-center