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
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.
Difference in time equals 5 minutes
Follow the graph downward to determine the distance in miles to the epicenter.
Chart page 124
• 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.
Distance to Epicenter
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
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