Lab # 6 – Pg. 121 Earthquakes and the Earth’s Interior.

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.

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