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? (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