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Transcript
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 • • • • • • 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