DYNAMIC CRUST AND THE EARTH S INTERIOR

Transcription

1 Name DYNAMIC CRUST AND THE EARTH S INTERIOR Regents Earth Science I EARTHQUAKES Earthquake Any natural shaking of the Earth caused by displacement of rock. Terms: (1) Focus- The point within the crust where an earthquake originates. (2) Epicenter- The point on the Earth s surface directly above the Focus of an earthquake. Elastic Rebound Theory- Earth materials can only be distorted (they will bend only) up to a certain point. When distorted beyond their limits they will break releasing tremendous amounts of energy (an earthquake). * The energy released by an earthquake is measured with a seismograph. A- Types of Seismic Waves P-Waves: Primary Waves (compress ional waves, push-pull waves) 1. Vibrate rock particles in the same direction as energy travels 2. Travels through solids, liquids, and gases 3. Fastest traveling waves (always first to arrive) S-Wave: Secondary Waves (shear or shake waves, transverse waves) 1. Second to arrive because they move slower P-waves ( 2/5 the speed of P-waves) 2. Vibrate rock particles at right angles to the direction of travel of the wave 3. Can only travel through solids (Cannot pass through liquid and gases) 4. Cannot pass through the Earth s outer core because it s in a liquid state ( The study of seismic waves allowed scientists to determine this) ** P and S waves are referred to as Body Waves because they only travel through the Earth s interior.

2 Dynamic Crust and the Earth s Interior Page 2 L-Wave: Long Waves (last or land waves) Caused by P and S waves reaching the surface Slowest moving wave, and has the longest distance to travel (last to arrive) Passes through all materials (solids, liquids and gases) ** L Waves are referred to as Surface Waves because they only travel on the Earth s surface. On a seismograph recording, the greater the time difference between the arrival times of P- waves and S-waves, the greater the distance to the earthquake. B- The Effects of Rock Density on Seismic Waves 1. The velocity of seismic waves depends on the physical properties of the materials through which they travel. 2. The denser the rock material, the greater the velocity of the waves. 3. The density of rock material increases as you move deeper onto the Earth s interior. 4. Seismic wave velocity increases as the waves move toward the Earth s center and decreases as the waves move toward the surface. C- Shadow Zones 1. Seismic waves do not travel in straight lines due to the changing Earth density. The waves are bent, or refracted, as they move from a medium of one density into a medium of a different density. 2. Due to the refraction of eaves there are places on the surface of the Earth where the earthquake will not be felt. 3. The shadow zone occurs 103 to 143 degrees from the earthquakes epicenter (since P-Waves are refracted by the Earth s liquid outer core and S-Waves can t pass through it).

3 Dynamic Crust and the Earth s Interior Page 3 D- Locating the Epicenter of an Earthquake 1. Determining the distance of an epicenter form seismograph station does not determine the location of the epicenter. 2. Knowing the distance simply places the epicenter on a circle having a radius equal to its distance from the recording station. 3. To determine the exact location of an epicenter, its distance form 3 seismograph stations must be determined and 3 circles drawn. 4. The epicenter is located at the point where all 3 circles intersect. II-EARTH S INTERIOR A-Crust: Solid rocky outer surface of the Earth (Thin outer most layer of the lithosphere) 1. Continental Crust a. Thickest portion of crust b. 30 to 50 km thick (18.30 miles) c. Least dense crust -2.7 g/cm3 d. Composed mostly of Granite e. Rich in silicon and aluminum 2. Oceanic Crust a. Thinnest portion of crust b. 5 to 8 km thick (3-5 miles) c. Most dense crust 3.0g/cm3 d. Mostly composed of Basalt e. Rich in silicon, iron, and magnesium B- Mohorovicic Discontinuity (MOHO) 1. Interface between the crust and the mantle 2. Discovered by a Yugoslavian scientist Andriija Mohorovicic when he noticed that P waves traveling deeper into the Earth arrive at a seismograph before shallow ones. 3. Properties change abruptly across the discontinuity 4. Earthquake waves bend sharply ad they cross the Moho

4 Dynamic Crust and the Earth s Interior Page 4 C- Mantle 1. Plastic like layer km thick (1800 miles) 3. P and S waves pass through this layer, therefore it s solid 4. No crystal structure Acts like plastic or glass 5. More dense then crust Average density = ³.5 g/cm3 (3.3 to 5.5 g/cm3) 6. Composed of Ferromagnesian minerals (iron and magnesium heavy metals) * Gutenberg Discontinuity- Interface between the Mantle and Core D- Core 1. Outer Core a. 26 km thick (1500 mi) b. Temperature is about 4000 degrees F c. S-Waves do not pass through, only P-Waves, therefore the Outer Core must be liquid d. Density ranges from 9.9 to 12.1 g/cm3 e. Composed possibly of iron E- Inner Core a km thick (780 mi) b. Temperature is between 5000 and 10, 000 degrees F c. Pressure = 100 million pounds / square inch therefore it must be solid. Substances can t melt because the tremendous pressure prevents the molecules form moving apart to become liquid d. Density ranges form 12.7 to 13.0 g/cm3 e. Composed of iron and nickel ** THE OUTER CORE IS COMPOSED OF IRON, AND THE INNER CORE IS COMPOSED OF IRON AND NICKEL. SCIENTISTD HAVE DETERMINED THIS FORM THE STUDY OF CERTAIN METEORITES.

5 Dynamic Crust and the Earth s Interior Page 5 III EVIDENCE OF MINOR CRUSTAL CHANGES Most Sedimentary rock and certain Igneous rock (that which flows on the surface-lava) are deposited in horizontal layers called strata. Therefore, most strata found in other then horizontal positions are said to be deformed by crustal movement. Evidence of minor crustal changes can be observed in exposed rock strata called outcrops. Deformed rock Strata 1. Folded strata 2. Tilted strata 3. Faulting Displacement (movement) of rock layers along a break in the mass of rock. The movement of rock along a fault is called an earthquake. Faulting often results in obvious changes in the positions of surface features. (sometimes forming cliff or mountains like the Grand Tetons in Wyoming) B- Displaced Fossils: 1. Marine fossils found at high elevations indicate that the sedimentary rock in which they were deposited has been uplifted. Rising Crust (ex. Marine fossils located on Mt. Everest) 2. Sometimes shallow water fossils are found in deep ocean area. This indicates Subsidence. Sinking Crust.

6 Dynamic Crust and the Earth s Interior Page 6 C-Vertical Movements 1. Displacement of strata, which may accompany earthquakes, provides direct evidence of crustal movements 2. This is similar to faulting but usually affects large portions of the Earth s crust 3. Examples: Rising of the land to form the Grand Canyon, Raised Shorelines, and Raised Bench Marks V- CONTINENTAL DRIFT, SEA FLOOR SPREADING, PLATE TECTONICS *Theory first proposed by Alfred Wegener in 1912* A- Major Concepts 1. Earth lithosphere is divided into six major plates. (Pacific, American, Indian, African, Eurasian, Antarctic, and a number of minor ones) 2. Each of these plates is moving in relation to one another 3. The cause of the plate motions is ht spots in the mantle and core that cause convection cells or currents in the mantle 4. Major Plate features: a. Ridge (usually Mid-Ocean Ridge) Hot mantle material (called plume) rises at this

7 Dynamic Crust and the Earth s Interior Page 7 point due to convection. As the magma nears the surface it causes the crust to split apart. The magma solidifies forming new crust. Spreading continues to occur from this point. b. Transform Fault- Plates moving sideways along side each other. The San Andreas Fault in California is an example. c. Subduction Zone- Convergence of oceanic crust and continental crust. The denser oceanic crust dives down under the lighter continental crust. (an ocean trench is formed) As the oceanic crust dives down it melts the molten rock will then rise to the surface causing earthquakes and the formation of an Island Arc Volcanic chain. Examples include the Cascade Mts., Aluetian Islands, Japanese Islands d. Converging Plates (continental plates usually) As the two plates collide they fold and fault producing a Folded Mountain Chain. Examples: Himalayas, Appalachians, Rockies. B- Evidence of Plate Movement 1. The outlines of the continents appear to fit together like pieces in a jigsaw puzzle. 2. At places where the continents once fit together there is a similarity of minerals, fossils, and rock types. Rocks are also of similar age on western South America and eastern Africa.

8 Dynamic Crust and the Earth s Interior Page There are similar prehistoric animal species separated by today s oceans. Such a wide distribution of the same plants and animals probably could not have occurred unless the continents were connected. 5. Viewing the ocean floors (Longest mountain chain is Mid Atlantic Ridge), and the major mountain chains of the world. 6. Upwelling of heat along Mid Ocean Ridges supports the convection idea 7. Age of the ocean floors: rocks along the ridges are much younger than rocks at continental edges. This supports Sea Floor Spreading. 8. Patterns of earthquakes and volcanoes around the world follow the plate boundaries. 9. Pacific islands get older as you move westward away from Hawaii. 10. Paleomagnetism Prehistoric remaining magnetism in rocks points to different positions for the continents. 11. Magnetic Reversals- Flip flopping of magnetic north and South Poles recorded at intervals of equal distance on either side of the Mid-ocean Ridge.

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10 NAME: Dynamic Crust and the Earth s Interior Page 10 SEISMIC WAVES Answer the following questions using your ESRT. 1. How far will a P-wave travel in 10 minutes? 2. How far will an S-wave travel in 10 minutes? 3. Why is there a difference in distance traveled over the same amount of time? 4. How long does it take an S-wave to travel 6,000 km? How long does it take a P-wave to travel the same distance? 5. After 4 minutes, how much further will a P-wave travel than an S-wave? 6. After 9 minutes, how much further will a P-wave travel than an S-wave?

11 Dynamic Crust and the Earth s Interior Page As the distance from the epicenter increases, what happens to the difference in travel time between P-wave and S-waves? 8. At 4,000 km from the epicenter what will be the difference in travel time (arrival time) between P-waves and S-waves? 9. How far from the epicenter are you if the difference in arrival time of P-wave and S-wave is 4 minutes and 20 seconds? 10.How far from the epicenter are you if the P-waves arrive at 1:23:00 pm and the S-waves arrive at 1:29:40 pm?

12 Dynamic Crust and the Earth s Interior Page 12 EARTHQUAKES WORKSHEET 1. If your seismograph begins recording P-waves at 4:00pm and begins to record S-waves at 4:06pm, how far away is the earthquake? 2. At what time did the earthquake take place? 3. How long would it take a P-wave to travel 10,000 km? 4. How far away is an earthquake whose first P-wave is received at 9:33am and whose first S- wave is received at 9:41am? 5. At what time did this earthquake take place? 6. How far will an S-wave travel in 14 minutes? 7. If the difference in arrival times between P and S waves is 1 minute. How far away is the earthquake? 8. In 1 minute an S-wave will travel how far? 9. How far will P-wave travel in 1 minute? 10. An earthquake took place at 5:00pm if your seismograph is 4000km away: (A) At what time would the first P-wave arrive? (B) At what time would the first S-wave arrive? 11. If it takes 15 minutes for S-waves from an earthquake to get to you. How far away is the earthquake?

13 Dynamic Crust and the Earth s Interior Page 13 NAME: PLATE BOUNDARIES 1) What are the three types of plate boundary? 2) What are the three types of converging plate boundaries? 3) Give an example of how density plays a role in plate collisions. 4) What is happening to the plates at a divergent plate boundary? 5) List two examples of supporting evidence that the sea-floor is spreading? (BE SPECIFIC IN YOUR EXLANATION)

14 Dynamic Crust and the Earth s Interior Page 14 NAME: PLATE BOUNDARIES (ESRT PG 5) ANSWER QUESTIONS USING PG. 5 IN ESRT. 1) What type of plate boundary exists between the Indian-Australian Plate and the Pacific Plate? 2) Give an example of two plates that are converging and an example of two plates that diverging. 3) Give an example of two plates that are separated by a transform boundary. 4) What type of plate boundary separates the South American Plate and the African Plate? 5) What type of plate boundary is located at the San Andreas Fault? 6) What type of plate boundary is found at the following locations: a) 30 N Latitude and 80 E Longitude: b) 50 S Latitude and 140 W Longitude: c) 35 N Latitude and 120 W Longitude: 7) Which general direction is the South American Plate moving? Which general direction is the Nazca Plate moving? (N, E, S, W)

15 Dynamic Crust and the Earth s Interior Page 15 8) Which directions are the Eurasian and Indian-Australian Plate moving in relationship to each other? 9) What type of geological features would you most likely find along the boundary between the Pacific Plate and Philippine Plate? 10) What type geological features would you most likely find along the boundary between the African Plate and the North American Plate? 11) What type of geological features would you most likely find along the boundary between the South American Plate and the Nazca Plate? 12) What mountain range is located at 30 N Latitude and 80 E Longitude. How were these mountains formed? (Be specific) 13) What is located at 20 N Latitude and 150 W Longitude. How was it formed?

16 Dynamic Crust and the Earth s Interior Page 16 Name: Earth's Interior Review With the use of your N.Y.S. Earth Science Reference tables answer the questions below. A. Properties of the Earth's Interior 1. The Moho is the interface between which two layers? 2. What is the depth at the bottom of the mantle? km 3. The Earth's greatest density is g/cm³. This occurs in the 4. S-waves don't travel through the because it is in the state of matter. 5. The pressure at the Mantle/Outer Core boundary = 6. The temperature at the center of the Earth = C 7. Where in the Earth is the temperature of the rocks greater than the melting point of those rocks?. What is the result of this situation? 8. The Outer/Inner Core boundary (interface) is at a depth of 9. As the depth below the surface increases, the pressure in the rocks 10 As the depth below the surface increases, the temperature in the earth 11. What is happening to the Pacific Ocean plate where it meets the North American crustal plate? 12. What is happening to the crust along the Mid-Atlantic Ridge? 13. What is the composition of the inner core? 14. Which is more dense the continental crust, or the oceanic crust?

17 Dynamic Crust and the Earth s Interior Page 17 B. Earthquake Graph 1. How many Kilometers will a P-wave travel in 9 minutes? km 2. How long will it take an S-wave to travel 2500 km? 3. If a P-wave arrives at your seismograph at 1:20:30pm and the S-wave arrives at 1:27:00pm, how many kilometers away was the epicenter of the earthquake? km xlo³km 4. How far away is an earthquake if there is a 3-minute interval between the arrival times of P and S waves? km 5. An earthquake occurred at 5:00:00 a.m. At what time would the P-wave reach a seismic station 3000-kIn from the epicenter? 6. A P-wave reaches a seismograph station 2600 km from an earthquake epicenter at 12:10:00 GMT. At what time did the earthquake occur?

18 Dynamic Crust and the Earth s Interior Page 18 Name: Layers of the Earth 1. Label the layers of the earth on lines A-D. 2. Which layers can only be studied by indirect means? 3. Which layer contains the highest mountains and the deepest oceans? 4. Which layer is the thickest? 5. Which layer is the coolest? 6. Which layer is composed of liquid iron and nickel? 7. On which layer do we live? 8. Which layer is the densest? 9. Which layer is the hottest?