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Name: ______________________________________________ Date: _________________ Period: _______ Due Date: ______3/4/16_____________________ Test Date: ______3/10/16______________ Plate Tectonics Study Guide Earthquakes: Vocabulary: The focus of an earthquake is the point inside the earth where the earthquake begins. The epicenter of an earthquake is the imaginary point on the earth’s surface above the focus. Primary waves (P-waves) are seismic waves that arrive first. They compress and expand the ground. Secondary waves (S-waves) are seismic waves that arrive second. They move the ground up and down or side to side. Surface waves are seismic waves that move along the earth’s surface and are the most destructive. How to Read a Seismograph: 1. The smaller wave on the seismograph is a P-wave. The larger wave on the seismograph is a S-wave. 2. The difference in time between the P and S waves is known as lag time. 3. The city with the smallest amount of lag time is the one that is closest to the epicenter. 4. P Waves arrive first and S Waves arrive second. 5. The times that the waves arrive at each city are different because the cities are different distances away from the epicenter. The scale used to measure earthquake magnitude is the Richter Scale. How do mountains form? o An oceanic plate sinks beneath another plate and forms volcanic mountains or islands. o Hot rock/hot spots from within the earth rise through the ocean floor, forming volcanic mountains. o Two continental plates collide forming a mountain. Earthquakes occur before volcanic eruptions because… o The force of magma causes rock to fracture (or break) o Pressure from escaping gases causes nearby rocks to fracture (or break) o Pressure on rocks from magma causes rocks to break (or break) Volcanoes Volcanoes can be both constructive (good/helpful) and destructive (bad/damaging. o Constructive: creating new landforms like islands and mountains o Destructive: hot lava can destroy towns and ash from a violent eruption can cause breathing problems in humans, cover cops, and block sunlight. The difference between magma and lava: o Magma is molten rock beneath the earth’s surface. Lava is molten rock on the earth’s surface. Types of Volcanoes: o Composite: A volcano that forms from alternating eruptions of viscous lava and broken rock. It is steep near the summit and flat toward the base. It has the most explosive eruptions. Mt. Pinatubo is an example of a composite volcano. o Shield: A wide, broadly sloping volcano that forms from runny lava. It is the largest of volcanoes. See also cinder cone; composite volcano. Mt. Kilauea and Mauna Loa in Hawaii are examples. o Cinder Cone: A small (less than 400 meters high), cone-shaped volcano made of broken rocks or blobs of hardened lava, called “cinders,” that accumulate around the volcanic vent. Instruments scientists use to study and predict volcanic activity: o Tiltmeter – instrument used to measure slight changes in the inclination of the earth’s surface. o Seismograph – an instrument that detects, records, and measures the vibrations produced by an earthquake. o Gas sensor – detects the presence of gases in an area Regions of volcanic activity: o The Ring of Fire o The Mid-Atlantic Ridge o Hawaii and other hot spots Volcanic Ash: o Hot ash clouds rise to the sky because of the upward force of the volcanic eruption, pressure release, density differences between ash and air, and convection. o The direction of the wind can affect the placement of ash. o Geologists can tell if ancient deposits of sediment are from a volcanic ash if there are tiny fragments of volcanic remains/glass in the sediment. Review Sheet Part 1: Reading a Seismograph A 3:06 3:08 3:10 3:12 3:14 3:16 3:18 3:20 3:22 3:24 1:02 1:04 1:06 1:08 1:10 1:12 1:14 1:16 1:18 1:20 7:07 7:09 7:11 7:13 7:15 7:17 7:19 7:21 7:23 7:25 B C Directions: Three different seismograph stations (A, B, and C) recorded an earthquake. Complete the table below and answer the following questions. Station A is from Olympia, Washington, Station B is from Honolulu, Hawaii, and Station C is from Columbia, South Carolina Time of Arrival at Station . Seismograph S-wave minus PPrimary Wave Secondary Wave wave Station (P-wave) (S-wave) A. Olympia, 3:09 3:17 8 minutes Washington B. Honolulu, Hawaii 1:07 1:17 10 minutes C. Columbia, South Carolina 7:14 7:25 11 minutes 1. Which station is closest to the epicenter? Explain. Station A/Olympia, Washington is closes to the epicenter. You know this based on the distance between the p and s waves or shortest lag time. 2. Why are the times that each earthquake wave arrived at each city different? The further you are from the epicenter the longer it takes the waves to travel. Part 2: Earthquakes – “Recognizing Differences” 3. What is the difference between the focus and the epicenter of an earthquake? Focus: where the earthquake begins inside the earth Epicenter: the imaginary point on the earth that pinpoints the earthquake’s location 4. What is the difference between primary waves and secondary waves? P-waves arrive first and are compressional waves/back and forth motion. S-waves arrive second and move like a snake or at right angles. 5. What is the difference between a seismograph and a seismogram? Seismograph-device/machine that measures earthquake waves Seismogram-reading from the seismograph 6. What is the difference between a body wave and a surface wave? Body waves move through the earth. Surface waves move on the surface of the earth. Part 3: Earthquakes – “Three Reasons” 7. What are the three ways that mountains form? Oceanic plate sinks beneath another plate. Hot spots Two continental plates collide/convergent boundary 8. What are the three reasons why earthquakes occur before volcanic eruptions? The force of magma Pressure from escaping gases Pressure on rocks from magma Part 4: Volcanoes – Vocabulary 9. Composite ______D__ 10. Cinder Cone ___C_____ A. A wide, broadly sloping volcano that forms from runny lava. B. Molten rock on the earth’s surface. 11. Shield ___A_____ C. A small cone-shaped volcano made of broken rocks or blobs of hardened lava. 12. Magma __E______ D. 13. Lava ___B_____ E. Molten rock below the earth’s surface. A volcano that forms from alternating eruptions of viscous lava and broken rock. It has the most explosive eruptions. Part 4: Volcanoes – Questions 14. Why do hot ash clouds rise to the sky? The force from a volcanic eruption, density differences and convection. 15. What are the three regions of intense volcanic activity? Ring of Fire The Mid-Atlantic Ridge Hot spots like Hawaii 16. What are the three instruments that scientists use to study and predict volcanic activity? Seismograph Tiltmeter Gas Sensor 17. Can volcanoes be constructive and destructive? Yes, they are both. Constructive: make new landscapes, fertile soil, geothermal energy. Destructive: mudflows/lahars or pyroclastic flows killing people, destroying everything in its path.