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EARTHQUAKES

Explore the geological manifestations of plate tectonics, such as earthquakes, and their impact on societies and the environment. Learn how waves are used for practical purposes, and examine investigations of current interest in science.

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EARTHQUAKES

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  1. EARTHQUAKES

  2. Standards • Describe the geological manifestations of plate tectonics, such as earthquakes • Describe the impact of plate motions on societies and the environment • Describe how waves are used for practical purposes (e.g., seismic data) • Examine investigations of current interest in science

  3. Major Earthquakes in History • The following are just a few of many notable earthquakes through history

  4. 1811: New Madrid Missouri • Magnitude 7.5 (followed by 7.3 & 7.5 in 1812) • Large areas sank into the earth • New lakes were formed • The Mississippi River changed its course and even flowed backward • Sand blows (geysers) occurred, can still see remnants today

  5. 1906: San Francisco • Felt from southern Oregon to south of Los Angeles and inland to central Nevada • Estimated magnitude of 7.8 • >3000 killed • Massive fires

  6. San Francisco Burning Photo: http://www.stvincent.ac.uk/Resources/EarthSci/Tectonics/cons1906.html

  7. Aerial View of San Francisco from balloon Photo: http://er1.org/docs/photos/Disaster/san%20francisco%20earthquake %201906%20view%20from%20balloon.jpg

  8. Photo: http://www.eas.slu.edu/Earthquake_Center/1906EQ/sanfran/m031.html

  9. San Francisco Financial District Photo: http://www.sfmuseum.org/hist/pix49.html

  10. 1985: Mexico City • Magnitude 8.1 • Epicenter 350 km away off Pacific coast • Shaking lasted 3 – 4 minutes • Collapse of poorly constructed buildings • Liquefaction of soils under city • >10,000 killed

  11. Mexico City Photo: http://latimesblogs.latimes.com/laplaza/2010/09/earthquake-mexico-city-1985-memorial.html

  12. Mexico City Photo: http://www.objectlessons.org.uk/default.asp?image=GEO000XP5018&document=500.0021.0020

  13. 1960: Valdivia, Chile • Largest earthquake ever recorded • Magnitude 9.5 • Caused tsunamis in many parts of the Pacific, including Chile (80 ft. high) and Hilo, Hawaii • 1,655 people killed

  14. 2004: Sumatra, Indonesia EQ and Indian Ocean Tsunami • Magnitude 9.2 • Rupture continued for 9 minutes & moved 1300 km along a thrust fault – the longest single fault break ever recorded • Resulted in tsunamis that killed 230,000+ in Sumatra, Sri Lanka, Thailand, the Maldive Islands and Somalia

  15. Banda Aceh Pre-Tsunami June 23, 2004 Banda Aceh Post-Tsunami December 28, 2004 Photos: http://www.baird.com/ baird/en_html/indian_ocean/ indianocean.html

  16. Indian Ocean Tsunami, Thailand Photo: http://en.wikipedia.org/wiki/Image:2004-tsunami.jpg

  17. Original Photo from John Thompson taken on December 26, 2004 in Khao Lak

  18. 2008: Eastern Sichuan, China • Magnitude 7.9 • Schools and hospitals collapsed • ~90,000 killed (>5300 children attending class) • Strong aftershocks and landslides • May have been triggered by dam holding 315 million tons of water

  19. Photo: http://welovecomments.wordpress.com/2009/08/12/reaction-from- someone-who-was-in-china-during-the-2008-magnitude-8-0-earthquake-in-sichuan/

  20. Photo: http://www.telegraph.co.uk/news/worldnews/asia/china/4434400/Chinese-earthquake-may-have-been-man-made- say-scientists.html

  21. 2010: Haiti Earthquake • Magnitude 7.0 • ~220,000 – 300,000 killed • ~ 1 million homeless • Major damage to city of Port-au-Prince

  22. Photo: http://image3.examiner.com/images/blog/EXID12837/images/haiti.jpg

  23. Photo: http://i.telegraph.co. uk/telegraph/multimedia/ archive/01558/presidential- palac_1558531i.jpg

  24. 2011: JapanEarthquake and Tsunami • Magnitude 9.0 earthquake • Rupture along thrust fault at the subduction zone between the Pacific & N. American plates • Fault moved upwards by 30-40 m (this is 98 to 131 feet!) and slip occurred over an area 300 km long • Foreshocks occurred over 2 days preceding the quake (a M 7.2 and 3 greater than M 6 on same day) • Several aftershocks have occurred, many over a M 6

  25. 2011: Japan Earthquake and Tsunami • Resulting 30 fttsunamiswept through many coastal regions of Japan, reaching as far as 6 mi inland • 19,300 people killed and missing • Caused failure of nuclear power plant All following photos from MSN.com unless otherwise noted

  26. Collapsed House_SukagawaCity,Fukushima

  27. JapanEQ_SplitRoad_SacrementoBee

  28. TsunamiSwirl_Oarai,Ibaraki_3-11-11

  29. JapanTsunami_Iwanuma, Miyagi_3-11-11

  30. JapanTsunami_Natori_3-11-11

  31. Japan Tsunami_SendaiAirport_3-11-11

  32. JapanTsunami_3-11-11_Cleveland.com

  33. JapanTsunami_HousesSweptToSea_NatoriCity_3-11-11

  34. JapanTsunami_SendaiAirport_3-11-11

  35. OnagawaTown,MiyagiPrefecture_3-26-11

  36. What is an Earthquake? • We inhabit a fragile builtenvironment of houses, buildings& transportation systems that is anchored in Earth’s crust • This environment is vulnerableto seismic vibration, ground rupture, landslides and tsunamis

  37. What is an Earthquake? • Plate movements generate forcesat the boundaries that can be described in terms of stress, strain and strength • Stress– local forces per unit area that cause rocks to deform • Strain– relative amount of deformation • Rocks fail – break – when they are stressed beyond a critical value called their strength

  38. What is an Earthquake? • Earthquakes are the result of stress that builds up over time, as tectonic forces deform rocks on either side of a fault • They occur when the stress exceeds the strength of the rocks, which suddenly breakalong a new or preexisting fault • The two blocks of rock on each side of the fault slip,releasing the stress suddenly, causing an earthquake, which generates seismic waves

  39. Elastic Rebound Theory • Faults remain lockedwhile strain energyaccumulates in the rocks on either side, causing them to deform until a sudden slip along the fault releases the energy • Elasticmeans the rocks spring back to their undeformed shape when the fault unlocks • The distance of displacement is called the faultslip

  40. Photo: http://www.winona.edu/geology/MRW/mrwimages/elasticrebound.jpg

  41. Focus and Epicenter • Focus– point at which the slip begins – somewhere belowthe surface • Most earthquakes in continental crust have focal depths from 2 – 20 km (rocks behave in a ductile manner below 20 km) • Subduction zone earthquakes can have foci as great as 690 km deep • Epicenter– the geographic point on Earth’s surfacedirectly above the focus

  42. Photo: http://www.yorku.ca/esse/veo/earth/image/1-10-15.JPG

  43. Fault Rupture • Does not happen all at once • Starts at focusand expands outward on fault plane at ~2 – 3 km/s • Rupture stops when stress can no longer break the rocks • Sizeof earthquake is related to total areaof fault rupture

  44. Fault Rupture • Most earthquakes are very small and the rupture never breaks the surface • However, in large, destructive earthquakes, surface breaks are common • Ex: 1906 San Francisco EQ caused surface displacements averaging 4m (13 ft.) along a 400km section of the San Andreas

  45. Tree displaced 15 ft (from where person is standing) Photo: http://www.stvincent .ac.uk/Resources/EarthSci/Tectonics/images/ranch.jpg

  46. Fault Rupture • Faulting in largest Earthquakes can extend more than 1000 km and the slip can be as large as 20 m (~60 ft) • Stored strain energy is released in the form of frictional heatingand seismic waves

  47. Foreshocks and Aftershocks • Aftershocksoccur as a consequence of a previous EQ of larger magnitude • Their foci are distributed in and around the rupture plane of the main shock • They can last from weeks to years • They can compound damage from the main shock

  48. Foreshocks and Aftershocks • Foreshocksare small earthquakes that occur near, but before, a main shock • Many large earthquakes have been preceded by foreshocks • Scientists have tried to use them to predict large earthquakes • Hard to distinguish foreshocks from other small earthquakes

  49. Seismic Waves • Ground vibrationsproduced by an earthquake • Enable us to locateearthquakes and determine type of faultingthat produced them • 4 types: • Body Waves a. P waves b. S waves • Surface Waves a. Rayleigh waves b. Love waves

  50. Primary or P Waves • Travel through Earth and are firstto arrive at seismic station • Compressionalwaves • Can be thought of as push-pull waves: they push or pull particles of matter in the direction of their travel

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