EARTHQUAKES Standards ò Describe the geological manifestations

EARTHQUAKES

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

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

1811: New Madrid Missouri ò Magnitude 7. 5 ò Large areas sank into the earth ò New lakes were formed ò The Mississippi River changed its course and even flowed backward ò Sand blows (geysers) occurred,

1906: San Francisco ò Felt from southern Oregon to south of Los Angeles and inland to central Nevada ò Estimated magnitude of 7. 8 ò >3000 killed ò Massive fires

San Francisco Burning Photo: http: //www. stvincent. ac. uk/Resources/Earth. Sci/Tectonics/co

Aerial View of San Francisco from balloon Photo: http: //er 1. org/docs/photos/Disaster/san%20 francisco%20 ea %201906%20 view%20 from%20 balloon. jpg

Photo: http: //www. eas. slu. edu/Earthquake_Center/1906 EQ/sanfra

San Francisco Financial District Photo: http: //www. sfmuseum. org/hist/pix 49. html

1985: Mexico City ò Magnitude 8. 1 ò Epicenter 350 km away off Pacific coast ò Shaking lasted 3 – 4 minutes ò Collapse of poorly constructed buildings ò Liquefaction of soils under city ò ~10, 000 killed

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

Mexico City Photo: http: //www. objectlessons. org. uk/default. asp? image=GEO 000 XP 5018&document=500. 0021. 0

1960: Valdivia, Chile ò Largest earthquake ever recorded ò Magnitude 9. 5 ò Caused tsunamis in many parts of the Pacific, including Hilo, Hawaii ò 1, 655 people killed

2004: Sumatra EQ and Indian Ocean Tsunami ò Magnitude 9. 2 ò Rupture continued for 9 minutes & moved 1300 km along a thrust fault – the longest single fault break ever recorded ò Resulted in tsunamis that killed 300, 000 on Sumatra, Sri Lanka, Thailand, the Maldive Islands and Somalia

Banda Aceh Pre-Tsun June 23, 2004 Banda Aceh Post-Tsun December 28, 2004 Photos: http: //www. baird. c baird/en_html/indian_ocea indianocean. html

Indian Ocean Tsunami, Thailand Photo: http: //en. wikipedia. org/wiki/Image: 200

Original Photo from John Thompson taken on December 26, 2004

2008: Eastern Sichuan, China ò Magnitude 7. 9 ò Schools and hospitals collapsed ò ~70, 000 killed ò ~18, 000 missing ò Strong aftershocks and landslides ò May have been triggered by dam holding 315 million tons of water

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

Photo: http: //www. telegraph. co. uk/news/worldnews/asia/china/4434400/Chinese-earthquake-may-hav say-scientists. html

2010: Haiti Earthquake ò Magnitude 7. 0 ò ~212, 000 killed ò ~ 1 million homeless ò Major damage to city of Port-au-Prince

Photo: http: //image 3. examiner. com/images/blog/EXID 12837/images/haiti. jpg

Photo: http: //i. telegraph. co. uk/telegraph/multimedia/ archive/01558/presidentialpalac_1558531 i. jpg

2011: Japan Earthquake and Tsunami ò Magnitude 9. 0 earthquake ò Rupture along thrust fault at the subduction zone between the Pacific & N. American plates ò Fault moved upwards by 30 -40 m (this is 98 to 131 feet!) and slip occurred over an area 300 km long ò Foreshocks occurred over 2 days preceding the quake (a M 7. 2 and 3 greater than M 6 on

2011: Japan Earthquake and Tsunami ò Resulting 30 ft tsunami swept through many coastal regions of Japan, reaching as far as 6 mi inland ò 13, 116 people killed, 14, 377 missing ò Caused failure of nuclear power plant All following photos from MSN. com unless otherwise noted

Collapsed House_Sukagawa. City, Fukushima

Japan. EQ_Split. Road_Sacremento. Bee

Tsunami. Swirl_Oarai, Ibaraki_3 -11 -11

Japan. Tsunami_Iwanuma, Miyagi_3 -11 -11

Japan. Tsunami_Natori_3 -11 -11

Japan Tsunami_Sendai. Airport_3 -11 -11

Japan. Tsunami_3 -11 -11_Cleveland. com

Japan. Tsunami_Houses. Swept. To. Sea_Natori. City_3 -11 -11

Japan. Tsunami_Sendai. Airport_3 -11 -1

Onagawa. Town, Miyagi. Prefecture_3 -26 -11

What is an Earthquake? ò We inhabit a fragile built environment of houses, buildings & transportation systems that is anchored in Earth’s crust ò This environment is vulnerable to seismic vibration, ground rupture, landslides and tsunamis

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

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

Elastic Rebound Theory ò Faults remain locked while strain energy accumulates in the rocks on either side, causing them to deform until a sudden slip along the fault releases the energy ò Elastic means the rocks spring back to their undeformed shape when the fault unlocks ò The distance of displacement is called

Photo: http: //www. winona. edu/geology/MRW/mrwimages/elasticre

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

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

Fault Rupture ò Does not happen all at once ò Starts at focus and expands outward on fault plane at ~2 – 3 km/s ò Rupture stops when stress can no longer break the rocks ò Size of earthquake is related to total area of fault rupture

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

Tree displaced 15 ft (from where person is standing) Photo: http: //w. ac. uk/Resources/Earth. Sci/Tectonics/images/ranch. jpg

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

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

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

Seismic Waves ò ò ò 1. 2. Ground vibrations produced by an earthquake Enable us to locate earthquakes and determine type of faulting that produced them 4 types: Body Waves a. P waves b. S waves Surface Waves a. Rayleigh waves

Primary or P Waves ò Travel through Earth and are first to arrive at seismic station ò Compressional waves ò Can be thought of as push-pull waves: they push or pull particles of matter

Secondary or S Waves ò Follow the P waves through Earth, and arrive second at the seismic station ò Shear waves ò Displace material at right angles to their path of travel

Surface Waves ò Arrive last after traveling around Earth’s surface ò Speed slightly less than S waves ò Rayleigh waves – travel in rolling motion over surface ò Love waves – shake the ground in sideways motion

Locating the Epicenter Time interval between P and S wave arrival depends on distance waves have traveled from focus ò If three or more seismic stations know the distance, then the epicenter can be located ò

Measuring the Size of an Earthquake Magnitude of an earthquake is the main factor that determines the intensity and potential destructiveness of an earthquake ò Two scales: 1. Richter magnitude 2. Moment magnitude ò

Richter Magnitude ò Developed by Charles Richter in 1935 ò Each earthquake is assigned a number on a logarithmic scale ò Two earthquakes differ by one magnitude if the size of their ground motions differs by a factor of 10 ò This means the ground motion of a magnitude 6 earthquake is 10 times greater than a magnitude 5 and 100 times greater than a magnitude 4 ò The energy released as seismic waves

Moment Magnitude ò Seismologists now prefer a measure of EQ size more directly related to the physical properties of faulting that causes the EQ ò Moment magnitude is the product of the area and the average slip across the fault break ò It increases by about 1 unit for every 10 -fold increase in the area of faulting ò It produces roughly the same numerical values as Richter’s method, but can be measured from seismograms and determined by field measurements of the fault

Earthquake Size and Frequency ò Large earthquakes occur much less often than small ones ò Worldwide figures of earthquake size per year: ü 1, 000 with magnitudes greater than 2. 0 ü 100, 000 greater than 3. 0 ü 1000 greater than 5. 0 ü 10 greater than 7. 0 ü Earthquakes with magnitude above 8. 0 occur about once every 3 years ü Very large ones like the 2004 Sumatra quake (magnitude 9. 2), 1964 Alaska (9. 2) and 1960

Shaking Intensity ò Amplitude of shaking depends on distance from fault rupture ò Damage from shaking depends on distance from populated areas ò Estimated shaking determined with modified Mercalli intensity scale – values from I (not felt) to XII (damage total) (for full scale see page 307 of textbook)

Shaking Intensity maps of 1906 & 1989 San Francisco Earthquake Photo: http: //pubs. usgs. gov/of/2005/1135/1906_Boatwright/downlo Boatwright_BA_intensity. jpg

Earthquakes and Faulting ò Most earthquakes occur at plate boundaries ò Largest earthquakes occur at convergent boundaries on megathrust faults that form where one plate subducts beneath another ò Exs: Sumatra (2004), Alaska (1964) & Chile (1960): largest EQ ever recorded, magnitude 9. 5

Intraplate Earthquakes òA small percentage of earthquakes occur in plate interiors ò Foci are shallow and occur mostly on continents ò Many occur on old faults that use to be part of plate boundaries and are now areas of crustal weakness ò Examples include some of most famous in American history: New Madrid, Missouri (1811 -1812), Charleston, South Carolina (1886), and Cape Ann,

Regional Fault Systems ò Zones of deformation between plate boundaries usually have a network of interacting faults – a fault system – rather than a single fault ò Ex: in California, the “master fault” is the San Andreas, however, there are many subsidiary faults on either side that generate large earthquakes. ò Most of the damaging earthquakes in California during the last century have

San Andreas Fault System Photo: http: //pubs. usgs. gov earthq 3/map 1 a. gif

Earthquake Destructiveness ò Over the last century, earthquakes worldwide have caused an average of 13, 000 deaths per year and hundreds of billions of dollars of damage ò Two California earthquakes – 1989 Loma Prieta (mag 7. 1 & $10 billion in damage) and 1994 Northridge (mag 6. 8 & $40 billion in damage) – were among the costliest disasters in U. S. history because of nearby urban areas

Loma Prieta Earthquake Damage

Nimitz Freeway after the Loma Prieta Earthquake, 1989 Photo: http: //www. dot. ca. gov/hq/esc/geotech/photos/south 2/cypre

Column collapse along Cypress Viaduct, Loma Prieta EQ Photo: GSA, Explore Earthquakes CD-Rom

Marina District after Loma Prieta Earthquake, 1989 Photo: GSA, Explore Earthquakes CD-Rom

Damage to garages in Marina District, Loma Prieta EQ, 1 Photo: GSA, Explore Earthquakes CD-Rom

House that slid off foundation during Loma Prieta

Collapsed walls of house, Loma Prieta

Collapse of 5 story tower, Loma Prieta EQ, 1989 Photo: GSA, Explore Earthquakes CD-Rom

Northridge Earthquake Damage

Collapse of Interstate 5, Northridge EQ, 1994 Photo: http: //pubs. usgs. gov/fs/1999/fs 110 -99/

Highway damaged during Northride EQ, 1994 Photo: http: //boxer. senate. gov/ students/resources/features/1906/ committee. cfm

Highway Damage, Northridge Earthquake, 1994 Photo: http: //mceer. buffalo. edu/research/resilience/default. asp

Damaged Building, Northridge EQ, 1994 Photo: http: //www. calstatela. edu/dept/geology/Geocareer. htm

Earthquake Destructiveness ò Destructive earthquakes are even more common in Japan than in California ò Japan is the best prepared nation to deal with earthquakes, with strong public education campaigns, building codes and warning systems ò Despite this, more than 5600 people were killed in a mag 6. 9 EQ in Kobe in 1995 ò Casualties and structure failure (50, 000 buildings destroyed) occurred because of less stringent building codes that were in effect

How Earthquakes Cause Damage ò Primary effects: ü Faulting (breaks in ground surface) ü Ground shaking (from seismic waves) ò Secondary effects: ü Landslides ü Tsunamis ü Fires

Faulting and Shaking ò Ground surface can subside or uplift during faulting ò Ground accelerations near the epicenter can exceed the acceleration of gravity, so gravity objects lying on the surface can be thrown into the air

Faulting and Shaking ò Seismic waves can shake structures so hard that they collapse, which is the collapse leading cause of casualties and economic damage ò Examples: ü Tangshan, China 1976: >240, 000 killed ü Spitak, Armenia 1988: 25, 000 killed ü Izmit, Turkey 1999: 15, 600 killed ü Etc…

Landslides and Other Ground Failures ò Landslides can bury towns ü Ex: debris flow in China’s Kansu Province, 1920, covered >100 km 2, 200, 000 killed ò Water saturated soils can behave like a liquid – called liquefaction – and flow away, taking buildings, bridges, etc along with it ü Ex: cause of massive building collapse

Liquefaction in Niigata, 1964 Photo: http: //www. ce. washington. edu/~liquefaction/selectpiclique /tiltedbuilding. jpg

Tsunamis ò Destructive sea wave triggered by earthquake beneath the ocean ò NOT called tidal wave – this term is incorrect, has nothing to do with tides ò Deadliest and most destructive hazard associated with largest earthquakes – megathrust quakes that occur in subduction zones

Tsunamis ò Megathrust ruptures can push the seafloor upward by as much as 10 m, displacing the overlying ocean water ò Resulting wave travels at speeds of up to 800 km/hr, as fast as a jetliner ò They are hardly noticeable in deep ocean, but waves slow down and pile up when they reach shallow coastal waters

Tsunamis ò Most common in Pacific Ocean, why? ü Ring of Fire – subduction zones ring the Pacific ò Examples: ü 1964 Alaska EQ caused tsunamis that hit thousands of kilometers from epicenter. At one location, near Valdez, AK, the tsunami ran up a mountainside to a height of 67 m (that’s 220 feet)! ü 2004 Indian Ocean EQ caused tsunamis that killed 300, 000 people in

1946 Tsunami Hilo, Hawaii. Caused by earthquake in Aleutian I Photo: http: //static. howstuffworks. com/gif/tsunami-5. jpg

Damage from 1946 tsunami, Hilo, Hawaii Photo: http: //soundwaves. usgs. gov/2005/01/fieldwork 2. html

Aftermath of 1960 tsunami at Hilo, Hawaii; caused by earthquake Photo: http: //earthquake. usgs. gov/regional/world/events/images/1 22_hilo. gif

Damage to hotel from Indian Ocean tsunami, 2004 Photo: http: //www. calstatela. edu/dept/geology/G 351. htm

Fires ò Are ignited by ruptured gas lines or downed electrical power lines ò Damage to water mains can making fighting them impossible, as happened in the 1906 San Francisco EQ

Reducing Earthquake Risk ò Seismic hazard – describes the intensity of seismic shaking and ground disruption that can be expected ò Seismic risk – describes the damage that can be expected for a specific region ò Risk depends on the seismic hazard, population, and number of built population structures

Reducing Earthquake Risk ò California leads the nation in seismic risk at 75% of the national total, with Los 75 Angeles county accounting for 25% 25 ò But 46 million people are at risk outside of California, including: Hilo, Honolulu, Anchorage, Seattle, Tacoma, Portland, Salt Lake City, Reno, Las Vegas, Albuquerque, Charleston, Memphis, Albuquerque Atlanta, St. Louis, New York, Boston &

United States seismic hazard map Photo: http: //pubs. usgs. gov/fs/2005/3038/images/seismic-hazard

Land Use Policies ò Exposure of built structures to earthquake risk can be reduced by policies that restrict land use ò It is unwise to erect buildings on known active faults, as was done in residential areas of San Francisco. ò California law now restricts construction across active faults. ò Real estate agents are required to disclose information about houses built on a fault

Earthquake Engineering ò Risk from seismic shaking can be reduced by good engineering and construction ò Building codes specify the forces a structure must be able to withstand from a seismic hazard ò U. S. building codes have been largely successful in preventing loss of life during earthquakes ò Ex: from 1983 to 2004, 131 people died in nine severe earthquakes in the western U. S. ,

Warning Systems ò When an earthquake occurs, automated seismic systems can send warnings tens of seconds before the arrival of destructive seismic waves ò Tsunamis travel 10 times slower than seismic waves, so distant shorelines can be given up to hours of warning time ò Unfortunately, no system had been installed in the Indian Ocean during the 2004 quake

Can Earthquakes be Predicted? ò Prediction means specifying time, time location and size ò Information from plate tectonics and geologic mapping of fault systems can allow geologists to forecast which faults are likely to produce earthquakes over the long term ò To specify precisely when a particular fault will rupture is very difficult

Long-Term Forecasting ò The longer the time since the last big EQ, the sooner the next one will be ò Recurrence interval – the average time between large earthquakes. ò Determined by strain rate – how long it takes for a fault to build up enough strain that rock strength is exceeded

Short-Term Prediction ò ò ò There have been a few successful short-term predictions Ex: in 1975, an EQ was predicted only hours before occurring near Haicheng, China Seismologists used precursors of swarms of tiny earthquakes to make prediction The next year, however, an unpredicted quake struck the Chinese city of Tangshan, killing more than 240, 000 No reliable method of short-term prediction has been found