More U.S. and Canadian Earthquakes Natural Disasters, 6 th edition, Chapter 7

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Transcript of More U.S. and Canadian Earthquakes Natural Disasters, 6 th edition, Chapter 7

  • Slide 1
  • More U.S. and Canadian Earthquakes Natural Disasters, 6 th edition, Chapter 7
  • Slide 2
  • U.S. and Canadian Earthquakes Earthquakes occur throughout North America, not just in California
  • Slide 3
  • U.S. and Canadian Earthquakes U.S. earthquakes above magnitude 3.5 (1974-2003) were mostly in Alaska, California, Hawaii and Nevada Look at large U.S. and Canada earthquakes not on tectonic boundary
  • Slide 4
  • Western North America: Plate Tectonic-Related Earthquakes North American plate moves southwest at 2.5 cm/yr Pacific plate moves northwest 8 cm/yr
  • Slide 5
  • Western North America: Plate Tectonic-Related Earthquakes Much of Farallon plate has subducted under North America Western United States uplifted, creating Rocky Mountains, Sierra Nevada, Colorado Plateau Earthquakes throughout western United States
  • Slide 6
  • Pacific Northwest: Oregon, Washington, and British Columbia Subduction of the Juan de Fuca plate caused earthquakes deep below surface (54 and 60 km).
  • Slide 7
  • Pacific Northwest: Oregon, Washington, and British Columbia Puget Sound, Washington, 1949 and 1965 magnitudes 7.1 and 6.5 Puget Sound, Washington, 2001 Earthquake near epicenter of 1949 earthquake, magnitude 6.8 and 52 km deep Did not result in any deaths, although 400 injured and $2 billion in damage Damage would have been far worse but for improved building codes after 1965 earthquake
  • Slide 8
  • Pacific Northwest: Oregon, Washington, and British Columbia Future Earthquakes in the Washington Region 1949, 1965 and 2001 earthquakes on subducting Juan de Fuca plate at depth under North America Much energy lost before reaching surface Earthquakes on near-surface faults also possible in region Seattle (Tacoma) fault zone 4 to 6 km zone with three or more south-dipping reverse faults Last major fault movement 1,100 years ago Uplift of shoreline in magnitude 7 earthquake Large landslides Tsunami deposits six major rock avalanches in Olympic Mountains Coarse sediment layers at bottom of Lake Washington Seattle sits on basin of soft sediments that amplify shaking
  • Slide 9
  • Western Great Basin: Eastern California, Western Nevada Western North America: Plate Tectonic-Related Earthquakes Figure 7.4 Owens Valley, California, 1872 Fault runs along Interstate 395, on east side of Sierra Nevada Third longest fault rupture in California history, after 1906 San Francisco and 1857 Fort Tejon Earthquake with estimated magnitude 7.4
  • Slide 10
  • Western North America: Plate Tectonic-Related Earthquakes Western Great Basin: Eastern California, Western Nevada The Western Great Basin Seismic Trend Earthquake belt through eastern California and western Nevada Nevada averages one magnitude 6 earthquake per decade and one magnitude 7 earthquake per 27 years Figure 7.5
  • Slide 11
  • Western North America: Plate Tectonic-Related Earthquakes The Western Great Basin Seismic Trend Area between Sierra Nevada in California and Wasatch Range in Utah is expanding in east-west direction, opening up by several 100 km (Basin and Range or Great Basin)
  • Slide 12
  • Western North America: Plate Tectonic-Related Earthquakes Intermountain Belt: Utah, Idaho, Wyoming, Montana North-trending curve 1,500 km long and 100- 200 km wide separating Basin and Range from Colorado Plateau and Rocky Mountains Faults on east side are down-to-the-west and on the west side are down- to-the east: center is down-dropped
  • Slide 13
  • Intermountain Belt: Utah, Idaho, Wyoming, Montana Hebgen Lake, Montana, 1959 Two faults moved within five seconds of each other with magnitude 6.3 and 7.5 earthquakes Created landslide that dammed canyon and formed Earthquake Lake Dropped north end of Hebgen Lake 7-8 m, creating seiche that sloshed back and forth for almost 12 hours
  • Slide 14
  • Borah Peak, Idaho, 1983 Lost River fault ruptured in 7.3 earthquake Borah Peak (Idahos highest point) 0.3 m higher, Thousand Springs Valley few meters lower Ground shaking caused fountains of groundwater Intermountain Belt: Utah, Idaho, Wyoming, Montana Western North America: Plate Tectonic-Related Earthquakes Figure 7.11
  • Slide 15
  • Intermountain Belt: Utah, Idaho, Wyoming, Montana The Wasatch Fault More than 80% of Utah population within sight of Wasatch Fault, which separates Wasatch Mountains from Great Basin Capable of generating magnitude 6-7 earthquakes every ~350 years No major earthquakes since arrival of Brigham Young (Brigham City next likely candidate)
  • Slide 16
  • Western North America: Plate Tectonic-Related Earthquakes Rio Grande Rift: New Mexico, Colorado, Westernmost Texas, Mexico Major continental rift: series of interconnected fault-block valleys for more than 1,000 km Continental crust is being heated and thinned by normal faulting In last 26 million years, 8 km of extension Historic earthquakes have been small to moderate but potential for large earthquake exists
  • Slide 17
  • Intraplate Earthquakes: Stable Central United States Clusters of earthquakes at few locations Away from active plate edges Fewer earthquakes, but can be just as large
  • Slide 18
  • Intraplate Earthquakes: Stable Central United States New Madrid, Missouri, 1811-1812 Series of earthquakes, with four very large events Eight considered violent, ten very severe Total of 1,874 events Hypocenters beneath thick sediments of Mississippi and Ohio Rivers at Mississippi River embayment, near town of New Madrid (called Gateway to the West before destruction by earthquakes) Long-lasting effects on topography Two new lakes Low cliffs and domes formed Waterfalls in streams
  • Slide 19
  • New Madrid, Missouri, 1811-1812 Felt Area Felt area was largest for any U.S. earthquake Must consider difference in wave propagation in eastern vs. western North America Young, tectonically fractured rocks of west coast impede wave propagation and cause wave energy to die out faster than older, more homogeneous rocks of central U.S.
  • Slide 20
  • Magnitudes - New Madrid, Missouri, 1811-1812 Using felt area to estimate magnitudes 8 to 8.3 Studies of small earthquakes occurring today (aftershocks of 1811-1812 events) in this area can map out the faults First earthquake on Cottonwood Grove fault, triggered two of following earthquakes on Reelfoot blind thrust Remaining earthquake difficult to locate Intraplate Earthquakes: Stable Central United States
  • Slide 21
  • New Madrid, Missouri, 1811-1812 Magnitudes Using fault-rupture length estimates from aftershock locations gives smaller moment magnitudes 7.3 to 7.7 Soft, water-saturated sediment of ground amplifies shaking; accounting for amplification gives magnitudes 7.0 to 7.5
  • Slide 22
  • New Madrid, Missouri, 1811-1812 The Future 1811-1812 New Madrid earthquakes did not cause great damage because population of area at time was so low Future earthquakes will affect population of St. Louis, Memphis Buildings not designed for earthquake shaking Soft sediments will amplify ground shaking Very large area will be affected
  • Slide 23
  • New Madrid, Missouri, 1811-1812 The Future Neotectonic analyses show earthquakes in the area around 500, 900, 1300 and 1600 Magnitude 7 or higher earthquakes occur here about every 500 years U.S. Geological Survey forecasts 90% probability of magnitude 6-7 earthquake in next 50 years Why do earthquakes occur here in middle of continent? Reelfoot Rift
  • Slide 24
  • Reelfoot Rift: Missouri, Arkansas, Tennessee, Kentucky, Illinois Why do earthquakes follow same linear pattern as deposition of sediments by Mississippi River system? Intraplate Earthquakes: Stable Central United States Linear structural depression underlying New Madrid region ancient rift valley, Reelfoot Rift Formed 550 million years ago and since filled with sedimentary rocks and covered with younger sediments Figure 7.20
  • Slide 25
  • Intraplate Earthquakes: Stable Central United States Ancient Rifts in the Central United States As Pangaea tore apart around 200 million years ago, many rifts formed Some separated the landmass and formed Atlantic Ocean Others were failed rifts, left behind weakened zones in continent Can be reactivated by plate-tectonic stresses
  • Slide 26
  • Ancient Rifts in the Central United States Failed rifts correlate to active faults at the surface St. Louis arm St. Genevieve fault zone Rough Creek rift Rough Creek fault zone Southern Oklahoma rift Wichita Mountains frontal-fault system, Meers fault across Oklahoma Southern Indiana arm Wabash Valley fault zone Intraplate Earthquakes: Stable Central United States Figure 7.22
  • Slide 27
  • Intraplate Earthquakes: Eastern United States New England Earthquakes Offshore from Cape Ann, Massachusetts: 1638 earthquake with estimated 5.5 magnitude Newbury, Massachusetts: 1727 earthquake caused damage, quicksand conditions Offshore from Cape Ann, Massachusetts: 1755 earthquake felt from Nova Scotia to South Carolina with estimated magnitude of 6.3 May be related to reactivated faults bounding former rift valleys, with potential for future earthquakes, with proportionally more damage across densely populated East Coast Figure 7.23
  • Slide 28
  • St. Lawrence River Valley Earthquakes River follows path of 500-