Lecture Outlines Natural Disasters, 7 th edition

1. Lecture OutlinesNatural Disasters, 7th edition Patrick L. Abbott

2. Earthquakes in Continental US and Canada plus HawaiiNatural Disasters, 7th edition, Chapter 7

3. U.S. and Canadian Earthquakes • Earthquakes occur throughout North America, not just in California • Earthquake hazard maps based on historic records, show hazard across U.S. Figure 7.1

4. 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

5. Western North America: Plate Boundary-Zone Earthquakes Pacific Northwest: Oregon, Washington, and British Columbia Puget Sound, Washington, 1949 and 1965 • Subduction within the Juan de Fuca plate caused earthquakes deep below surface (54 and 60 km), magnitudes 7.1 and 6.5 Figure 7.3

6. Western North America: Plate Boundary-Zone Earthquakes Pacific Northwest: Oregon, Washington, and British Columbia Puget Sound Update, 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 • Would have been far worse but for improved building codes after 1965 earthquake Figure 7.3

7. Western North America: Plate Boundary-Zone Earthquakes Pacific Northwest: Oregon, Washington, and British Columbia Deep Earthquakes beneath the Puget Sound • 1949, 1965 and 2001 earthquake hypocenters within subducting Juan de Fuca plate at depth under North America • Earthquakes 30 to 70 km deep occur about every 30 years • Can be as great as 7.5 magnitude

8. Western North America: Plate Boundary-Zone Earthquakes Pacific Northwest: Oregon, Washington, and British Columbia Shallow Earthquakes in the Puget Sound Region • Seattle 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

9. In Greater Depth:Human-Triggered Earthquakes Ohio Rocks (Ashtabula Township) • Began pumping industrial waste liquids underground in 1986 • Earthquakes began in 1987, up to magnitude 4.5 • Pressurized fluids flow from well and encounter faults, add stress to cause earthquake Dam Earthquakes (Oroville, California) • Construction of dam and filling of reservoir triggered earthquakes • Water from reservoir seeps into ground at pressure and triggers earthquakes on faults encountered Bomb Blasts (Nevada) • Underground nuclear explosions release energy equivalent to magnitude 5 earthquake, changes stress underground and triggers earthquakes

10. Western North America: Plate Boundary-Zone Earthquakes Western Great Basin: Eastern California, Western Nevada 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 Figure 7.4

11. Western North America: Plate Boundary-Zone 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

12. Western North America: Plate Boundary-Zone Earthquakes Western Great Basin: Eastern California, Western Nevada 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) Figure 7.6 Figure 7.7

13. Western North America: Plate Boundary-Zone Earthquakes Western Great Basin: Eastern California, Western Nevada The Western Great Basin Seismic Trend • Extension produces major earthquakes: • Magnitude 7.7 earthquake near Winnemucca, Nevada, 1915 • Magnitude 7.3 earthquake near Cedar Mountain, Nevada, 1932 • Magnitude 6.6-7.3 earthquakes throughout Nevada, 1954 • Many seismic gaps still exist between locations of past earthquakes

14. Western North America: Plate Boundary-Zone Earthquakes The Intermountain Seismic Belt • 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 Figure 7.9

15. Western North America: Plate Boundary-Zone Earthquakes 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 Figure 7.10

16. Western North America: Plate Boundary-Zone Earthquakes Intermountain Belt: Utah, Idaho, Wyoming, Montana Borah Peak, Idaho, 1983 • Lost Riverfaultruptured in 7.3 earthquake • Borah Peak (Idaho’s highest point)0.3 m higher, Thousand Springs Valleyfew meters lower • Ground shaking causedfountainsof groundwater Figure 7.11

17. Western North America: Plate Boundary-Zone Earthquakes 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 1847 • Brigham City next likely candidate Figure 7.12

18. Western North America: Plate Boundary-Zone 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 Figure 7.14 • Historic earthquakes have been small to moderate but potential for large earthquake exists

19. 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 Figure 7.1

20. 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 beneaththick sedimentsof Mississippi and Ohio Rivers at Mississippi River embayment, near town of New Madrid ( ‘Gateway to the West’ before earthquakes) • Long-lasting effects on topography • Two new lakes • Low cliffs and domes formed • Waterfalls in streams Figure 7.15

21. Intraplate Earthquakes: “Stable” Central United States • 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. Figure 7.17

22. Intraplate Earthquakes: “Stable” Central United States • Magnitudes • Using felt area to estimate magnitudes  8 to 8.3 • Studies of small aftershocks occurring today can map out faults • First earthquake on Cottonwood Grove fault, triggered two of following earthquakes on Reelfoot blind thrust • Remaining earthquake difficult to locate Figure 7.18

23. Intraplate Earthquakes: “Stable” Central United States • 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

24. Intraplate Earthquakes: “Stable” Central United States • 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 Figure 7.19

25. Intraplate Earthquakes: “Stable” Central United States • 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

26. Intraplate Earthquakes: “Stable” Central United States Reelfoot Rift: Missouri, Arkansas, Tennessee, Kentucky, Illinois • Why do earthquakes follow same linear pattern as deposition of sediments by Mississippi River system? • 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

27. 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 Figure 7.22

28. Intraplate Earthquakes: “Stable” Central United States 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 Figure 7.21

29. 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 Figure 7.23 • 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

30. Intraplate Earthquakes: Eastern United States St. Lawrence River Valley Earthquakes • River follows path of 500-600 million year old rift valley, coinciding with most of significant earthquakes in southeastern Canada up to magnitude 7 Figure 7.23 • Most active area is Charlevoix: earthquakes occurred in 1534, 1663, 1791, 1860, 1870, 1925 • Site of large meteorite impact 350 million years ago, fracturing the area into faults that are being reactivated

31. Intraplate Earthquakes: Eastern United States Charleston, South Carolina, 1886 • After Civil War, devastated by 1885 hurricane • 1886 earthquake destroyed 90% of buildings • No surface faulting from earthquake • At least five similar earthquakes in last 3,000 years – recurrence interval of about 600 years Figure 7.25

32. Earthquakes and Volcanism in Hawaii • Movement of magma can cause earthquakes • Expansion forces fracturing of surrounding brittle rock • Magma movement generates continuous swarm of small earthquakes  harmonic tremors • Movement can also cause up to magnitude 6 and 7 events • 1975 magnitude 7.2 earthquake was caused by movement on normal fault of block into sea – caused tsunami up to 12 m high Figure 7.26 Figure 7.27

33. End of Chapter 7