Lecture Outlines Natural Disasters, 7 th edition Patrick L. Abbott

Earthquakes in Continental US and Canada plus Hawaii Natural Disasters, 7 th edition, Chapter 7

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

U.S. and Canadian Earthquakes U.S. earthquakes above magnitude 3.5 ( ) were mostly in Alaska, California, Hawaii and Nevada Look at large U.S. and Canada earthquakes not on tectonic boundary

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

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 Western North America: Plate Boundary-Zone Earthquakes Figure 7.3

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 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 Western North America: Plate Boundary-Zone Earthquakes

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

Western Great Basin: Eastern California, Western Nevada Western North America: Plate Boundary-Zone 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

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

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) Western North America: Plate Boundary-Zone Earthquakes Figure 7.7 Figure 7.6

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 earthquakes throughout Nevada, 1954 Many seismic gaps still exist between locations of past earthquakes Western North America: Plate Boundary-Zone Earthquakes

The Intermountain Seismic Belt North-trending curve 1,500 km long and 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 Western North America: Plate Boundary-Zone Earthquakes Figure 7.9

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 Western North America: Plate Boundary-Zone Earthquakes Figure 7.10

Borah Peak, Idaho, 1983 Lost River fault ruptured in 7.3 earthquake Borah Peak (Idaho’s 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 Boundary-Zone Earthquakes Figure 7.11

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 Western North America: Plate Boundary-Zone Earthquakes Figure 7.12

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

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

New Madrid, Missouri, 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 Intraplate Earthquakes: “Stable” Central United States Figure 7.15 New Madrid ( ‘Gateway to the West’ before earthquakes) –Long-lasting effects on topography Two new lakes Low cliffs and domes formed Waterfalls in streams

Felt Area –Felt area was largest for any U.S. earthquake –Must consider difference in wave propagation in eastern vs. western North America Intraplate Earthquakes: “Stable” Central United States Figure 7.17 –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.

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 Intraplate Earthquakes: “Stable” Central United States Figure 7.18

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 Intraplate Earthquakes: “Stable” Central United States

The Future – 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 Intraplate Earthquakes: “Stable” Central United States Figure 7.19

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 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? 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

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 Intraplate Earthquakes: “Stable” Central United States Figure 7.22

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 7.21

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

St. Lawrence River Valley Earthquakes River follows path of million year old rift valley, coinciding with most of significant earthquakes in southeastern Canada up to magnitude 7 Intraplate Earthquakes: Eastern United States 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 Figure 7.23

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

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 Earthquakes and Volcanism in Hawaii Figure 7.27 Figure 7.26

End of Chapter 7