Lecture Outlines
Natural Disasters, 7th edition
Patrick L. Abbott
Earthquakes in Continental US and
Canada plus Hawaii
Natural Disasters, 7th 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 (1974-2003)
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
Western North America:
Plate Boundary-Zone Earthquakes
Pacific Northwest: Oregon,
Washington, and British
Columbia
Figure 7.3
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
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
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 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
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 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
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
Western North America:
Plate Boundary-Zone Earthquakes
The Intermountain
Seismic Belt
• North-trending curve
1,500 km long and 100200 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 downto-the east: center is
down-dropped
Figure 7.9
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
Western North America:
Plate Boundary-Zone Earthquakes
Intermountain Belt: Utah, Idaho, Wyoming,
Montana
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
Figure 7.11
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
Figure 7.12
candidate
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
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
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 ( ‘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
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
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
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
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
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
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
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
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
Intraplate Earthquakes:
Eastern United States
New England Earthquakes
Figure 7.23
• 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
Intraplate Earthquakes:
Eastern United States
St. Lawrence River Valley
Earthquakes
Figure 7.23
• River follows path of 500600 million year old rift
valley, coinciding with most
of significant earthquakes in
southeastern Canada up to
magnitude 7
• 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
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
Earthquakes and Volcanism in Hawaii
• Movement of magma can cause
earthquakes
• Expansion forces fracturing of
surrounding brittle rock
• Magma movement generates
Figure 7.26
continuous swarm of small
earthquakes  harmonic
tremors
• Movement can also cause up to
magnitude 6 and 7 events
Figure 7.27
• 1975 magnitude 7.2 earthquake
was caused by movement on
normal fault of block into sea –
caused tsunami up to 12 m high
End of Chapter 7