Faults and Earthquakes
Some Important Earthquakes
1755 - Lisbon, Portugal
• Killed 70,000, Raised Waves in Lakes all over
Europe
• First Scientifically Studied Earthquake
1811-1812 - New Madrid, Missouri
• Felt over 2/3 of the U.S.
• Few Casualties
1886 - Charleston, South Carolina
• Felt All over East Coast, Killed Several Hundred.
• First Widely-known U.S. Earthquake
Some Important Earthquakes
1906 - San Francisco
• Killed 500 (later studies, possibly 2,500)
• First Revealed Importance of Faults
1923 – Tokyo - Killed 140,000 in firestorm
1964 - Alaska
• Killed about 200
• Wrecked Anchorage.
• Tsunamis on West Coast
Some Important Earthquakes
1976 - Tangshan, China
• Hit an Urban Area of Ten Million People
• Killed 650,000
2004 – Indian Ocean
• 300,000 killed
• Worst Tsunami Disaster in History
2010 – Haiti
• Not very strong but 200,000 killed
Seismic Waves
Elastic Rebound
Epicenter and Focus
Focus
• Location within the earth where fault
rupture actually occurs
Epicenter
• Location on the surface above the focus
Types of Faults
Faults Are Classified According to the Kind of
Motion That Occurs on Them
• Joints - No Movement
• Strike-Slip - Horizontal Motion
• Dip-Slip - Vertical Motion
Joints
• Aseismic: No Earthquake Hazard
• Environmentally Important Because They
Influence
– Rock Strength
– Landslides and Slope Failure
– Ground Water Movement
Joints, Utah
Joints, Marathon County
Joints, Door County
Strike-Slip Fault – Left Lateral
Strike-Slip Fault – Right Lateral
San Andreas Fault, California
Crystal Springs Dam
Fault Gouge, San Andreas Fault
San Andreas
Fault, San
Bernardino,
California
San Andreas Fault, California
San Andreas Fault, Cajon Pass, California
Hayward Fault, California
Fault Creep,
Hayward
Fault,
California
Fault Creep, Hayward Fault, California
Hollister, California
Hollister, California
Hollister, California
Mission Impossible
1812 Earthquake Damage
Carizzo Plain, California
Carizzo Plain, California
Carizzo Plain, California
Offset Stream, California
Tsunami Alert!
Rapid Uplift, Sierra Nevada
California Earthquakes … Then …
…And Now
Dip-Slip Faults
• Normal Faults: Extension
• Reverse Faults: Compression
–Reverse Faults are often called
Thrust Faults
Dip-Slip Fault - Normal
Fault Surface, Provo, Utah
Normal Fault, California
Moab Fault, Utah
Front Range Fault, Colorado
Sierra Nevada, Manzanar, California
Owens Valley, California
Owens Valley, California
Horsts and
Grabens,
California
Horsts and
Grabens,
California
Soft-Sediment Graben
Graben, Wasatch Fault, Utah
Horst,
Nevada
1950 Fault Rupture, Nevada
1950 Fault Rupture, Nevada
1950 Fault Rupture, Nevada
Dip-Slip Fault - Reverse
Thrust Fault, Antarctica
Sheared Rock on Thrust Fault, Antarctica
Thrust Faults, Appalachians
Thrust Fault, Tennessee
Thrust Fault Structures
Mountain Scenery, Tennessee
Window, Tennessee
Floor of Window, Tennessee
Chief Mountain, Montana
Above the Thrust Fault
Below the Thrust Fault
“Ice-Free Corridor”
Thrust Faults in Snow
Moine Thrust, Scotland
Moine Thrust, Scotland
Melange, Newfoundland
Melange, Newfoundland
Major Hazards of Earthquakes
•
•
•
•
Building Collapse
Landslides
Fire
Tsunamis (Not Tidal Waves!)
Safest & Most Dangerous Buildings
•
•
•
•
•
Small, Wood-frame House - Safest
Steel-Frame
Reinforced Concrete
Unreinforced Masonry
Adobe - Most Dangerous
Not the Best Place to Build?
Construction, Turkey
Construction, Turkey
Construction, Turkey
Construction, Bosnia
Tile Roof, Costa Rica
Tile Roof, Costa Rica
Adobe Buttresses, Texas
Rebar in Freeway, California
Earthquake
Bolts,
Charleston SC
Tsunamis
Probably Caused by Submarine Landslides
Travel about 400 M.p.h.
Pass Unnoticed at Sea, Cause Damage on Shore
Warning Network Around Pacific Can Forecast
Arrival
• 2004 disaster creates push for global system
Whether or Not Damage Occurs Depends on:
• Direction of Travel
• Harbor Shape
• Bottom
• Tide & Weather
Tsunami Warning Sign
Fire
•
•
•
•
Tokyo, 1923
San Francisco, 1906
San Francisco, 1989
Hazards
– Broken water mains
– Broken gas lines
– Electrical shorts
– Broken or overturned fuel tanks
– Streets blocked
Firestorms
•
•
•
•
Old Growth Forests (Peshtigo, 1871)
Pre-WWII Cities (Dresden, Hamburg, Tokyo)
Not second growth or modern cities
Requires several pounds of combustible
material per square foot
• A true firestorm is a mesocyclone
– Term often used loosely and inaccurately
Magnitude and Intensity
Intensity
• How Strong Earthquake Feels to Observer
Magnitude
• Related to Energy Release
• Determined from Seismic Records
• Rough correlation between the two for
shallow earthquakes
Intensity
How Strong Earthquake Feels to Observer
Depends On:
• Distance to Quake
• Geology
• Type of Building
• Observer!
Varies from Place to Place
• Mercalli Scale- 1 to 12
Mercalli Scale
• I. Only the most sensitive people notice any movement.
• II. A few people notice movement if they are at rest or on
the upper floors of tall buildings.
• III. Many people indoors feel movement. Hanging objects
swing back and forth. People outdoors might not notice
anything.
• IV. Most people indoors feel movement. Dishes, windows,
and doors rattle. A few people outdoors may feel
movement. Parked cars rock.
• V. Almost everyone feels movement. Sleeping people are
awakened. Small objects move or are turned over. Trees
might shake. Liquids might spill out of open containers.
• VI. Everyone feels movement. People have trouble
walking. Objects fall from shelves. Pictures fall off walls.
Furniture moves. Plaster in walls might crack. No major
structural damage.
Mercalli Scale
• VII. People have difficulty standing. Drivers feel their cars
shaking. Damage is slight to moderate in well-built buildings;
considerable in poorly built buildings.
• VIII. Drivers have trouble steering. Houses might shift on their
foundations. Towers and chimneys might twist and fall. Wellbuilt buildings suffer slight damage. Poorly built structures
suffer severe damage.
• IX. Well-built buildings suffer considerable damage. Houses
move off their foundations. Some underground pipes are
broken. The ground cracks. Reservoirs suffer serious damage.
• X. Most buildings and their foundations are destroyed. Some
bridges are destroyed. Dams are seriously damaged. Large
landslides occur. Railroad tracks are bent slightly.
• XI. Most buildings collapse. Underground pipelines are
destroyed. Railroad tracks are badly bent.
• XII. Almost everything is destroyed. Objects are thrown into
the air. The ground moves in waves or ripples.
Isoseismals
from the
1906 San
Francisco
Earthquake
Intensity and Geology in
San Francisco, 1906
Intensity and Bedrock Depth in
San Francisco, 1906
Candlestick Park
California Faults
San Francisco and New Madrid
Compared
New Madrid, Missouri
New Madrid, Missouri
1811-12 Sand Blows, New Madrid, Missouri
1811-12 Sand Blow, New Madrid, Missouri
1811-12 Subsidence, New Madrid, Missouri
Magnitude - Determined from
Seismic Records
Richter Scale:
• Related to Energy
Release
• Exponential
• No Upper or Lower
Bounds
• Largest Quakes about
Mag. 8.7
• Magnitude-Energy
Relation
–
–
–
–
–
–
4-1
5 - 30
6 - 900:
1 Megaton = about 7
7 - 27,000
8 - 810,000
Magnitude
and Energy
Magnitude
and Energy
Seismic - Moment Magnitude
A Seismograph Measures Ground Motion at
One Instant But -• A Really Great Earthquake Lasts Minutes
• Releases Energy over Hundreds of
Kilometers
• Need to Sum Energy of Entire Record
• Modifies Richter Scale, doesn't replace it
• Adds about 1 Mag. To 8+ Quakes
Are Earthquakes Getting More
Frequent?
Earthquake Fatalities Since 1800
Earthquake Fatalities Since 1800
Earthquake Fatalities
• The dozen or so events with more than
100,000 fatalities account for a large fraction
of the total.
• 2.9 million earthquake fatalities since 1900
• 3.8 million since 1800
• 7.7 million since 1500
• Known total for all recorded earthquakes is
around 12.5 million.
Strategies of Earthquake Prediction
Lengthen Historical Data
Base
• Historical Records
• Paleoseismology
Short-term Prediction
• Precursors
Long-term Prediction
• Seismic Gaps
• Risk Levels
Modeling
• Dilatancy - Diffusion
• Stick - Slip
• Asperities
• Crack Propagation
Seismic Gaps
A Prediction
Strategy That
Just Didn’t
Work:
Cienega
Winery,
Hollister, CA
Lidar Mapping
900 AD Fault Scarp, Washington
Trenched Fault, Washington
Tacoma Fault and Glacial Troughs
Earthquakes and Plate Margins
Intraplate Earthquake Analogy
US Seismic Risk