Earthquake Hazards and Earthquake Risks in the Central US Phyllis J. Steckel, RG Earthquake Insight LLC Washington, Mo. In cooperation with the US Geological Survey
Earthquake Hazards and
Earthquake Risks in the Central US
Phyllis J. Steckel, RG
Earthquake Insight LLC
Washington, Mo.
In cooperation with the US Geological Survey
The plan for today….
• ‘Earthquakes 101’
• Regional Earthquake
history
• Earthquakes & structures
• Putting it all together
• Questions & discussion
Earthquake Vocabulary
• Magnitude
• Intensity
• Depth
• Duration
• Aftershocks
• Faults (not ‘fault lines’)
• Location
• And more….
Earthquake Magnitude
• Amount of energy
released
• Only one magnitude
for any one
earthquake
Earthquake Magnitude
• Logarithmic scale
• M2.0 ~30 times more
energy released
than M1.0
• M3.0 ~1000 times
more energy
released than M1.0
Earthquake Intensity
• Measures energy
delivered to any one
site
• Depends on location
• Many intensities for
any one earthquake
Earthquake Intensity
• Subjective measurement
• Estimated from felt
reports
• Depends on population
distribution
• More is better
Earthquake Depth
• Range from shallow to
deep – surface to ~450
miles
• Shallow = more energy
and intensity at the
surface
• Deep = less energy and
intensity at the surface
Earth’s Crust
• Thinner than an
apple peel
• Floats on viscous
mantle
• Pieces ‘bump and
grind’ along edges =
plate tectonics
Faults (Fault lines)
• Normal
• Thrust
• Strike-slip
Normal Faults
Thrust Faults
Strike-slip Faults
Earthquake Duration
• Felt for a few seconds
– Small earthquake, near
epicenter
• Felt for several minutes
– Large earthquake, farther
from epicenter
• Extreme earthquakes
‘ring the earth’ for hours
Aftershocks
• Occur after most large
earthquakes
• Become smaller and
less frequent over time
• Can cause significant
damage – sometimes
more than the main
shock
Did You Feel It?
• April 18, 2008
• 4:36 am (CDT)
• M5.4
• Depth ~11 km
• Epicenter near Bellmont, Ill.
Earthquake Locations
• Need three
earthquake records
(seismograms)
• Measure distance
from each recorder
• Common point is
epicenter
Earthquake Locations
• Regional velocity of earthquake waves is known
• Distance from epicenter is estimated
• More records = more accuracy
Where do earthquakes occur?
• Plate boundaries
• Near volcanoes
• Mountain ranges
• Just about
everywhere else,
too!
Plate Boundary Earthquakes
Near volcanoes
• Aleutians & Alaska
• Montserrat &
Caribbean
• Iceland
• Mount St. Helens
Near Mountain Ranges
• Apennines
• Andes
• Sierra Nevada
• Wasatch Range
• Southern
Appalachians
• Ouachitas (Ark. &
Okla.)
• Ozarks
Geologic Structures
Regional Mega-Structures
• Illinois Basin
• Kankakee Arch
• Ouachita Fold Belt
• Arkoma Basin
• Mississippi Embayment
• And lots more!
Mississippi Embayment
• Very clear on maps!
• Bedrock trough
• Dips & widens to the
southwest
Mississippi Embayment
• New Madrid fault
zone
– ‘Bottom’ of trough
– North end of trough
• Filled with
sediments
• Mississippi River
follows ‘easiest’
route
New Madrid fault zone
• Southeast Missouri &
northeast Arkansas
• Old crustal weakness
• Active for hundreds
of millions of years
New Madrid fault zone
• Active historically
• Active now
• Not ‘dormant’
• Not ‘shut down’
Central US Earthquakes
• SE Missouri & NE
Arkansas
• Old crustal weakness
• Active for hundreds
of millions of years
New Madrid fault zone
• 2013 research: weak rocks extend deeper into crust
• Consistent with past & future active seismicity
Central US Earthquakes
• New Madrid fault
zone
• Wabash Valley FZ
• East Tennessee FZ
• Meers FZ, Nemaha
FZ, etc.
New Madrid in 1811-12
• Founded in 1789 on
high ground
• Swamps surrounded
by heavy forests
• Largest settlement
between St. Louis &
New Orleans
New Madrid in 1811-12
• River was the 1811
super-highway
• Part of Louisiana
Purchase (1803)
• Spanish, French, and
US heritage
New Madrid Earthquakes 1811-12
• December 16, 1811
– ~M7.5
• January 23, 1812
– ~M7.3
• February 7, 1812
– ~M7.6
New Madrid Earthquakes 1811-12
• Thousands of
aftershocks
• Wracked land,
choked river
• Most residents left
the area
Eliza Bryan
• Born Pennsylvania
1780
• Arrived New Madrid
1791
• Survived 1811-12
• Wrote letter 1816
• Died New Madrid 1866
New Madrid Earthquakes 1811-12
• Eliza Bryan account….
– ‘Violent shocks…’
– ‘Continuous agitation…’
– ‘Sand…from fissures…’
– ‘Twenty-foot waves…’
• Field evidence still
visible today
New Madrid Earthquakes 1811-12
• River recedes from bank
• ‘Waters gathered like a mountain’
• Boats torn from moorings
• “Water took groves of cottonwood trees’
• Evidence still visible today
• ‘Retrograde current…’
– Fault uplifted downstream
land surface
– Natural dam
– Backflow made Reelfoot Lake
– Channel soon reclaimed
• Evidence still visible today
New Madrid Earthquakes 1811-12
• Probably hundreds died
• African and Native Americans not counted
• Insurance records show losses of lives and insured cargoes
New Madrid Earthquakes 1811-12
• Aftershocks for years
• 2000+ felt reports from Louisville
• Damage in Cincinnati, Georgia, Annapolis, and New York
New Madrid Earthquakes 1811-12
• Aftershocks for years
• 2000+ felt reports from Louisville
• Damage in Cincinnati, Georgia, Annapolis, and New York
New Madrid Earthquakes of 1811-12
• Felt area larger than same-size California earthquake – Rock is
different here!
• What is odd about this map?
Other Central US Earthquakes….
• 1843 – NE Arkansas, M6+
• 1895 – SE Missouri, M5.9
• 1917 – St. Louis area, M5.1
• 1968 – Mt Vernon, Ill., M5.2
• 2008 – Mt Carmel, Ill., M5.2
• Many M3 – M4 – Minimal & “lucky” damage
• ‘Wake-up calls’ mostly ignored
Switching gears ….
From
“Earthquakes”
To
“What Happens to Structures During
Earthquakes”
Types of Structures
• Buildings – Wood-frame
– URM
– Steel-frame
– Concrete-frame
– Tilt-up
• Bridges
• Pipelines
• Levees, dams, embankments
• Utility towers
Structures & Earthquakes
• Compact vs Sprawl?
• Age & maintenance?
• Engineering design?
• Seismic design?
Structures & Earthquakes
• Flexibility?
• Center of gravity?
• Footprint?
• Earthquake energy input – direction?
Wood frame
• Most newer residential
• Flexible
• Low center of gravity
• Chimneys problematic?
• Foundation & utility connections critical
• Damage may be high, but few lives lost
Unreinforced masonry -- URM
• Inflexible
• Less resistant to ground shaking
• Many older and historic buildings
• Structural load on walls
• Heavy and brittle
• Not the best in Earthquake Country
If walls could talk….?
Braced Steel Frame
• Cross-bracing
• Lightweight & flexible
• Most newer mid- and high-rises
• Usually performs well if design & construction detailing done well
Concrete frame
• Concrete columns, beams & girders
• Exterior cladding or glass
• Strength depends on – Steel reinforcement
– Design quality
– Construction quality
• Devil is in the details!
Concrete frame
• Seismic design
needed
• Rebar needed!
• Uncompromised
construction
Concrete frame with URM Infill
Concrete Tilt-Up
• Poured concrete walls, then ‘tilted up’
• Critical connections at corners, foundation & roofline
• Many big retail, factories, warehouses, etc.
• Devil is in the details!
2011 Christchurch, NZ
1994 Northridge, Calif.
2010 Chile
1992 Landers, Calif.
1971 San Fernando, Calif.
2011 Christchurch, NZ
2002 Alaska
Bringing it all together
• Geoscience
• Engineering
• Building stock
• Building codes & jurisdiction
–Seismic building code not adopted everywhere
Geoscience
• USGS research results
• Detailed hazard maps – St. Louis
– Memphis
– Evansville, Ind.
• Groundshaking & liquefactions
• Not site-specific!
Engineering
• Earthquake engineering is not ‘automatic’
• Jurisdiction may not have or enforce building codes
• Earthquake engineering may not be required
• Building codes = life safety only
Building Codes
• Never assume….
• Negotiated document
• No statewide code in Missouri
• Recent effort in Tennessee to dismantle building codes in some areas, including fire, wind, and ADA
Regional vulnerabilities
• Most domestic structural steel is made in NE Arkansas
• Critical transportation corridors – highway, rail, river – straddle the New Madrid seismic zone
• Central US pipelines move fuels to northeast US
Regional vulnerabilities
• Only US uranium reprocessing plant
• Much of the US domestic inventory (FedEx) – Surgical instruments to consumer
goods
• Critical commodity transport (coal, steel, cotton, grains, fuels, ores, etc.)
• Critical national security facilities
Words to Remember
• Significant earthquake hazards exist in central US
• Future earthquakes will occur here
• Significant earthquake risks exist here
Consider these Action Items?
• Educate your organization
• Evaluate your portfolio
• Advise your legislatures – Penny wise, pound
foolish
Any questions?
Phyllis Steckel, RG Earthquake Insight LLC