Earthquake Hazards and Earthquake Risks in the Central US · history • Earthquakes & structures...
Transcript of Earthquake Hazards and Earthquake Risks in the Central US · history • Earthquakes & structures...
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