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Earthquake Impacts - THE Midwest Threat PowerPoint PPT Presentation


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Earthquake Impacts - THE Midwest Threat. Gregory L. Hempen, PhD, PE, RG Geophysicist (retired, St. Louis District) URS Corporation, St. Louis Office SAME Regional Conference, 5 OCT 06. Natural Hazard Issues. natural hazards: eqks, ... our special Midwest problems

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Earthquake Impacts -THE Midwest Threat

Gregory L. Hempen, PhD, PE, RG

Geophysicist (retired, St. Louis District)

URS Corporation, St. Louis Office

SAME Regional Conference, 5 OCT 06


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Natural Hazard Issues

  • natural hazards: eqks, ...

    • our special Midwest problems

  • sustained-design environment

  • risk acceptance

  • probabilities of extremes


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Earthquakes - Where? When? No Advance Warning!

  • Tornadoes are more common in the Midwest, but impact far less area.

  • Some equivalence with other rapidly developing hazards: high wind threats, seismic related hazards (liquefaction, lateral spreading, slope instability), terrorism, …

  • An all-hazards approach is best.


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Where? Epicenters & Sources

EQE International Inc.


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20 APR 02, ML 5.1, Plattsburgh NY Earthquake


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10 SEP 06, M 5.8, Gulf of Mexico Earthquake

USGS


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CENTRAL US SOURCE ZONES


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When?

  • Multiple timeframes & reference sets.

    • For a future earthquake:

      • When will the earthquake occur? What year?

      • How long will the earthquake last?

      • One big earthquake, right?

    • Emergency response, response, recovery:

      • When will emergency help arrive?

      • How long will response take?

      • How long will recovery take? To get back to “normal?”


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New Madrid Seismic Zone

  • Commerce-Benton Hills

  • East Prairie Limb, NMSZ

    • M: a 8.1, b 8.1, c 7.2

  • Reel-foot Thrust Limb, NMSZ

    • M: a 8.0, b 8.0, c 8.0

  • Blytheville Arch Limb, NMSZ

    • M: a 7.8, b 7.0, c 7.8

      Tuttle, et al, 2002

    • a 1811 – 1812 AD

    • b 1450 AD

    • c 900 AD


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When relative to the hazard?

  • When will the earthquake occur?

    • Large events recur about every 550 years (Cramer, 2006).

    • Intraplate strains and energy release by the magnitude scale suggests a M6 event perhaps every 50 years.

    • M6, 70 - 90 yr; M7, 250 - 500 yr; M8, 550 – 1,200 yr (Rogers, 2005). Overdue for M6; M7 possible.

  • How long will the earthquake shaking last?

    • 60 sec, M8; 30 sec, M7; 18 sec, M6 (Krinitzsky & Chang, 1977).

  • One big earthquake, right?

    • No, likely a foreshock with one or more main events within days to months (several references).


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When for response issues?

  • When will emergency help arrive for the public?

    • Hours to days later, depending upon event size, location within the damaged area, and government preparation. [Supplies for 7 days.]

  • How long will response take?

    • Weeks to months, depending upon extent of the event’s damage and government preparation.

  • How long will recovery take to get back to “normal?”

    • M6 recovery will take months to get back to some normalcy. M7 and larger will have long-term effects and may never return to present economic conditions.


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No Advance Warning!

  • Even a M6.5 to 7.0 in the Midwest will be a devastating and society-changing event. There may be no warning at all.

  • Even the 1993 Mississippi flooding is a poor model for earthquake damage.

  • Hurricane Katrina is a more similar analogy in the wide spread damage to structures and lifelines (dominantly levee, electrical transmission, and telephone systems).

  • 1900 Galveston Hurricane, 1954 Hurricane Hazel & 1966 Hurricane Inez, having practically no warning but wide spread devastation, compare better to a large earthquake in the Eastern US.


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Special Central US Concerns

  • Complacency

    • Preparedness

    • Similarities to Katrina Disaster

    • Use of Eqk Codes

  • Low attenuation

    • Great area of significant ground shaking

    • Dispersion – long/tall structure impacts

  • Liquefaction / Lateral Spreading and Foundation impacts


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CA & CENTRAL US MMI


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Structures & Risks

  • Significant ground motion at greater distance.

  • Due to dispersion of the waves, distant structures may be placed into resonance.

    • Long or tall structures are particularly susceptible to resonance effects.

    • More distant towns: tall buildings in Chicago; bridges across major rivers; dams; pipelines.

  • Evaluation of geotechnical issues: activation of slides, liquefaction/lateral spreading, bearing capacity, differential settlement.


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New Madrid Seismic Zone

  • Commerce-Benton Hills

  • East Prairie Limb, NMSZ

    • M: a 8.1, b 8.1, c 7.2

  • Reel-foot Thrust Limb, NMSZ

    • M: a 8.0, b 8.0, c 8.0

  • Blytheville Arch Limb, NMSZ

    • M: a 7.8, b 7.0, c 7.8

      Tuttle, et al, 2002

    • a 1811 – 1812 AD

    • b 1450 AD

    • c 900 AD


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Infrastructure - Dams & LeveesWappapello’s 2002 High-Water Event

Emergency Overflow Spillway

Outlet Works & Tunnel

Embankment Dam with flat slopes & crest road

Designed in the 1930’s & completed in 1941, its defensive measures are the dam’s stiff, gravelly clay, wide embankment base, & high freeboard.


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SUSTAINED DESIGN – Integration of the Hazard

  • Hazard assessment

  • Acceptance of risk OR mitigation of risk OR lessening of project requirements

  • Risk to be mitigated

  • Design to be resolved


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HAZARD versus RISK

  • Hazard - an occurrence that imperils life or property [assessed by science].

  • Risk - quantification of a known hazard to an inventory (of life or property) that is vulnerable [mitigated by engineering]; the risk may be apportioned between acceptance of or mitigation of the hazard [distributed by the owner’s policy].


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SITE & HAZARD ASSESSMENT

  • Earthquake sources and seismicity

  • Travel path parameters

  • Static & dynamic parameters of earth systems (naturally placed, not designed)

  • Site response analysis

  • Other hazard impacts

  • Engineering designs to abate the hazards’ risk and meet the projects’ requirements


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SEISMIC DAMAGE TYPES

  • Fault displacement (rupture)

  • Ground motion (induced inertia)

  • Indirect Physical Impacts

    • Tectonic Changes (seiches / tsunamis)

    • Liquefaction

    • Triggering Landslides

    • Foundation Failures (Diffrt’l Settlement)

    • Tertiary Lifeline Impacts


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IMPACTED EPICENTRAL DISTANCES (km)


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CODES - Seismic Provisions of the 2003 IBC

  • Sections 1613 through 1616 of the 2003

  • IBC pertain to Earthquake Loads on structures with rules for exceptions, existing structure additions, occupancy, alterations, QA, & wind.

  • Design spectral response acceleration, SA, is specified from

    • Mapped bedrock acc [Eqk Source Region]: SS & S1,

    • Site Class Determination [Site Assessment] – T 1615.1.1,

    • Site Class Coefficients - T 1615.1.2(1&2), &

    • The structure’s fundamental period, T, in s.


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OTHER SEISMIC HAZARDS(not only the ground motion value)

  • Fault displacement

  • Tectonic Changes [seiches (waves) / tsunamis]

  • Foundation Impacts

    • Dynamic Bearing Capacity

    • Differential Settlement

    • Liquefaction (Flow Liq, Cyc Mobility, Cyc Liq)

  • Triggering Landslides

  • Tertiary Lifeline or Project Subsystem Impacts


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Probabilities of Extremes

  • Standard statistical assessments have been used. Earthquakes are not independent events.

  • Stresses within the plate increase in time so the risk increases with time.

  • Statistics of once or more occurrences.

  • 2% exceedance in 50 years

    (x>1 in 2,450-year period).


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Statistics for the Uncommon

  • Earthquake swarms: several events in one area

  • Foreshocks & Aftershocks use little of the main event’s energy

  • New Madrid Series, 1811-12, within 8 months:

    • 3 or 4 Great (?) Earthquakes

    • 10 – 15 Large Earthquakes

    • Scores of Major Earthquakes


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Actions for Earthquakes

  • For your awareness, you can improve your survivability and your resources’ sustainability.

    • Earthquake Preparation

    • During an Earthquake

    • Earthquake Recovery


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Earthquake Preparation

  • Learn first aid,

  • have water, food and supplies for three days,

  • prepare the structure/community for eqk,

  • know what to do when we feel an eqk,

  • have a plan to meet at a specific place after an earthquake occurs, and

  • have an earthquake drill.


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During an Earthquake

  • When inside, stay inside at a protective location: door way, corner or beneath a sturdy table. Drop, cover, and hold. Try to be away from windows.

  • When outside, stay outside. Try to get away from tall buildings and overhead utilities.

  • In a car when an eqk is recognized, slow and pull off at a safe location.


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Earthquake Recovery

  • Aid those nearby,

  • stay at a secure place until it is okay to go home,

  • go to your meeting place,

  • do not go sight-seeing, and

  • expect other earthquakes, called aftershocks.


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SUMMARY

  • Earthquakes should be regarded as a significant and special hazards, particularly near the New Madrid Seismic Zone.

  • Designs for many structures need to consider the acceptable earthquake risk.

  • Seismic Ground Motion appraisal may be developed from accepted code procedures.

  • Other seismic foundation impacts for the site should be considered.

  • Be aware of individual actions before, during and after earthquakes.


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