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Earthquake Impacts - THE Midwest Threat

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

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  1. 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

  2. Natural Hazard Issues • natural hazards: eqks, ... • our special Midwest problems • sustained-design environment • risk acceptance • probabilities of extremes

  3. 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.

  4. Where? Epicenters & Sources EQE International Inc.

  5. 20 APR 02, ML 5.1, Plattsburgh NY Earthquake

  6. 10 SEP 06, M 5.8, Gulf of Mexico Earthquake USGS

  7. CENTRAL US SOURCE ZONES

  8. 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?”

  9. 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

  10. 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).

  11. 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.

  12. 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.

  13. 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

  14. CA & CENTRAL US MMI

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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].

  20. 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

  21. 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

  22. IMPACTED EPICENTRAL DISTANCES (km)

  23. 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.

  24. 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

  25. 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).

  26. 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

  27. Actions for Earthquakes • For your awareness, you can improve your survivability and your resources’ sustainability. • Earthquake Preparation • During an Earthquake • Earthquake Recovery

  28. 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.

  29. 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.

  30. 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.

  31. 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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