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Seismology and Earthquake Engineering :Introduction Lecture 2

Seismology and Earthquake Engineering :Introduction Lecture 2. Basic Concepts of Seismology. Elastic rebound theory Plates are in continuous motion Stresses and strains build up near boundaries Strain energy stored in crust near faults, then released

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Seismology and Earthquake Engineering :Introduction Lecture 2

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  1. Seismology and Earthquake Engineering :IntroductionLecture 2

  2. Basic Concepts of Seismology • Elastic rebound theory • Plates are in continuous motion • Stresses and strains build up near boundaries • Strain energy stored in crust near faults, then released • Aseismic movement - slow creep in ductile rock • Seismic movement - rupture of brittle rock

  3. Basic Concepts of Seismology Seismic Gaps Loma Prieta Gap San Francisco San Juan Bautista Portola Valley Loma Prieta Parkfield 1969-89 seismicity

  4. Basic Concepts of Seismology Seismic Gaps Loma Prieta Gap San Francisco San Juan Bautista Portola Valley Loma Prieta Parkfield Loma Prieta earthquake and aftershocks

  5. Basic Concepts of Seismology Seismic Gaps

  6. Basic Concepts of Seismology Near-field effects “Directivity” Rupture moving away from observer Rupture moving toward observer

  7. Basic Concepts of Seismology Near-field effects Fault parallel “Directivity” Fault normal Fault normal accelerations exceed fault parallel accelerations

  8. Basic Concepts of Seismology Earthquake size • Intensity - qualitative measure of observed effects • Modified Mercalli Intensity (MMI) MMI IV During the day felt indoors by many, outdoors by few; at night some awakened; dishes, windows, doors disturbed; walls make cracking sound; sensation like heavy truck striking building; standing motor cars rocked noticeably

  9. Basic Concepts of Seismology Earthquake size • Intensity - qualitative measure of observed effects • Modified Mercalli Intensity (MMI) MMI IV During the day felt indoors by many, outdoors by few; at night some awakened; dishes, windows, doors disturbed; walls make cracking sound; sensation like heavy truck striking building; standing motor cars rocked noticeably MMI VII Everybody runs outdoors; damage negligible in buildings of good design and construction, slight to moderate in well-built structures, considerable in poorly built or badly designed structures; some chimneys broken; noticed by persons driving motor cars

  10. Basic Concepts of Seismology Earthquake size • Intensity - qualitative measure of observed effects • Modified Mercalli Intensity (MMI) MMI IV During the day felt indoors by many, outdoors by few; at night some awakened; dishes, windows, doors disturbed; walls make cracking sound; sensation like heavy truck striking building; standing motor cars rocked noticeably MMI VII Everybody runs outdoors; damage negligible in buildings of good design and construction, slight to moderate in well-built structures, considerable in poorly built or badly designed structures; some chimneys broken; noticed by persons driving motor cars MMI X Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked; rails bent; landslides considerable from river banks and steep slopes; shifted sand and mud; water splashed over banks

  11. Basic Concepts of Seismology Seismic waves p-waves Body waves s-waves Love waves Surface waves Rayleigh waves

  12. Basic Concepts of Seismology Earthquake size • Magnitude - quantitative measure of size of event • Several types • Local magnitude • Body wave magnitude • Surface wave magnitude All based on instrumental measurements

  13. Basic Concepts of Seismology Earthquake size • Seismic moment - measure of work done by eq. • Mo = m A D • where • m = shear modulus of rock • A = rupture area • D = average displacement over rupture area • Units = F/L2 x L2 x L = F x L Work Energy

  14. Moment magnitude • Mw = ------------ - 10.7 log Mo 1.5 Ms M = Mw ML mb Magnitude Moment magnitude Basic Concepts of Seismology Earthquake size Magnitude saturation

  15. Earthquake Size

  16. Seismic Waves • Arrives first • Sometimes audible • Shakes ground horizontally and vertically • Wave damages structures • Similar to “S” wave • Moves ground horizontally • Like rolling ocean wave • Shakes ground vertically and horizontally

  17. Alcott Elementary, Redmond November 15, 11:10 am Seismic Waves Strong motion seismograph

  18. Seismic Waves • Triaxial accelerometers • 3 components Horizontal motions are very important

  19. So What? • Deaths and injuries • Economic loss

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