Seismology and Earthquake Engineering :Introduction Lecture 2

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Seismology and Earthquake Seismology and Earthquake Engineering :Introduction Engineering :Introduction Lecture 2 Lecture 2

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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 - PowerPoint PPT Presentation

Transcript of Seismology and Earthquake Engineering :Introduction Lecture 2

Page 1: Seismology and Earthquake Engineering :Introduction Lecture 2

Seismology and Earthquake Seismology and Earthquake Engineering :IntroductionEngineering :Introduction

Lecture 2Lecture 2

Page 2: Seismology and Earthquake Engineering :Introduction Lecture 2

Basic Concepts of SeismologyBasic Concepts of Seismology

Elastic rebound theory

Plates are in continuous motionStresses and strains build up near boundariesStrain energy stored in crust near faults, then released

Aseismic movement - slow creep in ductile rockSeismic movement - rupture of brittle rock

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Basic Concepts of SeismologyBasic Concepts of Seismology

Seismic Gaps

1969-89 seismicity

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Loma Prieta earthquake and

aftershocks

Basic Concepts of SeismologyBasic Concepts of Seismology

Seismic Gaps

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Basic Concepts of SeismologyBasic Concepts of Seismology

Seismic Gaps

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Basic Concepts of SeismologyBasic Concepts of Seismology

Near-field effects

“Directivity”

Rupture movingaway from observer

Rupture movingtoward observer

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Basic Concepts of SeismologyBasic Concepts of Seismology

Near-field effects

“Directivity” Faultparallel

Faultnormal

Fault normalaccelerationsexceed faultparallel accelerations

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Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Intensity - qualitative measure of observed effectsModified Mercalli Intensity (MMI)

MMI IVDuring 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

Page 9: Seismology and Earthquake Engineering :Introduction Lecture 2

Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Intensity - qualitative measure of observed effectsModified Mercalli Intensity (MMI)

MMI IVDuring 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 VIIEverybody 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

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Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Intensity - qualitative measure of observed effectsModified Mercalli Intensity (MMI)

MMI IVDuring 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 VIIEverybody 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 carsMMI 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

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Basic Concepts of SeismologyBasic Concepts of Seismology

Seismic waves

p-waves

s-waves

Love waves

Rayleigh waves

Body waves

Surface waves

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Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Magnitude - quantitative measure of size of eventSeveral types

Local magnitudeBody wave magnitudeSurface wave magnitude

All based oninstrumental

measurements

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Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Seismic moment - measure of work done by eq.

Mo = A D

where = shear modulus of rockA = rupture areaD = average displacement over rupture area

Units = F/L2 x L2 x L = F x L

Work Energy

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Basic Concepts of SeismologyBasic Concepts of Seismology

Earthquake size

Moment magnitude

Mw = ------------ - 10.7log Mo

1.5

Moment magnitude

Mag

nitu

de

mb

ML

Ms

M = M w

Magnitudesaturation

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Earthquake Size

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Shakes ground horizontally and vertically

Wave damages structures

Similar to “S” wave Moves ground

horizontally Like rolling ocean wave Shakes ground vertically

and horizontally

Arrives first Sometimes audible

Seismic WavesSeismic Waves

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Seismic WavesSeismic Waves

Strong motion seismograph

Alcott Elementary, Redmond

November 15, 11:10 am

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Seismic WavesSeismic Waves

Triaxial accelerometers3 components

Horizontal motions are very important

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So What?• Deaths and injuries

• Economic loss