Seismology and Earthquake Engineering Introduction Engineering for Earthquakes

Seismology and Earthquake Engineering : Introduction

Engineering for Earthquakes Earthquake Hazard Analysis Seismic Waves Seismologists Geotechnical Engrs Geologic Effects Response Analysis Structural Response Loss Analysis Losses Geotechnical Engrs Structural Engrs Loss Analysts

The Earth (outside)

The Earth (inside) Cold Hot

Convection

Convection

Plates 6 continental size 14 sub-continental size

Plates White: Political boundaries Yellow: Plate boundaries Red: Epicenters

Plates Based on continental shelves

Plates

Plates

Plates

Plate Boundaries Spreading Ridge Boundary

Spreading Ridge

Spreading Ridge Eastern Pacific Ridge

Spreading Ridge Thingvellir

Plates Subduction Zone

Subduction Zone

Plates Transform Boundary

Transform Boundaries Crystal Spring Reservoir Carrizo Plain

Faults Main types: Normal Faulting

Faults Main types: Reverse Faulting

Faults Main types: Strike Slip Faulting Calaveras Fault

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

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

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

Basic Concepts of Seismology Seismic Gaps

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

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

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

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 MMI VII sound; sensation like heavy truck striking building; standing motor Everybody runs damage negligible in buildings of good carsoutdoors; rocked noticeably 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

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 MMI VII sound; sensation like heavy truck striking building; standing motor Everybody runs damage negligible in buildings of good carsoutdoors; rocked noticeably design and construction, slight to moderate in well-built structures, considerable in poorly built or badly designed structures; some MMI X chimneys broken; noticed by persons driving motor cars 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 mud; water splashed over banks

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

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

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/L 2 x L = F x L Work Energy

Basic Concepts of Seismology Earthquake size Moment magnitude log Mo - 10. 7 Mw = ------1. 5 Magnitude Ms M = Mw ML mb Magnitude saturation Moment magnitude

Earthquake Size

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

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

Seismic Waves Triaxial accelerometers 3 components Horizontal motions are very important

So What? • Deaths and injuries • Economic loss

Hall of Fame (famous earthquakes) 1906 San Francisco

Hall of Fame (famous earthquakes) 1964 Niigata

Hall of Fame (famous earthquakes) 1964 Alaska

Hall of Fame (famous earthquakes) 1960 Chile

Hall of Fame (famous earthquakes) 1971 San Fernando

Hall of Fame (famous earthquakes) 1985 Mexico City

Hall of Fame (famous earthquakes) 1989 Loma Prieta

Hall of Fame (famous earthquakes) 1994 Northridge

Hall of Fame (famous earthquakes) 1995 Kobe

Hall of Fame (famous earthquakes) 1999 Chi (Taiwan)