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6.1Earthquake-InducedVibrationofStructuresTopicsSeismicityandGroundMotionsInfluenceofLocalSiteConditionsResponseofStructurestoGroundMotionsSeismicityandGroundMotionsTheearthismadeupoffourlayers,thecrust,themantle,theoutercore,andtheinnercore.Lithosphereisbrokenintoanumberoftectonicplates.
Tectonicplates
arerigid,relativelycoolslabsabout100kmthick
consistoftheearth'scrustandlithosphere.Tectonicplates
构造板块floatonthemolten
mantle(asthenosphere软流圈)oftheEarthandmoverelativetooneanotherattherateof10to100mm/year.The6,000-km-plusjourneyoftheIndialandmass(IndianPlate)beforeitscollisionwithAsia(Eurasian[juE5reiViEn]欧亚大陆Plate)about40to50millionyearsago.IndiawasoncesituatedwellsouthoftheEquator[i5kweitE],nearthecontinentofAustralia.Iftheplatesarepushingtogether,oneplatetendstodiveundertheotherand,dependingonthedensityofthematerial,itmayresurfaceintheformofmountainsandvalleys.*Insomecases,theplatemarginsaremovingawayfromoneanother.Inthosecases,moltenrockappearsfromdeepintheEarthtofillthegap,oftenmanifestingitselfasvolcanoes.*Anotherpossibilityisthattheplateboundarieswillslidesidewayspasteachother,essentiallyretainingthelocalsurfaceareaoftheplate.pullapart平滑断层,横向断层*Thebasicmechanismcausingearthquakesintheplateboundaryregionsappearstobethatthecontinuingdeformationofthecrustalstructureeventuallyleadstostresses/strainswhichexceedthematerialstrength.Rocksfracture.Thesefracturesarecalledfaults.*ArupturewilltheninitiateatsomecriticalpointalongthefaultlineandwillpropagaterapidlythroughthehighlystressedmaterialattheplateboundaryItisbelievedthatapproximatelythreequartersoftheworld’searthquakesareaccountedforbythisrubbing–striking–slippingmechanism,withrupturesoccurringonfaultsonboundariesbetweentectonicplates.Suchearthquakesarereferredtoas
interplate
earthquakes
边缘地震.Intraplateearthquakes板内地震*Earthquakesalsooccuratlocationsawayfromtheplateboundaries.Sucheventsareknownasintraplateearthquakes板内地震
andtheyaremuchlessfrequentthaninterplateearthquakes.*Earthquake-occurrencemapsusuallyindicatethelocationofvariousepicentersofpastearthquakes*theseepicentersarelocated(确定
,找出)byseismological[7saizmE5lCdVikEl]adj.
地震学上的
analysisoftheeffectofearthquakewavesonstrategicallylocatedreceivinginstrumentscalledseismometers[saiz5mCmitE]n.
测震仪.EnergyspreadsoutthroughtheearthindifferentwavetypesP-Waves
S-Waves
SurfaceWaves*Whenanearthquakeoccurs,severaltypesofseismicwaveareradiatedfrom自...发出therupture.Themostimportantofthesearethebodywaves(primary(P)andsecondary(S)waves).
Magnitudeoftheearthquake*Thetotalstrainenergyreleasedduringanearthquakeisknownasthemagnitudeoftheearthquake
震级
anditismeasuredontheRichterscale*Richterscaleisdefinedquitesimplyastheamplitude
振幅
oftherecordedvibrationsonaparticularkindofseismometerlocatedataparticulardistancefromtheepicenter.Modernseismometers(orseismographs)providedigitized
[5didVitaiz]将资料数字化orgraphicalrecordsofearthquake-inducedaccelerations加速度
inboththehorizontalandverticaldirectionsataparticularsite.Accelerometersproviderecordsofearthquakeaccelerationsandtherecordsmaybeappropriatelyintegratedtoprovidevelocityrecordsanddisplacementrecords.Peakaccelerations,velocities,anddisplacementsareallinturnsignificantforstructuresofdifferingstiffness.Therecordingoftheaccelerationofthegroundduringanearthquake.Acceleration,Velocity,DisplacementIntensity
Ameasureoftheeffect,orthestrength,ofanearthquakehazardataspecificlocationbasedonobservedhumanbehaviorandstructuraldamage.*Thelocalintensity
ofaparticularearthquakeismeasuredonthesubjectiveModifiedMercalliscalewhichrangesfrom1to12唐山7.8级地震等震线图唐山7.8级地震等震线图ModifiedMercalliscaleAmeansbywhichdamagemaybeassessedafteranearthquake.
albeit[C:l5bi:It]虽然subjectiveandqualitative,regionsofvaryingseismicriskmaybeidentified.usedtoassistinthedelineation
[dI9lInI`eIFEn]
描绘
oftheseregions.InfluenceofLocalSiteConditionsLocalgeological
地质的
andsoilconditionsmayhaveasignificantinfluenceontheamplitudeandfrequencycontentofgroundmotions.InteractionbetweenthebedrockearthquakemotionandthesoilcolumnwillmodifytheactualgroundaccelerationsinputtothestructureThesoilpropertiesintheproximity[prCk5simiti]
邻近ofthestructurecontributesignificantlytotheeffectivestiffnessofthestructuralfoundation.
strength(andresponse)ofthelocalsoilunderearthquakeshakingmaybecriticaltotheoverallstabilityofthestructure.ResponseofStructurestoGroundMotionsTheeffectofgroundmotiononthevariouscategoriesofstructuresisdictatedalmostentirelybythedistributionofmassandstiffnessinthestructure.Itisimportanttoappreciatethat,inanearthquake,loadsarenotappliedtothestructure.Rather,earthquakeloadingarisesbecauseofaccelerationsgeneratedbythefoundationlevel(s)ofthestructurebeinginfluencedbytransientgroundmotions.Specifically,theproductofthestructuralmassandthetotalaccelerationproducestheinertialoadingexperiencedbythestructure.
thetotalaccelerationistheabsoluteaccelerationofthestructure,namely,thesumofthegroundaccelerationandthatofthestructurerelativetotheground.Stiffstructurelittleadditionalaccelerationrelativetothegroundmotionearthquakeloadingexperiencedisessentiallyproportionaltothebuildingmass.Flexiblestructures(high-riseorlong-span)absoluteaccelerationislowThisoccursbecausethegroundaccelerationandtheaccelerationofthebuildingrelativetothegroundtendtoopposeoneanother.
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