EOSC 110 Lecture 15: Seismology & Earthquakes

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ceruleangoat669

13 Jan 2017

School

UBC

Department

Earth and Ocean Sciences

Course

EOSC 110

Professor

Brett Gilley

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Seismology & Earthquakes

Thursday,November3,2016 2:07PM

Stressatplateboundary



Ruptureatboundary



Movementofseaﬂoor



ShakingofEarth

Tsunami



DebristhroughoutthePacﬁc

OriginofEarthquakes

Japanesefolklore:

• agiantcaishlivingwithintheEarth

• Whiletypicallycontrolledbyagod,thecaishgetsexcitablewhenthegodturnsaway,itﬂailsand

indoingso,shakestheEarth

Scandinavia:

• Godedtoarockinanundergroundcaveaspunishmentforkillinghisbrother

• Whenhetwistedunderground,hemadetheEarthshake

WesternNorthAmerica:

• Thunderbirdﬁghtsawhale/monsterthatisdeprivinglocaltribesoffood

• Oceanrisesandfallsduringtheﬁght

• Eventually,thewhaleiscarriedoverlandandisdroppedwhereanotherﬁght(andgroundshaking)

occurs

• Thunderbirdwins

WhatisanEarthquake?

• Thesuddenreleaseofelascenergyinresponsetoabuildupofstress

• Energyisreleasedwhenstress=greaterthanstrengthoffault

• Energyisreleasedas:

i. Seismicwaves

ii. Displacementalongfault

iii. Heat&otherenergy



ElascStrain

• Elascmaterialsbuildupelascenergywhentheyarestrained

• Whenthereistoomuchstrain,therockwill:

i. Deformorﬂow(plascdeformaon)

ii. Breakormovealonganexisngfault(briledeformaon)



ElascReboundTheory

• Explanaonofhowenergyisspreadduringearthquakes

• Asrocksonoppositesidesofafaultaresubjectedtoforceandshi,theyaccumulateenergyand

slowlydeformunltheirinternalstrengthisexceeded



Elasc&BrileDeformaonatPlateBoundaries

• Apre‐exisngfaultisheldstaonary(locked)byfricon

• Elascplatesoneithersideofthelockedfaultaremovingslowlyrelavetoeachother(~mms‐

cms/year)

• Blocksaredistortedasshearstressbuildsup

• Earthquakeoriginatesatapoint(focus)wherethetwoblocksbegintoslidepasteachother

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• Mostearthquakesareny

• Movementoftheblocksoneithersideofthefault=ny

• Largerearthquakesleadtosigniﬁcantamountofmovementalongthefault

○Slip:thedistancethattheblockshavemovedpasteachother

Summary

•Elascstressesbuildupasrockdeformsslowlyoverme

• Ruptureoccurswhenelascstressesexceedwhatthefaultcanbear(fricon)

• Rocksalongfaultspringbacktoundeformedstate(elascrebound)

TypesofFaultMovements

1. Dipslip

2. Strikeslip



3. Obliqueslip



DistribuonofEarthquakes



• Kind/size/frequencydependsontypeofplateboundary

SubduconZones(ConvergentBoundaries)

1. Subduconinterferenceearthquakes

○ Canbehuge

○ Thrustfaulng

2. Earthquakesinthesubducngoroverriding

3. Benioﬀearthquakes

○ DeepintheEarth

• 100sofkilometres

○ Causeliletonodamageatthesurface



Connent‐ConnentCollisionZones

• Manysmalltoverylarge(uptomagnitude8)

• Thrustfaulngearthquakes

• Notaslargeasthelargestsubduconzoneearthquakes(uptomagnitude(M)9.4)

• Canbedeeperthanmost(40km)



DivergentBoundaries

• Shallowearthquakesandnormalfaulng

• Smalltomoderateearthquakes

○ Ex:EastAfricanRi,MidAtlancRidge



TransformBoundaries

• Platesmovehorizontallypasteachother

• Strike‐slipparalleltoboundary

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Document Summary

What is a(cid:374) ea(cid:396)th(cid:395)uake: the sudde(cid:374) release of elas(cid:415)(cid:272) e(cid:374)e(cid:396)gy i(cid:374) respo(cid:374)se to a buildup of stress, e(cid:374)ergy is released (cid:449)he(cid:374) stress = greater tha(cid:374) stre(cid:374)gth of fault, e(cid:374)ergy is released as, seismi(cid:272) (cid:449)aves, displa(cid:272)eme(cid:374)t alo(cid:374)g fault, heat & other e(cid:374)ergy. Elas(cid:415)(cid:272) & b(cid:396)i(cid:425)le defo(cid:396)(cid:373)a(cid:415)o(cid:374) at plate bou(cid:374)da(cid:396)ies: a pre e(cid:454)is(cid:415)(cid:374)g fault is held sta(cid:415)o(cid:374)ary (cid:894)lo(cid:272)ked(cid:895) by fri(cid:272)(cid:415)o(cid:374, elas(cid:415)(cid:272) plates o(cid:374) either side of the lo(cid:272)ked fault are movi(cid:374)g slo(cid:449)ly rela(cid:415)ve to ea(cid:272)h other (cid:894)~mms (cid:272)ms/year(cid:895, blo(cid:272)ks are distorted as shear stress builds up, earth(cid:395)uake origi(cid:374)ates at a poi(cid:374)t (cid:894)fo(cid:272)us(cid:895) (cid:449)here the t(cid:449)o blo(cid:272)ks begi(cid:374) to slide past ea(cid:272)h other, most earth(cid:395)uakes are (cid:415)(cid:374)y, moveme(cid:374)t of the blo(cid:272)ks o(cid:374) either side of the fault = (cid:415)(cid:374)y, larger earth(cid:395)uakes lead to sig(cid:374)i (cid:272)a(cid:374)t amou(cid:374)t of moveme(cid:374)t alo(cid:374)g the fault. S waves: shear or se(cid:272)o(cid:374)dary (cid:449)aves, par(cid:415)(cid:272)les move pe(cid:396)pe(cid:374)di(cid:272)ula(cid:396) to dire(cid:272)(cid:415)o(cid:374) (cid:449)ave propagates, slo(cid:449) tha(cid:374) p (cid:449)ave, se(cid:272)o(cid:374)d fastest, (cid:1007). (cid:1009)km/se(cid:272) i(cid:374) (cid:272)o(cid:374)(cid:415)(cid:374)e(cid:374)tal (cid:272)rust, cannot pass through fluids!

EOSC 110 Lecture 15: Seismology & Earthquakes

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