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IntroducingtheCajonPassEarthquakeGateAreaJulianLozosCaliforniaStateUniversity,Northridge
SCECAnnualMee=ng•PalmSprings,California•12September2017
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AModernChaconne:AStructuralandHarmonicAnalysisof“HotelCalifornia”JulianLozosCaliforniaStateUniversity,Northridge
SCECAnnualMee=ng•PalmSprings,California•12September2017
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TheEarthquakeofDecember8th,1812:ACasefortheCajonPassEarthquakeGateAreaJulianLozosCaliforniaStateUniversity,Northridge
SCECAnnualMee=ng•PalmSprings,California•12September2017
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EarthquakeGates
• Cri=calpointinafaultsystemthatmay(ormaynot)stopruptureormaycontrolwhichwayarupturegoes.• Dogatesswingthesamewayevery=me?
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CajonPassAjunc=onbetweenprimaryplateboundaryfaults,inadensely
populatedregion.
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SomeKeyQues=ons• Howdofaultinterac=onsaffecttheprobabilityofthrough-goingearthquakes?
• Howmuchdoesthegeometryofthecomponentfaultsmodulatethis?
• Howdopreviousrupturesaffectfuturerupturepathsandprobabili=es?
• Doesthecurrentstressfieldrepresentrecentrupturehistory?
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TheEarthquakeofDecember8th,1812• HeavydamageatMissionSanGabriel,40deathsatMissionSanJuanCapistrano.
• Ini=allyconsideredaNewport-Inglewoodevent.
• ReassignedtotheSanAndreasbasedontreeringevidence.
• Sinceiden=fiedinmanySanAndreaspaleoseismictrenches.
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Icannotdefini=velyproveanythinghere.
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HistoricandPaleoseismicRecords
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ModelingApproach
• 3Dfullydynamicrupturemodeling.• Finiteelementmethod(FaultMod,Barall,2009).
• Realis=cini=alcondi=ons:• Faultmeshwithcomplexgeometry.• Complexregionalvelocitystructure(SCECCVM).• Regionalstressfieldfromseismicitystudies.
• Varyini=alstressamplitudesun=lmodelsproduceslipconsistentwithpaleoseismicrecords.
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ModelGeometry
SAF
SJF
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ModelGeometry
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RegionalStresses
Maximumhorizontalcompressivestressorienta=oninsouthernCaliforniaYangandHauksson,2013
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On-FaultStresses
• Addi=onalheterogeneityfromfaultgeometry.
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PhysicalandComputa=onalParameters
Vp FromSCECCVM
Vs FromSCECCVM
Density FromSCECCVM
µstaMc0.6
µdynamic0.2
d0 0.4m
Principalstresses Variable(Bestfit:σV=30MPa,σNS=36MPa,σEW=12MPa)
StressorientaMon SAF:N5Enorthofjunc=on,N15Wsouthofjunc=on;SJF:N12E
Elementsize 200minnearfield,400minfarfield
NucleaMonradius 3000m
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SlipintheEarly1800s
Site Early1800sSlipPallett Creek 2 - 6 m
Wrightwood 2.5 - 4.5 m
Cajon Creek ~4 m
Pitman Canyon 3 - 4 m
Plunge Creek No surface rupture
Burro Flats Several cm on secondary structures
Colton Large liquefaction features
Quincy 1.8 - 3 m
Mystic Lake 1.8 - 3 m
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ModelSlipDistribu=ons
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GroundMo=on:SAFnorth
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GroundMo=on:SAFatjunc=on
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GroundMo=on:SJFatjunc=on
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GroundMo=on:SJFsouth
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CoulombStress:SJFsouth
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PreferredModel
•Groundmo=onsconsistentbothwithMissionrecordsandwithPBRs.•Stresschangesconsistentwithnorthward-propaga=ngEQsequence.
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Implica=onsfor1812
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Implica=onsforSAF-SJFInterac=ons• TheSanAndreasandSanJacintocanrupturetogether.• Eveniftheydidn’tin1812,it’sphysicallyplausibleundercurrentcondi=ons.
• CorroboratedbypaleoseismoloyandPBRs.
• HowloadedistheSanAndreasFaultsouthofitsjunc=onwiththeSanJacintoFault?
• DoesthischangethemostlikelyReallyBigOneforsouthernCalifornia?
• HowoRendoesthishappen?IsthisausualpaTern?
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Now,wewanttoaddmoredetail,clarity,andlengthtotheCajon
Passstory.
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SomeKeyQues=ons• Howdofaultinterac=onsaffecttheprobabilityofthrough-goingearthquakes?
• Howmuchdoesthegeometryofthecomponentfaultsmodulatethis?
• Howdopreviousrupturesaffectfuturerupturepathsandprobabili=es?
• Doesthecurrentstressfieldrepresentrecentrupturehistory?
![Page 28: Introducing the Cajon Pass Earthquake Gate Area](https://reader031.vdocuments.site/reader031/viewer/2022013018/61d1284b9306dd456f3249b3/html5/thumbnails/28.jpg)
SomeKeyQues=ons• Howdofaultinterac=onsaffecttheprobabilityofthrough-goingearthquakes?
• Howmuchdoesthegeometryofthecomponentfaultsmodulatethis?
• Howdopreviousrupturesaffectfuturerupturepathsandprobabili=es?
• Doesthecurrentstressfieldrepresentrecentrupturehistory?
![Page 29: Introducing the Cajon Pass Earthquake Gate Area](https://reader031.vdocuments.site/reader031/viewer/2022013018/61d1284b9306dd456f3249b3/html5/thumbnails/29.jpg)
CajonPassFaultGeometryCajon Pass Earthquake Gate Area
New CFM-5.2 faults
inferred 1812 rupture
Nicholsonetal.,2017
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DipontheSouthernSanAndreas
Fuis
et a
l., 2
012
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SomeKeyQues=ons• Howdofaultinterac=onsaffecttheprobabilityofthrough-goingearthquakes?
• Howmuchdoesthegeometryofthecomponentfaultsmodulatethis?
• Howdopreviousrupturesaffectfuturerupturepathsandprobabili=es?
• Doesthecurrentstressfieldrepresentrecentrupturehistory?
![Page 32: Introducing the Cajon Pass Earthquake Gate Area](https://reader031.vdocuments.site/reader031/viewer/2022013018/61d1284b9306dd456f3249b3/html5/thumbnails/32.jpg)
RecentRuptureHistory
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SomeKeyQues=ons• Howdofaultinterac=onsaffecttheprobabilityofthrough-goingearthquakes?
• Howmuchdoesthegeometryofthecomponentfaultsmodulatethis?
• Howdopreviousrupturesaffectfuturerupturepathsandprobabili=es?
• Doesthecurrentstressfieldrepresentrecentrupturehistory?
![Page 34: Introducing the Cajon Pass Earthquake Gate Area](https://reader031.vdocuments.site/reader031/viewer/2022013018/61d1284b9306dd456f3249b3/html5/thumbnails/34.jpg)
Maximumhorizontalcompressivestressorienta=oninsouthernCaliforniaYangandHauksson,2013
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CajonPassPanelDiscussion
3-4PMtoday,inthisroom.