Earthquakes: Radiated Energy and the Physics of Faulting

319 Pages·2006·27.75 MB·English

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Geophysical Monograph 170
Earthquakes: Radiated Energy
and the Physics of Faulting
Rachel Abercrombie
Art McGarr
Giulio DiToro
Hiroo Kanamori
Editors
American Geophysical Union
Washington, DC
Published under the aegis of theAGU Books Board
Jean-LouisBougeret,Chair;GrayE.Bebout,CassandraG.Fesen,CarlT.Friedrichs,RalfR.Haese,W.BerryLyons,
KennethR.Minschwaner,AndrewNyblade,DarrellStrobel,andChunzaiWang,members.
LibraryofCongressCataloging-in-PublicationData
Earthquakes:radiatedenergyandthephysicsoffaulting/RachelAbercrombie...[etal.],editors.
p.cm.-- (Geophysicalmonograph,ISSN0065-8448;170)
ISBN-13:978-0-87590-435-1
ISBN-10:0-87590-435-1
1. Seismicwaves.2. Energydissipation.3. Faults(Geology)4. Seismology. I.Abercrombie,Rachel.
QE538.5.E252006
551.22--dc22
2006100346
ISBN-13:978-0-87590-435-1
ISBN-10:0-87590-435-1
ISSN0065-8448
Frontcoverimage:Pseudotachylytesareconsideredtheprimaryevidenceofancientearthquakes
onexhumedfaults.Theyareinterpretedassolidified,friction-inducedmeltproducedduringseismic
slip. These pseudotachylyte-bearing fault and injection veins are associated with Late Paleozoic
dextral strike-slip faulting in the ultramylonite of the Fort Foster Brittle Zone, Maine. Cross-cut-
tingveinsillustratetheeffectivenessoffrictionalweldingafterearthquakeslip(opticalmicroscope,
crossedpolars,1cm-wideview).CourtesyofRachelE.Abercrombie.
Copyright2006bytheAmericanGeophysicalUnion
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ContEnts
Preface
Rachel E. Abercrombie, Art McGarr, Giulio Di Toro, and Hiroo Kanamori . . . . . . . . . . . . . . . . .vii
Introduction
Rachel E. Abercrombie, Art McGarr, Hiroo Kanamori, and Giulio Di Toro . . . . . . . . . . . . . . . . . 1
Energy Partitioning During an Earthquake
Hiroo Kanamori and Luis Rivera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Section I:The Measure of Radiated Energy and its Behavior
A Brief Review ofTechniques Used to Estimate Radiated Seismic Energy
Anupama Venkataraman, John Boatwright, and Gregory C. Beroza . . . . . . . . . . . . . . . . . . . . . .15
The Scaling of Seismic EnergyWith Moment: Simple Models ComparedWith Observations
William R. Walter, Kevin Mayeda, Rengin Gok, and Abraham Hofstetter . . . . . . . . . . . . . . . . . .25
An Overview of the GlobalVariability in Radiated Energy andApparent Stress
George L. Choy, Art McGarr, Stephen H. Kirby, and John Boatwright . . . . . . . . . . . . . . . . . . . . .43
The Radiated Energy of the 2004 Sumatra-Andaman Earthquake
Hiroo Kanamori . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Uncertainties in Earthquake Source Spectrum Estimation Using Empirical Green Functions
Germán A. Prieto, Robert L. Parker, Frank L. Vernon,
Peter M. Shearer, and David J. Thomson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Source Parameters Determined From Microearthquakes in an Underground Ore Mine
Volker Oye, Michael Roth, and Hilmar Bungum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Source Scaling Relationships of Microearthquakes at Parkfield, CA, Determined Using
the SAFOD Pilot Hole SeismicArray
Kazutoshi Imanishi and William L. Ellsworth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Effects of Methods ofAttenuation Correction on Source Parameter Determination
Eleanor Sonley and Rachel E. Abercrombie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
Section II:TheView From the Lab
Inferring Earthquake Source Properties From Laboratory Observations and the Scope of Lab
Contributions to Source Physics
N. M. Beeler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Relating High-Velocity Rock-Friction Experiments to Coseismic Slip in the Presence of Melts
Giulio Di Toro, Takehiro Hirose, Stefan Nielsen, and Toshihiko Shimamoto . . . . . . . . . . . . . . .121
Shear Resistance Reduction due toVibration in Simulated Fault Gouge
Takane Hori, Hide Sakaguchi, Naoto Yoshioka, and Yoshiyuki Kaneda . . . . . . . . . . . . . . . . . .135
Quantitative Characterization of Permeability ReductionAssociated with Compactive
Cataclastic Flow
Wenlu Zhu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
Section III:TheView From the Field
The Habitat of Fault-Generated Pseudotachylyte: Presence vs.Absence of Friction-Melt
Richard H. Sibson and Virginia G. Toy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153
Pseudotachylyte-Bearing Strike-Slip Faults in Mylonitic Host Rocks,
Fort Foster Brittle Zone, Kittery, Maine
Mark T. Swanson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
Energentics of ChemicalAlteration In Fault Zones and its Relationship to the Seismic Cycle
Joseph R. Jacobs, James P. Evans, and Peter T. Kolesar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
HowThick is a Fault? Fault Displacement-Thickness Scaling Revisited
Zoe K. Shipton, Aisling M. Soden, James D. Kirkpatrick,
Aileen M. Bright, and Rebecca J. Lunn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193
Episodic Fluid Flow in anAseismic Overpressured Growth Fault, Northern Gulf of Mexico
Steven Losh and Matthew Haney . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199
Mechanics and Interpretations of Fault Slip
Stephen J. Martel and Christin Shacat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207
The Missing Sinks: Slip Localization in Faults, Damage Zones, and the Seismic Energy Budget
Zoe K. Shipton, James P. Evans, Rachel E. Abercrombie, and Emily E. Brodsky . . . . . . . . . . . .217
Section IV: Earthquakes inTheory
Seismic Radiation From Simple Models of Earthquakes
R. Madariaga, J.-P. Ampuero, and M. Adda-Bedia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223
On the MechanicalWorkAbsorbed on Faults During Earthquake Ruptures
Massimo Cocco, Paul Spudich, and Elisa Tinti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237
Properties of Dynamic Earthquake RupturesWith Heterogeneous Stress Drop
J.-P. Ampuero, J. Ripperger, and P. M. Mai . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255
The Effects of Flash-Weakening and Damage on theEvolution of Fault Strength andTemperature
A. W. Rempel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263
Impact of Friction and Scale-Dependent Initial Stress on Radiated Energy-Moment Scaling
Bruce E. Shaw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
On Scaling of Fracture Energy and Stress Drop in Dynamic Rupture Models:
Consequences for Near-Source Ground-Motions
P.M. Mai, P. Somerville, A. Pitarka, L. Dalguer, S. Song, G. Beroza,
H. Miyake, and K. Irikura . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283
Mechanics of Sliding in Rate/State Friction Experiments
J. B. Walsh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295
SectionV: How Efficient is the “Earthquake Machine” and how Strong
are its Working Parts?
The Strength of the SanAndreas Fault:A CriticalAnalysis
Christopher H. Scholz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .301
What do Faults Feel? Observational Constraints on the StressesActing on Seismogenic Faults
John Townend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313
PREFACE
Understanding the energy changes that take place dur- Giventhestateofthescience,weorganizedanAmerican
ing an earthquake is one of the most challenging problems Geophysical Union Chapman Conference from which this
confronting the earth science community. An earthquake monograph derives. “Radiated Energy and the Physics of
releasesaccumulatedelasticstrainenergy,partitioningitinto Earthquake Faulting” was held in Portland, Maine in June
radiated energy, the energy consumed in overcoming fault 2005.Nearly130earthscientistsfrom14countriesattended
friction, and the energy of expanding the rupture surface theconferencetodebatethemanycontroversialissuescon-
area.Althoughthisenergybudgetcanbestatedquitesimply, cerning the energy budgets of earthquakes. Their expertise
ourunderstandingofitisonlyqualitativeatbest;arguments represented many disciplines including observational and
concerning the magnitudes of the four components in this theoretical seismology, fault-zone geology, laboratory rock
budgetrangeoveranorderofmagnitude,ormore. mechanics,fracturemechanics,andgeochemistry.
The challenge posed by these fundamental uncertainties WechosePortlandasthevenuesitebecauseofitsproxim-
regarding the energy changes of earthquakes has attracted ity to the Two Lights fault zones and the Fort Foster brit-
earthscientistsfrommanydisciplines,spawningaconsider- tle zone, two coastal areas showing excellent exposures of
able amount of debate at meetings and in the literature in faults, exhumed due to uplift and erosion from depths of
recentyears.Inthismonograph,wecapturethecurrentspirit about10km,thathadproducedearthquakesapproximately
of debate by presenting an overview of what we know and 300 million years ago. A highlightof the conference was a
haveyettoknowaboutearthquakeenergybudgetphenomena. fieldtriptothesetwocoastaloutcropsthatwasledbyMark
Somepapersdescriberecentprogressinhowwellweunder- Swanson, who, with his students, has been studying these
stand energy changes associated with earthquakes whereas ancientfaultsfornearly20years.Duringthisouting,wewere
otherpapersemphasizetheoutstandingquestionsandindi- abletoobservefaultzoneevidenceofseismicslip,including
catenewresearchdirectionsthatprovidenovelinsightsinto pseudotachylyte (evidence of melting due to fault friction),
thephysicsoffaulting.Forexample,techniquesformeasuring at typical seismogenic depths. The fieldguides prepared by
radiatedenergyhaveimprovedinrecentyears,thusreducing MarkSwansontoboththeFortFosterandTwoLightsfault
theuncertaintyofthisimportantearthquakesourceparam- zonesareincludedontheCD-ROMwhichaccompaniesthis
eter.Despitethisprogress,however,thereremainssubstantial volume.
disagreementaboutthescalingofradiatedenergywithearth- This volume would have been impossible without the
quakesize.Pseudotachylytes,whichrepresentbothabreak- hard work of all the reviewers and the publishing team at
throughaswellasamajorgapinourunderstandingofhow AGU, including our Acquisitions Editor, Allan Graubard,
earthquakeswork,cannowbeproducedinlaboratoryexperi- and Production Manager, Maxine Aldred. We also thank
mentsundercontrolledloadingconditions.Nonetheless,we those who helped make the Chapman Conference a suc-
still do not know how relevant pseudotachylytes are to the cess.Wearepleasedtoacknowledgethecontributionsofthe
physicsofearthquakefaulting.Otherpapersreportprogress Chapman Conference Program Committee: Greg Beroza,
inourunderstandingoffractureenergy,anenigmaticcom- JudithChester,JimEvans,SatoshiIde,KevinMayeda,Jim
ponentoftheenergybudgetofearthquakes.Studiesbasedon Mori, Kim Olsen, Xyoli Perez-Campos, Eliza Richardson,
both geologic field work and dynamic rupture modeling of Bruce Shaw, Rick Sibson, Shri Singh, Mark Swanson and
earthquakessuggestthatseismologicalestimatesoffracture TerryTullis.BrendaWeaver,MarlieBrill,andMellisaFicek,
energymayincludefrictionalenergyaswell,afindingthat of the American Geophysical Union provided key logisti-
couldchangethewayweviewtheroleofthisparameterin cal support for the Conference. Finally, we acknowledge
the dynamics of earthquake rupture. How much energy is the generous support and endorsement from the National
consumed in overcoming the frictional strength of mature ScienceFoundation,theUSGeologicalSurvey,theSouthern
active faults (e.g., the San Andreas) is a question that has CaliforniaEarthquakeCenter,UF3Llc,andtheSeismological
vexed the earth science community for nearly forty years. SocietyofAmerica.
It needs to be answered if we are to understand the energy
budgetsofearthquakes.
RachelE.Abercrombie
ArtMcGarr
Earthquakes:RadiatedEnergyandthePhysicsofFaulting GiulioDiToro
GeophysicalMonographSeries170
HirooKanamori
Copyright2006bytheAmericanGeophysicalUnion.
10.1029/170GM01 Editors
vii
Earthquakes: Radiated Energy and the Physics of Faulting
RachelE.Abercrombie,ArtMcGarr,GiulioDiToro,andHirooKanamori
INTRODUCTION earthquakesthesameordifferent?Towhatextentdoother
factors, such as the effects of tectonic setting, confound
Whenanearthquakeoccurs,elasticstrainenergyiscon- attemptstodeterminethescalingbehaviorofE ?Thepaper
R
verted into radiated energy, the energy associated with byVenkataramanetal.reviewsvarioustechniquesusedto
expanding the rupture area over the fault zone, and the estimateradiatedenergyandindicatestheiradvantagesand
energyrequiredtoovercomefaultfriction.Thismonograph disadvantages.Ofspecialnotehere,thegreatM9.2Sumatra
explores recent advances in our understanding of these earthquakeofDecember2004motivatedtheorganizationof
fourcomponentsoftheearthquakeenergybudgetandalso aspecialeveningsessionattheChapmanConferencetodis-
attempts to describe the important challenges for future cusstheproblemsofestimatingE fromgreatearthquakes.
R
research. The volume begins with an overview paper by ThepaperbyKanamorisummarizesmuchofthediscussion
Kanamori and Rivera that describes some general aspects ofthatstimulatingsessionincludingmanyofthechallenges
oftheenergypartitioningduringanearthquakeand,thus, ofmeasuringtheradiatedenergyfromthistrulydevastating
serves as a technical introduction. The following chapters earthquake. The controversial topic of the scaling of seis-
entailthevariouscomponentsoftheenergybudgetandthe micenergyisreviewedbyWalteretal.whereasChoyetal.
techniquesusedtostudythem.Eachchapterincludesover- exploretheeffectsoftectonicsettingonradiatedenergyby
view papers, which review the state-of-the-art concerning making a global survey of apparent stress in various plate
recentprogressaswellasimportantquestionsasyetunan- tectonicenvironments.
swered.Additionally,thereareshorter,morefocused,papers Section2,“TheViewfromtheLab,”providesadifferent
thatdescribesomeoftherecentbreakthroughseitherinour perspectiveonthequestionofwhethersmallandlargeearth-
understanding of earthquake energy changes or improved quakesarethesameordifferentintermsoftheirphysicsof
methodstodefinethesechanges. rupture by investigating, through laboratory experiments,
Section , “The Measure of Radiated Energy and its mechanisms that have been invoked by seismologists in
Behavior,”istheleastpoorlyunderstoodcomponentofthe supportoftheideathatlargeearthquakescausemorefault
energybudgetbecausethisistheonlyonethatcanbemea- weakeningthansmallones.Onesuchmechanismislubri-
sureddirectly.Eventhoughthisfundamentalmeasureofan cation due to the production of melts along the fault zone
earthquakehasahistoryextendingbackalmost90yearsto byfrictionalheatingasaconsequenceoflargefaultslipat
theestimateoftheenergyradiatedbythe9Pamirearth- highnormalstressandhighsliprates.DiToroetal.review
quakereportedbyGalitzinin95,thereisstillconsiderable theresultsofexperimentsthatdemonstratethegeneration
debate concerning the best methods for measuring radi- of melts at slips exceeding about  man d slip rates of ~ 
ated energy and substantial disagreement between differ- m/s(whicharethoughttobetypicalforlargeearthquakes)
entseismicenergy(E )estimatesforthesameearthquake. andthelowstrengthofexperimentalfaultsinthepresence
R
The key questions addressed in this chapter include the offrictionalmelts.Thesemeltsgeneratedinthelaboratory
following.Towhatextentdodifferentmethodsofmeasur- may be analogous to the natural solidified melts (pseudo-
ing E agree? How does the ratio E /M scale with seis- tachylytes)observedinthefieldbygeologistsinvestigating
R R 0
mic moment M ? More generally, from the perspective of fault zones that have been exhumed (next section). The
0
observationalseismology,arethephysicsofsmallandlarge paper by Beeler considers laboratory experiments entail-
ing low temperature friction, flash melting, bulk melting
Earthquakes:RadiatedEnergyandthePhysicsofFaulting and weakening associated with the formation of silica gel
GeophysicalMonographSeries70
andthencomparestheresultsofthesevariedexperiments
Copyright2006bytheAmericanGeophysicalUnion.
0.029/70GM02 to their counterpart observations for earthquakes. Beeler

2 EarthquakEs:radiatEdEnErgyandthEPhysicsoffaulting
demonstrates that, by making these comparisons between Section5,“HowEfficientIstheEarthquakeMachineand
laboratory and seismic source parameters for earthquakes, How Strong Are its Working Parts?” is mostly about the
he can address the question of how relevant the laboratory debatethatstartednearly40yearsagowhenearlymeasure-
resultsaretounderstandingearthquakerupturephysics. mentsofheatflowintheenvironsoftheSanAndreasfault
Section 3, “The View from the Field,” includes papers failed to show the anticipated peak centered over the fault
concerned with geological investigations of the physics of trace.ThetwopapersbyScholzandTownendrepresentthe
faultslip.OneofthequestionsreviewedbySibsonandToy twosidesofthedebatebyreviewingwhatisknownaboutthe
concerns whether or not pseudotachylytes are rare or just strengthofmaturefaults(activefaultsthathaveaccumulated
rarely observed. For his part, Swanson reviewed results a considerable amount of total slip). Both papers focus on
fromseveraldecadesofinvestigationsofexhumedevidence, theSanAndreas,thebeststudiedexampleofamatureactive
including veins of pseudotachylyte, from outcrops in the fault. The main question addressed by these two papers is
vicinityofPortland,Maine.Theearthquakesthatproduced whether the frictional strength of the San Andreas fault is
this evidence occurred about 300 million years ago when ashighaswouldbeexpectedfromlaboratoryrockmechan-
theserockswereapproximately0or2kmdeep. icsexperimentsorwhetheritissubstantiallylowerassug-
Section4,“EarthquakesinTheory,”isdevotedtopapers gestedbytheheatflowdataandothertypesofobservations.
that entail numerical models of earthquakes as a means of Thatis,formajorearthquakesthatrupturetheSanAndreas
resolving components of the energy budget that cannot be fault, how much energy is expended in overcoming fault
measureddirectly.Fractureenergy,inparticular,isperhaps friction?
best estimated by developing dynamic rupture models of The division of this monograph into these chapters does
earthquakes.Ofconsiderableinterestisthequestionofthe notthematicallyexhaustallthedirectionstakenbytheearth
realsignificanceoffractureenergy;forinstance,Coccoetal. sciencecommunitytounderstandtheenergychangesasso-
reviewwhetherseismicestimatesoffractureenergyinclude ciated with earthquakes. The monograph does provide an
a significant component of frictional energy. Other factors essentialviewofsignificantissues,whichshouldpromptfur-
influencing radiated energy, including the effects of fault therresearchandinterpretationsfromthemultidisciplinary
geometrycomplexity,arereviewedbyMadariaga. perspectivesemergingtoday.
Energy Partitioning During an Earthquake
HirooKanamori
SeismologicalLaboratory,CaliforniaInstituteofTechnology,Pasadena,California,USA
LuisRivera
EOST-IPGS;UniversitéLouisPasteur,Strasbourg,France
Weinvestigatethepartitioningofenergyreleasedduringanearthquaketoradi-
ated, fracture and thermal energies in an attempt to link various observational
resultsobtainedindifferentdisciplines.Thefractureenergy,E ,usedinseismology
G
isdifferentfromthatcommonlyusedinmechanicswhereitistheenergyusedto
producenewcracksurface.Intheseismologicallanguageitincludestheenergies
used for off-fault cracking, and various thermal processes. The seismic moment,
M , the radiated energy, E , and rupture speed, V , are key macroscopic param-
0 R R
eters.Thestaticstressdropcanbeacomplexfunctionofspace,butifanaverage
canbedefinedas∆t,itisalsoausefulsourceparameter.Fromthecombinationof
M ,E ,and,∆twecanestimatetheradiationefficiencyh ,orE whichcanalso
0 R R G
beestimatedindependentlyfromV .h providesalinktotheresultsofdynamic
R R
modelingofearthquakeswhichdeterminesthedisplacementandstressonthefault
plane. Theoretical and laboratory results can also be compared with earthquake
datathroughh .Also,thefractureenergyestimatedfromthemeasurementofthe
R
volumeandgrainsizeofgougeofanexhumedfaultcanbelinkedtoseismicdata
throughh .Inthesecomparisons,thethermalenergyisnotincluded,anditmust
R
beestimatedindependentlyfromestimatesofslidingfrictionduringfaulting.One
of the most challenging issues in this practice is how to average the presumably
highlyvariableslip,stressandfrictionalparameterstoseismologicallydetermin-
ableparameters.
InTROducTIOn ture of a solid. Rupture propagation in a solid material is
an irreversible process. Some amount of energy must be
duringanearthquake,thepotentialenergy(mainlyelastic continuously supplied near the rupture front to sustain its
strain energy and gravitational energy) stored in Earth is propagation.IntheideallybrittleGriffith[1920]modelof
released as radiated energy, fracture energy, and thermal crackpropagation,thisenergyisassociatedwithcreationof
energy. understanding the partitioning of energy is a key fresh new fault surfaces. Barenblatt [1959] completed this
toward understanding the physics of earthquakes. As a view by introducing a small “cohesive zone” behind the
useful analog of this process, we often consider the frac- idealrupturefront,inwhichsomeworkshouldbedoneto
vanquish the cohesive stresses. However, during an earth-
Earthquakes:RadiatedEnergyandthePhysicsofFaulting quake,manyadditionalphysicalprocessestakeplacenear
GeophysicalMonographSeries170
the rupture front and in the surrounding volume and con-
copyright2006bytheAmericanGeophysicalunion.
10.1029/170GM0 tribute to the energy budget [e.g., Shipton et al., 2006a].