Stress tensor inversions along the westernmost North Anatolian Fault Zone and its continuation ...

17 Pages·2002·0.72 MB·English

Geophys.J.Int. (2002)151,360–376
Stress tensor inversions along the westernmost North Anatolian
Fault Zone and its continuation into the North Aegean Sea
Anastasia A. Kiratzi
DepartmentofGeophysics,AristotleUniversityofThessaloniki,54124Thessaloniki,Greece.E-mail:[email protected]
Accepted2002April17.Received2002April4;inoriginalform2001April12
SUMMARY Do
w
Gephart&Forsyth’smethodhasbeenappliedtoestimatestressorientationsfromearthquake n
lo
fault-plane solutions of the westernmost North Anatolian Fault zone (NAFZ), its westward a
d
e
continuationintheNorthernAegeanSea,whereitinteractswiththenormalfaultingofcentral d
Greece,andofthewesterncoastalpartsofAnatolia.Intotal,163fault-planesolutionswere fro
m
used to invert for the stress tensor of 9 seismotectonic subregions. Magnitudes range from h
1.1to7.4.Alleventshaveshallowfocaldepths;mostoccurredintheuppermost15kmand ttp
s
very few in the 15 to 40 km depth range. The region studied is characterized by strike-slip ://a
c
(NAFZ), by transtension (Central Greece and western Anatolia) and by a strong signature a
d
of transpression in the Marmara area. From NAFZ to central Greece, the σ axis changes, em
3
continuously and smoothly, its orientation from N35◦E in the westernmost NAFZ to nearly ic.o
North–SouthincontinentalcentralGreece,andthemaximumhorizontalstress,σ changes up
Hmax .c
fromWNW–ESEto∼E–W.Thetotalangleoflateralvariationinthedirectionofeitherσ o
Hmax m
orσ is∼40◦.IncentralwesternAnatoliatheorientationofσ isNNE–SSW(N10◦E)while /g
itnhesmo3uatjhoerrngrwabeesntesr(nSiAmnaavt,oGliaediitzi,sMNeNndWe–reSsS)Eis(iNn3a3g◦rWee)m.eInntbw3oitthhcthaesersestohleveddevsetlroespsmteenntsoorf. ji/article
At the termination of the NAFZ against central Greece the regime is complex. The dextral -ab
s
shearmotiontransferredfromtheeastcrossesthePilionpeninsulaandnorthernEviaIsland tra
c
whereitinteractswiththemajornormalfaultsofcontinentalGreece.Thesefaultshavevariable t/1
orientations.TheE–WtrendingQuaternaryfaultsystemandtheNW–SEtrendingfaultsystem, 51
/2
which is inherited from the past. The latter faults under the presently acting stress field are /3
6
reactivated either as strike-slip faults with sinistral strike-slip component (when oriented at 0
small angle in respect to σ ) or as normal faults with small sinistral strike-slip component /61
3 4
(when oriented at high angle in respect to σ3). The occurrence of the recent 2001 July 26 928
Skyros event, which was clearly connected to a NNW–SSE fault with sinistral strike-slip b
y
motion, provides strong seismological evidence that the old structures can equally well be g
u
e
reactivatedunderthepresentlyactivestressfield. s
t o
n
Keywords:Anatolia,fault-planesolutions,Greece,stresstensorinversion. 0
5
A
p
ril 2
0
1
internaldeformation,expressedmainlyasextensionintheAegean 9
1 INTRODUCTION
domain,asoriginallydefinedbyMcKenzie(1972,1978).
TheAegeanSeaandthesurroundinglandareas(Fig.1)havebeen The presence of two major strike-slip faults, the North Anato-
considereda‘naturalgeophysicallaboratory’duetothewidevariety lian Fault (NAF) and the East Anatolian Fault (EAF), facilitates
oftectonicprocessesencompassed.Platemotionmodels(DeMets thewestwardmotionoftheAnatolianplate.TheNAFisadextral
etal.1990)suggestthattheArabianandAfricanplatesmovenorth- strike-slipfault(Fig.1)thatrunsforabout1400kmfromtheKar-
wards relative to Eurasia at a rate of ∼25 mm yr−1 and 10 mm liovatriplejunctionintheeasttotheAegeanextensionalregimein
yr−1, respectively. The northward movement of the Arabian plate thewest(McKenzie1972,1978;Dewey&Sengo¨r1979).Itswest-
causes the westward extrusion of the Anatolian plate (McKenzie ernportion,asitentersintotheNorthernAegeanSeasplaysinto
1970,1972,1978).Recentsynthesisofgeodeticdata(Papazachos several branches; the two most pronounced are shown in Fig. 1.
1999;McCluskyetal.2000)confirmsthefirstorderrigidbehaviour Thenorthernbranchisthemostseismicallyactiveanditsassoci-
ofAnatoliaandintroducesarigidAegeanplate.Therelativemotion atedbasinshavedepthsof∼1500m.Thesouthernbranchisnotas
betweenAnatoliaandtheAegeanplateisassociatedwithsignificant welldevelopedandtheassociatedbasinsarealsonotasdeep.The
360 (cid:5)C 2002RAS
StresstensorinversionsalongtheNAFZ 361
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/2
Figure1. SimplifiedmapoftheAegeanSeaandthesurroundingarea.Solidlinesaremajorstrike-slipfaults.Blackarrowsindicatethemotionoftheplates /3
6
relativetoEurasia(McCluskyetal.2000).Thesmalldivergingblackarrowsindicatethedirectionofinternaldeformation(extension)inthebroaderAegean 0
area.(CG:CorinthGulf;CP:Chalkidikipeninsula;FBZ:Fethiye-BurdurFaultZone;G:Ganosdag;M:Magnesiabasin;P:Peloponnese;S:Sperchiosbasin; /61
4
SP:Sporadesbasin.) 9
2
8
b
y
branches of the NAF stop abruptly at the Sporades and Northern accuratelytheinversioncodechoosesthefaultplanefromthetwo g
u
Evia Island basins and no-well defined structure has been recog- nodalplanesandfinally(c)toexaminewhethertheorientation,slip e
s
nisedsofarthatisresponsibleforthetransferoftheNAFmotion vectorsofthesefaultplanes,(i.e.thefailureplaneswiththesmaller t o
n
totheGulfofEviaandtotheGulfofCorinth.TheSporadesand misfit),complimentarytootheravailableinformationcanshedlight 0
5
Eviabasinsarebounded,eastofPilionandeastofEviabyNW–SE totheNAFzone-centralGreeceinteraction. A
settriakli.n1g9f9a6u)lt.s,TihnehseeritoelddfsrotrmucPtuliroecseanreetimmoersp(hCoalpoguitcoa1ll9y90d;oAmrimnaijnot thePrreegviioonuserxetleanteddinwgoerakswt oafsp3e2r◦fEo,rmbyedZbayncBheill&ierAentgaell.i(e1r9(9179)9f3o)r, pril 2
0
andareeasilyidentifiedfromtopographyandbathymetry(Lyberis whousedadifferentanalysismethodtoresolvetheregionalstress 19
1984). inwesternAnatoliaandbyCianettietal.(1997)whousedaFinite
Stresstensorinversionhasbeenappliedheretoalargesetoffocal Element (FE) approach to model the deformation in the Aegean-
mechanismsoftheregionthatextendswestof32◦Eandfollowsthe Anatolianregion.
northernboundaryoftheAegeanplatetothenormalfaultsystems
ofcentralGreece(at22◦E)andinthetransitionzonebetweenthe
2 STRESS TENSOR INVERSIONS
AnatolianandtheAegeanplate(Fig.1).Themaingoalwastoobtain
theorientationoftheprincipalstressaxesandinvestigatethelocal
2.1 Method
stressfieldatagreaterlevelofdetailthanpreviousstudies.Other
goalsofthisstudywerealso:(a)toinvestigatetheparameterres- ThestressorientationswerecalculatedfollowingGephart&Forsyth
olutioninthesubregionsforwhichearthquakefocalmechanisms (1984)andGephart(1990).Basicassumptionsofthemethodare:(a)
of variable magnitudes were simultaneously used (area of the in- thedeviatoricstresstensorisuniformwithinaregionandoverthe
teractionoftheNAFwithcentralGreece);(b)toinvestigatehow timeintervalconsidered(b)earthquakesaresheardislocationson
(cid:5)C 2002RAS,GJI,151,360–376
362 A.A.Kiratzi
pre-existingfaultsand(c)slipoccursinthedirectionoftheresolved 2.2 Data
shearstressonthefaultplane.Thegoaloftheinversionistofindthe
After some initial test inversions and mainly based on the distri-
stressstate,whichminimizesthediscrepancybetweentheresolved
butionoffault-planesolutions,theareawasdividedinto9subre-
shearstressdirectionandtheslipdirectionforallearthquakesinthe
gions.163focalmechanismswereusedintotal,whicharelistedin
dataset.Sinceonlygeometricalinformationisusedtheisotropic
Table1andplottedinFigs2(A)and(B).Theshadingvariationofthe
anddeviatoricstressmagnitudescannotbeestimatedandthereare
beachballsindicatesthedifferentsubregionsstudied.Magnitudes
onlyfourindependentmodelparameters.Thealgorithminvertsfor
are in the range 1.1 to 7.4. To construct the database I first col-
theorientationofthethreeprincipalstressaxesσ ,σ ,andσ (max-
1 2 3 lectedfocalmechanismsdeterminedbywaveformmodellingthat
imum,intermediateandminimumcompressiveprincipalstressaxis
werepublishedintheliterature.IthensearchedtheHarvardCMT
orientations,respectively,withmagnitudesσ ≥ σ ≥ σ )andthe
1 2 3 databasetocollectadditionalsolutions;thenIcollectedanyfirstmo-
parameterR{=(σ −σ )/(σ −σ );0<R<1}.Risascalarthat
2 1 3 1 tionsolutionsavailableandfinallyIcompiledthemicroearthquake
describes the relative size of the intermediate principal stress σ
2 focal mechanisms database. Most of the focal mechanisms used
relativetothemaximumσ andminimumσ compressivestresses.
1 3 have been determined by waveform modelling. Microearthquake
Thestressatapoint(oratavolumeofmaterialinthecaseof
focalmechanismsolutionswereonlyavailablefortheareanearthe
homogeneousstressfieldoverthisvolume)isgenerallyclassified D
terminationoftheNAFagainstcentralGreeceandtheyhavebeen o
accordingtotheshapeofthestressellipsoidatthatpoint.Atriaxial w
alldeterminedbyfirstmotionanalysis(mostoftheeventsofFig.2b n
stressstateisastateinwhichallthreeprincipalstressesarenonzero, lo
forinstancearesolutionspublishedinHatzfeldetal.1999).Itwas a
abiaxialstressstateisastateinwhichonlytwoprincipalstresses d
assumed that all mechanisms were determined with errors in the ed
ap(σrrein>ncoipσnazle≈srotσreas)n,sdRisaapnuponrnioazaxecirahole.ssWt1reh(saesxnsiatσal2tceoaimnsdparσes3stasatireoenin)naewnardhliywchheqeonuniσlvyalaoennndet setqruikaell,yd,iwp=an1d,rwakitehothfeneoxmceoprteiotnhaonfs1o0m◦.eAlalrlgdeasthaowckerse,fworeiwghhitcehd from h
σte1n1sairoenn)2.eTarhlye3seeqsutrievsaslesntatt(eσs1re≈quσi2r>eoσn3l)y,mRinaoprpflrouaccthueastio0n(saixnias2ltreexss- wveraerliougrehsstionwbtth=aeinf2eaduwltath-srpoalausnsgiehgsntoheleduit(niaovsnernsso(i∼oten1d(0is◦ne)e,TITacaboblenlec1l2)u).d,WaenditdthhthathteetahssesmustamrlelesFds ttps://ac
magnitudetochangefromastrike-sliptoacompressionalregime a
(0.85<R< 1),orfromastrike-sliptoanextensionalregime(with homogeneitycriterionisfulfilledinallcases.Ididnotattemptto dem
0<R< 0.15).TheintermediateR=0.5ratioindicatesabiaxial iFnivge.r2t).for smaller subsets than the regions defined in Table 1 (or ic.o
stressstateforwhichσ =0.Betweenthenearuniaxial(0<R< u
2 p
0.15or0.85< R<1)andthenearbiaxial(0.45<R<0.55)stress .co
m
states, the stress tensors characterize triaxial stress states. In this 3 REGIONAL STRESS TENSORS /g
case,R-valueshigherthan0.55indicatetranspressionalstrike-slip ji/a
regimes,inwhichσ2istensional,whereasR-valueslowerthan0.45 Table2summarizestheresultsoftheinversions,whicharedescribed rtic
indicatetranstensionalstrike-slipregimes,inwhichσ iscompres- inthefollowingforeachregionseparately. le
2 -a
sional(Bellieretal.1997). b
s
Theinversionschememinimizesthedifferencesbetweentheslip tra
c
direction,computedfromtrialstresstensorsandtheobservedslip 3.1 NorthAnatolianfault t/1
directionforbothpossiblenodalplanesforeachfocalmechanism. 51
The difference between computed and observed slip direction is E3loefvethnofsoectahlemfeacuhltapnliasmnesswweerreeuksneodwinnathperiinovrei,rssiionnce(Fthige.se2ae)v.eFnotsr /2/3
eavxaisl.uTatheedmthirsofiutgihstahneamnginuilmarurmotaantigolne(tmhaitsfirot)t,atFe,satbhoeustlaipnoafrbointrearoyf pJurolydu2c2e,d1e9x6t7enisnivMesuudrufarnceurVuapltlueryes(.ATmhebsreaseevyesnt&saZreattohpeeekve1n9t6o9f; 60/614
thetwonodalplanestomatchtheresolvedshearstressdirection. 9
Taymaz et al. 1991; Pinar et al. 1996), and the August 17, 1999 2
Thismisfitiscalculatedthroughagridsearch,systematicallyvary- (Izmit)andNovember12,1999(Du¨zce-Bolu)events(Bouchonetal. 8 b
ingtheorientationoftheprincipalstressesandtheparameterR.The 2000;Yagi&Kikuchi2000;Ayhanetal.2001;Kiratzi&Louvari y g
stresstensorthatcorrespondstotheminimumaveragerotationan- 2001;Tibietal.2001).InallthreecasestheE–Wtrendingplanes, ues
gleisassumedtobethebeststresstensorforthespecificpopulation exhibitingdextralstrike-slipmotion,weretakenasthefaultplanes. t o
offocalmechanisms. The computed stress tensor, as listed in Table 2 and shown in n 0
Theminimumaveragemisfit,Fandthe95or90percentcon- Fig.3(a),showspurestrike-slipregime(σ vertical).Requals0.5, 5 A
fidence limits of the best fitting model as described in Parker & 2 p
McNutt(1980)andGephart&Forsyth(1984)giveanestimationof σavHemraaxgteremndissfiEtSFEis–W3.3N◦W. andσHmin trendsNE–SW.Theminimum ril 20
thehomogeneityofthestressfield.Inaseriesoftestsforhomoge- 1
9
neousstresscases,Wyssetal.(1992)foundthaterrorsinthedata
(focalmechanisms)oftheorderof5◦,10◦,and15◦wereassociated
3.2 Marmara
withmisfitvaluesnotlargerthan3◦,6◦,and8◦,respectively.
In the commonly used inversion schemes the choice of the Twelve fault-plane solutions were used in the inversion (Fig. 2a).
fault plane from the two nodal planes is important. Some of the FewfocalmechanismsareintheMarmaraSeaitself,whereasmost
earthquakes used here, produced surface breaks or well defined data cover the coast of Turkey. The geometry and the nature of
aftershock zones. In this case the choice of the fault plane was theNorthAnatolianFaultundertheMarmaraSea,fromtheGulf
straightforward.Inallothercasesthefaultplanewaschosenbythe of Izmit up to Ganosdag˘ has been a matter of debate. The recent
inversioncodeandwasthatplanewiththesmallerangularmisfit. workofLePichonetal.(2001)basedonhighresolutionbathymetric
Gephart&Forsyth(1984)suggestthatthischoiceisoptimalwhen data, indicates the existence of a single through going strike-slip
themisfit,F,oftheactualnodalplaneislessthan20◦andthemisfit fault system nearly bisecting the Marmara Trough that connects
differencebetweentheauxiliaryplaneandthefaultplaneisgreater the1999Izmitearthquakefaultwiththe1912S¸aros-Gazikoyfault
than10◦. zone. However, the debate for the geometry of the continuation
(cid:5)C 2002RAS,GJI,151,360–376
StresstensorinversionsalongtheNAFZ 363
Table1. Earthquakedataused,listedforeachareaseparately.Shadedvaluesofstrike,dipandrakeindicateknownfaultplanes.Valuesofstrike,dipandrake
markedinboldlettersindicatethattheseplaneswerethe‘inferred’faultplanes(seetextfrommoreinformation).Focaldepthsasreportedinthecorresponding
references,anasterisknexttothevalueindicatesthattheyweretakenfromEngdahletal.(1998).Magnitudes,Maremomentmagnitudesinallcasesexcept
fortheHatzfeldetal.(1999)data,inwhichcasetheyarecodamagnitudes(regressionagainstML).Anasterisknexttothemagnitudeindicatesthattheweight
forthespecificeventwassetequalto2duringtheregression.
Date Origintime Coordinates Depth M Nodalplane1 Nodalplane2 Paxis Taxis Mo Ref
yr/mo/dd h/m/s (km) ∗10e17Nm
Lat.N Long.E Strike Dip Rake Strike Dip Rake Az Pl Az Pl
1.NorthAnatolianFault
430620 15:32 40.70 30.38 10 6.5 86 90 166 176 76 0 132 10 40 10 McKenzie1972
570526 6:33 40.50 31.25 10* 7.1 78 90 180 168 89 0 123 1 33 1 620.00 Jackson&McKenzie
1988
570526 9:36 40.60 31.30 10 6.0 78 90 180 168 89 0 123 1 33 1 JacksonMcKenzie1988
670722 16:56 40.67 30.69 12 7.2* 275 88 −178 185 88 −2 140 3 230 0 750.00 Taymazetal.1991
670730 1:31 40.70 30.40 16 5.6 301 50 −110 151 44 −67 146 74 45 3 McKenzie1972
990817 0:01 40.81 30.08 11 7.4* 266 85 −175 176 85 −5 131 7 221 0 1150.00 Kiratzi&Louvari2000 D
o
990831 8:10 40.79 29.94 15 5.1 82 78 −141 342 52 −16 309 36 207 17 0.47 Kiratzi&Louvari2000 w
n
990913 11:55 40.42 30.24 16 5.7 269 49 180 360 89 41 127 27 233 28 4.90 Kiratzi&Louvari2000 lo
990929 0:13 40.55 29.69 15 5.2 66 48 −171 330 83 −42 279 34 25 23 0.69 HarvardCMT-solution ad
e
991111 14:41 40.95 30.10 13 5.6 297 55 −179 206 89 −35 156 25 257 23 2.64 Kiratzi&Louvari2000 d
991112 16:57 40.93 31.25 12 7.1* 262 53 −177 170 88 −37 119 27 222 24 471.00 Kiratzi&Louvari2000 fro
m
2.Marmara h
530318 19:06 40.02 27.25 7* 7.3* 60 90 180 150 89 0 105 1 15 1 870.00 Jackson&McKenzie ttp
s
641006 14:31 40.30 28.20 14 6.4* 100 40 −90 280 50 −90 190 85 10 5 41.00 Tay1m98a8zetal.1991 ://ac
a
690303 0:59 40.10 27.50 5 6.0 60 40 68 268 53 108 346 7 231 74 5.00 Taymazetal.1991 d
e
710223 19:41 39.60 27.37 15 5.4 185 72 26 86 65 160 314 5 47 31 Zanchi&Angelier1993 m
720426 6:30 39.50 26.35 26 5.1 150 73 −26 248 65 −161 107 30 200 5 Zanchi&Angelier1993 ic.o
750327 5:15 40.34 26.14 15 6.2* 68 55 −145 316 62 −41 279 48 13 4 20.00 Taymazetal.1991 up
830705 12:01 40.32 27.22 10 6.1* 254 49 −173 159 85 −41 108 32 214 24 16.40 HarvardCMT-solution .co
m
831010 10:17 40.23 26.80 11 5.5 70 64 176 162 86 26 293 15 29 21 1.62 Louvari2000 /g
630918 16:58 40.80 29.10 15 6.4* 304 56 −82 110 35 −102 241 77 28 11 9.60 Taymazetal.1991 ji/a
888301402241 2200::4394 4400..8039 2289..2343 1155 55..34 325157 7900 −18101 38097 8809 −1600 321632 211 212712 71 11..0644 HHaarrvvaarrddCCMMTT--ssoolluuttiioonn rticle
990819 15:17 40.68 29.10 15 5.1 273 45 −120 133 52 −63 105 69 204 4 0.63 HarvardCMT-solution -a
b
s
3.NorthAegeanSea tra
644900471213 1165::0003 4308..3508 2246..8203 331 56..57 311401 8695 −310 222405 8693 −117592 216052 308 117953 11 MMccKKeennzziiee11997722 ct/15
651220 0:08 40.20 24.80 33 5.6 132 32 −90 312 58 −90 222 77 42 13 McKenzie1972 1/2
670304 17:58 39.20 24.60 10 6.3 313 43 −56 90 56 −118 305 66 199 7 24.30 Taymazetal.1991 /3
6
680219 22:45 39.40 24.90 10 7.0* 216 81 173 307 83 9 81 1 172 11 345.00 Kiratzietal.1991 0/6
811219 14:10 39.00 25.26 6 7.0* 47 77 −167 314 77 −13 271 19 181 0 224.00 Kiratzietal.1991 1
4
811227 17:39 38.90 24.90 6 6.4 216 79 175 307 85 11 81 4 172 11 38.20 Taymazetal.1991 9
2
811229 8:00 38.38 25.06 15 5.4 330 63 10 235 81 153 285 12 189 26 1.37 HarvardCMT-solution 8 b
820118 19:27 39.80 24.40 7 6.5* 233 62 −173 140 84 −28 93 24 190 15 73.20 Taymazetal.1991 y g
830806 15:43 40.05 24.79 9 6.7* 50 76 177 141 87 14 275 8 6 12 121.00 Kiratzietal.1991 u
e
830826 12:52 40.46 23.96 15 5.2 72 73 −168 338 79 −17 294 20 26 4 0.64 HarvardCMT-solution st o
831010 10:17 40.23 25.32 11 5.5 70 64 176 162 86 26 293 15 29 21 1.62 Louvari2000 n
840506 9:12 38.77 25.94 9 5.5 237 89 −161 147 71 −1 104 14 10 13 1.79 Louvari2000 05
840617 7:48 38.86 25.72 15 5.1 156 73 −9 249 81 −163 113 19 22 6 0.62 HarvardCMT-solution A
p
886600332295 181::3461 3388..3374 2255..1179 146 55..46 15623 7579 −15222 124695 6731 −11457 110237 396 382 298 12..2555 LLoouuvvaarrii22000000 ril 20
920723 20:12 39.81 24.40 8 5.4 272 51 −148 161 66 −43 120 47 220 9 1.13 Louvari2000 19
971114 21:38 38.81 25.86 10 5.7 58 83 175 149 85 7 283 1 14 9 4.04 Louvari2000
4.Sporadesisls
650309 5:57 39.30 23.80 7 6.1* 135 85 15 44 75 175 269 7 0 14 14.7 Taymazetal.1991
920710 16:28 39.19 23.34 11 1.9 200 60 −152 95 66 −33 56 40 149 4 Hatzfeldetal.1999
920710 17:36 39.20 23.32 11 1.4 205 80 −154 110 64 −11 70 26 335 11 Hatzfeldetal.1999
920713 3:44 39.29 23.09 11 1.6 35 60 −160 295 73 −31 252 34 347 8 Hatzfeldetal.1999
920716 2:52 39.11 23.34 12 1.3 60 45 −130 290 57 −57 255 62 357 7 Hatzfeldetal.1999
920722 21:42 39.21 23.47 11 2.0 245 75 161 340 72 16 293 2 202 24 Hatzfeldetal.1999
920722 22:27 39.22 23.49 11 1.7 245 75 161 340 72 16 293 2 202 24 Hatzfeldetal.1999
920723 12:41 39.23 23.54 11 2.3 155 60 −10 250 81 −150 117 28 19 14 Hatzfeldetal.1999
920724 1:06 39.16 23.24 11 2.0 130 50 −36 245 63 −134 104 51 5 8 Hatzfeldetal.1999
920726 1:50 39.24 23.69 10 2.3 60 70 −153 320 65 −22 281 33 189 3 Hatzfeldetal.1999
920727 19:07 39.21 23.21 11 2.4 70 45 −166 330 80 −46 279 38 28 22 Hatzfeldetal.1999
(cid:5)C 2002RAS,GJI,151,360–376
364 A.A.Kiratzi
Table1. (Continued.)
Date Origintime Coordinates Depth M Nodalplane1 Nodalplane2 Paxis Taxis Mo Ref
yr/mo/dd h/m/s (km) ∗10e17Nm
Lat.N Long.E Strike Dip Rake Strike Dip Rake Az Pl Az Pl
920823 2:02 39.30 23.16 8 1.6 140 65 0 230 90 −155 98 17 2 17 Hatzfeldetal.1999
920824 1:22 39.19 23.25 11 1.3 255 30 −77 60 61 −97 312 73 155 16 Hatzfeldetal.1999
920824 11:35 39.22 23.56 11 1.7 275 70 −14 10 77 −159 234 24 142 5 Hatzfeldetal.1999
920824 23:52 39.14 23.30 11 2.2 340 75 19 245 72 164 112 2 203 24 Hatzfeldetal.1999
920825 2:31 39.28 23.13 7 1.6 130 60 −74 280 34 −116 76 70 208 13 Hatzfeldetal.1999
5.EviaIsland
920709 9:49 38.96 23.13 10 2.5 250 60 −144 140 59 −36 105 46 15 1 Hatzfeldetal.1999
920710 1:30 38.74 23.35 13 2.7 120 60 −49 240 49 −139 83 55 182 6 Hatzfeldetal.1999
920715 8:29 39.01 23.25 10 1.8 275 35 −90 95 55 −90 5 80 185 10 Hatzfeldetal.1999
920716 11:58 38.76 23.34 13 2.2 70 75 161 165 72 16 118 2 27 24 Hatzfeldetal.1999
920718 19:45 38.86 23.35 12 1.6 120 65 −32 225 61 −151 81 40 173 3 Hatzfeldetal.1999
D
920721 11:08 38.99 23.34 9 1.2 120 60 −28 225 66 −147 84 40 351 4 Hatzfeldetal.1999 o
w
920721 15:13 38.70 23.34 13 2.3 120 60 −55 245 45 −135 82 58 186 8 Hatzfeldetal.1999 n
920722 10:19 38.76 23.36 10 1.7 55 60 −152 310 66 −33 271 40 4 4 Hatzfeldetal.1999 loa
920723 3:35 38.78 23.44 12 1.8 110 80 −26 205 64 −169 65 26 160 11 Hatzfeldetal.1999 de
d
992200772289 107::3531 3388..8770 2232..4990 1142 22..33 223400 8700 −−115543 113450 6645 −−1212 19051 2363 09 113 HHaattzzffeellddeettaall..11999999 from
920730 20:05 38.90 22.92 14 1.6 160 70 −14 255 77 −159 119 24 27 5 Hatzfeldetal.1999 h
920731 16:54 38.79 23.22 11 1.6 120 75 −19 215 72 −164 77 24 168 2 Hatzfeldetal.1999 ttps
920806 14:45 38.92 23.43 14 2.3 284 85 22 192 68 175 56 12 150 19 Hatzfeldetal.1999 ://a
920807 19:44 38.67 23.37 11 1.7 120 60 −20 220 73 −149 83 34 348 8 Hatzfeldetal.1999 ca
920809 5:09 38.90 23.69 12 2.1 145 50 −23 250 73 −138 116 41 13 14 Hatzfeldetal.1999 de
920809 14:32 39.01 23.34 7 1.6 120 50 −29 230 68 −136 93 46 351 11 Hatzfeldetal.1999 mic
920818 3:39 38.64 23.53 13 1.8 290 65 22 190 70 153 241 3 149 33 Hatzfeldetal.1999 .o
u
920820 10:36 38.88 23.39 12 1.8 210 65 −132 95 48 −35 71 51 329 10 Hatzfeldetal.1999 p
920823 9:36 38.81 23.20 14 2.8 113 60 −23 215 70 −148 77 37 342 6 Hatzfeldetal.1999 .co
m
920824 1:28 38.58 23.12 15 2.1 130 65 −32 235 61 −151 91 40 183 3 Hatzfeldetal.1999 /g
6.Magnesiabasin(Thessaly) ji/a
800709 2:10 39.23 22.98 1 5.7* 80 43 −78 244 48 −101 89 82 342 3 Papazachosetal.1983 rtic
800709 2:11 39.27 23.09 10 6.6* 58 41 −128 283 58 −62 243 65 354 9 86.7 HarvardCMT-solution le-a
800709 2:35 39.16 22.65 18 6.1* 84 40 −90 264 50 −90 174 85 354 5 Papazachosetal.1983 b
s
850430 18:14 39.26 22.88 11 5.6* 77 50 −105 280 42 −73 287 78 178 4 3.00 Taymazetal.1991 tra
992200770079 187::0391 3399..2557 2222..6784 1132 22..37 19005 6300 −−9806 227800 3600 −−9902 1803 7755 18102 1155 HHaattzzffeellddeettaall..11999999 ct/15
1
920711 17:49 39.39 22.94 10 2.1 80 45 −97 270 45 −83 265 85 355 0 Hatzfeldetal.1999 /2
920711 21:13 39.38 22.95 10 1.5 90 50 −119 310 48 −61 292 69 200 1 Hatzfeldetal.1999 /36
920711 23:56 39.42 22.81 12 1.7 250 52 −116 109 45 −60 98 69 358 4 Hatzfeldetal.1999 0/6
920712 1:46 39.42 22.81 11 1.4 95 40 −88 272 50 −92 167 85 3 5 Hatzfeldetal.1999 14
920715 0:34 39.26 22.85 9 1.3 95 55 −93 280 35 −86 354 80 187 10 Hatzfeldetal.1999 92
920717 2:08 39.35 23.02 8 1.2 300 87 −59 35 31 −174 238 40 4 35 Hatzfeldetal.1999 8 b
920730 16:46 39.33 22.78 11 2.0 265 60 −103 110 33 −69 143 72 5 14 Hatzfeldetal.1999 y g
920731 20:26 39.24 22.72 10 1.6 80 60 −90 260 30 −90 350 75 170 15 Hatzfeldetal.1999 ue
920731 20:29 39.24 22.72 7 1.5 80 60 −90 260 30 −90 350 75 170 15 Hatzfeldetal.1999 st o
920801 2:32 39.25 22.88 7 1.3 90 50 −114 305 46 −64 293 71 197 2 Hatzfeldetal.1999 n
920807 6:16 39.40 22.91 9 1.6 290 70 −67 60 30 −136 232 59 3 22 Hatzfeldetal.1999 05
920809 19:01 39.40 22.81 12 2.1 233 80 −127 130 38 −16 108 43 351 26 Hatzfeldetal.1999 Ap
992200881100 1114::5482 3399..4307 2222..8815 1101 22..40 218100 4500 −−6914 215005 4580 −−11897 8389 6894 118903 15 HHaattzzffeellddeettaall..11999999 ril 20
1
920814 5:41 39.41 22.80 12 1.6 295 35 −78 100 56 −99 342 77 196 11 Hatzfeldetal.1999 9
920817 16:54 39.28 22.95 8 1.1 210 25 −158 100 81 −67 35 49 171 32 Hatzfeldetal.1999
920819 20:15 39.34 22.63 12 2.7 85 40 −94 270 50 −87 204 84 358 5 Hatzfeldetal.1999
920819 21:20 39.35 22.62 13 1.8 70 65 −139 320 54 −32 290 46 193 7 Hatzfeldetal.1999
920819 22:11 39.35 22.63 11 2.0 110 25 −62 260 68 −102 149 65 359 22 Hatzfeldetal.1999
920819 23:11 39.36 22.62 12 1.7 100 40 −47 230 62 −119 94 61 341 12 Hatzfeldetal.1999
920821 1:59 39.36 22.62 11 1.8 70 40 −118 285 56 −68 246 70 360 8 Hatzfeldetal.1999
920823 22:06 39.26 22.79 6 1.5 65 70 −142 320 55 −25 288 40 189 9 Hatzfeldetal.1999
7.Lamia(Sperchiosbasin)
830919 1:18 38.74 22.43 8 5.1* 242 52 −100 78 39 −77 109 80 339 7 Burtonetal.1995
920714 12:35 38.91 22.49 12 1.9 90 60 −90 270 30 −90 0 75 180 15 Hatzfeldetal.1999
920714 21:08 39.04 22.46 19 1.3 75 40 −98 265 50 −84 215 83 350 5 Hatzfeldetal.1999
920729 11:00 38.98 22.44 14 2.9 90 50 −103 290 42 −75 301 79 189 4 Hatzfeldetal.1999
920804 5:47 38.69 22.68 12 2.1 105 60 −88 280 30 −94 22 75 193 15 Hatzfeldetal.1999
(cid:5)C 2002RAS,GJI,151,360–376
StresstensorinversionsalongtheNAFZ 365
Table1. (Continued.)
Date Origintime Coordinates Depth M Nodalplane1 Nodalplane2 Paxis Taxis Mo Ref
yr/mo/dd h/m/s (km) ∗10e17Nm
Lat.N Long.E Strike Dip Rake StrikeDip Rake Az Pl Az Pl
920807 10:39 38.91 22.50 11 1.9 265 40 −121 123 57 −67 83 68 197 9 Hatzfeldetal.1999
920808 4:00 38.92 22.42 10 2.1 155 −70 −64 280 32 −140 99 57 226 21 Hatzfeldetal.1999
920808 9:30 38.91 22.40 12 1.8 175 70 −38 280 55 −155 132 40 231 9 Hatzfeldetal.1999
920808 22:26 38.98 22.47 15 1.2 95 52 −79 257 39 −104 51 79 177 7 Hatzfeldetal.1999
920813 16:26 38.71 22.67 14 2.2 95 55 −90 275 35 −90 5 80 185 10 Hatzfeldetal.1999
920815 1:47 38.75 22.76 13 2.5 100 35 −86 275 55 −93 174 80 7 10 Hatzfeldetal.1999
920815 3:20 38.74 22.75 13 1.6 85 55 −90 265 35 −90 355 80 175 10 Hatzfeldetal.1999
8.CentralWesternAnatolia
390922 0:36 39.00 27.00 10 6.5 100 51 −70 250 43 −113 71 74 176 4 Ritsema1974
560220 20:31 39.86 30.49 10 6.5 141 57 −50 264 50 −135 108 57 204 4 McKenzie1972
680311 18:40 38.81 29.11 23 5.0 46 60 144 156 59 36 101 1 11 46 Zanchi&Angelier1993
D
690323 21:08 39.10 28.50 8 6.0 112 34 −90 292 56 −90 202 79 22 11 9.80 Eyidogan&Jackson o
w
1985 n
690324 1:59 39.11 28.51 30 5.0 165 45 −37 283 65 −129 146 53 40 12 Zanchi&Angelier1993 loa
690325 13:21 39.20 28.40 8 6.2 90 40 −104 288 51 −79 248 79 10 6 17.00 Eyidogan&Jackson de
d
690328 1:48 38.50 28.50 3 6.6* 300 41 −97 129 49 −84 83 84 215 4 129.00 Bra1u9n8m5iller&Nabelek from
1996 h
690406 3:49 38.50 26.40 16 5.9 116 60 −90 296 30 −90 26 75 206 15 McKenzie1972 ttps
690430 20:20 39.10 28.50 8 5.4 78 39 −114 288 55 −72 247 73 5 8 McKenzie1972 ://a
700328 21:02 39.20 29.50 8 7.1* 304 41 −97 133 49 −84 87 84 219 4 505.00 Braunmiller&Nabelek ca
d
1996 e
700328 23:11 39.12 29.55 33* 5.5 74 32 −110 277 60 −78 216 72 358 14 McKenzie1978 mic
700329 6:56 39.06 29.74 39 5.1 40 46 −135 275 59 −54 238 59 340 7 Zanchi&Angelier1993 .o
u
700330 7:59 39.34 29.26 8 5.0 100 22 −90 280 68 −90 190 67 10 23 Zanchi&Angelier1993 p
700416 10:42 38.97 29.92 8 5.6 112 60 −84 280 31 −100 38 74 198 15 2.70 Eyidogan&Jackson .co
m
1985 /g
700419 13:29 39.00 29.80 8 6.1 104 34 −90 284 56 −90 194 79 14 11 19.40 Eyidogan&Jackson ji/a
1985 rtic
700419 13:47 39.03 29.80 19* 5.8 114 24 −90 294 66 −90 204 69 24 21 Zanchi&Angelier1993 le
-a
700423 9:01 39.08 28.60 28* 5.6 77 50 −96 266 40 −83 310 83 171 5 McKenzie1978 bs
710413 12:52 39.03 29.89 13 5.3 120 50 −90 300 40 −90 30 85 210 5 Zanchi&Angelier1993 tra
c
710525 5:43 39.07 29.67 6 6.0 96 37 −108 298 55 −77 249 76 19 9 9.50 Eyidogan&Jackson t/1
1985 51
720314 14:05 39.30 29.46 18 5.6 101 35 −87 277 55 −92 178 80 9 10 McKenzie1978 /2
790614 11:44 38.80 26.60 8 5.9 105 51 −75 262 41 −108 71 77 184 5 6.70 Taymazetal.1991 /36
0
790616 18:42 38.46 26.77 15 5.3 127 45 −48 255 58 −124 112 61 8 7 1.20 HarvardCMT-solution /6
790718 13:12 39.44 29.19 15 5.3 111 34 −85 285 56 −93 183 79 17 11 1.15 HarvardCMT-solution 14
9
940128 15:45 38.67 27.48 14 5.4 114 60 −71 259 35 −120 64 69 190 13 1.14 Louvari2000 2
8
940524 2:05 38.83 26.49 10 5.5 136 49 −41 256 60 −131 113 55 14 6 2.10 Louvari2000 b
y
990725 6:56 38.96 28.19 15 5.2 151 70 −25 250 67 −158 110 31 201 2 0.83 HarvardCMT-solution g
u
e
9.SouthernWesternAnatolia s
550716 7:07 37.66 27.19 6 6.7 55 51 −137 295 58 −48 261 55 356 4 McKenzie1972 t o
n
590425 0:26 37.00 28.50 1 6.2 65 76 −70 189 24 −144 359 55 139 28 McKenzie1972 0
650613 20:01 37.80 29.30 2 6.0 91 74 −103 311 21 −52 342 59 192 28 8.53 Yilmazturk&Burton 5 A
710512 6:25 37.57 29.70 12 5.9 68 56 −80 230 35 −105 10 76 151 11 6.00 Tay1m99a9z&Price1992 pril 2
0
710512 10:10 37.60 29.70 5 5.6 73 14 −90 253 76 −90 163 59 343 31 Papazachosetal.1991 1
9
710512 12:57 37.60 29.60 12 5.7 53 25 −92 235 65 −89 147 70 324 20 2.50 Taymaz&Price1992
710909 15:10 37.30 30.24 34 5.6 160 90 173 250 83 0 205 5 115 5 2.21 Yilmazturk&Burton
1999
760819 1:12 37.70 28.89 4 6.1 164 45 −30 276 69 −131 142 49 35 14 14.80 Yilmazturk&Burton
1999
861011 9:00 37.91 28.53 8 5.7 80 67 −128 323 44 −35 304 52 197 13 4.35 Louvari2000
890224 0:40 37.76 29.44 15 5.3 113 39 −77 276 52 −101 141 79 14 7 1.11 HarvardCMT-solution
890427 23:06 37.10 28.20 7 5.4 114 35 −71 271 57 −103 145 74 10 11 1.12 Louvari2000
890428 13:30 37.06 28.01 12 5.5 107 44 −57 245 54 −118 97 67 354 5 1.55 Louvari2000
900718 11:29 37.04 29.51 14 5.4 53 55 −113 270 41 −60 270 70 159 7 1.40 Louvari2000
921106 20:06 38.02 26.97 6 6.0 146 76 13 53 77 166 100 1 9 19 10.87 Louvari2000
941113 6:56 37.12 28.02 15 5.4 139 36 −83 310 54 −95 198 80 44 9 1.33 HarvardCMT-solution
951001 15:57 38.06 30.13 4 6.3* 136 43 −87 312 47 −93 179 87 44 2 31.00 Wrightetal.1999
(cid:5)C 2002RAS,GJI,151,360–376
366 A.A.Kiratzi
Table1. (Continued.)
Date Origintime Coordinates Depth M Nodalplane1 Nodalplane2 Paxis Taxis Mo Ref
yr/mo/dd h/m/s (km) ∗10e17Nm
Lat.N Long.E Strike Dip Rake Strike Dip Rake Az Pl Az Pl
960402 7:59 37.84 26.87 9 5.4 124 46 −57 261 53 −119 110 67 11 4 1.14 Louvari2000
970121 20:47 37.98 28.33 18 5.2 85 28 −138 317 72 −68 256 58 30 24 0.78 HarvardCMT-solution
980404 16:16 38.10 30.16 15 5.2 154 46 −75 313 46 −105 144 79 234 0 0.86 HarvardCMT-solution
oftheNAFintotheMarmaraSeaisstillon-going(seeLePichon largest instrumentally recorded event is the 1965 March 9 event
etal.2001);severalscientistsfavourasegmentedpull-apartfault (M6.1).Nofaultplanewasknownapriori.Theinversionof16
geometry,indicatingatranstensionaltectonicregime,overastrike- focalmechanismsresultedinasteeplydippingσ (65◦)andshallow
2
slipregime. dippingσ andσ axes(Fig.3d),acharacteristicstrike-slipregime.
1 3
Nofaultplanewasassumedknownandtheresultsoftheinversion σ keepsthesameE–WorientationasintheNorthernAegean
Hmax
aresummarisedinFig.3(b).Thegeometryofthestresstensorindi- Sea. D
o
catesobliquemotion-normalfaultingwithaconsiderablestrike-slip w
n
component.σ trendsWNW–ESE(N145◦E)asintheNAF.The lo
Hmax a
distributionofR-valuesshownintherightofFig.3(b),whichhavea 3.5 EviaIsland de
d
tendencytowardsvalueslargerthan0.5,andtheR-valueforthebest The study area covers the northern part of Evia Island as well as fro
fittingmodel(0.7)isthesignatureofsomereversefaultingobserved m
inthearea(i.e.eventsofMarch3,1969;July5,1983amongothers). tGhuelNfoofrtChoerrinnEthv.oTikhoesNGourtlhfe(rFnigE.v2obi)k,oasgGuulflfsiismainlaarsiynmsimzeetwricithhatlhfe- http
Thisreversefaultingisprobablyaccommodatingasmallshortening s
componentonmainlyNE–SWtrendingfaultswhosemainmotion graben.Inthisregionnolargeeventsoccurredduringinstrumental ://a
time,soonlymicroearthquakedatacouldbeusedfortheinversion. c
isstrike-slipandthisisreflectedinthestresstensor,aswell. Thefocalmechanismsclearlyindicatestrike-slipmotions,com- ade
m
binedwithnormalcomponents.Thestrike-slipfaultingisalsocross- ic
ingtheNorthEvoikosGulfandreachesthecoastsofGreece.Fig.2 .o
3.3 NorthAegeanSea showsthattheshearmotionispenetratinguptothe22.9◦Emerid- up.c
o
As the NAF enters into the Aegean Sea, it branches into two ian.Westofthatmeridianthenormalfaultingsystemisprevailing. m
main segments. The northern branch passes between the islands ForEviaIslandonequestionthatarisesiswhetherthefocalmecha- /g
orafdSeasmboasthinra.kTihaensdoIumthverrons,bnroarntchho,fbLatehmymnoestraincadlleyndlessuspparotnthoeuSncpeod- nPirsemviso,ufsrowmorskmhaalslmshaogwnnittuhdaet,eivnegnetsn,erreafll,etchtetmheeraengfioocnaallmstreecshsafineislmd. ji/article
and less active, passes north of Lesbos and ends near the eastern obtainedfrommicroearthquakesdoesreflecttheregionalstressfield -a
b
coastofEviaIsland.Fromthe18focalmechanisms,forfourthe (Louvari2000).Inaddition,recentlydeterminedfault-planesolu- stra
faultplanewasknown.Forthe1968February19,AgiosEfstratios tions for earthquakes in the southern part of Evia Island indicate c
event,theruptureplanewasidentifiedbyPavlides&Tranos(1991), strike-slipfaulting,aswell(Panagiotou2001).Untilwehavedata t/15
1
forthe1981December19,the1982January18,and1983August from large events, the evidence we have from small magnitudes /2
6,events,theaftershocksequences,studiedbyRoccaetal.(1985) eventsindicatethatthedeformationattheislandofEviaistakenup /36
0
andKiratzietal.(1991),definethefaultplanes.Forallfourevents bystrike-slipfaultingcombinedwithnormalcomponentsofmotion. /6
1
theNNE–SSWtrendingplanewithadextralstrike-slipcomponent Thistranstensionalcharacterisalsoevidentfromthedirectionsof 4
9
wasthefaultplane.Theinversionresultedinapurestrike-slipstress theprincipalstressaxes,thesteeplydipping(75◦)σ axis(Fig.3e) 2
2 8
tensor(Fig.3c),withσ trendingE–W,σ trendingN–Sandan andthestressratio(R=0.3),listedinTable2.Onceagain,σ b
Hmax 3 Hmax y
R-valueequalto0.5. trends ∼E–W, the same trend as in Sporades Islands and North g
u
e
Thereisnostrongnormalcomponentintheresolvedstressten- AegeanSea. s
sor as I would expect, which indicates that the strike-slip motion t on
transferredfromtheNAFprevailsandcontrolsthestressregimein 0
5
theNorthernAegeanarea.Actually,exceptfromthe1967March 3.6 Magnesiabasin(Thessaly) A
p
4,event(Fig.2a)thatshowsnormalfaulting,allotherfocalmecha- Fromamorphotectonicpointofview,Thessalyrepresentsanalter- ril 2
nismsshowstrike-slipmotions.Therecentearthquakethatoccurred 0
nationofNWtrendingstructurallowsandhighsdissectedbyNNW 1
on2001July26nearSkyrosIsland(39.1◦N,24.3◦E;M6.4)hasalso 9
andENEtrendingfaults(Drakosetal.2001).Thisregionhasbeen
strike-slip mechanism (NP1: Strike 145◦, dip 80◦, rake 8◦; NP2:
thesiteofmanylargeearthquakesinthepast.TheVolos1980July
strike54◦,dip82◦,rake170◦,Benetatosetal.2002).Thus,theevi-
9(M6.6)seismicsequence,whichoccurredintheAlmyrosplain
dencesofarindicatesthatthedeformationintheNorthernAegean
(Fig.2b)isthemostrecentevent.Fortwoearthquakesoutof28used
Sea,southofthethree-legChalkidikipeninsulauptothenorthern
intheinversion,thefaultplanewasknownapriori.Basedonthe
boundaryoftheCycladesIslands,ismainlytaken-upbystrike-slip
surfaceexpressionofthefault,thespatialdistributionoftheafter-
faulting.
shocksandtheinversionoflevellingdata,thesouthdippingplanes
wereassumedfaultplanesforthe1980mainshockanditslargestaf-
tershock(Papazachosetal.1983;Drakosetal.2001).Theprincipal
3.4 SporadesIslands
stressaxes(Fig.3f)indicatenormalfaulting(σ steeplydipping)
1
TheSporadesbasinmarksthewesternmostpartoftheNorthAegean withaxisσ keepingtheregionalN–Strendandσ trending∼E–
3 Hmax
Trough,wheretheSporadesIslandsaresituated.Thebathymetryof W.However,acrossthepathfromtheSporadesIslandstoMagnesia,
thebasinisdominatedbyfaultstrendingNW–SEandNE–SW.The axesσ andσ have‘flipped’(Figs3dandf)eventhoughtheyretain
1 2
(cid:5)C 2002RAS,GJI,151,360–376
StresstensorinversionsalongtheNAFZ 367
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9
Figure 2. (a) Distribution of fault-plane solutions for earthquakes with epicentres along the North Anatolian Fault, its Aegean Sea strands as well as
WesternAnatolia(regions1,2,3and8,9inTables1and2).(b)Distributionoffault-planesolutionsforearthquakeswithepicentresincentralGreece
along the end point of the NAFZ in the Aegean Sea. Different beach-ball shading is used to denote the different regions, which are numbered as in
Table 1. (In Fig. 2a beach-balls are scaled relative to earthquake magnitude. In Fig. 2b all have the same size but strong earthquakes are identified by
date.)
(cid:5)C 2002RAS,GJI,151,360–376
368 A.A.Kiratzi
Table2. Regionalstresstensorinversionresultsforthesubregionsstudied.
Region Average σ1 σ2 σ3 R N σHmax
misfit,F(◦)
Az◦ Plunge◦ Az◦ Plunge◦ Az◦ Plunge◦
N.AnatolianF. 3.3 126 3 269 86 35 3 0.5 11 126
Marmara 5.2 321 46 149 44 55 4 0.7 12 145
NAegeanSea 5.2 274 4 147 83 4 5 0.5 18 274
SporadesIslands 4.3 95 6 199 65 2 24 0.4 16 95
EviaIsland 4.1 87 14 267 75 357 0 0.3 21 87
Magnesiabasin(Thessaly) 3.7 178 75 269 0 359 15 0.3 28 269
Lamia(Sperchiosbasin) 2.8 33 58 283 12 186 29 0.2 12 283
CentralWesternAnatolia 3.5 189 67 280 0 10 23 0.5 26 280
SouthernWesternAnatolia 4.8 227 77 57 13 327 2 0.4 19 57
Region—asdefinedinFig.2(A),B;F—averagemisfitangle;σ1—maximumcompressivestress;σ2—intermediateprincipalstress;
σ3—minimumcompressivestress;R—measureofrelativestressmagnitudes{R=(σ2−σ1)/(σ3−σ1),(0<R<1)};N—numberof Do
focalmechanismsusedintheinversion;σHmax—orientationoftheaxisofmaximumhorizontalcompression(followingZoback1992). wn
lo
a
d
e
thesameorientations.Thus,Magnesiaformsanareaofprogressive thelastcenturyoccurredalongtheNE–SWtrendingFethiye–Burdur d
transitionfromstrike-slipfaultingtonormalfaultingandthestyle faultzone.Thefaultzoneischaracterizedbynormalfaultingcom- fro
m
ofdeformationistranstensional. binedwithleftlateralstrike-slipmotion(Taymaz&Price1992). h
Nineteenfault-planesolutionswereusedintheinversion.Only ttp
s
3.7 Lamia(Sperchiosbasin) the fault plane of the 1995 October 1 Dinar event was assumed ://a
knownapriori,strikingNW–SEanddippingtotheSW(Pinar1998; ca
d
TheSperchiosbasinisboundedbyamajorfaultsystemthatborders Wrightetal.1999;Koral2000).TheDinareventoccurredatthe e
m
alsothesouthcoastsoftheNorthEvoikosGulfandcontinuesto NW–SEstrikingDinar-C¸ivrilfaultlocatedatthenortheasternend ic
Arkitsa(Figs2band5c).Nolargeinstrumentallyrecordedevents oftheFethiye-Burdurfaultzone(seeFig.4forlocations).The1971 .ou
p
occurredinthisarea.However,thetownofLamia(knownasZitouni May12Burdureventhadnoclearsurfacebreaks,onlycrackshave .c
o
atthattime)andnearbyvillageswereseverelyaffectedbyastrong beenreported;itisnotclearwhethertheSE(McKenzie1978)or m
earthquake(M6.6),whichoccurredduringthenightofOctober4, theNW(Taymaz&Price1992)dippingplaneisthefaultplane.I /gji/a
1740(Papazachos&Papazachou1997). didnotassumethefaultplaneknownforthisevent.HowevertheSE rtic
No fault planes were assumed known a priori, and the largest dippingplaneisinbetteragreementwiththeresolvedstresstensor le
event used is the September 19, 1983 with M 5.1 (Burton et al. thantheNWdippingplane. -ab
s
1995). The best fitting model (Fig. 3g) corresponds to a normal Theinversionresults(Fig.3iandTable2)confirmthetensional tra
σfaHumlatxinigssEtr–eWss,taesnfsoorr.thTeheMσa3ganxeissiatrbenasdisn∼. N–S,andthedirectionof cishwarealcltreersooflvfaeudlatisntghienaSroeausthdeerfinnWedesbtyertnhAelniamtoitlsiao.fTthheesotrrieesnsttaetniosnosr ct/151
ofσ andσ donotoverlap.Thedirectionofσ isNW–SEandof /2
σ 1 isN537◦E. 3 /36
3.8 CentralWesternAnatolia Hmax 0/6
1
CentralandSouthernWesternAnatoliaaredominatedbyanumber 49
4 ORIENTATION OF THE NODAL 2
of grabens with variable orientations (E–W or NE–SW or NW– 8
PLANES WITH THE SMALLER b
SE).Normalfaultsboundthenorthernandsouthernsidesofthese y
ANGULAR ROTATION g
grabens. The most pronounced structures are the Simav Graben u
e
andtheGedizGrabencorrespondingtotheextendedgrabensystem As I have previously mentioned, choosing the correct fault plane st o
north of the Menderes Massif between Manisa and Alas¸ehir (see fromthetwonodalplanesisamajorproblemencounteredinthe n 0
Fig.4). stress tensor inversion schemes of earthquake focal mechanisms. 5 A
26fault-planesolutionswereavailableandfortwoofthosethe Theselectioncriteriaareimportantbecausetheresultingstressten- p
faultplanewasassumedknownapriori.FortheMarch28,1969 sordependsonthechosenfaultplanes.Inthelackofothercriteria ril 2
0
Alas¸ehir M 6.6 event and for the March 28, 1970 Gediz M 7.1 (geological,aftershocksetc)acommonapproachtosolvethisprob- 1
9
event.BotheventsproducedextendedsurfacerupturesalongNW– lemistolettheinversionalgorithmchoosethefaultplanes.This
SEtrendingandtowardNEdippingfaults(Ambraseys&Tchalenko isalsofollowedinthemethodofGephart&Forsyth(1984).The
1970; Eyidog˘an & Jackson 1985; Braunmiller & Na´be˘lek 1996). ideaisthatthefaultplaneisthenodalplanewiththesmallermisfit
Theresultingstresstensor(Fig.3handTable2)correspondstoa (angularrotation)inthetestedstressfield.Thereadershouldrefer
transtensionalregime,withσ3striking∼N–S(N10◦E).The90per totheworkofMichael(1987)andofLund&Slunga(1999)fora
centconfidenceregionsarewellseparatedandnarrow.Thedirection discussion on the reliability of this fault picking technique. Lund
ofσHmaxis∼E–W. & Slunga (1999) tested the advantages and disadvantages of the
methodthoroughly.TheyconcludedthatthealgorithmofGephart
&Forsyth(1984)doesnotalwayspickthecorrectnodalplaneas
3.9 SouthernWesternAnatolia
faultplane;insomecasestheauxiliaryplaneispickedasfaultplane.
SouthernWesternAnatoliaisstructurallydominatedbypredomi- Inanattempttoseewhetherthenodalplanes,whichtheinversion
nantlyNE–SWstrikingfaults;asecondNW–SEstrikingfaultsys- algorithm inferred as fault planes, are in general agreement with
temisalsopresent.Alargenumberofsignificantearthquakesduring previousknowledgeoftheseismotectonicregime,Ihavedonesome
(cid:5)C 2002RAS,GJI,151,360–376
StresstensorinversionsalongtheNAFZ 369
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Figure3. (a)–(i)Orientationofprincipalstresses,forregions1–9(Fig.2)togetherwiththe90percentconfidencelimitsforσ1andσ3.Theinsetsshowthe ril 20
1
distributionofR-valuesformodelswithinthe90percentconfidencelimits. 9
furtherinvestigations.Firstofall,forthe12eventswithknownfault followthegeneraltrendoftheNorthAnatolianFaultzoneandits
planethealgorithmsucceededtopickthecorrectplanein9cases continuationinNorthernAegeanSea.Thealgorithmsuccessfully
(75percent).Fromthe163focalmechanismsusedinthisstudythe predictedtheNdippingplanefortheOctober6,1964Manyasevent
previouslymentionedconditionsforanoptimumchoiceofthefault (locatedbetweenthetwolakesinthesoutherncoastoftheMarmara
planewerefulfilledin104cases(64percent).InthefollowingIwill Sea). This event is known to have produced ∼40 Km of surface
callthesealgorithm-selectedfaultplanesas‘inferredfaultplanes’ breaksalonganorthdippingnormalfault(Taymazetal.1991).The
andfurtherexaminetheirorientationandspatialdistribution. NEdippingfaultplaneforthe1963September18C¸inarcikevent
Fig.4showsthe‘inferredfaultplanes’fortheNorthAnatolian (Nalbantetal.1998)wasalsosuccessfullypredicted.However,the
faultzoneanditscontinuationintheNorthernAegeanSeaandfor algorithm failed to choose the fault plane for the 1953 March 18
westernAnatolia(asinFig.2a).Thefocalmechanismsforsomeof Yenice-Go¨neneventandthe1967May26Abantevent,bothofwhich
theseeventsareplottedforcomparison.The‘inferredfaultplanes’ areknowntohaveproducedNE–SWtrendingsurfaceruptures.
(cid:5)C 2002RAS,GJI,151,360–376