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Journal of Geodynamics 67 (2013) 78– 96

Contents lists available at SciVerse ScienceDirect

Journal of Geodynamics

jo u r n al hom epage : ht tp : / /www.e lsev ier .com/ locate / jog

eformation of Central Anatolia: GPS implications�

ahadır Aktuga,∗, Erdem Parmaksızb, Mustafa Kurtb, Onur Lenkb,li Kılıc oglub, M. Ali Gürdalb, Soner Özdemirb

Bogazici University, Kandilli Observatory and Earthquake Research Institute, Geodesy Department, Cengelkoy, Istanbul, TurkeyGeodesy Department, General Command of Mapping, TR-06100, Ankara, Turkey

r t i c l e i n f o

rticle history:eceived 15 May 2011eceived in revised form 17 April 2012ccepted 8 May 2012vailable online 19 May 2012

eywords:lobal Positioning Systemrustal deformationectonicslate tectonicseodesyeodynamics

a b s t r a c t

Central Anatolia plays a key role to connect the theories about the subduction of African Plate alongHellenic and Cyprian Arcs and the collision of Arabia indenter along Bitlis-Zagros Thrust Zone. Takingplace between the North Anatolian and East Anatolian mega shear zones, the neotectonics of seismicallyless active Central Anatolia is often regarded as tectonic escape or extrusion tectonics. Although, avail-able GPS studies dating back to early 1990s reported coherent rotation, they were mostly focused onthe seismically more active and more populated Western Anatolia and lack sufficient spatial resolutionin quantifying second-order structures such as Tuz Gölü Fault Zone, Central Anatolia Fault Zone whichcomprises Ecemis Fault and Erciyes Fault, Ezinepazarı Fault and their related basins and associated pro-cesses. Besides, the new dense GPS velocity field of Central Anatolia exhibits systematic local patternsof internal deformation which is inconsistent with either coherent rotation or translation. The velocitygradients computed along the rotation profiles of Central Anatolia show nearly westward and smoothincrements which cannot be explained through a simple rotation/transport of Central Anatolia Basin.Moreover, estimating and removing an Euler rigid-body rotation rate which is computed from the siteslying in the middle part of Central Anatolia absorbs the velocity discrepancies between the Eastern andWestern part of Central Anatolia down to a few millimetres and leaves out systematic residuals. Uponcompletion of Turkish National Fundamental GPS Network (TNFGN) in 1999, early revision surveys werecarried out in Marmara region because of the 1999 Marmara earthquakes. Additional observations werecarried out in Central Anatolia, resulting in a velocity field of unprecedented spatial density with averageinter-station distance of 30–50 km.We computed the horizontal velocity field with respect to a not-netrotation frame, to Eurasia, and to a computed Anatolia Euler Pole. Two distinct models of Anatolia neo-tectonics, microplate and continuum deformation were tested through the rigid-body Euler rotations,block modelling and strain analysis. The results show that the decomposition of the Eurasia-fixed veloc-ity field into the rigid rotations and the residuals reveals systematic residuals up to 5 mm/yr with respectto a computed best-fit Euler Pole located at 31.6820N ± 0.05, 31.6130E ± 0.02 and with a rotation rateof 1.3800/Myr ± 0.01. The relative velocities computed along rotation paths exhibit westward increasinglinear gradients of 0.7–1.3 mm per 100 km depending on the latitude which is mechanically inconsistentwith the assumptions of a coherent transport or a rigid rotation due to an extrusion in the east. Moreover,the strain analysis results show E-W extension rates up to 100 nanostrain/yr along approximately N-Sstriking faults within the region from the west of Karliova to Isparta Angle, which is another indicationof the partitioned extensional strain across the Central Anatolia. On the other hand, the compressionalstrains were also obtained near the eastern branch of Isparta Angle, Tuz Gölü and southern Anatolia. In

this study, we provide new quantitative results about the fact that the deformation in Central Anatoliais not uniform and possibly driven by the extension through slab pull and/or suction in west-southwestand the compression in the south rather than a simple coherent rotation and/or translation/transport ofAnatolia driven by an extrusion process in the east. We also propose that the tectonics of Central Anatoliacomprises a dominant tensional driving force along Hellenic Arc in the southwest and a restraining beltalong Cyprian Arc in the south

� The manuscript solely reflects the personal views of the author and does not necessar∗ Corresponding author.

E-mail address: bahadir.aktug@boun.edu.tr (B. Aktug).

264-3707/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.jog.2012.05.008

.

© 2012 Elsevier Ltd. All rights reserved.

ily represent the views, positions, strategies or opinions of Turkish Armed Forces.

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. Introduction

Recent quantitative results of space geodesy in Aegean Seand Western Anatolia have raised new questioning and reason-ng in the geoscience community about Aegean Sea, Hellenicrc, Western Anatolia and even about the theoretical aspects ofontinental deformation which has been an interest for severalecades (McClusky et al., 2000; Jolivet, 2001; Jimenez-Munt et al.,003; Provost et al., 2003; Thatcher, 2003; Nyst and Thatcher, 2004;ktug and Kılıc oglu, 2006; Ozener et al., 2010). While Anatoliaas been an interest of GPS-oriented studies for more than twoecades, they are mostly concentrated on the seismically activearmara region, Western Anatolia and North Anatolian Fault Sys-

em and they lack spatial resolution to determine the slip rates ofndividual segments in Central Anatolia (Barka and Reilinger, 1997;eilinger et al., 1997; McClusky et al., 2000; Kahle et al., 2000; Aktugt al., 2009b). A tectonic map of Anatolia and surrounding regionss shown in Fig. 1.

Two main driving mechanisms are often cited within the frame-ork of Anatolia neotectonics: the push forces of Arabian northromontory due to the collision along Bitlis-Zagros thrust zone inhe east and the pull forces of subduction of African plate along Hel-enic Arc in the SW (McKenzie, 1972; Dewey and S engör, 1979; Leichon and Angelier, 1979; Jackson and McKenzie, 1984; Barka andadinsky-Cade, 1988; Taymaz et al., 1991; Reilinger et al., 1997;cClusky et al., 2000). However, the interaction of two mecha-

isms is still under debate (Meijer and Wortel, 1997; Jolivet, 2001;yst and Thatcher, 2004; Doglioni et al., 2002; Jimenez-Munt andabadini, 2002). For the extension regime in Western Anatolia,ifferent scenarios have been suggested depending on the driv-

ng mechanism: (1) westward tectonic escape of Anatolia startingn the east (McKenzie, 1972; Dewey and S engör, 1979; Deweyt al., 1986), (2) roll-back of African slab and associated back-arcpreading in Aegean lithosphere (Le Pichon and Angelier, 1979;eulenkamp et al., 1988), (3) orogenic collapse of overthickened

egean–Anatolian crust (Dewey, 1988; Seyitoglu and Scott, 1992),

4) E-W, NE-SW extension due to graben formation in two phaseKoc yigit et al., 1999), (5) translational and rotational forces dueo differential rates of subduction along Hellenic and Cyprus ArcsDoglioni et al., 2002; Reilinger et al., 2006), (6) three-phase pulsed

ig. 1. Tectonic structure of Anatolia and surrounding regions (KTJ: Karliova Triple Junct1992). Triangles along the subduction and thrust zones are on the upper blocks. Dashed

namics 67 (2013) 78– 96 79

extension (Purvis and Robertson, 2004), (7) slab break-off in theeast and migration of arcs (Regard et al., 2005; Faccenna et al.,2006), (8) various combinations of previous scenarios. In tectonicescape model, resulting forces of collision between Anatolia andArabia along the adjacent edges of Anatolian wedge extrude Ana-tolian block westward. However whether this caused migrationof Hellenic Arc is an on-going debate (Seyitoglu and Scott, 1996;Gautier et al., 1999). In the Agean extension model, the south-westward migration of the Hellenic Trench System is consideredto form the extensional neotectonic regime in the Aegean and inthe Western Anatolia with controversies about the onset age ofHellenic Arc subduction (McKenzie, 1978; Le Pichon and Angelier,1979; Kissel and Laj, 1988). In the post-orogenic collapse model,the gravitational potential energy accumulated in overthickenedAegean–Anatolian crust is assumed to drive the extension througha continuous graben formation since the beginning of the activeextension in Late Oligocene–Early Miocene. Koc yigit et al. (1999)proposed another model of extension through the horst-grabenformation which involves the previous mechanisms but in two dis-tinct phases interrupted by a compressional phase in Late Mioceneor Early Pliocene. This model differs from previous ones in incor-porating some part of Central Anatolia in the extension regimeof Western Anatolia. Doglioni et al. (2002) pointed out that theincreasing velocities to the west is not related to the squeezingeffect of Anatolia–Arabia interaction along the trailing edges ofAnatolia wedge but instead to the relatively lower subduction rateof Cyprian Arc with respect to Hellenic Arc. Purvis and Robertson(2004) suggest a three-phase pulsed extension in Western Ana-tolia comprising of two roll-back related phases initiated in LateOligocene and in Early Miocene and a third tectonic escape relatedphase from Pliocene to present. Another recent model was pro-posed by Regard et al. (2005) and Faccenna et al. (2006) as slabdetachment in the collision zone and the associated migrationof the subduction arcs to reconcile the difference between thetranstensional and transpression regimes in the west and in theeast, respectively. Although shear stresses are well determined

along Arabia indenter, there is no evidence for normal stresseslarge enough to drive whole Anatolian plate. Low seismicity of EastAnatolian Fault System prevents obtaining sufficient seismologi-cal evidence about the interaction of Arabian plate and Anatolia

ion). Major structures were adapted from McClusky et al. (2000) and S aroglu et al.lines were used to emphasize hypothetical borders within literature.

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long Anatolian wedge (Taymaz et al., 1991). Accordingly, a veryecent block model of Reilinger et al. (2006) involving Arabia, Africa,natolia and Greece show slip rates with very low normal com-onents along the Anatolia–Arabia boundary as opposed to thexpected in the extrusion tectonics theory claimed in previousorks (McKenzie, 1972; Jackson and McKenzie, 1984; Reilinger

t al., 1997; McClusky et al., 2000). In this study, we analyzed theelocity field of Central Anatolia for the two hypothesis of continen-al deformation: rigid block translation/rotation versus continuumeformation through computed Euler rotation poles, microblockodelling with elastic strain accumulation along block boundaries,

ssociated relative velocity frames and strain analysis for revealinghe intra-plate deformation. The GPS data were collected during thestablishment and the revision of Turkish National FundamentalPS Network (TNFGN) which provides a velocity field of unprece-ented spatial density in this part of Anatolia.

. Tectonic setting

Though Central Anatolia has been regarded as a deformation-ree region in many studies, Anatolia and the surrounding regionsncompass a wide variety of tectonic phenomena including theransform strike-slip faulting (North and East Anatolia Faults),ontinental collision and major thrust faulting (Bitlis-Zagros,aucasus), subduction (Nubia, Arabia), contraction (Caucasus, Mar-ara Sea), extension (Western Anatolia) and numerous relatively

mall scale processes (McKenzie, 1972; Jackson and McKenzie,984; Taymaz et al., 1991; Barka and Reilinger, 1997; Koc yigit andeyhan, 1998). Tectonic framework of Anatolia is a result of the

nteraction of Arabian and African Plates with Eurasia (McKenzie,972; Jackson and McKenzie, 1984; S engör et al., 1985; Taymazt al., 1991). While Eastern Anatolia is characterized by com-ression due to the northward motion of Arabian Plate alongitlis-Zagros suture zone (Koc yigit and Erol, 2001), Western Ana-olia is under a north-south extension driven by subduction ofubia in Hellenic Arc. Central Anatolia bounded by dextral Northnatolian Fault System (NAFS) in the north and sinistral East Ana-

olian Fault System (EAFS) in the east is a wedge-shaped structureith relatively low seismicity and with less internal deforma-

ion (Jackson and McKenzie, 1984; Taymaz et al., 1991; Barka andadinsky-Cade, 1988). While NAFS is one of seismologically mostctive fault zones in the world, there has been little seismicityssociated with the EAFS in this century although many large earth-uakes are known to have occurred within last 500 years (Taymazt al., 1991). Due to its seismically inactive state, S engör et al. (1985)efined Central Anatolia as “ova” province. However, there weretill moderate size earthquakes such as 1717 and 1835 Ecemis,914 Gemerek (M = 5.6), 1938 Kırs ehir (M = 6.8), 21 February 1940rciyes (M = 5.3), and 14 August 1996 Mecitözü–C orum (M = 5.6).eismicity in Central Anatolia is shown in Fig. 2.

In many neotectonic works, the coherent rigid-body rotation isonsidered the principal tectonic mechanism for Central AnatoliaBarka and Reilinger, 1997; McClusky et al., 2000). Paleomagneticvidence also confirms the rotation of Anatolia for about 30 Ma. Theumulative anti-clockwise rotation in Central Anatolia since Lateocene has been reported as 33◦ by Tatar et al. (1996). Similarly,nticlockwise rotations of 24–30◦ during the Neogene in Centralnatolia are given in Platzman et al. (1998). The GPS studies reveal

rotation of 1.2–1.4/Ma (McClusky et al., 2000; Ayhan et al., 2003;ktug et al., 2009b). Similar inconsistency also exists between GPSnd the geological studies for the motion of eastern boundary ofentral Anatolia along EAFS (DeMets et al., 1990; McClusky et al.,

000; Aktug et al., 2009b). Taking place between the compressionnd the extension regimes in the east and in the west respectively,natolia has different tectonic characters in the west and in the east.hile east-west and east-northwest horst-graben structures are

namics 67 (2013) 78– 96

dominant in the west, the eastern part is characterized by dextral tosinistral strike-slip faults and related pull-apart basins (Westaway,1994; Taymaz et al., 1991; Allen et al., 2004).

Seismically very active NAFS is well studied and defines thenorthern boundary of Central Anatolian Block (CAB) whereas fun-damental problem arises about the boundaries of this rigid-bodyrotation in the east and in the west. EAFS is more often regardedas the eastern lineation of CAB. Koc yigit and Beyhan (1998) identi-fies the Central Anatolian Fault Zone (CAFZ) as an intracontinental(intraplate) deformational structure cutting across the CentralAnatolia. CAFZ lies across Anatolian plateau and defined as a730 km long, 2–80 km-wide sinistral intracontinental megashearzone (Koc yigit and Beyhan, 1998). Koc yigit and Beyhan (1998) alsoreported late Paleozoic-early Mesozoic displacements of 75 km forthe structures and the rocks in the central part of CAFZ, Miocene dis-placements of 4–24 km for continental sequences and Quaternarydisplacements up to 3.1 km for deposits and various drainage sys-tems. The finite element model of Kasapoglu (1987) gives a slip rateof about 3 mm/yr for the southern part of CAFZ. However this is anongoing dispute about whether there exists such an active zone orwhether it can take up the all relative motion between Central Ana-tolia and Arabia to be the boundary of EAFS in the future (Koc yigitand Beyhan, 1998, 1999; Westaway, 1999).

The major tectonic structures in the Central Anatolia consistof intraplate strike-slip faults and pull-apart basins. The mostnotable structures are Tuz Gölü Fault, Ecemis Fault, Erciyes Fault,Ezinepazarı Fault, Tuz Gölü basin, and Erciyes strato-volcanocomplex (S aroglu et al., 1992; Koc yigit and Beyhan, 1998; Koc yigitand Erol, 2001). The relatively small Karsantı-Karaisalı Fault, Ös ünFault, Deliler Fault, Akpınar Fault, Salanda Fault and Delice Faultcomprise the minor tectonic features of the region (S aroglu et al.,1992; Koc yigit and Erol, 2001). Major tectonic structures wereshown in Fig. 3.

Tuz Gölü Basin (TGB) is the largest basin located in the middle ofCentral Anatolia. The structural, stratigraphic, and sedimentologicevidences suggest that it started as a fault-controlled basin dur-ing late Maastrichtian tectonism (C emen et al., 1999). The basin isbounded by Tuz Gölü Fault Zone (TZFZ) to the east and Cihanbeyliand Yeniceoba faults to the west. The initiation of the present faultsbounding the basin corresponds to the same period. Görür et al.(1984) suggested that TGB consists of two independently devel-oped Tuz Gölü and Haymana subbasins. Accordingly, C emen et al.(1999) referred the basin as Tuz Gölü Basin Complex including thesetwo subbasins. Like other Maastrichtian faults in the Central Ana-tolia, TGFZ was initiated as a strike-slip fault in response to Eoceneshortening. However, the neotectonic evidence shows that TGFZ ispredominantly a normal fault with a right-lateral strike-slip com-ponent (Uygun et al., 1982; S aroglu et al., 1992; C emen et al., 1999;Koc yigit and Beyhan, 1998; Koc yigit and Erol, 2001). Uygun et al.(1982) also found 500 m separation in Eocene sedimentary rocksnear Aksaray town. The time when movement along the TFZ initi-ated is disputable whether it is Late Cretaceous or Miocene (Görüret al., 1984; Uygun et al., 1982; Dellaloglu and Aksu, 1984; C emenet al., 1999). The N-S and NE-SW trending distribution of volcaniccones is another indication of the dextral and normal faulting alongthe Tuzgölü Fault Zone (Toprak and Göncüoglu, 1993).

Erciyes pull-apart basin is a volcanic province in Central Anato-lia and includes the Erciyes strato-volcano complex (Koc yigit andErol, 2001). The basin is a 35 km-wide, 120 km-long, 1.2 km deepsingle depression due to a releasing double bend along the CAFZnear the city of Kayseri during Plio-Quaternary times (Koc yigitand Erol, 2001). The normal faults surrounding the basin started

in Early Messinian followed by strike-slip faulting (Koc yigit andErol, 2001; Jaffrey et al., 2004). Jaffrey et al. (2004) point out thatthis directly corresponds to the timing of the faulting in EcemisFault Zone bounding the basin. Ezinepazarı Fault splays off the

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 81

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ig. 2. Seismicity in Central Anatolia (1900–2005) compiled from Harvard CentroKOERI, http://www.koeri.boun.edu.tr). Earthquakes with moment magnitudes (Mw

AFZ and runs into the southwest with dextral slip rates (S aroglut al., 1992). This fault zone was named as Yagmurlu-Ezinepazarıault Zone in (Koc yigit and Beyhan, 1998) and other parallel zoness Lac in and Almus Fault Zones were also defined in the sametudy. 31 July 2005 Bala Earthquake occurred on the intersectionoint of TGFZ and Ezinepazarı Fault. The focal mechanism solu-ion of Bala Earthquake shows a northeastern-striking left-lateral

aulting. Eskis ehir and Kaymaz Faults are located in the west of Cen-ral Anatolia and regarded as dextral with the considerable normalomponent (Bozkurt, 2001; Koc yigit, 2003; Koc yigit and Deveci,007). The Sultandag fault lies to the southwest of Central Anatolia

ig. 3. Major tectonic features in Central Anatolia (TGF: Tuz Gölü Fault Zone; ERF: Erciyeasin; CAFZ: Central Anatolian Fault Zone; CB: C ankırı Basin; LF: Lac in Fault; KF: Kaymaz

ment Tensor (CMT) and Kandilli Observatory and Earthquake Research Institute0 are shown as dots and earthquakes with published focal mechanisms were given.

bounding the Aks ehir Graben. It was defined as a normal fault andwas named as Aks ehir Fault in Koc yigit (1984). Previously, it wasidentified as a thrust fault in Boray et al. (1985) and in S aroglu et al.(1992). The recent Aks ehir Earthquake, Mw 5.6, 15 December, 2000and C ay Earthquake, 6 June 2002 show a normal focal mechanism(Taymaz and Tan, 2001, http://www.koeri.boun.edu.tr, HarvardCMT, Aktug et al., 2010). C ankırı Basin takes place between NAFS

to the north and Ezinepazarı Fault to the south. Lying above theIzmir–Ankara–Erzincan Suture Zone, it has evolved from Late Cre-taceous to Early Miocene times due to the collision and indentationof the Sakarya Continent and the Kırs ehir Block. The paleomag-

s Fault; EF: Ecemis Fault; EPF: Ezinepazarı Fault; TGB: Tuz Gölü Basin; EB: Erciyes Fault; EFZ: Eskis ehir Fault Zone; SF: Sultandag Fault).

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etic results show both clockwise and counter-clockwise rotationsithin the basin since Eocene to Oligocene (Kaymakc ı et al., 2003).

. GPS data handling and velocity field

Although, the GPS observations in Turkey date back to late980s, the installation of TNFGN (Turkish National Fundamen-al GPS Network) was completed in 1999. TNFGN, with over 600omogenously distributed stations forms the framework of geo-ynamical studies in Turkey (Ayhan et al., 2002a). The re-surveyf sites has been completed in Central Anatolia and produced aelocity field of 30–50 km spatial resolution. The observation spanf the sites is given in Table 1. Previous studies in Turkey werearried out with a focus on NAF (North Anatolian Fault), EAF (Eastnatolian Fault) and Marmara Region (Altiner et al., 1994; Straubnd Kahle, 1995; Kahle et al., 1995; Kılıc oglu, 1999; Kılıc oglu andksoy, 1999; Ayhan et al., 2002b; McClusky et al., 2000). This studyrovides new quantitative data in terms of focusing on Central Ana-olia with a dense GPS coverage. GPS data were processed withernese Software V4.0 using standard IGS products (Rothacher andervart, 1996; Brockmann, 1996). We analyzed GPS data using the

ombined loosely constrained solutions with GLOBK v5.06 soft-are (Herring, 1997). The campaign solutions were combined in

TRF2000 (Altamimi et al., 2002). The daily repeatabilities of about–5 mm and 4–9 mm were obtained for the horizontal and verticalomponents, respectively. The data reduction and the combina-ion procedure were handled in a three-step quasi-observationpproach described in Dong et al. (1998) and Aktug (2004).

First, the individual GPS campaign observations from 1992 to003 were processed by using Bernese software (Mervart, 1996;othacher and Mervart, 1996). Standard IGS orbit and earth ori-ntation products were incorporated into the analyses togetherith a sufficient number of IGS fiducial site observations. IGS

ites and the available continuous GPS sites in Turkey were alsoncluded in the analysis. Having detected and eliminated cycle-slipshrough the single and double-differenced observations, single-ayer regional ionosphere models were computed deterministicallyor each day using spherical harmonics. Integer phase ambiguitiesave been fixed by QIF (Quasi-Ionosphere Free) strategy given inervart (1996) and Rothacher and Mervart (1996). Using double-

ifferenced observations, daily loosely constrained (free) solutionsere obtained. For individual campaigns, loose solutions were pro-uced through the combination of daily solutions by ADDNEQ as

ntroduced in SINEX 1.1 format (Brockmann, 1996; Kılıc oglu, 1999).econd, loosely constrained individual campaign solutions wereoupled with weekly loose solutions of CODE (Center for Orbitetermination) (ftp://cddisa.gsfc.nasa.gov). This strategy provided

he flexibility of defining reference frame as well as stability. Toetter assess the quality of processing strategy, separate coordi-ate solutions were obtained for the individual campaigns andODE loose solutions, and they were compared before combiningegional solutions with loose solutions of CODE. The loosely con-trained solutions were investigated for the consistency and theaming integrity in the long-term repeatability. Third, the refer-nce frames (datum) for both coordinate and velocity estimatesere defined. Although, GPS observations are supposed to involve

cale, many deficiencies in the modelling of the observations coulde eliminated through estimating a scale parameter (Herring,997; Tregoning and Van Dam, 2005). However, estimation scalearameters could also absorb tectonic signals in the networks of

arger time span. Therefore scale parameters were left out and

eference frames (datums) for both coordinate and velocity esti-ates were defined by estimating 12-parameter transformation

3 translations, 3 rotations and their associated rates) to ITRF2000oordinates of 17 IGS sites rather than 14 parameters. Estimating

namics 67 (2013) 78– 96

12 transformation parameters in an iterative least squares intrin-sically involves minimizing the misfit between the solutioncoordinates and the published ITRF2000 coordinates. The details ofHelmert Method and the transformation can be found in Altamimiet al. (2002). The selection of sites for reference frame definition ofboth coordinates and velocities was made based on site history, thelong-term repeatability, the geographic coverage of the region andthe availability in pre-processed regional solutions. The selectedgroup of sites according to criteria mentioned above is also a com-bination of those given by Altamimi et al. (2002) and McClusky et al.(2000). The IGS sites VILL, ZWEN, METS, JOZE, POL2, KIT3, BOR1,MATE, GRAZ, POTS, WTZR, ONSA, ZIMM, KOSG, BRUS, HERS, GOPEwere employed to define the reference frame. The combinationof the loose campaign solutions (quasi-observations) was imple-mented in a Kalman filter approach using GLOBK software (Herring,1997). Post-fit rms (root-mean-square) of 17 stations was found tobe ±1.9 mm and ±0.3 mm/yr for the coordinates and the velocities,respectively. Taking the data interval spanning six years and thenumber of sites used for reference frame definition into consider-ation, the post-fit root-mean-square is an indication of a consistentreference frame definition both for coordinates and velocities. Thehorizontal velocities with respect to ITRF2000 were shown in Fig. 4.

Definition of a Eurasia-fixed frame for the sites in Anatolia hasimproved over the years depending on the available global net-work, plate models and ITRS realizations. Several strategies havebeen employed in the literature to define a plate-fixed referenceframe such as minimizing the velocities of a few sites in the northof NAFS (Kılıc oglu, 1999), minimizing the velocities of Eurasia sitestaken from a geological model (Reilinger et al., 1997), minimizingthe horizontal velocities of Eurasia sites down to zero (McCluskyet al., 2000), 12-parameter transformation of velocities into a platemodel determined from space-based studies (Aktug et al., 2009b),using data-derived Eurasia Euler vector (Reilinger et al., 2006).The distribution of IGS sites which can be used to define a refer-ence frame in Central Anatolia is not geometrically homogenousand a great majority of sites lies in the Western Europe. In thissense, assuming zero velocities for sites used in reference framedefinition may bias velocity solution up to a few millimetres. Thesame is true for IGS sites lying in the east of Anatolia. McCluskyet al. (2000) reported 1–2 mm shifts due to the inclusion of sitesin Central Asia. Besides, the computations are carried out in anearth-centered, earth-fixed global Cartesian frame and up veloc-ities which are irrelevant for spherical plate rotations should bekept as they are while producing a priori velocities in a Eurasia-fixed frame. Thus, minimizing the velocity field with respect to zerovelocity field of reference sites requires selection of sites withinnon-deforming part of Eurasia. Many sites with good history aresubject to different affects such as KIT3 and POL2 in Central Asiaand ONSA and NYAL which take place in a region affected by post-glacial rebound and identified as stations of in a deforming regionin Altamimi et al. (2002). For using an external source for a platerotation, caution should be exercised to account for the frame-differences and the time interval of the source. Geological models(e.i. NUVEL-1A-NNR) which are an average of plate motions over∼3 Ma may not represent the present day plate motions (DeMetset al., 1994). Another issue is using the different realizations of thedifferent ITRF/IGS frames. For instance, the velocity fields of ITRF-96and ITRF2000 are different and involve transformation parame-ters (Altamimi et al., 2002). The respective effects of rotational andtranslational rates at site velocities between ITRF-2000 and ITRF-96are not uniform in Eurasia and show SE-NW and SW-NE gradi-ents up to 1 mm for East and North velocities respectively (Aktug,

2005). Therefore, for defining a Eurasia-fixed frame, residual veloc-ities of 17 IGS sites were obtained by differencing Eurasia platevelocities from ITRF2000 velocities rather than constraining themto zero. The corresponding Eurasia-fixed velocities for reference

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 83

Table 1Observation span of the campaign sites.

Site 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

ABAN – – – – – – X – – – – – X X –ABDI – – X – X – X – – – – – X – –AFYO X – X – X X X – – – – – – – –AKCK – – – – – – X – – – – – X X –AKGE – – – – – – X – – – – X – – –AKPN – – – – – – X – – – – – X X –AKSH – – – – – X – – – X – – – – –AKTS – – – – – – X – – – – X – – –AKYA – – – – – – X – – – – – X – –ALAC – – – – – X – – – – – – – X –ALHK – – – – – – X – – – – X – – –ALTI – – – – – – X – – – – – X – XANDR – – – – – – X – – – X X – – –ANKR X – – – X X X X – – – X – X XANMR – – – – – – X – – – – X – – –ARAP – – – – – – X – – – – X – – –ATEK – – – – – – X – – – – X – – –AYAG – – – – – – – – X X X X X X XAYAS – – – – – – – – – X X X X – XAYDI – – – – – – X – – – – X – – –AYRN – – – – – – X – – – – X – – –AYVA – – – – – – X – – – – – X X –BLBN – – – – – – X – – – – X X X –BLVD – – – – – – – – – – X X X X –BRCK – – – – – – X – – – – – X – –BTTL – – – – – – X – – – – – – X –BUNY – – – – – – X – – – – X – – –BYRL – – – – – – X – – – X – – – –BYSH – – – – – X – – X – X X – – –CAMA – – – – – – X – – – – X X – –CAVS – – – – – – X – X – X X – – –CBUK – – – – – – – – – X X X X – XCEML – – – – – – X – – – – X – X –CEYH – – – – – – X – – – – X – – –CFTH – – – – – – X – – – – – X – –CICE – – – – – X – – – X X X – – XCKRK – – – – – X – – – X X X X X XCMLN – – – – – – – – X X X X X X XCORD – – – – – – X – – – X – X X –DDKY – – – – – – – – – X X X X – XDKNT – – – – – – X – – – X X – – –DOLK – – – – – – X – – X X X X X XELBI – – – – – – X – – – X X – – –EREN – – – – – – X – – – – – X – –ERKL – – – – – – X – – – – X – – XESKI – – X – X X – – – – – – – – –FELA – – – – – – X – – – – – X X –GAZI – – – – – – X – – – – – X X –GMRK – – – – – – X – – – X X X X –GUDU – – – – – – – – – X X X X – XGUND – – – – – – X – – – – X X – –GZLB – – – – – – X – – – – X X – –HUYK – – – – – X – – – – – – X X –ILGN – – – – – – – – – – X X X X –IRMA – – – – – – – – X X X X – – XKAD4 – – – – X – – – – – – – X – –KAHA – – – – – – X – – – – X – – XKART – – – – – – X – – – – X – – –KAYI – – – – – – X – – – – X X – XKBSK – – – – – – X – – – – – X – –KKIR – – X – X – X – – X X X – – XKOLU – – – – – – X – – – – X – – –KONY – – – – – X – – – X X X X X –KOZA – – – – – – X – – – – X – – –KRCT – – – – – – – – – – – X X X –KRHY – – – – – – X – – – X X – – –KRKV – – – – – – X – – – – X – – –KRLK – – – – – – X – – X X X – – XKSRY – – – – – – X – – – – X – – –KVKK – – – – – – X – – – – – X X –KYMZ – – – – – – – – – – – X X X –KZKB – – – – – – X – – – – X X – –MANS – – – – – – X – – – – X – – –MELE X X X X X X X – – – – X – X –MERS – – X – X – X – – – – – – – –MERX – – – – – – – – – X X X X X –

84 B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96

Table 1 (Continued)

Site 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

MESE – – – – – – – – X X X X X – XMHGZ – – – – – – – – X X X X X X XMIHX – – – – – – – – – – – X X X XMRDV – – – – – – X – – – X X – – –NALL – – – – – – – – X X X X X X XOGUZ – – – – – – X – – – – – X X –OLME – – – – – – X – – – – X – – –ORTK – – – – – X – – – – – – – X –PASD – – – – – – X – – – – X X – XPAZR – – – – – – – – – X X X X – XPNLR – – – – – – X – – – X – – – –PNRB – – – – – – X – – – – X – X –SAIM – – – – – – X – – – – – X – XSBNZ – – – – – – – – – X X X X – XSEKI – – X – X – X – – – X – – – –SERE – – – – – – X – – – – – X – –SINC – – – – X – X – – – X – X X XSIVA – – – – – – X – – – X – X X –SIVR X – X – – X X – – – – – – – –SLCH – – – – – – X – – – – X X – –SLCK – – – – – X – – – X X X X X –SLFK – – – – – – X – – – – X – – –SLKY – – – – – – X – – – – – X – –SLSR – – – – – – X – – – – X – – –SNCK – – – – – – X – – – – X – – –SORG – – – – – X – – – – – X X – XSRYN – – – – – X – – – – – – X X –SUCT – – – – – – X – – – – X – – –SULA – – – – – – – – – X X X X – XTASP – – – – – – X – – – – X X – XTAVS – – – – – – X – – – – – X – –TEKK – – – – – – X – – – – – X X XTOMA – – – – – – X – – – – X – – –TRMN – – – – – – – – X – – X – – –TSPN – – – – – – X – – – – X X – XUGRL – – – – – X – – – X X X – X XULAS – – – – – – X – – – – X – X –UZUN – – – – – – X – – – – X – – –YEME – – – – – – – – – – – X X X –YLDZ – – – – – – X – – – – X X X –YNAK – – – – – X – – – X – – – – –YOZG X – X – X X X X – X X X – X X

seua(±i

4

twtraAiT0Prtn1

YUMU – – – – – – X

YZYR – – – – – – X

ites were computed using the rotation pole of Eurasia in Altamimit al. (2002). Realization of a Eurasia-fixed frame was performedsing the stabilization (transformation) strategy described abovend using the residual velocities of 17 IGS sites. The post-fit rmsroot-mean-square) of 17 stations was found to be ±1.9 mm and0.7 mm/yr for coordinates and velocities, respectively. Velocities

n a Eurasia-fixed frame are shown in Fig. 5 and given in Table 2.

. Rotation of Central Anatolia

To test the hypothesis of rigid-block behavior (either transla-ion or rotation or both) of Anatolia, the rigid-body rotation ratesere dispersed from velocity field by simultaneously estimating

he rotation rates and strain rates through the least squares. Theotation rates for Central Anatolia with respect to Eurasia are givens 1.2–1.4◦/Myr in the previous GPS studies (McClusky et al., 2000;yhan et al., 2003; Aktug et al., 2009b), 0.5–1.7◦/Myr in geolog-

cal and seismological estimates (Le Pichon and Angelier, 1979;aymaz et al., 1991; Westaway, 1994; Le Pichon et al., 1995),.7–1.3◦/Myr in paleomagnetic studies (Tatar et al., 1996, 2002;latzman et al., 1998). While in general, the GPS-derived rotation

ates are larger, the results vary. The simultaneous computation ofhe rotation and translation rates through the strain analysis giveson-uniform rotation rates with one-sigma deviations of about–2 order higher than the original estimates. However, significant

– – – – X – – X– – – – – X X –

translation rates are obtained. While the statistically insignificant,rigid-body rotations were still shown in Fig. 6 to show the inhomo-geneous distribution of the rotation rates within the micro-plateassumption. Similarly, estimating the translations both togetherwith an Euler Pole and strain parameters shows that motion of Ana-tolia is better represented by a translation rather than a rotation.Although the positive rotations of varying rates are dominant, thereare several areas where the negative rotation rates (clockwise) arealso observed. To compute velocities in an Anatolia-fixed frame, anEuler-vector of Anatolia–Eurasia was employed. Anatolia–Eurasiapole representing this rigid-body rotation was computed using 79sites lying in the central part of Anatolia and given in Table 3. Theselection of sites in defining an Anatolia-fixed frame was based onthe strain analysis results and the residual velocities of all sites asdescribed in Aktug et al. (2009b). The Anatolia–Eurasia pole givenin McClusky et al. (2000) is also similar. It is considered that eventhere exist differences in the determination of Euler pole parame-ters due to the correlation of pole location and rotation rate; it hasnegligible effect on the regional velocities. However, the sensitiv-ity of Euler pole parameters to the site selection is also shown inTable 3. The use of different subsets of sites could easily lead to a

large variation in the estimate of Euler parameters. Therefore, twodifferent sets of sites were used to estimate the Euler parameters.

The velocities of sites with respect to the rigid part of Anatoliawere then obtained by removing the effect of rigid-body rotation

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 85

Table 2Velocities and 1 − � uncertainties in a Eurasia-Fixed frame.

Site Long. (◦) Lat. (◦) Ve (mm/yr) Vn (mm/yr) �Ve (mm/yr) �Vn (mm/yr) �VeVn

ABAN 32.910 36.321 −9.5 2.9 0.3 0.4 −0.139ABDI 34.803 39.106 −19.1 8.0 0.2 0.2 −0.048AFYO 30.644 38.769 −22.2 −2.0 0.2 0.3 0.001AKCK 36.324 39.553 −17.7 9.6 0.3 0.4 −0.088AKGE 33.312 36.810 −11.0 7.2 0.3 0.4 −0.069AKPN 32.207 37.200 −11.3 2.6 0.3 0.3 −0.070AKSH 31.481 38.342 −19.6 2.3 0.5 0.6 −0.088AKTS 34.732 38.000 −15.8 8.2 0.5 0.6 −0.074AKYA 35.896 37.771 −13.4 11.1 0.2 0.3 −0.037ALAC 34.814 40.145 −19.9 5.5 0.3 0.4 −0.139ALHK 34.043 38.047 −17.6 6.5 0.4 0.5 −0.047ALTI 33.789 38.605 −22.9 11.7 0.2 0.3 0.001ANDR 36.330 37.572 −7.9 9.5 0.4 0.4 −0.075ANKR 32.758 39.887 −22.2 −0.4 0.1 0.1 0.000ANMR 32.803 36.025 −7.1 3.6 0.3 0.3 −0.129ARAP 35.105 38.242 −18.8 9.9 0.4 0.4 −0.110ATEK 35.657 39.339 −19.3 9.3 0.4 0.4 −0.080AYAG 32.812 39.660 −26.4 0.4 0.3 0.3 −0.087AYAS 32.349 40.018 −24.9 1.3 0.5 0.6 −0.049AYDI 33.315 36.152 −10.3 5.0 0.4 0.4 −0.069AYRN 33.703 37.366 −13.1 6.7 0.4 0.4 −0.132AYVA 35.542 38.382 −14.5 9.7 0.3 0.3 −0.054BLBN 37.607 38.488 −14.9 13.0 0.3 0.3 −0.041BLVD 31.035 38.693 −17.2 −1.6 0.6 0.7 −0.053BRCK 34.964 37.779 −13.8 10.5 0.3 0.3 −0.060BTTL 35.032 39.523 −22.2 8.1 0.4 0.4 −0.174BUNY 35.881 38.870 −16.5 9.1 0.4 0.4 −0.116BYRL 32.386 36.961 −14.1 3.1 0.4 0.5 −0.033BYSH 31.658 37.656 −13.5 −0.5 0.3 0.3 −0.011CAMA 34.811 37.207 −12.7 8.6 0.3 0.3 −0.020CAVS 31.932 37.617 −16.0 1.6 0.3 0.4 −0.035CBUK 33.101 40.246 −22.8 2.6 0.3 0.3 −0.046CEML 36.479 39.307 −16.1 8.2 0.3 0.4 −0.097CEYH 35.839 37.055 −10.1 10.1 0.4 0.4 −0.094CFTH 34.686 37.525 −13.9 8.6 0.3 0.3 −0.041CICE 34.408 39.574 −19.9 7.0 0.3 0.4 −0.153CKRK 35.498 40.077 −18.6 8.2 0.3 0.3 −0.140CMLN 30.916 40.118 −28.5 −0.6 0.3 0.4 −0.114CORD 36.554 40.237 −17.0 10.8 0.3 0.3 −0.032DDKY 33.788 40.439 −19.8 3.2 0.5 0.6 −0.062DKNT 35.375 36.820 −13.5 10.0 0.4 0.4 −0.071DOLK 35.803 39.860 −19.9 8.9 0.3 0.3 −0.077ELBI 37.220 38.179 −12.7 12.8 0.2 0.3 −0.098EREN 34.155 36.718 −11.4 7.9 0.3 0.4 −0.049ERKL 35.429 38.818 −23.1 10.7 0.5 0.6 −0.055ESKI 30.637 39.658 −27.1 −1.3 0.4 0.5 −0.064FELA 35.568 39.102 −19.2 9.7 0.3 0.3 −0.077GAZI 32.283 36.283 −8.9 1.1 0.3 0.3 −0.116GMRK 36.055 39.183 −16.9 10.4 0.3 0.3 −0.070GUDU 32.421 40.236 −23.3 1.3 0.3 0.3 −0.058GUND 31.984 36.792 −11.7 −0.1 0.4 0.4 0.017GZLB 31.773 36.606 −11.9 0.1 0.3 0.4 0.013HUYK 31.571 37.898 −15.3 −1.2 0.3 0.3 −0.038ILGN 31.896 38.326 −21.8 2.7 0.7 0.8 −0.173IRMA 33.405 39.942 −22.5 5.8 0.4 0.5 −0.115KAD4 36.073 37.394 −12.1 10.1 0.2 0.3 0.000KAHA 34.688 39.303 −22.2 8.6 0.5 0.6 −0.023KART 35.340 36.543 −12.6 11.9 0.3 0.3 −0.100KAYI 32.744 38.764 −21.6 5.0 0.2 0.3 0.008KBSK 35.369 37.560 −16.0 8.4 0.3 0.3 −0.067KKIR 34.875 40.453 −18.3 5.9 0.2 0.2 −0.057KOLU 33.668 38.050 −15.9 6.3 0.4 0.5 −0.081KONY 32.394 37.869 −16.1 3.7 0.3 0.3 0.009KOZA 35.685 37.376 −14.1 10.8 0.3 0.4 −0.114KRCT 30.617 39.260 −21.7 −2.7 1.0 1.2 −0.265KRHY 35.076 37.221 −14.1 11.6 0.4 0.4 −0.083KRKV 34.296 38.579 −17.5 7.8 0.3 0.4 −0.075KRLK 35.875 40.355 −19.0 9.6 0.4 0.4 −0.099KSRY 34.257 37.377 −12.5 10.6 0.5 0.5 −0.138KVKK 37.470 39.283 −16.6 11.2 0.3 0.3 −0.008KYMZ 31.261 39.503 −24.4 1.4 0.9 1.2 −0.152KZKB 32.968 37.240 −11.4 5.0 0.3 0.3 −0.024MANS 35.632 37.851 −14.2 10.4 0.4 0.5 −0.069MELE 33.191 37.378 −14.5 2.9 0.1 0.1 −0.162MERS 34.552 36.900 −12.1 5.2 0.3 0.3 −0.084MERX 34.256 36.566 −10.6 8.8 0.1 0.2 −0.032

86 B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96

Table 2 (Continued)

Site Long. (◦) Lat. (◦) Ve (mm/yr) Vn (mm/yr) �Ve (mm/yr) �Vn (mm/yr) �VeVn

MESE 32.577 39.869 −23.1 1.5 0.3 0.3 −0.053MHGZ 30.570 40.028 −26.0 −0.9 0.3 0.4 −0.108MIHX 31.495 39.871 −20.8 1.3 0.3 0.4 −0.068MRDV 33.203 37.729 −14.8 5.4 0.3 0.4 −0.045NALL 31.460 40.148 −25.5 2.4 0.2 0.3 −0.069OGUZ 36.188 38.651 −16.8 11.1 0.4 0.4 −0.119OLME 32.760 38.277 −18.1 5.0 0.4 0.5 0.005ORTK 35.267 40.272 −19.3 6.9 0.4 0.4 −0.100PASD 33.256 39.238 −22.8 6.1 0.2 0.3 0.065PAZR 32.756 40.322 −24.7 0.1 0.2 0.3 −0.045PNLR 36.245 38.231 −13.9 11.7 0.5 0.6 −0.071PNRB 36.484 38.971 −17.9 10.7 0.3 0.3 −0.168SAIM 36.082 37.977 −10.4 9.1 0.3 0.4 −0.129SBNZ 33.294 40.484 −19.8 1.5 0.3 0.3 −0.072SEKI 32.160 36.431 −11.7 1.3 0.2 0.2 −0.050SERE 33.605 38.951 −22.5 5.4 0.2 0.3 0.049SINC 37.958 39.454 −16.0 12.4 0.2 0.2 −0.049SIVA 37.095 39.786 −18.2 11.6 0.3 0.3 −0.069SIVR 31.814 39.564 −21.1 −1.3 0.2 0.3 −0.012SLCH 35.018 36.824 −13.3 9.5 0.2 0.3 −0.060SLCK 32.506 38.022 −17.8 3.5 0.1 0.2 −0.015SLFK 33.944 36.370 −10.5 5.4 0.6 0.6 −0.048SLKY 34.477 37.783 −15.4 8.2 0.3 0.3 −0.060SLSR 34.711 38.712 −21.2 8.7 0.2 0.3 −0.070SNCK 36.521 38.447 −13.7 10.6 0.4 0.4 −0.083SORG 35.334 39.723 −20.5 7.8 0.3 0.3 −0.082SRYN 32.471 38.237 −18.5 4.2 0.3 0.3 −0.108SUCT 36.697 37.761 −10.4 10.4 0.4 0.4 −0.053SULA 33.703 40.163 −22.3 4.7 0.4 0.6 −0.182TASP 33.157 38.444 −20.7 6.7 0.2 0.3 −0.024TAVS 33.010 38.901 −23.7 6.3 0.2 0.2 0.023TEKK 37.757 39.867 −16.2 12.5 0.3 0.3 −0.079TOMA 35.825 38.455 −16.4 11.5 0.3 0.4 −0.114TRMN 30.387 39.431 −21.9 1.1 0.6 0.8 −0.211TSPN 36.318 40.136 −19.2 9.6 0.3 0.3 −0.065UGRL 34.458 40.439 −19.9 5.1 0.3 0.4 −0.096ULAS 37.011 39.433 −17.7 10.6 0.3 0.4 −0.124UZUN 33.843 39.084 −22.5 6.6 0.4 0.5 0.033YEME 32.240 39.099 −23.0 1.8 0.9 1.1 −0.138YLDZ 36.580 39.894 −19.0 10.4 0.3 0.3 −0.073YNAK 31.706 38.831 −19.8 1.3 0.5 0.6 −0.004YOZG 34.813 39.801 −20.5 6.3 0.1 0.1 −0.097YUMU 35.795 36.808 −7.6 7.4 0.4 0.5 −0.091YZYR 36.934 38.799 −15.5 12.0 0.3 0.4 −0.079

Fig. 4. Horizontal velocity field in ITRF2000. Velocities were obtained by estimating 12-parameter transformation (3 translations, 3 rotations and their associated rates) toITRF2000 coordinates of 17 IGS sites given in Table 1. Error ellipses are at 95% confidence level.

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 87

Fig. 5. Horizontal velocity field in a Eurasia-Fixed Frame. For defining a Eurasia-fixed frame, residual velocities of 17 IGS sites were obtained by differentiating ITRF2000a ding EE d usinE

rvmtHlt

Fsia

nd Eurasia plate velocities determined from ITRF2000 velocities and the corresponurasia in Altamimi et al. (2002). Realization of a Eurasia-fixed frame was performerror ellipses are at 95% confidence level.

ate of the Anatolian plate from the Eurasia-fixed velocities. Theelocities with respect to Anatolia are shown in Fig. 7. Describingotion of Central Anatolia as a rigid-body rotation and quantifying

his rotation by an Euler pole is useful as a first order approximation.

owever, the residual velocity field with respect to Central Anato-

ia exhibits a systematic dispersion with respect to the sites choseno define an Anatolia-fixed frame. One basic result of velocity field

ig. 6. Rigid-body rotations in◦/Ma computed independently from translation rates. Posimultaneously estimating translation, rotation rates together with strain parameters. Os statistically insignificant but important to show that estimating translation rates absornd that motion of Anatolia is better represented by a translation rather than a rotation.

urasia-fixed velocities for reference sites were computed using the rotation pole ofg the stabilization (transformation) strategy with the residual velocities of 17 sites.

in an Anatolia-fixed frame is that an Euler rotation computed usingthe sites in the middle absorbs the discrepancies between the eastand the west. As seen in Fig. 7, the residual velocities in the eastand west show systematic differences with opposite signs. The

relatively sparse distribution of sites in the previous works (Oralet al., 1995; Reilinger et al., 1997, 2006; McClusky et al., 2000) doesnot allow such an inference from the residual velocity field in an

itive rotations give counter-clockwise rotations. Rotation rates were computed byne-sigma deviations are about 1–2 order higher than the original estimates whichbs the westward motion of Central Anatolia leaving out insignificant rotation rates

88 B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96

Table 3Euler Poles for rotation of Central Anatolia from geodetic, geologic and seismologic sources given in different studies.

Modela (◦) �ϕ (◦) � (◦) �� (◦) (◦/My) �˝ (◦/My)

This study (a)a 32.016 ±0.04 31.658 ±0.02 1.426 ±0.01This study (b)b 31.682 ±0.05 31.613 ±0.02 1.380 ±0.01Aktug et al. (2009b) 31.68 ±0.06 31.83 ±0.03 1.45 ±0.01Aktug and Kılıc oglu (2005) 31.745 ±0.05 31.721 ±0.02 1.474 ±0.01Ayhan et al. (2003) 31.765 ±0.11 32.036 ±0.04 1.303 ±0.02Kreemer et al. (2003) 32.0 ±0.7 33.4 ±0.2 1.346 ±0.11McClusky et al. (2000) (1) 30.7 ±0.8 32.6 ±0.4 1.2 ±0.1McClusky et al. (2000) (2) 31.0 ±0.8 31.8 ±0.4 1.2 ±0.1Westaway (1994) 31.0 – 35.5 – 0.83 ±0.1Le Pichon and Angelier (1979) 30 – 34 – 0.44 –Le Pichon et al. (1995) 32.73 – 32.03 – 1.72 –Taymaz et al. (1991) 14.6 – 34 – 0.78 –

Ai

a(dAcemttiErgwcm

Fp

a Using all the sites.b Using selected group of 79 sites.

natolia-fixed frame and they assumed a rigid-body rotation withnternal deformation less than 2 mm/yr.

The difference in the magnitudes of velocities in the Easternnd Western Anatolia has been previously noted by Doglioni et al.2002). Assuming a rigid translation and or rotation of Anatolia, thisiscrepancy was often explained through the extension of Westernnatolia which is added to the extrusion forces arising from theollision of Arabia and Anatolia (Reilinger et al., 1997; McCluskyt al., 2000). However, Reilinger et al. (2006) report that westwardotion of Anatolia cannot be explained by the extrusion process in

he east. On the other hand, it is still assumed that internal deforma-ion of Anatolia is less than two millimetres and motion of Anatolias basically a westward transport (Reilinger et al., 2006). To assessurasia-fixed velocities independently from an Euler rotation, theelative velocities along rotation paths were computed and areiven in Fig. 8. To show that the velocity gradient are not confined at

estern and eastern parts of Anatolia, E-W and N-S gradients were

omputed along the rotation paths as shown in Fig. 8. To mini-ize the dependency of the velocity magnitudes on the distance to

ig. 7. Horizontal velocity field in an Anatolia-fixed frame. Velocities in an Anatolia-fixed

ole (Table 3) representing this rigid-body rotation was computed using 79 sites lying in

pole location (over radial path), eight profiles were formed and thewidths of the profiles were kept as narrow as possible. Computingthe velocity gradients was carried out by subtracting the velocitiesof sites from the first site located in the easternmost part of theprofile. In a typical rotation, the east and west velocity componentsare expected to increase and decrease smoothly along the rotationpath depending on the radius. However, linear velocities (velocitymagnitudes) should be the same along a rotation path. Thereforeit might be misleading to interpret velocities in Fig. 8 in termsof direction rather than magnitude. As seen in Fig. 8, the veloc-ity magnitudes gradually increase starting almost from the easternboundary of Anatolian wedge. To see the velocity increment in ananalytical aspect, the velocities along rotation paths were shown inFig. 9 as a function of distance from east to the west. The velocitygradients in profiles A–A′ and H–H′ are almost zero while all theother profiles except for E–E′ show approximately linear westward

increasing trends. The simple line fitting of distance-velocity scat-ters give 0.7–1.3 mm/100 km westward increments in the velocitymagnitudes.

frame were obtained through an Euler-vector of Anatolia–Eurasia. Anatolia–Eurasia the central part of Anatolia. Error ellipses are at 95% confidence level.

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 89

Fig. 8. Velocity gradients computed along eight rotation paths. Rotation paths were formed through an Euler-vector of Anatolia–Eurasia motion. Anatolia–Eurasia pole( in thed art of

5

ewoiai(oAtSw(dTtcpCascrp0saeJimcAs

Table 3) representing this rigid-body rotation was computed using 79 sites lyingifferentiating the velocities of sites with the first site located in the easternmost p

. Strain analysis and block modeling

Since the computed velocities depend on the datum (refer-nce frame) defined, we computed the strain field parametershich are invariant in the frame definition. For the computation

f strain parameters, the observed velocities were decomposednto three parts as strain tensor, rotation tensor and translations given in Feigl et al. (1990) and Demir (1999). The interpolationntervals for the strain computations were chosen as 12 in. × 12 in.∼20 km × 20 km) which is compatible with the spatial resolutionf the velocity field which has interstation distances of 30–50 km.ll the parameters were obtained at 12 in. × 12 in. grid nodes

hrough a least-squares adjustment using the method given inhen et al. (1996). The principal strain rates and the directionsere computed through the Eigen analysis of strain rate tensor

Turcotte and Schubert, 1982). The computed compression andilatation rates are mostly concentrated over the faults such asuz Gölü Fault, Erciyes Fault, Ecemis Fault, Deliler Fault and Sul-andag Fault and basin boundaries. The computed dilatation andompression rates are shown in Fig. 10. The shear strain rates andrincipal strain rates are also given in Figs. 11 and 12, respectively.omputed principal strains in Central Anatolia range between 10nd 100 nanostain/yr while mostly below 50 nanostain/yr. Earliertudies employing strain analysis are based on sparse networkonfigurations which makes it difficult to compare by specificesults. However, the overall magnitudes are comparable. The com-uted strain rates given in Kahle et al. (2000) range between

and 50 nanostrain/yr in Central Anatolia. However, since thetrain rates in NAFS are much higher (up to 300 nanostrain/yr)nd the number of sites in Central Anatolia is insufficient, Kahlet al. (2000) assumed nearly zero strain rates for Central Anatolia.imenez-Munt and Sabadini (2002) computed 20–40 nanostrain/yrn the same area through both modelling and GPS velocities. Seis-

ic strain rates given by Jimenez-Munt and Sabadini (2002) areomparable (3–30 nanostrain). However, the seismicity in Centralnatolia is too low to produce very reliable strain results througheismicity.

central part of Anatolia. Relative velocities within each profile were obtained bythe profile. Error ellipses are at 95% confidence level.

We also formed a detailed block model for Central Anatolia, toinvestigate how much of the deformation can be explained withrigid blocks. Similar studies have been performed for Western Ana-tolia (Aktug et al., 2009a; Nyst and Thatcher, 2004) and for a largerregion including Arabian peninsula (Reilinger et al., 2006). Weemployed an approach similar to McCaffrey (2002, 2005), whereall the Euler rotations of the micro blocks are simultaneously esti-mated by minimizing the misfit of the velocities. The backslipmodel given in Matsu’ura et al. (1986) was applied along eachfault segment to realize the interseismic velocity field. The elasticstrain along the block boundaries was computed using analyticalequations given in Okada (1985). ERBLOM (Elastic and Rigid BLOckModeling) software developed by the leading author was employedfor block modelling. The block boundaries were assumed verti-cal faults and were adapted from the Active Fault Map of Turkey(S aroglu et al., 1992). The locking depth of the block boundarieswas taken as 15 km similar to those specified in Reilinger et al.(2006). The defined blocks and the residual velocities are shownin Fig. 13. While the result of block modelling partially relies on thediscretization of the blocks, it is shown that even a very fine dis-cretization presented in Fig. 13, still produces significant systematicresiduals.

The computed shear strain rates of about 25 nanostrain/yr revealpositive shear strain in the west of Ezinepazari Fault, in the inter-section of Tuz Gölü Fault and Ezinepazarı Fault and in the northof Tuz Gölü Fault which are consistent with right lateral faultingand confirm their active state. North-south directed contractionswere observed along TGF and in its east which are also consistentwith right-lateral faulting. However, slip rates obtained from theblock modelling show that no significant slip rate exist in the west-ernmost segment of Ezinepazarı fault. Relative small positive shearstrains exist along Ezinepazari Fault in consistent with the right-lateral faulting. However, recent 31 July 2005 Bala Earthquake in

this region shows left-lateral strike-slip focal mechanism (Fig. 11).Largest positive shears were observed on the continuation of bothEzinepazari Fault and Tuz Gölü Fault. A right-lateral slip rate ofabout 5 mm/yr is obtained across Tuz Gölü Fault through block

90 B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96

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H-H'

F compd wn in

mlTtiFn1

ig. 9. Velocity magnitudes computed over profiles given in Fig. 8. Linear fits were

istance (in km) and velocity magnitudes (in mm) respectively. Error bars were sho

odelling. However, the shear strain rates show that the right-ateral slip is limited to the middle and/or southern part of the fault.he principal strains computed in the vicinity of Tuz Gölü fault showhat extension along this fault is confined to the southern part. Pos-

tive and negative shear strain sequence observed along Tuz Gölüault confirms the transition from extension to compression. Theormal component of the slip rate across Tuz Gölü Fault is about

mm/yr as obtained from the block modeling.

uted in least-squares sense and given as a line equation in which X and Y represent 1-sigma.

Negative shear strain rates are observed on Erciyes Fault and inits north along where Koc yigit and Beyhan (1998) defined the Cen-tral Anatolian Fault Zone (CAFZ). The negative shear strain ratesobserved in this region is consistent with a left-lateral Fault Zone

as EAFS. Similarly, slip rates obtained from block modelling sug-gest that left-lateral slip along this Fault Zone is about 1 mm/yr.1–2 mm/yr normal slip rates are obtained across CAFZ, which arealso consistent with computed contraction rates. The extension

B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96 91

F correg whichd

atitNoFssN

Ff

ig. 10. Dilatation and compression rates in nanostrain. Positive and negative valuesridding dilatation/compression rates at 12 in. × 12 in. (∼20 km × 20 km) grid nodesistance of 30–50 km.

long CAFZ is limited to the north of C ukurova Basin, where con-raction is observed to the south. No significant strain accumulations observed along Ecemis Fault in the south. NE-SW directed con-raction rates were obtained near Karacadag strato Volcanic center.W-SE directed contractions were obtained in the northeasternf Antalya Bay (in the northeast of Alanya). While the Eskis ehir

ault zone shows a right-lateral faulting along with extension, itsoutheastern continuation down to the south of Tuz Gölü Faulthows significant left lateral shear with contraction. Nearly NE-W oriented contraction rates were obtained in Kirka-Seyitgazi

ig. 11. Shear strains shear rates (εxy) in nanostrain/yr. Positive values indicate a right-laaulting.

spond to dilatation and compression, respectively. Contours were obtained through are considered reasonable as velocity field has spatial resolution with inter-station

region lying between Afyon and Eskisehir. Block modelling resultsalso suggest that the Isparta Angle often considered to the westerndelineation of extension regime does not accommodate more than1 mm/yr normal slip.

6. Results and discussion

The motion of Central Anatolia has been regarded as an almostnon-deforming rotating rigid block since early times (McKenzie,1972; Dewey and S engör, 1979; Dewey et al., 1986; Oral et al., 1995;

teral shear, whereas negative values show shear in left-lateral shear in strike-slip

92 B. Aktug et al. / Journal of Geodynamics 67 (2013) 78– 96

F en as 1s ned ati

MmtZWettoE

F

T

ig. 12. Principle strains. Interpolation intervals for strain computations were chospatial resolution with interstation distance of 30–50 km. All parameters were obtain Shen et al. (1996).

cClusky et al., 2000). In this respect, the suggested extrusionechanism for the rotation of Central Anatolia was attributed to

he compressional forces between Arabia and Eurasia along Bitlis-agros Belt. The possible extension which is the most obvious inestern Anatolia has been considered to be confined to the West-

rn Anatolia rather than the whole Anatolian block. In other words,

he motion of Arabia and Anatolia were separately investigated andhe rotation of Anatolia with respect to Eurasia was considerednly as a consequence of the convergence of the Arabian Plate withurasia. However, recent GPS studies reveal that counter-clockwise

ig. 13. Block model residuals. The positive values in the first and second (in parenthesis

he block boundaries were adapted from S aroglu et al. (1992) and Koc yigit (2009).

2 in. × 12 in. (∼20 km × 20 km) which is considered reasonable as velocity field has 12 in. × 12 in. grid nodes through least-squares adjustment using the method given

rotation with respect to Eurasia is not limited to Central Anatoliaand a broad area including Arabian, Anatolian, and Aegean regionsand the adjacent parts of the Zagros and central Iran are movingas a whole (Reilinger et al., 2006). Moreover, Reilinger et al. (2006)pointed out that the fault-normal components of velocities alongthe trailing edges of Anatolia–Arabia plate boundary are too low

to drive the whole Anatolia toward the east. The velocity profilesalong the computed rotation paths show that the westward motionof Anatolia is not uniform but presents linear gradients of from0.7 mm to 1.3 mm per 100 km. The westward increase of velocities

) rows correspond to left-lateral and normal slips, respectively.

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B. Aktug et al. / Journal of

s consistent with the idea that Anatolia’s motion is driven by forcesn southwest rather than in the east. Moreover, E-W extension ratesf up to 100 nanostrain/yr were obtained along approximately N-Striking faults within the region from the west of Karliova to Afyon,hich implies that differential velocities are partly absorbed along

pproximately N-S striking faults and E-W extensional basins.S engör and Yılmaz (1981) defined the extension regime in Ana-

olia as confined to the westernmost part of Anatolia (to the westf 31◦E). Koc yigit and Özacar (2003) enlarged the area of extensiono the east near Tuz Gölü Fault and to Eskis ehir-Inönü Fault Zonen the north. The main difference in these two approaches is treat-ng Anatolia either as an “ova” province (S engör and Yılmaz, 1981)r as a province of strike-slip regime (Koc yigit and Özacar, 2003).owever, both theories depend on the extrusion of Anatolia wedgelong North and East Anatolian Fault Systems. The velocity gradi-nts show that extension is not limited to the west of Tuz Gölü Faultone and it continues to the eastern boundary of Anatolian wedge.hile the principal strain rates in Central Anatolia are mostly below

0 nanostain/yr, the extensional rates up to 100 nanostain/yr werebserved along Central Anatolian Fault Zone, C ukurova Basin anduz Gölü Fault.

One remarkable result in strain analysis is that strain patternsppear to be concentrated near basin boundaries and extensionalreas. On the Erciyes Fault and in the northern part of Central Anato-ian Fault Zone defined in Koc yigit and Beyhan (1998), extensionalates up to 50–100 nanostrain/yr were observed. The proposed slipate (0.3 mm/yr) for CAFZ by Koc yigit and Beyhan (1998) requires arobably denser spatial coverage to be detected by GPS. The blockodel results of Reilinger et al. (2006) shows 3.3 mm/yr left lateral

nd 1.7 normal slip along northernmost part of CAFZ and 4.2 mmormal slip along the rest of CAFZ. However, our block modelingesults suggest that the extension rates along CAFZ are not morehan 2 mm/yr and they suddenly drops in the south near Ecemisault, consistent with the compression in the southern Anatolia. Inhis respect, CAFZ does not appear to accommodate any left-laterallip more than 1 mm/yr due to the interaction of Anatolia and Arabialates. On the other hand, the principal strains in Erciyes Basin and

n its north are almost purely extensional and the strain patternso not follow the suggested delineation of CAFZ in the south (i.e.cemis Corridor) rather combine with high extension in C ukurovaasin in the south. The results show that deformation along so-alled Central Anatolia Fault Zone is confined to middle and northart of CAFS zone near Erciyes Basin and show almost pure exten-ion. On the other hand, even with fine discretization of the possiblelocks, the residuals after block modeling show systematic pat-erns, which makes it difficult to be detected in sparse monitoringetwork configurations. And it is probably the reason for assumingn almost deformation-free rigid-body rotation for Central Anato-ia in previous works (Reilinger et al., 1997; McClusky et al., 2000).he palaeomagnetic data imply that the neotectonic deformationollowing collision initially produced crustal thickening resulting inplift of the Anatolian Plateau and was only subsequently accom-odated by the major differential block rotation during tectonic

scape (Tatar et al., 2002). Considering that the majority of basinsn Central Anatolia are Quaternary, the present-day deformationcheme is considered to have been active at least since Pliocene. Onhe other hand, Jolivet (2001) points out the resemblance betweennite strains of Oligo-Miocene and recent strains determined byeodetic studies implying that the present day deformation pat-erns predate an extrusion theory of Anatolia which was initiatedn Late Serravalian. However, recent geological findings show thathe deformation in some parts of the Anatolia was formed in a few

hases (Koc yigit and Deveci, 2007). In this respect, how long theresent day strain patterns have been active is not certain.

Quantifying the continental motion/deformation in micro-plateheory requires an Euler vector/pole. However, estimating Euler

namics 67 (2013) 78– 96 93

vectors representing a rotation pole together with its annual rateis somewhat arbitrary. Although, Aktug et al. (2009b) suggest a 2Dstrain analysis for specifying sites to compute a rotation pole, it stillrequires a priori assumptions about the geological properties of sitelocations. Moreover, local vertical velocities which are irrelevantfor an Euler rotation may bias the horizontal velocities in estimat-ing a 3D Cartesian rotation vector. Besides, the location of the poleand its rotation rate are highly correlated. Considering an arbitrarysite selection scheme and a limited amount of data, very similarrotation velocities could be obtained by a closer Euler Pole and ahigher rate for a far Euler pole with a lower rate (Aktug et al., 2009a).Moreover, estimating the location of an Euler Pole is more depend-ent on the direction of velocities than magnitudes. In practice, anyradial gradient in velocity field could easily be interpreted as arotation with sparse data with narrow tangential coverage. Conse-quently, velocity gradients up to 4–8 mm can be absorbed down to2–4 mm residuals in estimating and removing a rotation from localvelocities lying in the middle of the plate. Similarly, translationscan be reduced to some extent with estimating a rotation. On theother hand, the discrepancy of geological and GPS-derived rotationpoles for Arabia–Eurasia convergence has been known for a while(Reilinger et al., 1997; McClusky et al., 2000; Kreemer et al., 2003).This inconsistency was often considered due to the decelaration(change in the rate) over ∼3 Ma which is the interval NUVEL1A-NNR estimates represent the average of. Similarly, rotation ratesobserved for Anatolia are usually higher in paleomagnetic studiesthan in GPS estimates (Tatar et al., 2002; Platzman et al., 1998;Aktug and Kılıc oglu, 2005). Consequently, modelling of the motionof Central Anatolia as a rigid block rotation and/or translation couldbe misleading due to the lower internal deformation rate.

Two distinct compression and extension patterns with nearlysmooth gradients are observed along the eastern edge of IspartaAngle. While the compression is highly dominant in the southof eastern edge, extension is dominant in the north. This transi-tion is nearly balanced in the middle by strike-slip faulting. Thisdiscrepancy is also observed in the literature. Boray et al. (1985)and S aroglu et al. (1992) defined Sultandag Fault as a thrust faultwhile Koc yigit (1984) and Koc yigit and Özacar (2003) defined asa normal fault. Focal mechanism solutions of 15 December 2000Sultandag, Mw 5.9 and 03 February 2002 C ay, Mw 6.4 earthquakesoccurred near the intersection of Isparta Angle reveal normal faul-ting and are consistent the computed strain patterns. Availablefocal mechanisms also confirm the transition in strain patterns asthrust faulting in the south and normal faulting in the north ofIsparta Angle. This transition also implies a possible delineationof Cyprian Arc in the outer Isparta Angle. Block modelling resultswith homogenous regime assumption on eastern branch of IspartaAngle given in Reilinger et al. (2006) show −2.4 mm normal slip.

Velocities of sites lying in the south of Central Anatolia do notshow any significant southward motion with respect to inner partof Central Anatolia. Accordingly, lower seismicity with respect toHellenic Arc show that subduction along Cyrprian Arc is muchslower than that of Hellenic Arc for the present-day deformation.Moreover, very low subduction rates are considered for Cyprian Arcwith respect to Hellenic Arc in the minor shortening of the Quater-nary sediments (Doglioni et al., 2002). Observed large extensionalrates in C ukurova Basin and compressional rates on the easternbranch of Isparta Angle suggest that western and eastern branchesof Cyprian Arc lie in the west of eastern part of outer Isparta Angleand in the east of C ukurova Basin, respectively. A simplified blockmodel for Cyprian Arc and Florence Rise combining EAFS and Hel-lenic Arc in Reilinger et al. (2006) give −3.5 mm normal and 9.3 mm

thrust components for the east and west branches of an arc passingin the south of Cyprus Island. In this respect, they suggested thetransition from compression on the western branch of this arc andthe extension on the western branch of Cyprian Arc in the west of

9 Geody

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4 B. Aktug et al. / Journal of

yprus. However, dense GPS coverage identifies this transition onhe eastern branch of Isparta Angle implying compression to theast of Hellenic Arc continues to the inner part of Central Anato-ia near corner of Isparta Angle. Extension due to tensional forcesslab pull, suction) related with Hellenic Arc is obviously restrainedlong the eastern branch of Isparta Angle considering the com-ressional strains observed in this part. This clamping effect is alsoeen in the velocity gradients. In this sense, near zero incrementsf velocity magnitudes in the northeast of Central Anatolia whichs distinct in velocity profiles could be considered as a balancing

echanism in the northeast corresponding to compression in theouthwest. Results show the existence of a conjugate mechanism ofuz Gölü Fault Zone lying in the north of Tuz Gölü and in the west ofzinepazarı Fault. Recent Bala Earthquake, July, 31st, 2005 occurredn the intersection point of TGFZ and Ezinepazarı Fault. Focal mech-nism solution of this earthquake shows NE striking left-lateralaulting strike-slip faulting. Kaymakc ı et al. (2003) found counter-lockwise, clock-wise and counter-clockwise rotations in the west,iddle and east of C ankırı Basin during Eocene and Oligocene time.bserved extension rates delineate a zone starting from Erciyes andultansazlıgı basins up to the west of Deliler Fault. Large extensionates observed in the north of Iskenderun Bay ends in the West athe border of Taurides boundary. East side of Tuz Gölü is distinct inopography and is subject to compression and dilatation associatedith strike-slip faulting with dip slip component.

. Conclusions

Velocities in an Anatolia-fixed frame show that internaleformation of Central Anatolia not homogenous and on-goingxtension is not confined to the Western Anatolia. Estimating anuler Pole for Anatolia–Eurasia motion without simultaneouslystimating translation rates gives 31.682◦N ± 0.05, 31.613◦E ± 0.02ith 1.380◦/Myr ± 0.01 rate which is consistent with earlier studies.owever, computation of rotations through strain analysis giveson-uniform rotations with one-sigma deviations of about 1–2rder higher than the original estimates while significant transla-ion rates were obtained. The velocity gradients up to 4–8 mm cane absorbed down to 2–4 mm residuals in estimating and remov-

ng a rotation from local velocities lying in the middle of the plate.imilarly, translations can be reduced to some extent by estimat-ng a rotation. In order to obtain velocity gradients independentf the rotation pole, both east and north velocity gradient wereomputed on narrow E-W profiles along an average rotation pole.xcept for the profiles in the north and in the south, gradients ofast velocities from east to west exhibit a linear trend implyingn elastic elongation rather than a rigid-body rotation (Reilingert al., 1997; McClusky et al., 2000) or rather than a simple transportReilinger et al., 2006). Relative velocities computed along rotationaths exhibit westward-increasing linear gradients of 0.7–1.3 mmer 100 km depending on the latitude which is mechanically incon-istent with the assumptions of a coherent transport or rotationue to an extrusion in the east. Moreover, up to 100 nanostrain/yr-W extension rates are observed in the strain analysis alongpproximately N-S striking faults within the region from westf Karliova to Isparta Angle which is another indication of parti-ioned extensional strain across the Central Anatolia. In this respect,hile nearly no deformation is observed in basin interiors, east-

rn branch of Isparta Angle which is delieanation of Cyprian Arc,ight-lateral Tuz Gölü Fault Zone, right-lateral Ezinepazari Faultnd middle part of CAFZ where E-W extensions of 5–7 mm/yr are

bserved appear to dominate the internal deformation of Cen-ral Anatolia. Koc yigit and Beyhan (1998) proposed a slip rate of.3 mm/yr for CAFZ. The block modelling results also suggest up to

mm/yr extension along CAFZ. On Erciyes Fault and in the north of

namics 67 (2013) 78– 96

Central Anatolian Fault Zone defined in Koc yigit and Beyhan (1998),extensional rates up to 50–100 nanostrain/yr were observed. Oneremarkable result in strain analysis is that strain patterns appearto be concentrated near topographically distinct basin boundariesand extensional areas implying that current deformation mech-anism for Central Anatolia has been active at least since crustalthickening. Sites lying in the south of Central Anatolia do not showany significant southward motion with respect to inner part of Cen-tral Anatolia. Lower seismicity with respect to Hellenic Arc showthat subduction along Cyrprian Arc is much slower than that ofHellenic Arc for the present-day deformation. Accordingly, com-pression rates are observed in the southern Anatolia. The transitionfrom compression to extension to the north implies two differentmechanisms exist in Central Anatolia tectonics involving exten-sion due to dominant Hellenic Arc in the southwest and a possiblerestraining effect of Cyprian Arc in the south.

Acknowledgements

We thank many individuals who participated in the GPS sur-veys and the pre-processing of the GPS data. Generic Mapping Toolswere used for presenting the graphics (Wessel and Smith, 1995).The authors wish to express their gratitude to the anonymousreviewers who gave their time and energy to ensure the qualityof the paper.

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