Crustal Structure of Turkey from Aeromagnetic, Gravityand Deep Seismic Reflection Data

Abdullah Ates • Funda Bilim • Aydin Buyuksarac • Attila Aydemir •

Ozcan Bektas • Yasemin Aslan

Received: 5 October 2011 / Accepted: 2 May 2012 / Published online: 15 May 2012� Springer Science+Business Media B.V. 2012

Abstract In this paper, aeromagnetic and gravity anomalies obtained from the General

Directorate of Mineral Research and Exploration were subjected to upward continuation to

3 km from the ground surface to suppress shallow effects and to expose only regional, deep

sources. Then, a reduction to pole (RTP) map of aeromagnetic anomalies was produced from

the 3 km upward continued data. A sinuous boundary to the south of Turkey is observed in the

RTP map that may indicate the suture zone between the Anatolides and African/Arabian

Plates in the closure time of the Tethys Ocean. The sinuous boundary can be correlated with

the recent palaeo-tectonic maps. The southern part of the sinuous boundary is quite different

and less magnetic in comparison with the northern block. In addition, maxspots maps of the

aeromagnetic and gravity anomalies were produced to find out and enhance the boundaries of

tectonic units. Crustal thickness, recently calculated and mapped for the western Turkey, is

also extended to the whole of Turkey, and the crustal thicknesses are correlated with the

previous seismological findings and deep seismic sections. The average crustal thickness

calculations using the gravity data are about 28 km along the coastal regions and increase up

to 42 km through the Iranian border in the east of Turkey. Density and susceptibility values

used as parameters for construction of two-dimensional (2D) gravity and magnetic models

A. AtesDepartment of Geophysical Engineering, Engineering Faculty, Ankara University,Besevler, 06100 Ankara, Turkey

F. Bilim � O. BektasDepartment of Geophysical Engineering, Engineering Faculty, Cumhuriyet University, 58140 Sivas,Turkey

A. BuyuksaracDepartment of Geophysical Engineering, Canakkale Onsekiz Mart University, 17100 Canakkale,Turkey

A. Aydemir (&)Turkish Petroleum Corp., Sogutozu Mah., 2180. Cad., No: 86, Sogutozu, 06100 Ankara, Turkeye-mail: aydemir@tpao.gov.tr

Y. AslanGeological Engineering Department, Engineering Faculty, Fırat University, 23119 Elazig, Turkey

123

Surv Geophys (2012) 33:869–885DOI 10.1007/s10712-012-9195-x

were compiled in a table from different localities of Turkey. 2D models indicate that all of the

anomalous masses are located in the upper crust, and this could be well correlated with the

earthquakes which occurred at shallow depths.

Keywords Upward continuation � Reduction to the pole � Maxspots � Turkey � Crustal

thickness

1 Introduction

Turkey is mainly divided into three main tectonic units. These are as follows: (i) the

Pontides, (ii) the Anatolides-Taurides and (iii) the northern part of the Arabian Plate. The

Pontides to the north and Anatolides-Taurides to the south are separated from each other by

the Izmir-Ankara-Erzincan suture that was formed by the closure of the northern branch of

the Neo-Tethys Ocean. The northern part of the Arabian Plate at the south-east of Turkey

was separated from the Anatolides-Taurides by the southern branch of the Neo-Tethys

Ocean during the Mesozoic and Tertiary times (Sengor and Yilmaz 1981). Geological

maps of Turkey exhibit complexities, and these maps can be accessed at the official web

site of the General Directorate of Mineral Research and Exploration-MTA (

www.mta.gov.tr). Large areas are covered by the younger cover units and sedimentary

formations from Palaeozoic to Mesozoic. Volcanic, granitic and mafic–ultramafic rocks

can also be observed from the west to east of the country.

The gravity and aeromagnetic data (with 0.6 km flight altitude above the ground sur-

face) of Turkey were acquired by MTA, and maps of them were opened to the public

interest in the formal website of MTA. The gravity and aeromagnetic anomalies were

published by Ates et al. (1999) where the general characteristics and corrections applied to

the surveyed data were described. The grid interval of the anomaly maps is 10 9 10 km.

Sensitivity and resolution in these maps are suitable for the regional studies and palaeo-

tectonic features of Turkey (Moix et al. 2008; Gans et al. 2009) are consistent with the

aeromagnetic and gravity anomalies. There is no publication in the international earth

science literature about the regional tectonics of whole Turkey using the anomalies of the

potential field data. There are individual studies on the subsurface and tectonic structures

of the western, central and eastern parts of Anatolia using the same potential field data with

more frequent sampling intervals. Most of the aeromagnetic and gravity anomalies are

studied and interpreted by Ates et al. (2005), Aydemir and Ates (2006a, b), Bektas et al.

(2007), Bilim (2007, 2011), Buyuksarac et al. (2005) and Onal et al. (2008). In these

publications, crustal structure and geothermal energy potential of Turkey were also dis-

cussed. In addition to these studies, micro-block rotations were also estimated by analysing

the aeromagnetic anomalies (i.e. Bilim and Ates 1999, 2004, 2007). In general, the

aeromagnetic anomalies indicate little or no correlation with the surface geology. It is

thought that structures creating aeromagnetic anomalies are buried and only a correlation

may be found with the palaeo-sutures of Turkey. In order to observe apparent anomalies

created by deep-seated causative bodies and suppress the effect of the shallow bodies,

aeromagnetic and gravity anomalies were upward continued to 3 km above the ground

surface. The reduction to pole (RTP) transformation was applied onto the 3 km upward

continued data in this study. A sinuous boundary to the south of Turkey points out the

suture of Tethys Ocean and resembles to the palaeotectonic map of Moix et al. (2008).

Location and boundaries of the Kirsehir Block were well correlated with the seismological

findings of Gans et al. (2009).

870 Surv Geophys (2012) 33:869–885

123

The crustal thickness map of Turkey was produced from the gravity anomalies by using

an empirical equation, and the crustal thickness map was correlated with the MOHO depths

estimated from the seismic sections and previous seismological investigations that are

apparently consistent with the crustal thickness map, but there are some differences in the

Eastern Anatolia. The thicker hinterland area thinning towards the shoreline in the crustal

thickness map resembles Greenland’s crustal structure (Artemieva and Thybo 2008;

Storetvedt and Longhinos 2011).

2-dimensional (2D) magnetic and gravity models were constructed along a profile

(about 500 km long) in central Anatolia by the help of density and susceptibility contrasts.

These models were constructed using the data before upward continuation. 2D models

indicate that all masses causing anomalies are in the upper crust (i.e. bottom of the

anomalous masses are 5–6 km deep from the surface). These findings imply that active

tectonics of Turkey is shallow and all destructive earthquakes occur at relatively shallow

depths, and this is also verified by the focal mechanism solutions.

2 Aeromagnetic Data and Interpretation

Recent palaeo-tectonic reconstruction of the Turkish territory was achieved by Moix et al.

(2008). Modified Palaeo-tectonic map of them representing Permo-Trias through Cenozoic

is given in Fig. 1. Moix et al. (2008) showed that the Turkey was divided into two areas in

SW and NE, and then these two regions were assembled in the recent geological history.

This division is well illustrated with the names of several locations: Beydaglari (Bd),

Menderes (Mn) and Geyikdagi-Anamas-Akseki (Gd) in the south, and Sakarya (Sk),

Istanbul (Is), Zonguldak (Zo) and east-Pontides (eP) to the north (Fig. 1). Curvature of the

line in the middle is the sinuous boundary between the southern and northern Turkey that

will be illustrated in the following aeromagnetic anomaly and RTP maps produced within

this paper. It is well known that the interpretation of aeromagnetic anomalies is quite

difficult, because the Earth’s magnetic field and body magnetizations may cause disori-

entations on polarities of the magnetic anomalies. These disorientations can be removed

from the anomalies by the reduction to pole (RTP) transformation, and details of the RTP

transformation method in the Fourier domain are given by Blakely (1996). RTP trans-

formation correcting the polarity disorientations was applied onto the 3 km upward con-

tinued aeromagnetic anomalies (including the flight height of 0.6 km), because the surface

effects are well suppressed in the 3 km upward continued aeromagnetic map (Fig. 2). In

RTP map of Turkey (Fig. 3), it was observed that most of the polarities were corrected

successfully and aligned in the north–south direction, indicating that the remanent mag-

netization is not existent in the west and the central part of Anatolia, in contrast to the east

where polarities of the anomalies are different from the north–south direction. This situ-

ation represents the existence of strong remanent magnetization, and anomalies remain

very complex even after RTP correction was applied. The sinuous boundary is evident in

the RTP map. This boundary could be correlated with the Izmir-Ankara-Erzincan suture in

the west and Inner Taurid suture in central and eastern Anatolia (Sengor and Yilmaz 1981).

Intense magnetic anomalies are located to the north of this boundary while the magnetic

anomalies are generally weak or causative bodies are deep seated in the south (Ates et al.

1999).

A method was developed by Blakely and Simpson (1986) to identify maxima on a

contoured horizontal gradient magnitudes of magnetic or gravity anomaly data. The hor-

izontal gradient data are available on a rectangular grid, and each grid node is compared

Surv Geophys (2012) 33:869–885 871

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Fig. 1 a Palaeotectonic map of Turkey (modified from Moix et al. 2008). Arrows indicate the direction ofmovements. Bd Beydaglari, Mn Menderes, Gd Geyikdagi-Anamas-Akseki, Sk Sakarya, Is Istanbul, ZoZonguldak, eP east-Pontides, WBS Western Black Sea, EBS Eastern Black Sea, MP Mersin-Pozantiophiolites, Ay Antalya, Tp Trodos, Kb Karaburun, El Elazig-Guleman ophiolites. b Geological map ofTurkey (simplified from Bingol 1989). Mafic–Ultramafic rocks generally coincide with ophiolites

872 Surv Geophys (2012) 33:869–885

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with its nearest eight neighbours in four directions along the row, column and both

diagonals to inspect whether a maximum is present. The aim of this method is to produce a

plan view of inferred boundaries of magnetic or gravity sources. The steepest gradient will

be located directly over the edge of the body if the edge is vertical and far removed from all

other edges or sources (Blakely 1996). This method was applied to the original

45o

27o

36o

42o

200 km

nT

Black Sea

SeaMediterranean

LONGITUDE (Degree)

LA

TIT

UD

E (

Deg

ree)

Fig. 2 Upward continued (3 km) aeromagnetic anomaly maps of Turkey (600 m flight altitude is includedto the upward continuation)

45o

27o

36o

42o

200 km

nT

SB SB

Black Sea

SeaMediterranean

LONGITUDE (Degree)

LA

TIT

UD

E (

Deg

ree)

Fig. 3 Reduction to the pole (RTP) transformation of the 3 km upward continued aeromagnetic anomalies(600 m flight altitude is included to the upward continuation). Contour interval: 50 nT. SB sinuousboundary. Inclination and declination angles of the geomagnetic field are 55� and 4�, respectively

Surv Geophys (2012) 33:869–885 873

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aeromagnetic anomalies given in Ates et al. (1999) including shallow sources. Maxspots

are displayed as circles, and all circle sizes are assigned to the magnitudes of the horizontal

gradients. Locations of maximum horizontal gradient of the pseudogravity from the

aeromagnetic anomalies in Fig. 4 display significant alignments numbered from 1 to 9 that

are given in the figure caption. In addition, the southern boundary of Eastern Pontides is

also represented by the high maxima amplitudes to the NE of Turkey (parallel to the

Eastern Black Sea shoreline).

3 Gravity Anomalies and Interpretation

Upward continued (3 km) gravity anomaly map of Turkey is given in Fig. 5. Maxspots of

the horizontal gradients of the original Bouguer anomalies were also calculated in this

study. Locations of maximum horizontal gradient of the gravity anomalies in Fig. 6 display

significant alignments numbered from 1 to 9 that are given in the figure caption. In

addition, the boundary of the Miocene Adana Basin is also clear to the SE of the Tuzgolu

Basin (to the NE corner of the eastern Mediterranean shoreline).

Gravity anomalies can be used for determination of the MOHO depth. There are dif-

ferent empirical equations proposed by different authors (i.e. Riad et al. 1981; Riad and El

Etr 1985; Rivero et al. 2002; Tirel et al. 2004) to calculate crustal thicknesses from the

gravity anomalies. Most optimum relation for the crustal thickness of Turkey is the

equation given by Riad et al. (1981) as follows:

H ¼ 29:98� 0:075Dg

where H is the crustal thickness in kilometres, and Dg is the gravity anomaly values in

mGal. Initial crustal thickness map calculated with the same equation was given by

Buyuksarac et al. (2009). In their study, thicknesses were calculated by using gravity data,

Fig. 4 Maxima locations determined for the horizontal gradient of the pseudogravity anomalies ofaeromagnetic data. Sizes of circles are proportional to the amplitude of maxima. (1) Biga PeninsulaAnomaly (BPA), (2) North Anatolian Fault (NAF), (3) Suluklu-Cihanbeyli-Goloren (SCG) Anomaly, (4)Cankiri-Corum Ophiolitic Complex (CCOC), (5) Cappadocia Volcanic Complex (CVC), (6) Hatay-Iskenderun Anomaly (HIA), (7) Ecemis Fault (EF), (8) Bitlis-Poturge Massif (BPM), (9) Van Lake Anomaly(VLA)

874 Surv Geophys (2012) 33:869–885

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and there were some fluctuations, especially in the eastern and central Anatolia. This was

caused by high frequencies of near surface bodies or noise in the gravity data. In this study,

the original gravity anomaly map given in Ates et al. (1999) was filtered using various cut-

off values until obtaining similar amplitude of 3 km upward continued gravity anomaly

map given in Fig. 5. In order to estimate the top depth of the causative bodies and

determine the cut-off frequency for the low-pass filter, power spectrum analysis was

45o

27o

36o

42o

200 km

mgal

Black Sea

SeaMediterranean

LONGITUDE (Degree)

LA

TIT

UD

E (D

egre

e)

Fig. 5 Upward continued (3 km) gravity anomaly map of Turkey

Fig. 6 Maxima locations determined for the horizontal gradient of the gravity anomalies. Sizes of circlesare proportional to the amplitude of maxima. (1) Aegean Region Grabens (ARG), (2) Isparta Angle (IA), (3)North Anatolian Fault (NAF), (4) Konya Anomaly (KA), (5) Tuzgolu (Salt Lake) Basin, (6) Sivas Basin, (7)South-eastern palaeo-highs and, related fold and thrust belts, (8) North East Anatolian Fault (NEAF), (9)Van Lake Anomaly (VLA)

Surv Geophys (2012) 33:869–885 875

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applied onto the gravity data by using the method of Spector and Grant (1970). This

method is well established and used in many earth science applications (Dobrin and Savit

1988; Telford et al. 1990; Kearey et al. 2002). The low-pass filtering process was applied

before the calculation of the crustal thickness in this study. The cut-off frequency was

selected as 0.06 radian/km. Deep-seated anomalies are enhanced in the low-pass filtered

map (Fig. 7), and shallow effects were suppressed. Filtered gravity anomaly map is more

complex than the upward continued gravity anomaly map. Reasons and examples of

complexity in the filtering process were given by Kearey (1991) and Buyuksarac et al.

(2005). The crustal thickness map produced from the low-pass filtered gravity anomalies of

Turkey is given in Fig. 8, and this map indicates smooth and more accurate results.

It is possible to interpret the crustal thickness map of Turkey dividing into three regions.

In the west, crustal thickness from the shorelines to the hinterland, especially in the Aegean

Grabens varies from 26 to 34 km, respectively. In the central part, the crustal thicknesses

from the Black Sea to Mediterranean region vary from 28 km for coastal areas and

34–38 km inland (33–35 km in average). In the east, the thickness from the Black Sea to

the Arabian Block varies between 30 and 33 km, and it increases up to 43 km towards the

border between Turkey and Iran.

MOHO depth was calculated using analysis of earthquake arrival times in Anatolia by

Necioglu et al. (1981) for the first time, and they found the crustal thickness was about

25–32 km in western Turkey (Table 1). Saunders et al. (1998) calculated 30–34 km

thickness in the western Turkey by using receiver functions. In central Turkey (Anatolian

Plateau), they calculated the thickness about 38 km. Findings of Saunders et al. (1998)

were supported by Tezel et al. (2007) who found thickness about 25–40 km from western

to the eastern Turkey by using surface wave dispersion analysis (Table 1). Becel et al.

(2009) estimated the MOHO interface at about 26 km deep under the Northern Marmara

Trough by modelling of reversed Pn waves. These results are quite consistent with the

crustal thickness (about 32.5 km) calculated using gravity anomalies by Bilim (2007) in

western Turkey. Angus et al. (2006) proposed the crustal thickness varying from 30 to

55 km from western to eastern Turkey, although either of the two sketches prepared by

them does not show MOHO depth deeper than 50 km. Thickness of 30 km correlates well

with the near Black Sea coast in Fig. 6 of their study, but 55 km thickness does not seem to

Fig. 7 Low-pass filtered gravity anomaly map (Cut-off frequency: 0.06 radians/km)

876 Surv Geophys (2012) 33:869–885

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be consistent with our crustal thickness map (Table 1). Recently, Arslan et al. (2010)

investigated the crustal structure of Turkey using the gravity data, and they found the

shallowest crust as 31.4 km and the deepest crust about 50 km around the Iranian border.

These depths are higher than depths presented in this study and previous seismological

calculations. This result was possibly caused by the use of unfiltered data. More recently,

Cakir and Erduran (2011) calculated 38 km crustal thickness from the P- and S-wave

receiver function. They also calculated a depth of 350 km down to the Lower Mantle Low

Velocity Zone in central Turkey.

Deep seismic data with recording time up to 16 s were acquired near the Lake Tuzgolu

(Salt Lake) in central Anatolia by the Turkish Petroleum Corp. (TPAO) in 1987. Inline 5

vibrators were used to make a source pattern. All measures were taken to improve the

signals coming from the deep reflectors during recording and processing steps. However,

the quality of the seismic sections was not good due to geological conditions and existing

thick salt layers in near surface. Despite all difficulties, one of the seismic sections located

to the south-east of the Lake Tuzgolu was used to correlate with the results obtained in this

study. The location of that deep seismic section and the Profile AA0 that 2D magnetic and

gravity models are constructed and are shown in the aeromagnetic and gravity anomaly

maps of the Central Anatolia (Fig. 9a and b, respectively). Several horizons were observed

in this seismic section (Fig. 10a). Windowed parts between 9 and 11 s numbered from 1 to

3 were enlarged and interpreted in detail. In these windows, traces indicating a set of

horizons were marked with arrows (Fig. 10b–d). The RMS velocities at these shot points

are around 6–7 km/s. These velocities correspond to 30–35 km in depth. These depths are

well consistent with the crustal thickness map of central Anatolia (Fig. 8) produced from

the gravity anomalies and seismological MOHO depth calculations given in Table 1.

In order to create crustal models of Anatolia in N–S direction, 2D models were con-

structed on the aeromagnetic and gravity data. The location of 2D magnetic and gravity

models (Profile AA0) is illustrated in the Central Anatolian aeromagnetic and gravity

Fig. 8 Crustal thickness (CT) map of Turkey calculated from the low-pass filtered gravity anomalies shownin Fig. 7. Contour interval: 1 km

Surv Geophys (2012) 33:869–885 877

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anomaly maps (Fig. 9a, b). Available density and susceptibility data compiled for whole

Turkey (given in Table 2) were used as parameters to construct these models, the length of

the profile is over 500 km. Bodies causing magnetic anomalies are generally dike-shaped

Table 1 Significant seismological MOHO depth calculations in different parts of Turkey

Region/location Crustal thickness/MOHO depth(km)

Method References

Western Turkey 20–35 Receiver function Tezel et al. (2010)

25–32 Seismic wave velocity Necioglu et al. (1981)

Western Turkey 30–34 Receiver functions Saunders et al. (1998)

Central Turkey 38

Northern Marmara Trough 26 Seismic wave velocity Becel et al. (2009)

Eastern Turkey 30–55 S-wave receiver function Angus et al. (2006)

Arabian Platform 36 Seismological records Gok et al. (2007)

Anatolian Block 44

Anatolian Plato 48

NE of Anatolian Block 30–38

From west to eastof Turkey

25–40 Surface wave dispersionanalysis

Tezel et al. (2007)

From west to east ofTurkey

31–50 Gravity data Arslan et al. (2010)

Central Anatolia 38 P and S-wave receiverfunction

Cakir and Erduran(2011)

Fig. 9 a Aeromagnetic anomalies of central Anatolia. AA0 shows the location of the profile to be modelledfor 2-dimensional gravity and magnetic structures. The location of the deep seismic section GTRS-87-802 isalso illustrated. b Gravity anomalies of central Anatolia. AA0 shows the location of the profile to bemodelled for 2-dimensional gravity and magnetic structures. The location of the deep seismic sectionGTRS-87-802 is also illustrated

878 Surv Geophys (2012) 33:869–885

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structures (Aydemir and Ates 2006a), while the bodies creating gravity anomalies are

sedimentary basins (Aydemir 2008, 2011; Aydemir and Ates 2006b), and all causative

bodies are situated in the upper crust (Figs. 11a, b). In construction of 2D magnetic model,

anomalous bodies are considered having susceptibility values in the range of the highest

(0.0879 SI = 0.007 cgs) and the lowest values (0.0212 SI = 0.0017 cgs) according to the

data available in the north-east of Tuzgolu (Salt Lake) and Cappadocia regions, respec-

tively (Table 2). Average densities of Andesite and Basaltic rocks and Gabbro around

Cappadocia and north-northeast of the Tuzgolu (Salt Lake) were used to construct 2D

gravity model (Table 2). Then, a mean density of 2.93 g/cm3 was obtained for these

lithologies. Previously, densities of the sedimentary formations were obtained in the range

of 2.23–2.43 g/cm3. Thus, density contrasts of 0.7, 0.5 and 0.6 g/cm3 were used for the

sedimentary basins from the south to the north. Density contrast of 0.5 g/cm3 was also

justified by means of 3D modelling of the Konya Anomaly by Ates and Kearey (2000).

4 Discussions and Conclusions

There are a few references using the potential field data in the geosciences literature about

the tectonic structure of Turkey. Bilim (2007) investigated the tectonic and structural

Fig. 10 a Complete view of the seismic section. Location of the seismic section is illustrated in Fig. 9a andb. Annotated rectangles show the detailed investigated regions: b Enlarged view of part a shown in (a),(c) Enlarged view of part b shown in (a), (d) Enlarged view of part c shown in (a)

Surv Geophys (2012) 33:869–885 879

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alignments of central-western Anatolia using gravity and magnetic data. In that study, the

CPD (Curie Point Depth) map of Kutahya-Denizli and surrounding area was constructed.

Similarly, CPD map was exposed by using aeromagnetic anomalies in central Anatolia by

Ates et al. (2005). It was shown that Curie Depth (580�C) descends down to 8 km in the

central Anatolia.

Buyuksarac et al. (2005) and Buyuksarac (2007) evaluated the potential field data of

Cappadocia and central eastern Anatolia, respectively. Aeromagnetic anomalies of both

regions are complex, and block rotations were determined in the Cappadocia Region

according to the palaeomagnetic analyses. Buyuksarac et al. (2005) suggested that an

uplifted magmatic intrusion created the widespread volcanic activity in the Cappadocia

region. Genc and Yurur (2010) suggested that this uplift could not only be explained by a

magmatic intrusion, but there should have been a hot and low-density asthenospheric

material emplacement. If it is correct, this asthenospheric uplift may be a hot spot by

definition as given by Kearey et al. (2009). Tectonic trends of central eastern Anatolia are

aligned in the similar directions with the East Anatolian Fault Zone. East–west disorien-

tations in the deep-sourced aeromagnetic anomalies of the Cappadocian region are

determined at 30� in the counter clockwise direction in central Anatolia (Buyuksarac et al.

2005) which is consistent with the mobilistic system (Storetvedt 2003). The mobilistic

theory was also supported with the palaeomagnetic data (Gursoy et al. 1997, 1998; Piper

et al. 2010) and GPS measurements (McClusky et al. 2000). Bilim and Ates (2007)

investigated the effect of remanent magnetization and the rotations of geologic causative

bodies in the northern central Anatolia with the application of a new method developed by

them. Their method depends on the correlation between the analytic signal of magnetic

anomalies and the horizontal gradient of pseudogravity data using correlation coefficients.

They found that almost all anomalies include remanent magnetization and proposed the

existence of rotating micro plates in a gear mechanism.

The most obvious, linear aeromagnetic anomaly in central Turkey which is named as

the Suluklu-Cihanbeyli-Goloren Anomaly (Aydemir and Ates 2006a) extends in NW–SE

direction along the western margins of the Tuzgolu (Salt Lake) and Haymana Basins

(Aydemir 2008, 2011). It was modelled in 2D with a proposal of a geological model that

explains tectonic setting and evolution of a causative magmatic intrusion (Aydemir and

Ates 2006a).

Table 2 Density and susceptibility values of significant rocks in Turkey

Location Rock type Density(g cm-3)

Susceptibility 9 103

SISamplenumbers

References

North-east of SaltLake

Gabbro 3.02 87.9 13 Ates and Kearey(2000)Granit 2.71 6.3 11

Sandstone 2.72 1.0 14

Cappadocia Andesites 2.9 21.2 115 Buyuksarac et al.(2005)Basalts

North of SaltLake

Andesites 2.63 – 6 Ozturk (1997)

Gabbro 3.07 – 13

Inner East (SivasBasin)

Ofiolites 2.80 3.0 3 Onal et al. (2008)

Sandstones 2.47 0.0 3

Gypsum 2.35 0.01 3

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Bektas et al. (2007) investigated regional geothermal characterization of East Anatolia

using aeromagnetic, gravity and heat-flow data where the topography and crustal thickness

increase from the west to the east. It was suggested that topographically higher regions can

be correlated with the aeromagnetic anomalies because of the magnetic nature of the

volcanic rocks on the surface. Low-pass filtering was applied onto the aeromagnetic

anomalies to remove topographical effects. They also calculated CPD values from the low-

pass filtered aeromagnetic anomalies and applied total gradient method to the high-pass

filtered anomalies. They suggested that high-amplitude total gradient anomalies extended

from the Black Sea shoreline through the north of Erzincan and down to the west of the

Van Lake may be correlated with the ophiolitic rocks on the surface, but are not correlated

with the locations of the hot springs and volcanic formations. In a similar way, Bilim

Fig. 11 a Magnetic profile AA0 shown in Fig. 9a with interpreted model, b Gravity profile AA0 shown inFig. 9b with interpreted model. Numbers indicate susceptibility and density contrast of the anomalousbodies

Surv Geophys (2012) 33:869–885 881

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(2011) studied the Galatien volcanic complex in the northern central Turkey, recently. She

studied the thermal structure of the Galatien volcanic complex and found low CPD-high

heat-flow values in the region.

In conclusion, aeromagnetic anomalies of Turkey are quite complex, and they cannot be

correlated with the surface geology implying that causative sources are deep seated.

Aeromagnetic anomalies thus, first upward continued and then processed with the tools

like RTP (Fig. 3), display a good correlation with the sinuous boundary in the palaeo-

reconstruction map of Turkey (Fig. 1). Investigations of the aeromagnetic anomalies in the

western Anatolia are very useful to indicate shallow heat-flow transfer zones caused by the

segmented African lithosphere beneath the Anatolian region as inferred from the telese-

ismic P-wave tomography (Biryol et al. 2011). In the eastern Turkey, shallow heat-flow

sources are related with the individual young volcanic masses. Earthquake data are well

correlated with the aeromagnetic anomalies and earthquakes with magnitudes bigger than

7.0 which are located near the major faults in NW Turkey (Ates et al. 2008; 2009). We

suggest that the aeromagnetic anomalies of Turkey were shaped during the palaeo-suture

occurrence.

Regional gravity anomalies reflect density variations of subsurface structures. In gen-

eral, contour values decrease from west to the east in Turkey. Most of the crustal structures

are well correlated with the previous, detailed gravity and magnetic investigations, sup-

porting earlier findings of hydrocarbon exploration studies. Sedimentary basins are clearly

apparent. Particularly, central Anatolian (Aydemir 2008, 2011; Aydemir and Ates 2006b)

and Thrace Basins (Demir et al. 2012) are outstanding basins. This geophysical evidence

could be well correlated and support the previous geological findings (Sengor and Yilmaz

1981). Spatial correlation was performed with the seismological study of Gans et al.

(2009). For instance, approximate boundary of the Kirsehir Block (massif) was exposed

clearly. However, most of the apparent anomalies were removed in the low-pass filtered

map (Fig. 7) that was obtained by using 0.06 radian/km cut-off frequency. Smooth low-

pass filter map indicates that most of the causative bodies in Turkey are shallow and they

are not related with the deep-seated bodies. This result is considered that causative bodies

are generally young and produced from the active tectonics throughout the geological

history. Crustal thickness map calculated from the gravity anomalies indicates that the

crust is thicker in Turkey in comparison with the normal crustal thickness (about 30 km).

The crustal thickness map was well correlated with the previous seismological MOHO

depth calculations. Furthermore, MOHO depth of 35 km obtained from a deep seismic

section in central Turkey can also be well correlated with the crustal thickness map. In

general, shorelines of Anatolian Peninsula and the European part of Turkey are thinner

than the hinterland. This situation is similar to the example of Greenland. In that region, the

thick continental crust thins through shorelines where it is delaminated by the thin oceanic

crust on three sides (Labrador Sea/Baffin Bay and North Atlantic) (Artemieva and Thybo

2008; Storetvedt and Longhinos 2011).

It is clear that there are two magnetised domains in aeromagnetic anomalies. One of

them is in the north with strong anomalies, the other one is in the south with subdued

anomalies. This partition gives a good consistency and is well correlated with the latest

palaeotectonic map of Moix et al. (2008) who define a sinuous suture in the middle of

Turkey along the east–west direction. This tectonic trend is in line with the GPS velocity

study of McClusky et al. (2000). Reilinger et al. (2006) also showed counterclockwise

tectonic swing from Nubia (Africa) via Arabia, Iran, along Turkey, before ending in a

south-directed tectonic front along the Aegean Arc. Those observations are consistent with

the east–west regional mobilistic system of Storetvedt (2003). Inertia-driven Alpine

882 Surv Geophys (2012) 33:869–885

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lithospheric rotations (counterclockwise for Africa and clockwise for Eurasia) turn the

intervening tectonic belt into an overall transpressive belt. Apparently, this produced an

E-W shear along Turkey. Palaeomagnetic evidence for this system was also outlined by

Storetvedt (1990). In addition, the counterclockwise rotation of Africa is also demonstrated

by the marked swing in the Pelusium Megashear System across Africa (Neev et al. 1982).

Maximum horizontal gradient method (Blakely and Simpson 1986) was applied to the

aeromagnetic and gravity anomalies, and the maxspots maps were obtained. In aeromag-

netic maxspots map, the Suluklu-Cihanbeyli-Goloren Anomaly (Aydemir and Ates 2006a)

and edges of several other significant structures are very clear. In a similar way, North

Anatolian and Ecemis Faults (Aydemir 2009) are also evident.

In central Anatolia, 500 km long, 2D aeromagnetic and gravity models in N–S direction

were constructed. These models indicate that all of the anomalous masses are in the upper

crust. Beneath the upper crust down to MOHO discontinuity appears to be homogenous. In

Turkey, destructive earthquakes occur at shallow depths (i.e. at about 8–10 km, http://

www.deprem.gov.tr), and this is consistent with the aforementioned results. In conclusion,

we suggest that the active tectonics events of Turkey at the upper crust are fault controlled,

because deep structure of Turkey is different than the earthquake distribution.

Acknowledgments Authors are grateful to the General Directorate of Mining Research and Exploration ofTurkey for the provision of gridded aeromagnetic and gravity data that were used for a Turkish ScientificResearch Council (TUBITAK) and European Scientific Exchange Program (ESEP) during 1997. Ourkindest thanks go to Prof. Karsten M. Storetvedt and Dr. M. Nuri Dolmaz for their comprehensive anddelicate review of this paper. We also thank Prof. Rycroft for the editorial handling of our paper. Reductionto the Pole transformation map was produced by using GEOSOFT-OASIS software. Seismic sections usedin this study were provided by the General Directorate of Petroleum Affairs for a Cumhuriyet UniversityScientific Research Project (Project No: CUBAP M-394). This research was also granted and supported byTUBITAK (Project No: 107Y288).

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