GeolCarp_Vol70_No3_193

GEOLOGICA CARPATHICA

, JUNE 2019, 70, 3, 193–208

doi: 10.2478/geoca-2019-0011

www.geologicacarpathica.com

Deformation patterns in the Van region (Eastern Turkey)

and their significance for the tectonic framework

M. ALPER ŞENGÜL

, ŞULE GÜRBOĞA



, İSMAİL AKKAYA

and ALİ ÖZVAN

Istanbul University, Institute of Natural and Applied Sciences, Department of Geological Engineering, Campus Avcılar, 34320 İstanbul, Turkey

General Directorate of Mineral Research and Exploration, Department of Marine Researches, Dumlupınar Boulevard, no:139,

06800 Çankaya/Ankara, Turkey;



sule.gurboga@gmail.com

Yüzüncü Yıl University, Institute of Natural and Applied Sciences, Department of Geophysical Engineering, Bardakçı Street, 65090 Van, Turkey

Yüzüncü Yıl University, Institute of Natural and Applied Sciences, Department of Geological Engineering, Bardakçı Street, 65090 Van, Turkey

(Manuscript received September 26, 2017; accepted in revised form March 25, 2019)

Abstract: The area of investigation is located on the south-eastern shore of Lake Van in Eastern Turkey where a destructive

earthquake took place on 23

October, 2011 (Mw = 7.1). Following the earthquake, different source mechanisms,

deformations, and types of faulting have been suggested by different scientists. In this research, Edremit district and

vicinities located on the southern side of Van have been investigated to understand the deformation pattern in a travertine

(400 ka) formation on the surface, and its structural and stratigraphic relationships with the main faults under the surface

by using two-dimensional (2D) Electrical Resistivity Tomography (ERT) profiles. The results were used to document

the deformation pattern of rocks with the Miocene and the Holocene (400 ka travertine) in ages. By means of

the investigations, deformation patterns implying the tectonic regimes during the Oligocene–Miocene–Pliocene, and

Quaternary time have been determined. According to detailed field work, the local principal stress direction has been

defined as approximately N 35° W. This is also supported by the joint set and slip-plane data. Moreover, Oligocene–

Miocene units provide a similar principal stress direction. Our data suggest that the southern part of the Elmalık fault is

characteristic of reverse faults rather than of the normal fault system that has been previously reported. In addition,

the Gürpınar fault controlling the deformation patterns of the region is a reverse fault with dextral component.

Keywords: deformation pattern, travertine, Van–Edremit area, Eastern Turkey.

Introduction

The Arabian (from south to north) and Eurasian (from north to

south) plates move towards each other at a relative rate of

15–20 mm/yr. Eastern Anatolia has been squeezed between

these two mega-plates and enormous tectonic activity has

been manifested (Şengör & Yılmaz 1981; Şengör et al. 1985;

Dewey et al. 1986; Koçyiğit et al. 2001; Oruç et al. 2017). This

tectonic activity has caused the formation of a number of

faults, complex structures and a very strange plateau, which

have been reported by many scientists (Ketin 1977; Aksoy &

Tatar 1990; Koçyiğit et al. 2001; Örçen et al. 2004; Dhont &

Chorowicz 2006; Şengör et al. 2008; Üner et al. 2010;

Koçyiğit 2013). The studies have some controversial results

related to fault types, current tectonic regime, and deformation

patterns. In addition, the most recent events of 23

October,

2011 Van earthquake (Mw = 7.1) and 9

November, 2011

(Mw = 5.7) earthquakes by having its epicentres located on

Edremit (Van) district have encouraged these discussions.

After the earthquakes, some national and international resear-

chers have been attracted to the area to investigate different

characteristics of the places and recent earthquakes (Özkaymak

et al. 2011; Koçyiğit 2013).

The faults giving rise to the 2011 main shock were not

known until the two main earthquakes and were not indicated

on the active fault map of Turkey by Şaroğlu et al. (1992).

On the other hand, Ambraseys & Finkel (1995) reported that

many disastrous earthquakes around the Province of Van are

known from historical records. One of them was the 1646

earthquake that caused significant loss in the Hoşap–Van

region. A huge number of medium to small-sized earthquakes

have also been recorded in and around Van city in the instru-

mental time.

The existences of active faults and their effect on the Oli-

gocene–Quaternary units are the main target in recent study.

Some of them have been reactivated and led to the occur-

rence of devastating earthquakes. The study of these faults

and deformations of units in different ages could indicate

the types of tectonic regimes and deformation in the aforesaid

units.

In the content of this paper, two main subjects have been

investigated: (1) geological and geophysical field data to

describe the types of active faults that are the source of strong

earthquakes, because there is a controversial issue about

the types of fault in the study area, and (2) to study the defor-

mation style of the Late Quaternary aged travertine to define

the deformation style during the neotectonic period and

the com parison of the results with Oligocene–Miocene units.

It is the only way to understand the older and younger defor-

mation patterns around Van city.

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Geological settings

Tectonic significance

The Van region and its surroundings are located on the nor-

thern side of the Bitlis–Zagros Suture Zone (BZSZ) in the East

Anatolian–Iranian Plateau, which has been formed from

the collision between the Eurasian and Arabian Plates in

the Late Miocene (Şengör & Kidd 1979; Şengör & Yılmaz

1981). The Anatolian Plate has two mega shear fault systems

with dissimilar sense of motion in lateral direction, dextral

North Anatolian Fault (NAF) and sinistral East Anatolian

Fault (EAF). These two structures join with each other around

Karlıova Triple Junction (KTJ) in Eastern Anatolia (Fig. 1).

Different ideas have been proposed about their initiation

ages and the initiation of the neotectonic period. The move-

ment of the Arabian Plate towards the Eurasian Plate occur-

ring along the BZSZ has been continuing from the Serravalien

(~12 Ma) to the present (Şengör & Yılmaz 1981). On the other

hand, the initiation age of a strike-slip faulting-dominated

neotectonic regime is proposed as Pliocene represented by

N–S compressional axis (σ

) (Koçyiğit et al. 2001; Dhont &

Chorowicz 2006; Gürboğa 2015). Not only the initiation of

the neotectonic period in Eastern Anatolia, but also the types

of faults have been discussed in literature. Göğüş & Pysklywec

(2008) claim that the lithospheric thinning is the main process

in Eastern Anatolia that results in plateau uplift, heating, and

syn-convergent extension resulted from the delamination of

the mantle lithosphere and the sites of contraction are only in

the northern and southern margins. The Kağızman, Tuzluca,

Hınıs, Karlıova, and Muş are located in extensional basins that

have been controlled by E–W trending normal faults. Thus,

the extension has been reported as the syn-convergent exten-

sion (Göğüş & Pysklywec 2008). In contrast, the nature of

both geological features and their deformation style detected

in the East Anatolian Plateau are related to strike-slip motions

triggered by transpressional regime (Koçyiğit et al. 2001;

Dhont & Chorowicz 2006). For example, sinistral strike-slip

fault zones are named as the Horasan, Digor, Kağızman,

Başkale, Posof; dextral strike-slip fault zones as the Pambak–

Sevan, Salmas, Çaldıran, Erciş and the Yüksekova, and

the Muş–Gevaş thrust to reverse fault zones (Arpat et al. 1977;

Koçyiğit et al. 2001; Şaroğlu & Yılmaz 1986; Şaroğlu et al.

1987; Cisternas et al. 1989; Rebai et al. 1993; Dhont &

Chorowicz 2006; Horasan & Boztepe-Güney 2007). Global

positioning system (GPS) has indicated 18±2 mm/year in

the N 24

W direction for the Arabian Plate in the south of

BZSZ and that this north-westward motion of the Arabian

Plate is mostly transmitted to Eastern Anatolia (McClusky et

al. 2000; Reilinger et al. 2006; Utkucu 2013).

Seismicity of the region

The Lake Van Basin and its surroundings have a number of

faults that play important roles in the deformation of the area

and the occurrence of earthquakes (Ambraseys & Finkel 1995;

Fig. 1. a — Location map of Eastern Turkey. ASFS: Akşehir-Simav Fault System, BZSZ: Bitlis-Zagros Suture Zone, CAFS: Central Anatolian

Fault System, EAFS: East Anatolian Fault System, IEFS: İnönü-Eskişehir Fault System, NAFS: North Anatolian Fault System; b — simplified

tectonic map of East Anatolian–Iranian Plateau and adjacent areas (modified from Koçyiğit 2013) and E: Erciş, KF: Kağızman fault zone,

MGFZ: Muş-Gevaş thrust to reverse fault zone, TF: Tutak fault, VFZ: Varto fault zone. Locations of Figs. 1b, 2 and 3 are inserted on the map.

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Guidoboni et al. 1994). From the historical and instrumental

records, earthquakes with various magnitudes have been

recorded.

Historical earthquakes

The intensity of historical earthquakes has a range between

I = V to X (Fig. 2, Table 1). Some of these earthquakes caused

damage and loss of lives (Ambraseys & Finkel 1995).

The records indicate earthquakes and their destructive results

in the years 1101, 1646, 1715, and 1881 A.D. although there is

no information about the earthquake source. For example,

the 1646 earthquake has a I = X value, but the location of its

epicentre is not clear. The areas near Gevaş and Gürpınar in

the west and Hoşap through east and all rural areas that remain

at its west along E–W trending were affected (Ambraseys &

Finkel 1995) (Fig. 2). It is strongly probable that the Gürpınar

Thrust Fault is the source of this event. No damage was

reported on the southern side of the fault (foot-wall block).

Another example is the A.D. 1101 earthquake. It caused

damage in Van city and its surrounding areas and formed wide

fractures on the surface (Erdem & Lahn 2001). The source

fault of this earthquake is also uncertain and this can be asso-

ciated with the thrust faults cited in literature (Erdem & Lahn

2001).

Instrumental earthquakes

The most recent earthquake that caused the damage and

loss of life around Van was the Tabanlı (Van) earthquake of

October, 2011. Another one sourced from the Çaldıran

Fault is the Çaldıran earthquake that took place in 1976 with

the magnitude of M = 7.3. The earthquake resulted from a dex-

tral strike-slip fault and 380 cm displacement at the surface

has happened (Arpat et al. 1977). After the earthquake, sha-

king activity continued in the area in 1976 and 1977 and many

of the faults were reactivated. However, the magnitudes of

the aftershocks remained around M = 5.5. The Çaldıran

earthquake did not affect Van city and nearby villages much

and it mostly caused damage in the northern sections.

Fig. 2. Epicentres of historical (green points) and instrumental (red points) period earthquakes around Lake Van (earthquakes from KOERI

2009, 2011 and active faults from Emre et. al. 2013). Yellow and blue stars indicate the epicentral location of the 23

October, 2011 Van earth-

quake and Çaldıran earthquake, respectively.

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The earthquakes that affected Van city and the study area are

M = 5.4 in 1988, M = 5.3 in 2000, and M = 4.7 in 2001. These

earthquakes did not cause any destruction around the Lake

Van area (Fig. 2). The focal mechanism solutions of the events

indicate that they are related to reverse faulting with strike-slip

component (KOERI 2009).

To understand the structures that gave rise to the earthquake,

the distribution of aftershocks belonging to the Tabanlı earth-

quake should be examined. The epicentre of this earthquake

has been given as around the Edremit district and the general

trend is N–S direction. Moreover, left lateral strike-slip move-

ment is the characteristic feature (Koçyiğit 2013). On the other

hand, both the earthquake distributions and the acceleration

values indicate that the earthquake resonance was closer to E–W

directions than N–S directions (Poyraz et al. 2011; Şengül et

al. 2012). Except for this earthquake, no earthquake with

a magnitude of more than M = 4 has happened in the research

area and its surroundings. According to our field work, we

defined and mapped some main faults. When the trace of

faults could not be seen at the surface, ERT profiles were used

to understand the structure beneath the surface.

Stratigraphic outline

There is diversity in types and ages of rock units around

the Lake Van region ranging from Paleozoic to Holocene.

The region consists of metamorphic rocks of the Bitlis Massif

in the south, Upper Cretaceous ophiolites in the east, and

Cenozoic marine sediment on the southern shore of Lake Van.

Detailed unit description is not the scope of the current study,

but a short description has been given below. The formations

that outcrop in the southern part of Lake Van are the Bitlis

Massif, Yüksekova Complex, Lake Van Formation, Edremit

Travertine, and recent sediments (Aksoy 1991; MTA 2007;

Koçyiğit 2013). The Lake Van Basin is underlain by Upper

Paleozoic rocks in the south, the Campanian–Maastrichtian

Yüksekova Complex in the north-east, the Oligocene–Miocene

Van Formation consisting of conglomerate, sandstone, clay-

stone, and limestone intercalation with turbidites, the Pliocene

Kurtdeliği Formation composed of red conglomerate, sand-

stone, claystone alternation in the east, and Quaternary traver-

tine, fluvial–lacustrine clastic rocks in the east of Lake Van

(MTA 2007; Acarlar et al. 1991). The Late Paleozoic basement

consists of marble, recrystallized limestone, amphibolite,

quartz–amphibole schist, and actinolite schist. The Yüksekova

Complex consists of a mixture of various calc–alkaline volca-

nites, deep sea pelagic limestone to radiolarite–radiolarian

chert, mudstone, greywacke, and all-sized tectonic slices of

pillow lava, diabase, gabbro, and serpentinized peridotite

derived from both the oceanic crust and uppermost mantle

(Perinçek 1978). The formations that outcrop in the study area

are the Van Formation, Kurtdeliği Formation, Edremit Traver-

tine, and the Lake Van Formation (Fig. 3). The Van Formation

tectonically overlies the Plio–Quaternary colluvium units.

It consists of sandstone, marl, claystone, and conglomerate.

The target rock unit, which has been observed on the southern

side of Edremit settlement is the Edremit Travertine. The for-

mation is located between the Oligocene-Miocene Van Forma-

tion and Quaternary Lake Van Formation in the study area and

is bordered by the Gürpınar and Elmalık thrust faults (Fig. 3).

The deformation patterns of the area during the neotectonic

period can be observed in the Edremit Travertine, which has

Table 1: List of historical earthquakes which occurred around the Lake Van Basin (KOERI: Kandilli Observatory and Earthquake Research

Institute 2009, 2011).

Latitude

Longitude Date

Location

Reference

869

6.5

Erivan

KOERI

38.47

43.3

1101

Van

Ergin et al. 1967

38.47

43.35

1111

6.6

Van

Erdem & Lahn 2001; Ergin et al.1967; Soysal et al. 1981; Tan et al. 2008

38.7

42.5

1208

6.5

Ahlat–Van–Bitlis

Tan et al. 2008

38.74

42.5

1245

VII

Ahlat–Van–Bitlis–Muş

Ergin et al. 1967; Soysal et al. 1981; Tan et al. 2008

38.8

42.5

1275

6.8

Ahlat–Van

Tan et al. 2008

38.9

42.9

1276

VII

Ahlat–Erciş–Van

Ergin et al. 1967; Soysal et al. 1981; Tan et al. 2008

38.9

42.9

1282

Ahlat–Erciş

Soysal et al. 1981; Tan et al. 2008

38.6

42.3

1439

Van–Bitlis–Muş

Ergin et al. 1967; Soysal et al. 1981; Tan et al. 2008

38.35

42.1

1441

VIII

Van–Bitlis–Muş

Ergin et al. 1967; Soysal et al. 1981; Tan et al. 2008

38.3

43.7

1646

6.7

Van

Ambraseys & Finkel 2006; Tan et al. 2008

39.15

1647

6.5

Van–Tebriz–Bitlis–Muş Soysal et al. 1981; Tan et al. 2008

38.47

43.3

1648

6.8

VIII

Hoşap–Van

Soysal et al. 1981; Ambraseys & Finkel 2006; Tan et al. 2008

39.1

43.9

1696

6.8

Van

Tan et al. 2008

38.47

43.65

1701

VII

Van

Ergin et al. 1967; Soysal et al. 1981; Ambraseys & Finkel 2006; Tan et al. 2008

38.47

43.65

1704

VII

Van

Ergin et al. 1967; Soysal et al. 1981; Ambraseys & Finkel 2006; Tan et al. 2008

38.4

43.9

1715

6.6

VII

Van–Erciş

Ergin et al. 1967; Soysal et al. 1981; Ambraseys & Finkel 2006; Tan et al. 2008

43.7

1791

Van–Tebriz–Erzurum

Ergin et al. 1967

38.5

43.4

1871

6.9

VII

Van

Ergin et al. 1967; Soysal et al. 1981; Tan et al. 2008

38.75

42.3

1881

7.3

Van–Bitlis–Nemrut

Soysal et al. 1981; Ambraseys & Finkel 2006; Tan et al. 2008

38.5

43.3

1881

VII

Van and Nemrut region Ergin et al. 1967

38.4

42.1

1884

6.1

Van

Ergin et al. 1967; Soysal et al. 1981

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been was dated to 400 ka years (Degens et al. 1978). The traver-

tine deposit is 50–70 m thick and is observed mostly between

Edremit and Gevaş settlements (Fig. 3). It was first studied by

Valeton (1978) and then mapped and named by Acarlar et al.

(1991) as the Edremit Travertine that is extremely fissured,

brecciated, and faulted (Örçen et al. 2004). Charac teristics of

the current and active deformation in the travertine were

revealed by the position of the layer and joint systems.

In the scope of this, bedding and joint measurements have

been realized within the study area and the active stress state

have been determined.

Methodology

In the scope of this study, geological mapping, fault-slip

data, and identification of sub-surface structures by Electrical

Resistivity Tomography (ERT) study have been applied.

To be more specific, these methods meant: (a) geological map-

ping to identify the spread of units and their stratigraphic asso-

ciations; (b) deformation forms of faults and units to clarify

the types of tectonic regimes; (c) measurements from bed-

dings, joints (the program “DIPS” was used), faults’ slip data

(the program “Win-Tensor” was used) to reveal the dominant

stress distribution on the area and their differences; (d) to eva-

luate and recognize the types of faulting; (e) ERT images

have been used to see the continuation of the faults under

the surface.

The first two methods have been applied during the field-

work and geological mapping. The third and fourth ones are

numerical approaches for the kinematics of the structures. By

using the measurements from beddings and joints sets, their

dominant directions and rose diagrams have been determined

with the program “DIPS”. Thus, fault-slip data were analyzed

by using the Win-Tensor program with P–T–B method to deter-

mine the size and orientation of the principle stress directions.

In this program, principal stress directions have been defined

for each fault separately and at least 3 measurements are

required. During the field study, limited slip plane data could

be found. Thus, the same measurements were used for one

fault. In this case, only one plane was seen in the stress

diagram.

The last method is the ERT method used to understand

the sub-surface structures. It is used most widely on geophy-

sical investigations that has been applied successfully in deter-

mining the fault zone under the surface (Demanet et al. 2001;

Caputo et al. 2003, 2007; Wise et al. 2003; Colella et al. 2004;

Rizzo et al. 2004; Nguyen et al. 2005; Giocoli et al. 2008;

Fazzito et al. 2009). The ERT method is one of the methods for

verifying discontinuations under the surface. In our study area,

six short cross-sections 2D ERT profiles have been conducted

across and near the active faults. Geoelectrical data have been

collected using a Super Sting R8/IP/SP with 84 electrodes

instrument. Measurements of the apparent resistivity have

been realized using the dipole–dipole (DD) and/or Wenner–

Schlumberger (WS) configuration. Different electrode spacing

was used for the resistivity measurements collected within

the study area. Processing of the geoelectrical data pseudo sec-

tion has been accomplished using the Earth Imager provided

by the AGI Advanced Geosciences modelling software so as

to achieve the 2D resistivity data inversion software. Some

parts of major faults that could not be seen on the surface have

been determined by the ERT images. It has been applied on

the probable fault to verify its continuation under the surface.

These methods provided new field data which led to precise

findings about the controversial issues.

Fig. 3. Geological map of the study area indicating the Edremit Travertine and main features (modified from MTA 2007).

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Interpretations

Structural analysis

Beddings

The travertine deposits predominantly strike in the NE–SW

with their dip north-westward (Fig. 3). It seems that the bed-

ding planes indicate a scattered pattern at the study area and

main trend is determined by the WNW and the range of their

dip angles are 5

–30

southward (Fig. 3). It is thought that

the differences in the direction and dip angles have formed as

a result of paleotopography during the formation of the traver-

tine and/or as a result of the tilting linked with the com-

pression. The E–W trending layers have been formed during

the north- vergent thrusting. The SW dipping beds in the southern

part of the area are related to the Gürpınar Thrust Fault and

initial depositional conditions that indicate approximately

NE– SW directed compressional axis. After the plotting,

the dominant compression direction is NE–SW with NW-

dipping (Fig. 4a).

Analysis of joints

The initial phases of buckling/bending of a layer resulted in

open folds with a fixed wavelength/thickness proportion.

During this process, different trending joints could be formed

in further stages depending on the thickness of bed, lithology

and additional mechanisms (Bayly 1971, 1974; Bhattacharya

1992). Thus, some time-based distinctions in the distribution

of joints and fissures during the folding (compression) depend

on rheology for shallow crustal conditions. The development

of fracture and joint patterns and distribution can radically

change the rheology and mechanism of the forces (Ismat &

Mitra 2005). In the mature periods of deformation, penetration

of joints and fractures are the main components that control

the deformation. From this result in the literature, it can be

said that the different periods of deformation yield various

joints and/or folding depending on the rheology. In many

parts of our study area, joints that are crossing rigidly to

each other have been observed (Fig. 5). The existence of

joints with many different directions has been determined.

The joints have dominantly been measured in the N 10º E

and N 10º W tren ding. Moreover, two different trends in N 75º E

and N 75º W have been measured. The first order set is in

the approximately N 10º W direction and repeating at average

100–300 cm distances. The second set is perpendicular to

the first joint set in the NW-SE direction and with the wider

distances compared with the first one. Even though a third

joint set has been observed in the direction of NE–SW,

field observation indicated that there is a high correlation

between the third joint set and the second sets. Thus, these

Fig. 4. Rose diagram and stereographic projection of bedding (a) and joint sets (b) in the Edremit Travertine. Approximate contraction force

operating in the NW–SE direction. Fold axes have NE–SW-trends and a small amount of plunge. A rose diagram depicting the orientations of

ground fractures measured in the field.

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planes have been evaluated together with the second set

(Fig. 4b).

Fault-slip analysis

There are some active faults, which deform the Edremit

Travertine that have been handled in detail in the scope of this

study. Some of these faults have been mapped in the previous

studies (Özkaymak 2003; Koçyiğit 2013). These faults have

been observed in the northern and southern section of

the Edremit Travertine as strike-slip and reverse faults, respec-

tively. The existence and kinematics of these faults is impor-

tant because of the young age (400 ka) of the Edremit

Travertine. It gives chances to compare the active faults,

which intersect the travertines and older faults, that occurred

only in the Miocene deposits. If there is any difference between

their characteristics, it can be evidence for tectonic regime dif-

ferentiation. For example, the Oligocene–Miocene Van For-

ma tion is located under the travertine and it is deformed by

reverse to thrust faults. The faulting within this area can

be associated with the compression tectonic regime after

the Miocene (Koçyiğit et al. 2001). These faults have the same

character as the large scale reverse / thrust faults bordering

the south and east of the study area (Fig. 6). The main

faults that have been suggested in this research are named

the Erdemkent, Elmalık, Gürpınar, and Çiçekli faults.

Together with the NE–SW trending beddings, the joints

standing in ~ E–W directions and slip-plane data from the fault

surfaces, we detected the orientation of a compressional

axis with an approximately NW–SE direction. Depending on

the strike of fault, different types of faulting have been

observed in the field. Slip plane measurements at diagrams 3,

4, 5, and 6 indicated dominantly reverse faulting with no or

only minor strike slip component (Fig. 6). On the other hand,

strike slip faulting with a minor amount of reverse component

(diagram 1 in Fig. 6) and normal faulting with strike slip com-

ponent (Fig. 6) in the releasing part of the faults could be

observed in the study area.

ERT analysis

The morphological expressions of some faults could not be

followed clearly on the surface. In those cases, geophysical

methods are used to define the structures. In our study area,

six ERT profiles were obtained with the order ERT-1 from

the Erdemkent, ERT-2, 3, and 4 from Elmalık, ERT-5, and 6

from Gürpınar faults. The results of these profiles are given in

Fig. 7. Subsurface resistivity views from related fault sections

clearly indicate the location of discontinuations. ERT-1 shows

that the Erdemkent fault is not interrupted as it is seen at

the surface. Moreover, ERT-2 obtained in front of the Elmalık

fault indicates the existence of some small scale faults.

Active faults

Erdemkent fault

The Erdemkent fault has been named in this study. Its name

comes from the settlement just on the SE of the fault. The fault

is clearly observed within the Edremit Travertine Unit (Fig. 8)

and its dip direction is N 80º W, 82º. This fault, that has been

observed at the less resistant, shrub type travertine levels, is

a left lateral strike slip fault with a minor normal component

(Fig. 9). The displacement is about 30–40 cm at the travertine

layers that have been observed through fault zone among

the crashes and split offs (Fig. 8).

The southern half of the fault was mapped by Özkaymak

(2003). During our field work, the northern continuation of

the fault was observed and mapped. The southern part of

the fault plane is measured in N 110º E, 85º. It is uncovered in

a stone quarry operated by Edremit Municipality. The slicken-

line was measured N 30º E trending with a plunge of 64º SE

(Table 2). A breccia zone about 5 m thick is observed in

the fault zone (Fig. 9). Left lateral strike-slip faulting with

a normal component has been analyzed from the slickenlines

(Table 2).

Because of the slip data differences, the fault has two diffe-

rent motions, but the results of field observation suggest that

they could be connected under the surface. Thus, determina-

tion of subsurface investigation by means of ERT survey has

proved that these two faults are joined to each other that as

the same with fault surface observation. The ERT-1 profile is

placed to the north of the Edremit settlement (Fig. 6). 126 m

long dipol–dipol (DD) array has been used, with 84 electrodes

divided by 1.5 m. A maximum depth of 35 m has been

modelled (Fig. 7a). The ERT-1 profile has been measured in

the NW–SE direction that is perpendicular to the fault.

The root mean square relative (RMS) error between the mea-

surement and calculated apparent resistivity is small (3.55 %)

implying that these interpretative results are good. The ascent

has a small topographic relief and it is located at a distance of

36 m. The inverse model is consistent with the travertine unit.

According to the figure, a weak strength travertine has been

determined at about 10 m, suggesting that the low resistivity

region in this part of the cross-section includes the space from

Fig. 5. Field photography of travertine showing two joint sets and

bedding planes. Location of field photograph is given in Fig. 3.

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place to place. Under this part of the cross-section, resistivity

values are increasing with depth. The high resistivity amounts

have been characterized by strong travertine because of

the massive internal feature. Even, the slip data indicates dif-

ferent motion types; these two faults are actually a single fault.

The reason for the differences is the various trend amounts

of northern and southern parts of the faults connected with

a buckling.

Elmalık Reverse fault

There are many discontinuity planes inside the Oligocene–

Miocene aged Van Formation, which lie under the travertine

formation. One of the most important structures is the Elmalık

Reverse fault observed in the channel diggings with the strike

and dip NW–SE and reverse character (Fig. 10) near Lake Van.

This fault starts in a N–S direction from the south side of

the Haramigediği Valley, at its middle part after a bend it

continues in a NW–SE trend up to the shore of Lake Van

(Fig. 11a). This plane, dipping to the east, has developed inside

the Oligocene–Miocene Van Formation. The Elmalık Reverse

fault displaces the Gürpınar reverse fault in a dextral direction

at the southernmost end and deforms younger sedimentary

strata at its northernmost side on the shore of Lake Van. Based

on the field measurement, dip amounts are approximately 27º

in the southern part and 70º in the northern part (Fig. 11b).

According to our field measurements and ERT results,

the Elmalık Reverse fault has two motions; dextral strike-slip

and reverse on the southern and northern parts, respectively.

Moreover, small scale reverse faulting has also developed in

the sandstones belonging to the Van Formation to the south of

the Haramigediği valley (Fig. 11c). With the effect of defor-

mation formed after the Miocene, this type of reverse fault

section with N 120º E, 35º attitude is commonly observed

(Şengül et al. 2012).

Three ERT surveys (ERT-2, ERT-3, and ERT-4 profiles seen

in Fig. 6) have been obtained to determine the location of

the Elmalık Reverse fault (Fig. 6). ERT-2 profile, which is

a 252 m long DD array has been used along the profile with

84 electrodes separated by 3 m electrode spacing (Fig. 7b).

Figure 7b shows the inverse model for the sub-surface resis-

tivity results of the ERT-2 profile. The RMS error of the ERT-2

profile was 3.53 % after 2 iterations. The ERT-2 profile sho-

wing the low resistivity zone (5–25 Ω m) might be associated

with a higher water content of the Oligocene–Miocene Van

Formation. The ERT-2 profile shows between 72 and 105 m

Fig. 6. Main tectonic features, bedding planes and ERT locations in the study area. Slip-plane data indicate the contractional regime

dominantly.

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uplifted low resistivity unit from the S–W part of the cross-

section. The N–S fault zone can be followed from the surface

down to 35 m depth. In this section, reverse faulting has been

seen within the Van formation and this has been interpreted as

the Elmalık Reverse fault (Fig. 7b).

The ERT-3 profile has an E–W direction and a 252 m

long DD array, with 84 electrodes separated by 3 m electrode

spa cing (Fig. 7c). Figure 7c shows the inverse model for

the subsurface resistivity results of the ERT-3 profile. The RMS

error of the ERT-3 profile was 3.45 % after 5 iterations.

The low resistivity zone (4.6–45 Ω m) shown by the ERT-3

profile can be related to the Oligocene–Miocene Van For-

mation. The eas tern part of the cross-section includes high

resistivity (127–385 Ω m), this part can be related to the Upper

Miocene–Pliocene Kurtdeliği For -

ma tion. The scarp has a small

topographic relief and it is located

at 148 m distance that shows and

up lif ted part on the eastern side.

The ERT-3 profile has two faults.

The first one is defined as the El -

malık Reverse fault between 119

and 142 m uplifted low resistivity

unit from the N–S direction of

the cross- section. The second fault

is located at a distance of 190 m

in the eastern part of the profile

from the surface down to depth.

The second fault is probably the

antithetic fault of the Elmalık

Reverse fault. ERT-4 profile is

a 420 m long DD array, with 84

electrodes separated by 5 m elec-

trode spacing (Fig. 7d). Figure 7d

shows the inverse model for

the subsurface resistivity results

of the ERT-4 profile. The RMS

error of the ERT-4 profile was

4.5 % after 3 iterations. The ERT-4

profile shows the low resistivity

zone (8.6–40 Ω m) that could be

related to the Oligocene–Miocene

aged Van Formation. The eas tern

part of the cross-section includes

high resistivity (153–399 Ω m),

this part can be related to the Upper

Miocene–Pliocene Kurtdeligi For-

mation. The ERT-4 profile shows

a change between 145 and 195 m

from low resistivity to high resis-

tivity that defines the N–S Elmalık

Reverse fault. The N–S fault can

be followed from the surface down

to 55 m depth.

Gürpınar Reverse fault

The Gürpınar Reverse fault has

an E–W trend with a dip angle

towards the north borderline bet-

ween the travertine and the Lake

Van Formation borderline in

the southern section of the study

Fig. 8. General view of the Erdemkent fault plane (a), and 40 cm vertical displacement (b). Location

of field photograph is given in Fig. 3.

Fig. 9. General view of the Erdemkent fault plane, and breccia and slickenlines on the Erdemkent

Fault. Location of the field photograph is given in Fig. 3.

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area (Fig. 12). This fault is mostly

observed within the Van For-

mation along a 12 km length in

the study area and it extends 30 km

more to the east up to the Engil

valley (Koçyiğit 2013; Şengül et

al. 2012). It is probably the last

reverse fault on the southern side

of the Eastern Anatolia Accretion

Complex. It is thought that this

fault is the source of the 1646

earthquake in the historical period

(Ambraseys & Finkel 1995; Soysal

et al. 1981). The deformation pat-

terns are detected in the layers

belonging to the Van Formation

and the Travertine by reverse dis-

placement. Measurements from

the slickenline on the fault surface

show that the fault is E–W tren-

ding with 50º–55º dip amount northwards, the slickenlines are

NW–SE trending with 55º plunge amount (Table 2).

The electricity tomography method has been applied to

the east section of the Gürpınar Reverse Fault (Fig. 6). ERT-5

profile is a 420 m length DD array, with 84 electrodes sepa-

rated by 5 m electrode spacing (Fig. 7e). Figure 7e shows

the inverse model for the subsurface resistivity results of

the ERT-5 profile. The RMS error of the ERT-5 profile is

2.33 % after 3 iterations. The ERT-5 profile shows the low

resistivity zone (10–45 Ω m) that can be related to the Oligo-

cene–Miocene aged Van Formation. The cross-section includes

partially high resistivity (> 250 Ω m) values; these values can

be related to the travertine slope rash blocks. The scarp has

a minor topographic relief and it is located at a distance of

159 m, showing uplifted low resistivity units from the surface.

The Gürpınar Reverse fault is seen in the inverse model for

the sub-surface resistivity results. 159 m uplift is observed on

the low resistivity unit relative to high resistivity unit along

the E–W direction of the cross-section. The N part of the cross-

section (at distance of 80 m) and S part of the section

(at distance between 238 and 278 m) have been affected by

the reverse faulting. The ERT-6 profile is located on N–S

direction on the Gürpınar Reverse fault (Fig. 2). Figure 7f

shows the inverse model for the subsurface resistivity results

Fault

Plane’s

Fault Line’s

Fault Type

Kinematic Axes

Focal

Mech.

Dip Dir.

Dip

Trend

Plunge

Erdemkent

280

008

Sinistral/

Inverse

324/03

221/75

054/15

Erdemkent

110

030

Normal/

Sinistral

315/44

198/25

088/35

Elmalık

132

102

Inverse/

Dextral

296/03

205/15

037/74

Elmalık

080

Inverse/

Reverse

253/18

161/04

058/71

Gürpınar

354
290
005

55
50
55

330
285
335

57
57
50

Inverse/

Dextral

330/04

061/09

217/80

Çiçekli

020

328

Inverse/

Dextral

354/00

084/29

264/61

Tear Fault

084

355

Dextral/

Inverse

040/01

137/80

309/10

Table 2: Fault plane features and kinematic solutions (P–T axis) of faults in study area.

Fig. 10. General view of the Elmalık Reverse fault in an open pit, south of Edremit. Location of

the field photograph is given in Fig. 3.

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of the ERT-6 profile. The ERT-6 profile

has a 272 m length with roll-along con-

figuration DD array, with 84 electrodes

separated by 3 m electrode spacing

(Fig. 7f). The RMS error of the ERT-6

profile was 3.59 % after 5 iterations.

Figure 7f indicates massive travertine

about 10 m thick with high resistivity

(> 450 Ω m) re gion in the cross-section.

In the sout hern part of the cross-section,

low resistivity values (5–30 Ω m) can be

related to an increased water content of

the Quaternary aged Van Lake Formation.

In the northern part of the cross-section,

low-middle resistivity values (30–120 Ω m)

could be related to the Van Formation

proving the uplift relative to the Van

Lake Formation in the cross-section.

The Gürpınar Reverse fault was deter-

mined along the E–W trend between

125 m and 140 m.

Çiçekli fault

The Çiçekli fault is placed on the south-

east side of the Edre mit Travertine and just at the north-east of

Çiçekli Village (Fig. 6). The fault has a strike and dip of

N 290º W, 52º and it nearly has the same trend as the Gürpınar

Reverse Fault. The fault surface has been observed in a mine

pit, but it is very difficult to follow its surface expression.

The observable extent of the fault on the surface is about 1 km,

where the travertine has been crushed and folded. Brown

coloured fault clay is present along the crushed zone (Fig. 13).

The slickenlines have NW–SE direction with a plunge of 38

to the NW (Table 2). Current colluvial materials have been

deposited in front of the layers folded on top the fault. Because

of the deformation in the travertine, the fault has been eva-

luated as active and it is conformable with the Gürpınar

Reverse fault.

Discussion

According to previous geological and geophysical studies

and all the data observed during our fieldwork, Eastern

Anatolian has been experiencing ~ N–S trending contraction

that yields various structures such as reverse-thrust faults,

strike-slip faults, oblique-slip normal faults, folds and diffe-

rent types of basins. The main shortening direction was deter-

mined from the bedding planes, kinematic analyses of joints

and slickenlines of fault surfaces. Especially the slip plane

data from the fault proved this result. The kinematic results of

Gürpınar Reverse fault indicate that the dominant shor tening

direction is N 30º W. This fault emplaced the clastics derived

from the Edremit Travertine and the Van Formation on top of

the Plio-Qua ternary unit located along the Engil Valley. This

is the most important evidence for the reverse motion in

that the younger unit is located under the older deposits.

According to pre vious research, this fault produced

the 1646 earthquake with the intensity of IX (Ambraseys &

Finkel 1995). It probably indicates that the source of the 1646

earthquake is related to this thrust fault. Before the event, there

is no historical record resulting from the fault. Approximately

350 years have already passed after the last event (1646) and it

might be a seismic gap. The Gürpınar Reverse fault is ~ 40 km

in length and in the case of accumulated stress, a destructive

earthquake could be generated. From this perspective, the fault

is very important for the area and it needs paleoseismological

studies.

The Elmalık Reverse fault is another important structure

in the study area. This fault was mapped by some authors,

but with a different faulting character (Örçen et al. 2004;

Özkaymak et al. 2004; Koçyiğit 2013). According to them,

the Elmalık Reverse fault is a NW–SE trending thrust fault

with right lateral component and interrupted by the Van Fault

that is a N–S trending normal fault. This description defines

the northern part of the Elmalık Reverse fault. On the other

hand, the fault continues with a bending towards the south

with small changes in type of fault. Thus, during our field

work, thrust motion along the fault surface from slickensides

and folds on the northern parts of Elmalık Reverse fault points

out the compressional regime (Fig. 10). In the ERT results

applied under the surface, thrust motion of the same units were

detected along the southern half of the fault (ERT-2, ERT-3,

and ERT-4). At the southern end of the Elmalık Reverse fault,

strike-slip motion with thrust component has been observed

and measured (Fig. 12). Thus, dextral displacement along

Fig. 13. General view of the Çiçekli Fault near Çiçekli village with dark brown fault gouge

in the fault zone shown in the inset. Location of the field photograph is given in Fig. 3.

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the Elmalık Reverse fault cut and displaced the Gürpınar

Thrust fault (Fig. 12).

In this study, a number of small scale faults have been

observed and measured deforming the Plio-Quaternary

Edremit travertine. According to their single plane solutions,

approximately N 35º W compression direction has been

determined.

Conclusions

Based on this study, we can conclude that:

• Totally, 71 measurements have been collected from bedding

planes showing mostly NE–SW trending, north-western

dipping in the northern and ENE–WSW-trending, north-

western dipping planes in the southern side of the area.

• The Edremit Travertine is an important deposit in that it

records the recent deformation history in the area. The re-

sults indicate that the main compression direction is appro-

ximately N 35º W (Fig. 6). The travertine records two

different motions on the faults. It means that the geological

evolutionary history of the area included at least two diffe-

rent tectonic regimes.

• The upper layers of the travertine deposit to be in the soft-

porous rock quality as lithological have made it difficult to

observe the joint sets clearly over a large area (Ismat &

Mitra 2005). This fact has caused the developing joints to be

widely separated and have gaps. 54 measured joint planes

belonging to the travertine have a N–S trend that is confor-

mable with the direction of left lateral strike-slip faults

deforming the travertines. Mainly, three groups of joint sets

have been defined in the travertine (Fig. 4b)

• The contraction direction N 35º W has been proved by

the joints and beddings developed in the Edremit Traver tine.

It supports recent configurations of principal stress axes.

• The Elmalık reverse fault has a bend at its middle sector

and these two parts (northern and southern). This bending

creates a different character in faulting. The northern

part is a reverse fault with dextral component and

southern part is a dextral strike-slip fault with reverse

component.

• The Elmalık Reverse fault is a tear fault in its southern edge

that deforms the Gürpınar Reverse fault in dextral

displacement.

Acknowledgements: This article includes some results of

doctoral research which was supported by Istanbul University

Research Fund (project no:19486) of first author. The authors

would like to thank Prof. Hayrettin Koral for editing and

guiding this paper. Our students from Van Yuzuncu Yil Uni-

versity Department of Geology were helpful on field studies,

we would thank their effort too. The authors are also grateful

for support of Handling Editor Prof. Rastislav Vojtko spending

much time for editing this paper. Finally, the reviewers are

appreciated. Their suggestions and critical reading signifi -

cantly improved this manuscript.

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