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Turkish Journal of Earth Sciences
(Turkish J. Earth Sci.), Vol. 10,2001, pp. 69-82.
Copyright ©TÜB‹TAK
69
The June 6, 2000, Orta (Çank›r›, Turkey) Earthquake:
Sourced from a New Antithetic Sinistral Strike-slip
Structure of the North Anatolian Fault System, the
Dodurga Fault Zone
AL‹ KOÇY‹⁄‹T, BORA ROJAY, MUSTAFA C‹HAN & ARDA ÖZACAR
Middle East Technical University, Faculty of Engineering, Department of Geological Engineering,
Tectonic Research Unit, TR-06531, Ankara - TURKEY
(e-mail: akoc@metu.edu.tr)
Abstract: The ‹smetpafla-Karg› section of the North Anatolian Fault System (NAFS) consists of six subfault zones,
namely the Eskipazar, the Ulusu, the Tosya, the Çerkefl-Kurflunlu, the Devrez and the newly detected Dodurga fault
zone (DFZ). Together these fault zones form a well-developed dextral strike-slip-faulting pattern, in which the DFZ
is an antithetic secondary strike-slip component, indicated by focal-mechanism solutions of moderate and large
earthquakes that have occurred in the ‹smetpafla-Karg› section of the NAFS.
The DFZ is a ∼36-km-long, ∼N-S-trending strike-slip structure located in the area between Saçak village in the
north and Kösrelik village in the south. Pre-Upper Pliocene rocks are cut and tectonically offset for a distance of
about 6 km. Upstream tributaries of the Devrez River are deviated in the shape of an “S” and are offset sinistrally
up to 2.5 km. These values explain a 2.3 mm/yr rate of slip on the DFZ. In addition, several Plio-Quaternary pull-
apart basins occur within the DFZ.
An intermediate-magnitude (Mw= 6.0), shallow-focus earthquake, the Orta earthquake, struck on Tuesday,
June 6, 2000, at 5:42 (local time) in the Orta area, and resulted in two deaths and severe damage to a total of
4842 structures, almost all of rural-style construction. Most of severe damage was confined to a narrow area along
the Dodurga fault; that is, the master strand of the DFZ. Isoseismal lines display an ellipsoidal pattern with a long
axis that parallels the Dodurga fault. Both fore- and after-shocks of the June 6, 2000 Orta earthquake form a
highly concentrated, N-S-trending distribution pattern that parallels the DFZ. Focal-mechanism solutions of the
main shock carried out by various seismographic stations, except for DER-DDR station, indicate sinistral strike-slip
faulting with a normal-slip component. Consequently, taken together these field observations and seismological
data indicate that the Dodurga fault is an antithetic sinistral strike-slip structure included in the NAFS, and that the
June 6, 2000 Orta earthquake resulted from its activation.
Key Words: North Anatolian Fault System, Antithetic Fault, Sinistral Strike-slip Fault, Orta Earthquake
Kuzey Anadolu Fay Sisteminde Tan›mlanan Sol Yanal At›ml› Bir Fay Kufla¤›:
Dodurga Fay Kufla¤› ve 6 Hairan 2000 Tarihli Orta (Çankar›-Türkiye) Depremi
Özet: Kuzey Anadolu Fay Sisteminin (KAFS) ‹smetpafla-Karg› bölümü Eskipazar, Ulusu, Tosya, Çerkefl-Kurflunlu,
Devrez ve yeni tan›mlanan Dodurga fay kufla¤› (DKF) olmak üzere alt› adet alt-fay kuflaklar›ndan oluflur. Bu fay
kuflaklar›n›n tamam› iyi geliflmifl sa¤ yanal-at›ml› fay deseni oluflturur ve bu sistem içerisinde DFK yanal at›m
bileflenli ikincil antitetik yap›y› temsil eder.
Yaklafl›k 36 km uzunlu¤unda ve kuzey-güney uzan›ml› bir yanal-at›ml› fay olan DFK, kuzey de Saçak ve
güneyde Kösrelik köyleri aras›nda yeral›r. Üst Pliyosen öncesi kaya topluklar›n› kesen ve öteleyen fay kufla¤›
boyunca belilenen hareket 6 km kadard›r. Devrez ›rma¤›n›n memba dereleri “S” flekilli dönmüfl ve sol yanal olarak
2.5 km’ ye kadar at›lm›flt›r. Bu de¤erler, DFZ üzerinde 2.3 mm/yr kayma miktar› verir. Bunlara ilaveten DFZ
üzerinde birçok Pliyo-Kuvaterner çek-ay›r havzalar geliflmifltir.
Orta ölçekli (Mw = 6.0) ve s›¤ odakl›, Orta depremi, 6 Haziran 2000 sal› sabah› saat 5.42 (yerel zaman ile)
Orta bölgesini vurdu. Deprem, iki ölüme ve ço¤u a¤›r olmak üzere k›rsal tarzda infla edilmifl toplam 4852 yap›n›n
hasar görmesine neden oldu. Ço¤unlukla hasar DFZ’nin ana kolu olan Dodurga fay› üzerinde dar bir kuflakta olufltu.
Eflde¤ersismik e¤rilerinin uzun ekseni Dodurga fay›na parallel uzanan elipsoidal bir desen oluflturur. 6 Haziran
2000 Orta Depremin öncül ve ardç›l depremlerinin da¤›l›m› kuzey-güney yönünde bir yo¤unlaflma gösterip,
Dodurga fay kufla¤›na paralellik sunarlar. DER-DDR d›fl›nda çeflitli sismograf istasyonlar›nda yap›lan odak
mekanizmas› çözümlemeleri normal bileflenli sol yanal-at›ml› faylanma göstermektedir. Sonuç olarak, arazi jeolojisi
gözlemleri ve sismik veriler birlikte Dodurga fay›n›n KAFS’i içinde antitetik sol yanal-at›ml› fay oldu¤unu ve 6
Haziran 2000 Orta depreminin bu fay›n hareketlenmesi ile olufltu¤unu ortaya koymaktad›r.
Anahtar Sözcükler: Kuzey Anadolu Fay Sistemi, Antitetik Fay, Sol Yanal-at›ml› Fay, Orta Depremi.
Introduction
An intermediate-magnitude (Mw= 6.0), shallow-focus (8-
33 km) earthquake struck on Tuesday, June 6, 2000, at
5:42 (local time). This seismic event was felt over a wide
region including many cities, counties and villages, such as
Çank›r›, Kastamonu, Zonguldak, Karabük, Bolu, Ankara,
Kayseri, Çerkefl, Kurflunlu, Atkaracalar, Orta, Çubuk and
fiabanözü, and caused severe damage to adobe structures
in rural areas. Early morning on same day, the field
epicenter of this seismic event was announced as Çerkefl
county by a national seismographic station, Kandilli
Observatory and Earthquake Research Institute, ‹stanbul-
Turkey. Later, several national and international
seismographic stations that recorded this event calculated
its various seismic parameters (Table 1). Thus, based on
instrumental data obtained from seismographic stations
(Table 1), the field epicenter of this event was found to
be somewhere in or near Orta county, 15-25 km SE of
Çerkefl county. However, until the occurrence of this
seismic event, there was no information about a fault
mapped or reported from this area. Therefore, the
source of this earthquake remained an unsolved
geological problem for a short time. For this reason, we
went to the Orta (Çank›r›) area, visited all of the severely
damaged settlements, and detected the structure that
produced this seismic event, and mapped it in detail on a
1/25,000 scale topographic map. This structure, an
approximately N-S-trending, left lateral strike-slip fault
zone located ∼5 km west of the Orta county (the largest
settlement nearest to the field epicenter of the seismic
event), we named the Dodurga fault zone. Accordingly,
the seismic event is herein first named the June 6, 2000
Orta earthquake.
This paper aims: (1) to introduce a new structure, the
Dodurga fault zone; (2) to explain its geometric-
kinematic characteristics and relationships with the NAFS;
and (3) to explain and document the origin of the June 6,
2000 Orta earthquake and the severe damage it caused
to structures in the Orta area.
Regional Tectonic Setting
Turkey is located in the Mediterranean-Himalaya seismic
zone, and approximately 90% of the country is under
seismic hazard. The main structures that are responsible
for high seismicity in Turkey and adjacent areas are the
North Anatolian, East Anatolian and Dead Sea fault
systems, and the Hellenic-west Cyprus arc (Figure 1). The
Hellenic-west Cyprus arc is an active subduction zone
along which the African plate has been subducting at a
slip rate of 35 mm/yr northwards beneath the Turkish
platelet (McKenzie 1972; Le Pichon & Angelier 1979;
Meulenkamp
et al.
1988; Kahle
et al.
1998). The Dead
Sea Fault System is a sinistral transform fault separating
DODURGA FAULT ZONE AND JUNE 6, 2000 ORTA EARTQUAKE
70
Table 1. Various seismic parameters of the 2000 June 6 Orta (Çank›r›) earthquake.
Origin Location Focal Seismic Fault Plane
Date Time Lat°.N-Long°.E depth Magnitude Moment Duration Mechanism Geographical References*
(yyyy/mm/dd) (GMT) (km) (Mo) (second) Solution Region
(strike/dip/rake)
2000/06/06 02:41:53.2 40.65 – 32.92 8 Mw= 6.0 1.25 x 1018 Nm ~ 6 1. 02°/46°/-29° Orta (Çank›r›) TT
2. 111°/70°/-132°
2000/06/06 02:41:53.16 40.621 – 32.967 33 Ms= 6.1 - - 1. 340°/26°/-53° Orta (Çank›r›) USGS-NEIC
2. 122°/69°/-106°
2000/06/06 02:41:51.46 40.63 – 33.03 10.5 Md= 5.9 - ~ 10 1. 262°/88°/-139° Orta (Çank›r›) DER-DDR
2. 170°/49°/-03°
2000/06/06 - 40.67 – 32.97 10 Md= 5.9 - - - Çerkefl (Çank›r›) KOERI
2000/06/06 02:41:52.0 40.75 – 32.70 15 Mw= 6.0 1.11 x 1018 Nm ~ 5.4 1. 356°/39°/-47° Orta (Çerkefl) HARVARD
2. 126°/62°/-119°
2000/06/06 - 40.60 – 33.00 33 Ms= 6.1 - - 1. 359.6°/47.6°/-46.8° Orta (Çank›r›) ERI
2. 125°/58°/-126°
* TT: Tuncay Taymaz - ‹stanbul Technical University, Department of Geophysical Engineering, USGS-NEIC: The United States of Geological Survey – National Earthquake Information Center,
DER-DDR: Department of Earthquake Research, General Directorate of Disaster Affairs, KOERI: Kandilli Observatory and Earthquake Research Institute, HARVARD: Harvard University Seismology
Group, ERI: Tokyo University Earthquake Research Institute.
A. KOÇY‹⁄‹T,
ET AL.
71
1. Ulusu-Gerede-Abant Subfault Zone
2. Tosya Subfault Zone
3. Çerkefl-Kurflunlu Subfault Zone
4. Karadere-Kaynafll› Subfault Zone
5. Dodurga Fault Zone
6. Hendek-Y›¤›lca Subfault zone
7. Northern Marmara Fault
8. Ganos Fault
9. Yenice-Gönen Subfault Zone
•sp
GREECE
AEGEAN SEA
AFRICAN PLATE
ARABIAN PLATE
Dead
Sea
Central
Line
RED SEA
EAST MEDITERRANEAN SEA
STRABO TRENCH
PLINY TRENCH
ANATOLIAN PLATELET
EAST ANATOLIAN FAULT SYSTEM
NORTH ANATOLIAN FAULT SYSTEM
EURASIAN
PLATE
Erzincan
Karl›ova
B
‹
T
L
‹
S
S
U
T
U
R
E
ZO
N
E
Van Lake
Ladik
BLACK SEA
Ankara
‹stanbul
Edremit
Tekirda¤
Athens
‹znik Geyve Beldibi
SHD
BGÇank›r›
Figure 2
Salt Lake
Kahraman Marafl
Karg›
1
2
3
4
6
O
1944/02/01
Bolu - Çerkefl
Earthquake
M= 7.6
1943/11/26
Tosya-Ladik
Earthquake
M=7.6
420
340
300
260
220
410
390
370
350
330
310
290
DEAD SEA FAULT SYSTEM
HELLENIC ARC
CYPRUS ARC
N
0 200
km
5
87
9
•sp
KEPHALONIA
FAULT ZONE
Kastamonu
Zonguldak
Kayseri
LEGEND
Fault-plane solution
Suture zone
Active subduction zone
Strike-slip fault
Relative motion sense of plates
‹smetpafla railway station
B: Bolu, G: Gerede, D: Düzce,
H: Hendek, O: Orta, S: Sakarya
Figure 1. Simplified map showing the study area and major neotectonic structures of Turkey and adjacent areas (Focal-mechanism solutions were taken from Can›tez &
Büyükafl›ko¤lu 1984).
the Arabian Plate in the east from the African Plate in the
west. The African Plate is moving NNW at an average slip
rate of 18 mm/yr (De Mets
et al.
1994; Reilinger
et al.
1997; Kahle
et al.
1998). The dextral North Anatolian
and sinistral East Anatolian fault systems are
intracontinental transform faults, along which the wedge-
shaped Anatolian platelet has been escaping west-
southwestward since Late Pliocene (2.6 Ma) (McKenzie
1972; Tokay 1973; Hempton 1987; fiaro¤lu 1988;
Koçyi¤it & Beyhan 1998). Average rates of slip along the
NAFS and the EAFS are estimated at 10 mm/yr and 6
mm/yr, respectively, based on field observations (Tokay
1973; Tatar 1978; Barka & Hancock 1984; Barka &
Gülen 1988; fiaro¤lu 1988; Koçyi¤it 1988, 1989, 1990)
while they appear to be 26 mm/yr and 15 mm/yr,
respectively, based on Global Positioning System (GPS)
and seismological data (McKenzie 1972; Can›tez 1973;
North 1974; Kasapo¤lu & Toksöz 1983; Taymaz
et al.
1991; De Mets
et al.
1994; Reilinger
et al.
1997; Stein
et al.
1997; Kahle
et al.
1998, 2000; McClusky
et al.
2000).
Tectonic Setting of the Study Area
The NAFS is an approximately 1500-km-long and 10-
100-km-wide dextral shear zone trending first NW, and
then E–W, and finally SW between Karl›ova in the east
and the northern Aegean Sea in the west (Figure 1). The
NAFS displays two common distribution patterns or
geometries along its length: (1) splay-type geometry, and
(2) anastomasing-type geometry. The splay type is well-
developed in both the Erzincan-Çerkefl and the Marmara
sections of the NAFS. In the area between Erzincan in the
east and Çerkefl in the west, a number of fault zones,
fault sets and isolated faults of varying sizes branch as
splay structures from the master strand of the NAFS.
These structures first trend E-W for some distance (up to
40 km), and then bend southward and trend ~NE-NNE,
traversing the Anatolian platelet for several hundreds
kilometers, cutting across and deforming it. Well-defined
examples of splay structures are the Ovac›k-Malatya,
Central Anatolian, Almus, Ya¤murlu-Ezinepazar› (or
“Sungurlu”), Merzifon-Laçin, Taflova-Çorum and the
K›z›l›rmak fault zones or splay fault zones (Koçyi¤it
1989, 1990, 1991a, 1991b, 1996; fiengör & Barka
1992; Özçelik 1994; Kaymakç› & Koçyi¤it 1995; Bozkurt
& Koçyi¤it 1995, 1996; Koçyi¤it & Beyhan 1998, 1999;
Kaymakç› 2000; Westaway 2001).
In the second pattern or geometry of the NAFS, the
master strand (Y-shear) first bifurcates into several
subfault zones, fault sets and isolated faults of varying
sizes, and then they rejoin and rebifurcate several times,
leaving behind a series of lensoidal highlands (pressure
ridges) such as Armutlu Peninsula, Almac›k Mountain,
Bolu Mountains, Arkotda¤, Ilgaz Mountains and Karada¤,
and lowlands (basins) whose long axes parallel the
general trend of the master strand of the NAFS. This
pattern is the most diagnostic characteristic of the Karg›-
East Marmara section of the NAFS. Examples of subfault
zones, fault sets and isolated faults having anastomosing
geometry along the NAFS in its Karg›-East Marmara
section are, from E to W, the Ulusu-Gerede-Abant, Tosya,
Çerkefl-Kurflunlu, Karadere-Kaynafll›-Mengen-Eskipazar
and the Hendek-Y›¤›lca subfault zones (Figures 1 & 2).
These zones have been mapped previously and introduced
into the geological literature (Öztürk 1968; Tokay
et al.
1973; Tokay 1973; Öztürk
et al.
1984; fiaro¤lu
et al.
1987; Barka & Kadinsky-Cade 1988; Andrieux
et al.
1995; Koçyi¤it
et al.
1999). Thus, usage of the term
“North Anatolian fault system” is preferred to the term
“North Anatolian fault zone” due to its aforementioned
complicated geometry.
One of newly detected splay faults of the NAFS is the
Dodurga fault zone, (DFZ) located south of the
‹smetpafla-Karg› section of the NAFS (Figure 2). It
branches from the E-W–trending Çerkefl-Kurflunlu
subfault zone and then runs South for a distance of ~36
km. The master strand of the Dodurga fault zone became
active and produced the June 6, 2000 Orta (Çank›r›,
Turkey) earthquake of Mw= 6.0. The present paper deals
with the various characteristics, including the geometry,
kinematics, size, age, and displacement of the Dodurga
fault zone, the Mw= 6.0 earthquake, and its damage to
various structures.
Dodurga Fault Zone (DFZ)
The Orta area was first studied by Türkecan
et al.
(1991), who identified various rocks of dissimilar facies
and age, and mapped them separately at a 1/25,000
scale. These rocks are from, oldest to youngest: an Upper
Cretaceous marine sedimentary sequence, Miocene
volcanic rocks, a Miocene continental sedimentary
sequence, Pliocene basalts and a Plio-Quaternary
continental sedimentary sequence. Türkecan
et al.
(1991)
DODURGA FAULT ZONE AND JUNE 6, 2000 ORTA EARTQUAKE
72
A. KOÇY‹⁄‹T,
ET AL.
73
Foreshocks Aftershocks
(1999/09/08 - 2000/06/06) (2000/06/06 - 2001/01/31)
(Seismic data were taken from Department of Earthquake
Research, General Directorate of Disaster Affairs, DER-DDR)
LEGEND
Epicenters of Korgun, Kurflunlu,
Çerkefl-Kurflunlu and
Mehmetler-Gökçeyaz› earthquakes
Epicenter of Orta Earthquake (epicentral
location was taken from DER-DDR)
Strike-slip fault with normal component
Strike-slip fault
Thermal water spring
Elevation
1653 m
45
<<
Bay›nd›r Pull-Apart
Basin
Bulduk
Çerkefl Pull-Apart
Basin
Bay›nd›r
(a)
(b)
(c)
Eskipazar
Bayramören
Kurflunlu
Çerkefl Atkaracalar
Belören
Yalaközü
Yalakçukurören
Çavundur
Elmal›
Alaçamda¤
1504 m
Aydosda¤
1653 m
Orta
Büyükyakal›
fiabanözü
Güldürcek Dam
Dodurga
‹smetpafla railway
station
23<<
34
<
<
<
5
Dolafllar
Afflar
Korgun
1902/03/09
Korgun
Earthquake
Hüyükköy
Mehmetler
N
1951/08/13
Kurflunlu Earthquake
M = 6.5
1953/09/07
Çerkefl-Kurflunlu Earthquake
M = 6.2
1977/10/05
Kurflunlu-Mehmetler
Earthquake
Ms = 5.8
Çerkefl- Kurflunlu Subfault Zone
Ulusu Sub-Fault Zone
Eskipazar Sub-Fault Zone
Devrez Subfault Zone
Kösrelik
Çardak
Saçak
Focal Mechanism of
Mainshock (ERI).
NP 1, NP 2 are nodal planes
41.00
32.50
40.46
33.50
Y: Y-shear (Master fault)
P: P-shear (Synthetic secondary strike-slip fault)
R-Riedel shear (Synthetic secondary strike-slip fault)
R’-Riedel shear (Antithetic secondary strike-slip fault)
T: Tensional structures (Normal faults)
Orientation of the principal
stress axis
STUDY AREA
(Figure 3)
0 5
km
<
5
45
<<
23<<
34
<
<
T
P
R’
R
Y
NP 1
NP 2
Oblique-slip normal fault
Dodurga Fault Zone
Figure 2. (a) Seismotectonic map of the area around Çerkefl, Orta, Kurflunlu, Korgun and Bayramören counties (focal-mechanism solutions were taken from Can›tez & Üçer 1967;
Jackson & McKenzie 1984) (see Figure 1 for location). (b) Pattern of dextral strike-slip faulting. (c) Focal-mechanism solution of the June 6, 2000 Orta (Çank›r›)
earthquake. NP1 fits well with the Dodurga fault.
have also observed and mapped a few short (0.5 to 3-
km-long), N-S- to NNW-trending isolated faults.
However, a continuous fault or fault set longer than 5 km
is not shown on their map. On June 6, 2000, a short time
after the occurrence of the Orta earthquake, we visited
the Orta area; there we detected a large fault zone and
prepared a detailed neotectonic map (Figure 3) via
geological field mapping carried out in the same area.
This neotectonic structure is here first named the
Dodurga fault zone (DFZ).
The DFZ is an 4 to 7-km-wide, 36-km-long and
approximately N-S trending sinistral strike-slip fault zone.
This zone is located in the area between Saçak village in
the north, Kösrelik village in the south (outside the study
area) and Orta County in the east (Figures 2a & 3). The
DFZ consists of a number of parallel to sub-parallel, ∼1 to
36 km long, N-S–, NNW– and NNE-trending, closely-
spaced sinistral strike-slip faults with considerable
normal-slip components as indicated by several Plio-
Quaternary pull-apart basins bounded by these faults
(Figure 3). Some of the larger faults comprising the DFZ
are, from E to W, the Kay›lar fault, the Buhya fault set,
the Hasanhac› fault set, the Sö¤ütözü fault, the Bü¤ren
fault, the Dodurga fault and the Yalaközü fault set (Figure
3).
The Kay›lar fault is about 7-km-long, NNW-trending
sinistral strike-slip fault. It occurs in three segments and
controls the eastern side of the Karal›k stream valley
(Figure 3). The Buhya fault set is located around Buhya
village in the southern part of the study area, and consists
of seven 1- to 5-km-long, closely-spaced, N-S– to
NNE–trending sinistral strike-slip fault segments. These
faults control the Buhya pull-apart basin (Figure 3). The
Hasanhac› fault set is located between Gökçeören village
in the south and Salur village in the north, and consists of
seven 1- to 3.5-km-long, NNE–trending sinistral strike-
slip faults with considerable normal-slip components.
Two longer segments of the Hasanhac› fault set control
the western margin of the Orta pull-apart basin and
sinistrally displace the Uludere stream course up to 0.5
km, north of Hasanhac› village (Figure 3). The Sö¤ütözü
fault, located 3 km east of Dodurga village, is an
approximately 15-km-long, N-S–trending sinistral strike-
slip fault. This fault controls both the Sö¤ütözü and ‹çin
streams and offsets them sinistrally up to 1 km (Figure
3). The Bü¤ren fault splays off the Sö¤ütözü fault near
the Gökçeviran plateau in the south, and then runs NW up
to the east of Derebay›nd›r village, where it bends
northward and continues for 10 km in the same
direction. Finally, this fault meets the Dodurga fault
DODURGA FAULT ZONE AND JUNE 6, 2000 ORTA EARTQUAKE
74
ÇERKEfi-KURfiUNLU SUBFAULT ZONE
Karamustafa
Uluçay
Saçak
Yalaközü
Ahurköy
De•irmen Str.
Yalakçukur.
Hac›lar
Kise Str.
Elden
Elden Str.
BU⁄URÖREN
FAULT
Bu¤urören
Yuva
Dodurga
DODURGA FAULT
Için Str.
Sö¤ütözü Str.
Derebay›nd›r
Kayviran
Güldürcek
Dam
Ortabay›nd›r
Tutmaçbay›nd›r
Çukurcaa¤›l
Plateau
Yeniyayla
Plateau
Gökçeviran
Plateau
Hasanhac›
Plateau
SÖ⁄ÜTÖZÜ FAULT
Bü¤düz
Plateau
K›saç
K›saç Str.
1346
1527
N
0km
1
Yalaközü pull-apart
basin
Yalakçukurören
pull-apart
basin
Dodurga
pull-apart
basin
LEGEND:
Orta
pull-apart
basin
Salur
KAYILAR FAULT
YALAKÖZÜ FAULT
SET
Alluvial Fans
Plio-Quaternary
Deposits
Elevation point
Landslide
YUVA FAULT
BUHYA FAULT
SET
Buhya
pull-apart
basin
HFS
Strike-slip fault
Strike-slip fault
with normal
component
Spring
Normal fault
Ruin
Hasanhac• fault set
Settlement
Pre-Upper Pliocene
volcanics and
volcano-sedimentary
rocks
ORTA
Kanl›ca
Bü¤düz
Hasanh. Ba¤tak
Uludere Str.
Gökçeören
Buhya
Kay›lar
Yaylabo•az• Str.
Aydos Str.
Karal›k Str.
Devrez R.
Yaz• R.
A
A’
B
B’
A-A’
B-B’
Offset contacts
HFZ:
Figure 3. Neotectonic map of the Dodurga fault zone (see Figure 2 for
location).
(Figure 3). The Bü¤ren fault has a length of ∼16 km and
displays a concave-eastward outcrop pattern. In addition,
the Bü¤ren fault is a transfer structure between the
Sö¤ütözü and the Dodurga faults and has a considerable
normal-slip component as indicated by the Plio-
Quaternary depressions located in its eastern block
(Figures 3). The Yalaközü fault set is located in the north
of the study area, and consists of a few relatively long (∼9
km) and several short (1-3 km), closely spaced, N-S–,
NNW– and NNE–trending, linear to curvilinear fault
segments (Figure 3). These faults control both the Elden
and Kise streams and the Yalaközü Plio-Quaternary pull-
apart basin, which resulted from the subsidence of a
block bounded by two major faults of the Yalaközü fault
set, also a sinistral strike-slip structure with a
considerable normal-slip component as indicated by the
Yalaközü pull-apart basin.
The Dodurga fault is the master structure comprising
the DFZ. This fault is located in the area between Saçak
village in the north and Kösrelik village (outside of the
study area) in the south. The Dodurga fault is an
approximately 36-km-long, N-S–trending sinistral strike-
slip fault with a well-developed curvilinear and
anastomosing outcrop pattern (Figure 3). In the area
around Yalakçukurören village, the Dodurga fault divides
into several sub-branches, resulting in a very young (Plio-
Quaternary) pull-apart basin due to the subsidence of a
wedge-like block bounded by the sinistral strike-slip
faults (Figure 3). Farther north around Saçak village,
each of the basin-bounding faults bends eastward and
meets the E-W–trending Çerkefl-Kurflunlu dextral strike-
slip subfault zone. However, farther south (outside of the
study area), the Dodurga fault continues for about 6 km
on the same trend, as indicated by both the
morphotectonic features and the linear distribution of
aftershocks of the June 6, 2000 Orta earthquake.
Age and Total Displacement
Within the Dodurga fault zone, steeply dipping and folded
rocks of dissimilar age and facies are cut across and
tectonically juxtaposed. In the area between Bü¤ren
village in the south and Yalakçukurören village in the
north, Miocene volcanic rocks, a Miocene continental
sedimentary sequence and Pliocene basalts are cut and
displaced sinistrally by the Dodurga fault, up to ∼6 km
and ∼4 km, respectively (A-A’ and B-B’ in Figure 3). In
addition, a number of streams, that comprise the
upstream part of the E-W–flowing Devrez River, are bent
into a concave-northward pattern, and then offset up to
2.5 km as they approach and pass across the Dodurga
and Bü¤ren faults around Bü¤ren, Tutmaçbay›nd›r and
Ortabay›nd›r villages. Three well-developed examples of
such a drainage system are the Yaz› River, ‹çin stream
and K›saç stream (Figure 3). In the area between Bü¤ren
village in the north and Derebay›nd›r village in the south,
both the Dodurga and Bü¤ren faults display a concave-
eastward outcrop pattern, in which their eastern blocks
have been downthrown (up to 180 m), and produce two
small Plio-Quaternary pull-apart basins with long axes
that parallel the general trend of the DFZ (Figure 3).
Briefly, the existence and activity of the DFZ is
indicated by a series of well-developed and very young
(most probably Late Pliocene-Quaternary)
morphotectonic features such as sudden breaks in slope,
anastomosing outcrop patterns, fault-parallel pressure
ridges, pull-apart basins, ruins of ancient settlements,
fault-parallel aligned alluvial fans, active landslides, S-
shaped bent and offset drainage systems (Figure 3). This
was substantiated also by the June 6, 2000 Orta
earthquake and its fore- and after-shocks aligned parallel
to the DFZ (Figure 2a). Sedimentary infill of the pull-
apart basins which developed under the influence of the
DFZ is loose to poorly lithified, undeformed and rests
along an angular unconformity on the erosional surface of
the pre-Upper Pliocene deformed (folded) rocks. The
Dodurga (Orta) area is located near the Çank›r› and
Ankara regions, experiencing the same tectonic regime
(strike-slip neotectonic regime), as indicated by minor but
frequent seismic activity (Figure 1). In both the Ankara
and Çank›r› regions, a number of isolated, 1- to 20-km-
long, N-S– and NNE–trending faults, fault sets and strike-
slip basins have also been previously detected and
reported by Koçyi¤it (1991a), Koçyi¤it
et al.
(1995),
Kaymakç› (2000), Kaymakç›
et al.
(2000). According to
those authors, these structures are sinistral strike-slip
faults with a considerable normal-slip components. These
structures are younger than Late Pliocene-Early
Quaternary since they cut across and displace the Lower
Miocene-lowermost Pliocene rocks, fold axes and thrust
faults developed in them, and their undeformed (nearly
flatlying) cover rocks of Late Pliocene-Early Quaternary
age. Therefore, the age of the pull-apart basins and their
margin-bounding faults is estimated as Late Pliocene or
Early Quaternary.
A. KOÇY‹⁄‹T,
ET AL.
75
Offset formation boundaries and drainage systems
reveal that the total sinistral displacement accumulated on
faults of the DFZ ranges between 0.5 km and 6 km since
Late Pliocene (∼2.6 Ma). From these values, it can be
concluded that the maximum rate of slip on the DFZ has
been 2.3 mm/yr since the Late Pliocene. In the same way,
almost all faults of the DFZ have a considerable normal-
slip component. The one that has a greater normal-slip
component (180 m) than others is the master strand of
the DFZ, namely the Dodurga fault. The ratio of the
normal-slip component to the sinistral strike-slip
component (180 m / 6000 m) is ∼1/33 at the ground
surface, consistent with that observed on the NAFS.
Mechanism of the Dodurga Fault Zone
As has been explained in foregoing sections, the
‹smetpafla-Karg› section of the NAFS displays a well-
developed pattern of a dextral strike-slip faulting (cf.
Wilcox
et al.
1973; Sylvester 1988). In this pattern,
originally the E-W–trending elements are dextral Y-shears
or master faults, the WNW– and WSW–trending elements
are synthetic secondary dextral strike-slip faults (Y, R and
P in Figure 2b), the NW–trending elements are
extensional structures such as dikes and oblique-slip
normal faults (T in Figure 2b), and the NNW–trending
elements (R’ in Figure 2b) are the antithetic secondary
sinistral strike-slip faults. In this context, the DFZ, as a
whole, is an antithetic secondary sinistral strike-slip
structure rotated clockwise up to 15° (Figure 2a) (Gürsoy
et al.
1997) due to the simple shear character of the
NAFS since the Late Pliocene. The antithetic sinistral
strike-slip character and considerable normal-slip
component of the master fault, namely the Dodurga fault
of the DFZ are also proved by both the aforementioned
morphotectonic structures (sinistrally offset drainage
systems, formation boundaries and pull-apart basins) and
focal-mechanism solutions of the mainshock of the June
6, 2000 Orta earthquake carried out by various stations
(Table 1, Figure 2c). Based on both the geologic data
(Koçyi¤it 1991a; Andrieux
et al.
1995) and various focal-
mechanism solutions of five intermediate- and high-
magnitude earthquakes (M= 5.8-7.6) that have occurred
in this region, the operation direction of the principal
stress that caused faulting and the June 6, 2000 Orta
earthquake was approximately NW-SE (McKenzie 1969,
1972; Nowroozi 1972; Jackson & McKenzie 1984;
Can›tez & Büyükafl›ko¤lu 1984; McClusky
et al.
2000)
(Figures 1 & 2).
Seismicity of the ‹smetpafla-Karg› Section of the
NAFS
One of the more geologically complicated parts of the
NAFS is the ‹smetpafla-Karg› section (Figure 1). Most of
the ‹smetpafla-Karg› section was first examined and
mapped at a 1/25,000 scale by Tokay
et al.
(1973).
According to those authors, the ‹smetpafla-Karg› section
of the NAFS consists of six subfault zones, namely the
Eskipazar, the Ulusu, the Tosya, the Çerkefl-Kurflunlu, the
Devrez and the Dodurga fault zones (Figures 1 & 2). The
Ulusu fault zone is the master strand of the NAFS while
the Dodurga and the Devrez fault zones are its splays
(Figure 2). In general, these fault zones range from 1 to
7 km in width and from 40 to 160 km in length. In
addition, except for the Dodurga fault zone, all of the rest
are right lateral strike-slip faults.
Seismicity of the ‹smetpafla-Karg› section has been
very high in both historical periods and recent times. In
the period 109 A.D. to 1900, four historical earthquakes
with intensities varying from V to IX took place in the
‹smetpafla-Karg› section (including Çerkefl, Orta,
Kurflunlu, Karg›n, Ilgaz and Tosya counties) of the NAFS
(Soysal
et al.
1981; Ambraseys & Finkel 1995;
Ambraseys & Jackson 1998); namely, the 109,
1668.08.17, 1845 and 1881.09.28 earthquakes. These
seismic events could not be recorded and well-
documented owing to lack of well-educated people and
technology in those days. However, it has been reported
that loss of life and heavy damage to various structures
was very high (Ambraseys & Finkel 1995). In addition to
these, recent paleoseismic studies, carried out in the
‹smetpafla-Karg› section of the NAFS, have identified five
paleoearthquakes, namely the 830, 399, and 92 B.C.
events, and the 1035 and 1668 A.D. events (Özaksoy
et
al.
1998; Özaksoy 2000).
In the 19th century, six destructive earthquakes
occurred in the ‹smetpafla-Karg› section of the NAFS.
These seismic events are the 1902.03.09 Korgun (Io=
IX), the 1943.11.26 Tosya-Ladik (M= 7.6), the
1944.02.01 Bolu-Çerkefl (M= 7.6), the 1951.08.13
Kurflunlu (M= 6.5), the 1953.09.07 Çerkefl-Kurflunlu
(M= 6.4), and the 1977.10.05 Mehmetler-Gökçeyaz›
(Ilgaz) (Ms= 5.8) earthquakes (Ergin
et al.
1967;
Ambraseys 1970; Alsan
et al.
1975; Ambraseys & Finkel
1987).
The epicenters of the1902, 1943, 1944, 1951, 1953
and 1977 events were located within the ‹smetpafla-Karg›
DODURGA FAULT ZONE AND JUNE 6, 2000 ORTA EARTQUAKE
76
section of the NAFS (Figures 1 & 2). These events
ruptured most parts of the Ulusu, Çerkefl-Kurflunlu and
Tosya fault zones and led to development of ground
ruptures. These were examined in the field and mapped
at a 1/25,000 scale in places (Taflman 1944; Blumental
1945; P›nar 1953; Öztürk 1968; Ketin 1969; Tokay
et
al.
1973). Lengths of ground ruptures resulting from
1943, 1944 and 1951 earthquakes have been reported
as 265 km, 190 km and 40 km, respectively (Blumental
1945; Ambraseys 1970). The 1902 event could not be
recorded well, but focal-mechanism solutions for the
other five events have clearly shown that these
earthquakes have been sourced from dextral strike-slip
faulting with minor normal and thrust components
(Can›tez & Üçer 1967; Can›tez & Büyükafl›ko¤lu 1984;
Jackson & McKenzie 1984). Other than the major
subfault zones described briefly in foregoing sentences,
there may be some other ill-defined or undefined faults in
the ‹smetpafla-Karg› section of the NAFS, and as such may
still retain their high seismicity. In this context, the
Dodurga fault zone has been a very recent example.
The June 6, 2000 Orta Earthquake
In at least the 19th century, the Dodurga fault zone may
have remained as a seismic gap - even if it had not been
detected - because its previous unknown situation does
not change the reality of a possible seismic gap. Starting
September 8, 1999, minor seismic events with
magnitudes ranging between 2.4 and 4 began to occur
(Figure 4) with an approximately N-S distribution pattern
(Figure 2a). The N-S–trending linear distribution of
foreshocks that occurred in the period 1990-1999 were
ascribed to the activation of a reverse fault, namely the
“Atkaracalar reverse fault”, that was detected in a trench
located farther north outside of the Dodurga fault zone
(Özaksoy 2000). Until the time (June 6, 2000) of the
main shock, 27 earthquakes were reported (Department
of Earthquake Research, General Directorate of Disaster
Affairs). The main shock, with a magnitude of 5.9 to 6.1,
struck on Tuesday, June 6, 2000 at 5:42 (local time),
and moved the Dodurga fault zone of the NAFS (Figures
2a & 4). The June 6, 2000 Orta earthquake was felt in
the cities of Ankara, Bolu, Zonguldak, Kastamonu,
Çank›r› and Kayseri, 80-300 km away from Orta county
(Figure 1). The destructive effects of this earthquake
were confined mainly to villages (Dodurga, Bü¤ren,
Elden, Derebay›nd›r, Ortabay›nd›r, Tu¤maçbay›nd›r,
K›saç, Yuva, Salur, Bü¤düz, Kanl›ca) located in a narrow
and approximately N-S–trending zone delimited by the
Dodurga fault zone in the western part of Dodurga
county (Figure 3). The June 6, 2000 Orta earthquake
resulted in two deaths, moderate to severe damage to a
total of 4842 structures of mostly rural-style
construction (unreinforced, poor-quality, single- to two-
story stone and/or adobe-masonry structures with mud
mortar). Some moderate damage to isolated concrete and
adobe structures has also been reported from settlements
such as Büyükyakal›, fiabanözü and Çubuk, far from Orta
county (Figures 2 & 5).
Based on the type and amount of damage and the
modified Mercalli’s Scale, an isoseismal map was prepared
for the June 6, 2000 Orta earthquake (Figure 5).
Isoseismal lines are labeled with roman numerals. The
maximum intensity value determined for this earthquake
was VII, and that was confined to a narrow, lazy
ellipsoidal area including the aforementioned and severely
damaged villages (Figures 3 & 5). In general, isoseismal
lines display an ellipsoidal distribution pattern with a
NNE-SSW–trending long axis paralleling the master fault
of the Dodurga fault zone, implying that this fault was
the source of the June 6, 2000 Orta earthquake.
From Table 1, it is seen that there are clear
differences in both focal depths (8-33 km) and
instrumental locations (coordinates) of the epicenter of
the June 6, 2000 Orta earthquake. However, the values
of focal-mechanism solutions found by various
seismographic stations, except for the DER-DDR station,
are very similar. When locations of field epicenters and
focal mechanisms are evaluated in the light of field
observations (field mapping of faults, their distributions,
trends, geometries, etc.), high concentration and the
distribution pattern of both fore- and after-shocks
(Figure 2a), and location and shape of the greatest
intensity line (Figure 5), the field epicentral location of
the DER-DDR station and the focal mechanism of ERI
(Table 1, Figure 2c) are more favourable than those of
remaining stations.
The number of aftershocks (M= 2.1-5) in the first
20-day period was 67, and aftershocks continue to occur
at present (Figures 2a & 4). Ground rupture did not
develop during the Orta earthquake. However, some
open cracks with uneven distribution patterns occurred
within mostly soft, infilling ground material and
unconsolidated slope screes as a result of ground shaking.
A. KOÇY‹⁄‹T,
ET AL.
77
In addition, several large-scale, ancient landslides in the
southern half of the Dodurga fault zone were activated
and became threats to nearby settlements, such as
Derebay›nd›r and Tutmaçbay›nd›r villages (Figure 3).
Source of the June 6, 2000 Orta Earthquake
The attitudes of first nodal planes and the characters of
faulting obtained from focal-mechanism solutions of the
various seismographic stations, except for the DER-DDR
station, fit well with those of the DFZ (Table 1, Figure 2).
In addition, in the Orta area, the longest (36 km) active
fault is the Dodurga fault, the master strand of the DFZ.
Most of sinistral strike-slip (∼6 km), activated landslides
and severe damage to structures were also concentrated
along the Dodurga fault. All of these data reveal that the
June 6, 2000 Orta earthquake originated from activation
of the Dodurga fault (Figures 2a & 3). This conclusion has
been corroborated by the field studies of Emre
et al.
(2000).
Discussion and Conclusions
Some small seismic events began to occur in and adjacent
to the Orta area in 1990, and continued until the
mainshock, namely the June 6, 2000, Mw= 6.0 Orta
earthquake. The N-S–trending linear distribution of these
foreshocks was previously ascribed to the activation of a
N-S–trending high-angle thrust fault, the “Atkaracalar
reverse fault”, observed in a trench located farther north
and outside of the study area (Özaksoy 1990). That
interpretation is incorrect because: (1) there is no a N-
S–trending reverse fault running from Atkaracalar in the
north to the west of Orta county in the south; (2) focal-
mechanism solutions of the mainshock yield sinistral
strike-slip faulting with a normal-slip component for the
source of the June 6, 2000 Orta earthquake; and (3)
there has been no damage to structures in Atkaracalar
area. In the same way, Demirtafl
et al.
(2000) interpreted
the source of the Orta earthquake as a dextral strike-slip
fault, the “Orta Fault” that strikes ENE and dips NNW.
This interpretation is also incorrect because it is in conflict
with the N-S–trending linear distribution of both fore-
and after-shocks and results obtained from focal-
mechanism solutions of the mainshock carried out by five
national and international seismographic stations (Table
1, Figures 2a & 2c).
In contrast to the aforementioned interpretations, we
detected – via detailed field geological mapping in the
DODURGA FAULT ZONE AND JUNE 6, 2000 ORTA EARTQUAKE
78
0
1
2
3
4
5
6
7
Time
Magnitude (Md)
1999.09.08
1999.10.08
1999.11.08
1999.12.08
2000.01.08
2000.02.08
2000.03.08
2000.04.08
2000.05.08
2000.06.08
2000.07.08
2000.08.08
2000.09.08
2000.10.08
2000.11.08
2000.12.08
Main Shock
(On Tuesday, June 6, 2000, at 5:42 local time)
2001.01.31
Figure 4. Histogram showing foreshocks, mainshock (Orta earthquake) and aftershocks in the period 1999.09.08 and 2001.01.31. (Seismic data
were taken from Department of Earthquake Research, General Directorate of Disaster Affairs: DER-DDR)
A. KOÇY‹⁄‹T,
ET AL.
79
EskipazarEskipazarEskipazar
Ovac›kOvac›kOvac›k
KarabükKarabükKarabük
MengenMengenMengen
GeredeGeredeGerede ÇerkeflÇerkeflÇerkefl KurflunluKurflunluKurflunlu
IlgazIlgazIlgaz
Çaml›dereÇaml›dereÇaml›dere K›z›lcahamamK›z›lcahamamK›z›lcahamam
OrtaOrtaOrta
ANKARAANKARAANKARA
ÇANKIRIÇANKIRIÇANKIRI
Yaprakl›Yaprakl›Yaprakl›
EldivanEldivanEldivan
fiabanözüfiabanözüfiabanözü
ÇubukÇubukÇubuk
KIRIKKALEKIRIKKALEKIRIKKALE
KalecikKalecikKalecik
SulakyurtSulakyurtSulakyurt
KazanKazanKazan
AyaflAyaflAyafl
32°32°32° 33°33°33° 34°34°34°
40°40°40°
41.25°41.25°41.25°
39.25°39.25°39.25°
VIIVIIVII
VIVIVI
DSFZDSFZDSFZ
ÇSFZÇSFZÇSFZ
NAFSNAFSNAFS
KorgunKorgunKorgun
DVSFZDVSFZDVSFZ
ÇLSFZÇLSFZÇLSFZ
ÇeltikçiÇeltikçiÇeltikçi
UruçUruçUruç
KFKFKF
KF: Korgun FaultKF: Korgun FaultKF: Korgun Fault
NAFS: North Anatolian Fault SystemNAFS: North Anatolian Fault SystemNAFS: North Anatolian Fault System
TSFZ: Tosya Subfault ZoneTSFZ: Tosya Subfault ZoneTSFZ: Tosya Subfault Zone
ÇLSFZ: Çeltikçi Subfault ZoneÇLSFZ: Çeltikçi Subfault ZoneÇLSFZ: Çeltikçi Subfault Zone
ÇSFZ: Çerkefl-KurflunluÇSFZ: Çerkefl-KurflunluÇSFZ: Çerkefl-Kurflunlu
Subfault Zone Subfault Zone Subfault Zone
DSFZ: Dodurga Subfault ZoneDSFZ: Dodurga Subfault ZoneDSFZ: Dodurga Subfault Zone
DVSFZ: Devrez Subfault ZoneDVSFZ: Devrez Subfault ZoneDVSFZ: Devrez Subfault Zone
VVV
TSFZTSFZTSFZ
Figure 5. Isoseismal map for the June 6, 2000 Orta (Çank›r›) earthquake.
Orta area – an approximately 36-km-long, 4- to 7-km-
wide and N-S–trending sinistral strike-slip fault zone with
a considerable normal-slip component . This structure is
here first named the Dodurga fault zone (DFZ). It consists
of numerous 1- to 36-km-long, closely-spaced, N-S–,
NNE–, and NNW–trending isolated faults. Sinistrally
offset (up to 6 km) formation boundaries, “S”-shaped
deviated and sinistrally offset (up to 2.5 km) drainage
systems, fault-parallel-aligned active landslides and Plio-
Quaternary pull-apart basins reveal that the DFZ is an
active sinistral strike-slip structure along which the rate
of slip is 2.3 mm/yr. This is also proved by focal-
mechanism solutions of various seismographic stations
(Table 1, Figures 2a & 2c), the N-S–trending linear
distribution of both fore- and after-shocks, and the high
concentration of severe damage to structures within the
DFZ.
Consequently, all of these geological field observations
and seismological data indicate that the June 6, 2000
Orta earthquake occurred because of the Dodurga fault,
the master strand of the DFZ.
Acknowledgements
The authors are grateful to two anonymous reviewers
whose comments have greatly improved the earlier
version of the text. Steven Mittwede helped with the
English.
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80
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82
Received 17 July 2000; revised typescript accepted 13 July 2001
