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The north Anatolian fault on the Hersek Peninsula, Turkey: Its geometry and implications for the 1999 Izmit earthquake rupture propagation

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Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol.
20, 2011,ET
pp.AL.
359–378. Copyright ©TÜBİTAK
Ö. KOZACI
doi:10.3906/yer-0910-45
First published online 15 October 2010

The North Anatolian Fault on the Hersek Peninsula,
Turkey: Its Geometry and Implications for the 1999 İzmit
Earthquake Rupture Propagation
ÖZGÜR KOZACI1,2, ERHAN ALTUNEL3, SCOTT LINDVALL2,
CHARLIE BRANKMAN2,4 & WILLIAM LETTIS2
1

4

İstanbul Technical University, Eurasian Earth Sciences Institute, Maslak, TR−34469 İstanbul, Turkey
2
now at Fugro William Lettis & Associates, Inc., Walnut Creek, 94596 California, USA
(E-mail: kozaci@lettis.com)
3
Eskişehir Osmangazi University, Engineering Faculty, Department of Geological Engineering,
TR−26040 Eskişehir, Turkey
now at Department of Earth & Planetary Sciences, Harvard University, Cambridge, Massachusetts, 02138, USA

Received 02 November 2009; revised typescripts receipt 23 June 2010 & 04 August 2010; accepted 03 September 2010
‘We dedicate this study to Aykut Barka who devoted his
life to understanding the earthquake phenomenon. He
was a brilliant scientist, a true friend and a giving advisor
besides his humble personality. He will be remembered as


a source of inspiration and kindness.’
Abstract: The western termination of the 1999 İzmit earthquake still remains as an intriguing problem for researchers
and the people residing around the Sea of Marmara. There have been numerous offshore mapping and modelling
studies performed in the Gulf of İzmit. However, the main debate about the western termination of the 1999 İzmit
surface rupture is linked to the Hersek Peninsula and corresponding fault geometry. We focused our efforts at resolving
the fault geometry on the Hersek Peninsula by applying geological mapping, geomorphic analyses, palaeoseismic
trenching and geophysical surveys. Our studies reveal that the North Anatolian Fault forms a restraining stepover and
did not experience surface rupture during 1999 İzmit earthquake in the vicinity of Hersek Peninsula. We tested this
fault geometry with a finite element model in half elastic space and correlated the results successfully with the existing
topography. In addition, we ran a simple Coulomb model to explain the possible cause of surface rupture termination at
this specific location. Our studies, combined with detailed offshore bathymetry data, suggest that the restraining step of
the North Anatolian Fault on the Hersek Peninsula is capable of creating an efficient earthquake rupture barrier.
Key Words: North Anatolian Fault, Hersek Peninsula, fault geometry, rupture termination, active tectonics

Kuzey Anadolu Fayı’nın Hersek Deltası’ndaki Geometrisi ve
1999 İzmit Depremi Kırığının İlerlemesine Etkileri
Özet: 1999 İzmit depreminin batıda sonlandığı yer araştırıcılar ve Marmara Denizi civarında yaşayanlar için önemli
bir sorun oluşturmaya devam etmektedir. İzmit Körfezi’ni konu alan pek çok kıyı ötesi haritalama ve modelleme
çalışmaları yapılmasına rağmen 1999 İzmit depremi yüzey kırığının sonlandığı yerle ilgili tartışmalar Hersek Deltası’na
ve Kuzey Anadolu Fayı’nın buradaki geometrisine düğümlenmiştir. Bu sorunu anlamak üzere çalışmalarımız Hersek
Deltası’ndaki fay geometrisini anlamamıza yardım edecek şekilde jeomorfolojik analizler, paleosismik hendek kazıları,
ve jeofizik araştırmalar üzerinde yoğunlaştırılmıştır. Çalışmalarımız Kuzey Anadolu Fayı’nın bu bölgede sıkışma
oluşturan bir geometriye sahip olduğunu ve 1999 İzmit depremi sırasında yüzey kırığı meydana getirmediğini ortaya
koymuştur. Yarı uzayda sonlu elemanlar yöntemiyle modellenen bu fay geometrisi çalışma alanının güncel topoğrafyası
ile uyum göstermektedir. Ayrıca, basit bir Coulomb modellemesi ile yüzey kırığının neden burada sonuçlanmış olduğu
açıklanmıştır. Deniz çalışmaları ile karada yaptığımız çalışmaların biraraya getirilmesi Kuzey Anadolu Fayı’nın Hersek
Deltası’ında sıkışmalı bir sıçrama yaptığını ve bu fay geometrisinin etkin bir deprem kırığı engeli oluşturduğunu ortaya
koymaktadır.
Anahtar Sözcükler: Kuzey Anadolu Fayı, Hersek Deltası, fay geometrisi, kırık sonlanması, aktif tektonik


359


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

Introduction
th

On August 17 1999, the M7.4 İzmit earthquake
struck the Marmara region of Turkey causing much
devastation. The İzmit earthquake is the seventh
surface rupturing, large-magnitude earthquake in
a westward migrating earthquake sequence on the
North Anatolian fault (NAF) during the 20th century
(e.g., Barka et al. 2000, Figure 1a). The section of
the NAF within the Sea of Marmara remains as a
seismic gap between the 1912 Saros and 1999 İzmit
earthquake ruptures and the probability of a surface
rupturing earthquake event is heightened for this
region (e.g., Parsons 2004). The ~1500-km-long
dextral transform NAF is one of the major tectonic
structures of Anatolia, accommodating ~90% of
the deformation between the Eurasian Plate and
Anatolian Block (McClusky et al. 2000; Reilinger et
al. 2006). During the İzmit earthquake, four segments
(Karadere, Sakarya, Sapanca, and Gölcük) of the
NAF experienced surface rupture with right-lateral
displacements of up to five metres. The ~126-kmlong surface rupture terminated near Gölyaka in
the east (Figure 1b), but the western termination of
the İzmit earthquake is more uncertain since it lies

offshore in İzmit Bay. According to some geodetic
models (i.e. Wright et al. 2001; Reilinger et al. 2000;
Bürgmann et al. 2002) and seismicity analysis (i.e.
Pınar et al. 2001) it was suggested that the 1999
surface rupture extended 10–30 km west of the
Hersek Peninsula. Offshore studies within the Gulf
of İzmit demonstrated the presence of underwater
fault scarps (Polonia et al. 2004; Cormier et al.
2006; Uçarkuş et al. 2008), but these were somewhat
inconclusive in addressing the location of the 1999
rupture termination.
Understanding where earthquake ruptures
terminate has fundamental implications for
Probabilistic Seismic Hazard Analysis (PSHA) and
earthquake physics. Structural complexities along
faults (i.e. asperities, stepovers, bends, and structural
junctions) may arrest rupture propagation and cause
perturbation of the state of stress on adjacent fault
segments. The first and most vital step is documenting
the characteristics (i.e. hypocentre, extent, geometry,
and slip distribution) of individual ruptures.
Documenting earthquake rupture endpoints and
understanding what caused a rupture to terminate at
360

that specific location are essential for estimating the
location and potentially the magnitude of future large
earthquakes. Researchers (e.g., Barka & KadinskyCade 1988; Stein et al. 1997; Wesnousky 2008) have
convincingly demonstrated that fault geometry and
Coulomb stress loading can significantly affect the

initiation point of the next large earthquake on a fault
system. Furthermore, it has been noted that rupture
end points usually coincide with discontinuities on
faults, such as stepovers (e.g., Segal & Pollard 1980;
Sibson 1985). Thus, gaining insights into the western
extent of the 1999 İzmit earthquake rupture is
essential to estimate the magnitude of the expected
Marmara earthquake. The Hersek Peninsula is central
to the debate on the western termination of the 1999
surface rupture because it is the westernmost locality
where the NAF can be observed directly before it
enters the Sea of Marmara (Figure 1b). This paper
aims to describe the geometry of the NAF on the
Hersek Peninsula and discusses its implications on
the fault rupture of the 1999 İzmit earthquake.
In this study we employed a comprehensive,
multi-technique approach on the Hersek Peninsula.
Specifically, we performed geomorphic analyses,
geological mapping, palaeoseismic trenching,
geophysical surveying, modelling of deformation in
half-elastic space with finite elements and Coulomb
stress change modelling. We also combined our on
land results with the existing offshore data in order
to present a complete fault model for the Hersek
Peninsula. We then present a detailed discussion of
the implications of fault geometry at our study area.
Study Site
A Historical Background
The Hersek Peninsula is a triangular fan-delta with
an area of ~25 km2 in the Gulf of İzmit (Figures 1b &

2). The tip of the Hersek Peninsula extends ~5.5 km
northward into the Gulf of İzmit creating the shortest
distance (~2.7 km) between the northern and
southern shores. The location and physiography of
the Hersek Peninsula not only allows for a shortened
gulf crossing but also controls the entrance to the
gulf and the route to İzmit (Nicomedia) and İznik
(Nicaea) while providing a suitable landfall area with
its beaches and delta plain. Consequently it has been


0

40 45’

W

W

S

S

N

0

29 30’

0


29 30’

Hersek

E

1912

E

0

7
1957

İzmit

0

30 00’

44
1999b Bolu 19

0

32

0


30 00’

Gölcük segment
Sapanca segment
Karamürsel
17 August 1999
epicenter Mw 7.4

196

1999a

İstanbul

Gulf of İzmit

28

Lake Sapanca

Sakarya

2 Niksar

30 30’

0

194


0

30 30’

segment

Adapazarı

Ilgaz 1943

360

d
Kara

1939

eg
ere s

Suşehri

BLACK
SEA

t

0


men

0

31 00’

10 km

0

31 00’

Erzincan

400

Figure 1. (a) Simplified map of the North Anatolian fault and westward migrating earthquakes since 1939 (from Barka 1999). (b) Location map of the study
area (dashed square) on LANDSAT image. Star symbol shows the epicentre of the 17 August 1999 earthquake. White bold lines are 1999 İzmit
earthquake surface rupture (from Lettis et al. 2000). Dashed lines in the Gulf of İzmit are our interpretation of the fault geometry based on Kuşçu
et al. (2002) bathymetry.

b

a

400

N

0


40 45’

Ö. KOZACI ET AL.

361


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

occupied for centuries as a strategic location in the
Gulf of İzmit (Supplementary figure 1).
The settlement on the Hersek Peninsula has
been known as various names by different cultures
throughout history. It was known as Drepanon until
318 A.D. when Byzantine emperor Constantine
renamed Drepanon as Helenopolis after his mother
who was born there. By 1087, the name Cibotos
and/or Civetot were used by Europeans. However,
with the effects of repetitive earthquakes and
battles Helenopolis was, sometimes, called ‘Eleinou
Polis’ meaning ‘the wretched town’ (The Catholic
Encyclopaedia 1910). Later in the 16th century
during the Ottoman Empire it was called Hersek
after Hersekzade Ahmed Paşa. Today, it is still called
Hersek Village.
The settlement on the Hersek Peninsula has
undergone three major construction phases during
history. The first major construction took place after
Constantine renamed Drepanon as Helenopolis.

Constantine stayed in Helenopolis on the way
back to İstanbul (Constantinople) from the Yalova
thermal baths, especially during his last years. After
Constantine, especially during Justinian’s time,
Helenopolis gained more importance when the
gulf crossing traffic was shifted between here and
Dakibyza (Gebze). Justinian rebuilt Helenopolis by
adding an aqueduct, a second public bath (a rare
situation for the time), churches, a palace and other
buildings (Supplementary figure 2). He also cleared
the entrance of the Drakon River (currently known
as Yalakdere), built bridges and widened the road
to Nicaea (İznik). During this period the Drakon
River valley was used as the route connecting
Constantinople (İstanbul), Helenopolis (Hersek) and
Nicaea (İznik). Later, in the 16th century, Hersekzade
Ahmed Paşa built a small harbour, 700 houses, a
mosque with two minarets named after him, two
inns, and a care house for the poor and a school of
Islamic theology.
Many great earthquakes (Supplementary table 1)
as well as battles throughout history affected the study
site. During the palaeoseismic excavations by Witter
et al. (2000) following the 1999 İzmit earthquake
two destruction horizons were identified within the
trenches. In addition, many graves and bones were
recovered. The remnants of an aqueduct (Justinian
362

era), baths, a cistern, and the Hersekzade Ahmed

Paşa Mosque can still be readily observed in the
vicinity of Hersek Village. The Hersekzade Ahmed
Paşa Mosque experienced extensive damage only
one year after its construction during the great 1509
earthquake. It experienced less extensive damage in
other large earthquakes affecting the region including
the 1999 İzmit earthquake.
Geology/Geomorphology of the Study Site
The Hersek Peninsula has four main geologic/
geomorphic units; (1) delta plain deposits, (2) marine
terrace deposits, (3) beach ridge deposits, and (4)
lagoon deposits (Figure 3).
The oldest deltaic unit is the Upper Pleistocene
Altınova formation (Chaput 1957; Akartuna 1968;
Sakınç & Bargu 1989), which includes sand with
widespread Ostrea shells, clayey sand, silty sand,
marl and sandy marl, and uncomformably overlies
the Yalakdere and Taşköprü sandstone. Dedeler Hill,
28 m a.s.l. (above sea level), is the most prominent
geomorphic feature on the peninsula. Uplifted
marine terraces on its flanks indicate it is an area
of active uplift. Dedeler hill is a NE–SW-trending
ridge, bounded by a steep scarp on its south-eastern
flank (Figure 2) and more gentle slopes on its northwestern flank.
The delta is ~2–3 m a.s.l. and constitutes most of
the Hersek Peninsula (Kozacı 2002) (Figure 2). It is
formed by the north-flowing Yalakdere River. The
headwaters of Yalakdere in the Samanlı Mountains
are ~480 m a.s.l. and ~17 km south of the Hersek
Peninsula. Recent deposition occurs in the northwest

portion of the delta (Figure 2).
The youngest marine terraces are composed of
marine sand with loose fabric and coarse Gastropod
packages, which in some places uncomfortably
overlie the Altınova formation. They are exposed
approximately 400–500 m inland near Hersek
Village at an average elevation of about 1–2 m a.s.l.
(Figures 2 & 3). The middle and youngest marine
terrace deposits overlie the oldest marine terrace
deposits with angular unconformity. Although all
marine terrace deposits have a similar lithology they
can be easily differentiated on aerial photographs by
their elevation difference. The oldest marine terrace


Ö. KOZACI ET AL.

Figure 2. Map showing the vicinity of the study area. Coloured contours are extracted from the 20X exaggerated
digital elevation model (DEM) and overlaid on the aerial photo. Colour-coded contour intervals represent
5-m elevation changes. Note that Dedeler Hill has a NE–SW-trending elongated shape located at the
north of the peninsula with an elevation of 28 m (a.s.l.). The delta morphology with its active and passive
lobes became easily recognized as a result of using 1/1000 scale survey data. Trench locations are shown
as yellow lines (T4, T5, T6…). Seismic reflection profile location is shown as white bold line (SRP). Very
Low Frequency-Electromagnetic profile locations are shown as a white box (VLF). Previous palaeoseismic
study site by Witter et al. (2000) is shown as a yellow box (1999). Dashed white box shows the area of
Figure 3 and yellow box north of Hersek Lagoon shows the location of Figure 4. The DEM was created
using 1/1000 scale topographic survey of T.C. İller Bankası.

363



NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

deposits, about 5–6 metres thick and 10–15 m a.s.l,
represent the shore facies with sand lenses and local
Ostrea rich zones.
Beach ridges of well-rounded pebbly sands
are well exposed west of Hersek Village. Modern
rounded pebbly beach sand is well exposed on both
the east and west shores of the Hersek Peninsula.
Modern basin deposits and tidal marsh is composed
of sandy silts and can be observed around Hersek
Lagoon (Figure 3).
Palaeoseismic Trenching
Following the 17 August 1999 İzmit earthquake,
Witter et al. (2000) excavated several palaeoseismic
trenches ~250 m northwest of the Hersek Lagoon
(Figure 2) in an effort to document the rupture
history of the North Anatolian Fault on the Hersek
Peninsula. However, this trench site unearthed
remnants of an ancient settlement (Witter et al.
2000). Walls, foundations, clay water pipes, graves,
bone fragments, and evidence of destruction were
documented during these excavations and the site
was abandoned.
During the summer of 2000, we performed
additional palaeoseismic trenching in two different
locations on the Hersek Peninsula (Figure 2). The
first set of trenches was located across the tonal
and vegetation lineaments that were mapped on

the delta plain as a result of our aerial photography
interpretations. We excavated six, approximately
north–south-oriented slot trenches (T-4, T-5, T-6,
T-7, T-8, and T-9) on the delta plain west of the
Witter et al. (2000) site (Figure 2). The total length
of these 1.5-m-wide trenches is ~604 m, with depths
ranging between 1 to 2.2 metres, depending on
ground water conditions and trench wall stability. The
trenches located on the delta plain exposed laterally
continuous and undeformed strata consisting of
predominantly marine sand overlying silty sand,
sand, and clay of deltaic and lagoonal origin, but no
faults were exposed. Nevertheless, these trenches
provide a spatial constraint for the fault locations on
the delta plain.
The second set of palaeoseismic trenches (T-10,
T-12, T-14, T-15, T-16 and T-17) were excavated
364

across a south-facing scarp forming the southern flank
of Dedeler Hill and the shore of the lagoon (Figures
2 & 4). Trench T-10 was excavated as a series of short
trenches down the southern flank of Dedeler Hill
(Figure 4). It exposed a marine terrace that abruptly
thickened and a drop of the abrasion platform, most
probably indicative of fault deformation. Strands of
the North Anatolian fault and related deformation
were exposed in Trenches T-12, T-14, and T-16.
Trench T-15 was excavated perpendicular to T-16
and parallel to the NAF (Figure 4), and exposed

secondary strands of the NAF at this locality. There
was no compelling evidence of deformation within
trench T-17.
Trench T-12
Trench T-12 was excavated across a N70°E-trending
dilatational crack that was formed during the 17
August 1999 İzmit earthquake in south of Dedeler
Hill (Figures 4 & 5a, b). Trench T-12 is 16 metres long,
1.5 metres wide and 2.5 metres deep, and exposes
the North Anatolian fault at station eight. The fault
strikes N70°E with a near vertical-dip and extends
to the surface (Figures 5b, c & 6). South-dipping
(30°), shell-rich units south of the fault and massive
clay with sand and gravel are juxtaposed along the
main fault. Secondary deformation is expressed as a
N65°W-trending near-vertical fissure at station two.
The tilting of the units south of the fault indicates
north-side-up deformation.
Trench T-14
Trench T-14, 22 metres long, 1.5 metres wide, and
approximately 2 metres deep, was excavated east of
trench T-12 (Figure 4). The fault zone is exposed
between stations six and seven with an orientation
of N70°E. Marine terrace deposits and fluvial
units are juxtaposed along the fault zone (Figure
7a). Units south of the fault zone dip gently to the
south consistent with T-12 stratigraphy (Figure 7b).
Radiocarbon samples T14-6, T14-9, and T14-14
yielded calibrated (2-sigma) ages of 2215 (+133,-65)
ybp (years before present), 1562 (+129,-39) ybp, and

3785 (+174,-93) ybp, respectively. These ages indicate
faults in the trench have experienced recurrent late
Holocene ruptures.


Ö. KOZACI ET AL.

N

Qhb

E

W

Qhpk

S

Qhb
Qmt1

Gulf of İzmit
Qmt3

Qhpk

Qmt1

Qhpk


Qpu

Qhp Qmt
2

T10

T10

Qmt2

Qmt1

Hersek Lagoon
hA
Nort

nato

l

aul t
ian F

Qhb

Qha

0


1 km

Explanations
Qhpk
Qhb

modern beach sand

Qmt2

modern basin and tidal marsh

Qmt3

oldest marine terrace

Qpu

Pleistocene Altınova formation

middle marine terrace

Qhp

Holocene beach ridge deposits

Qha

Holocene alluvium


terrace riser

Qmt1

young marine terrace

drainage system

Figure 3. Geomorphic and geologic map of the Hersek Peninsula.

Trench T-16

N
E

W

T-14

S

T-17

T-16

E
N68
0


T-12a
T-15
Hersek Lagoon
fractures

T-12b
0

30 m

Figure 4. Detailed map showing trench locations (T12, T14,
T15, T16, and T17) and mapped fault traces on the
south-facing scarp of Dedeler Hill.

Trench T-16, 27 m long, 1.5 m wide, with its deepest
section reaching 2.2 metres in depth, is located
between trenches T-12 and T-14 (Figure 4). The
fault zone was observed between stations zero
and eight (Figure 8a, b). A vertical fault juxtaposes
horizontal units in the south against north dipping
units in the north at station 0.5. The main fault zone,
however, is oriented ~N65°E and exposed between
stations five and eight. This north-dipping reverse
fault is accompanied with almost vertical antithetic
deformation around station seven. Furthermore, the
stratigraphic units north of the main fault zone are
folded and uplifted as a result of transpression in this
area. Radiocarbon samples T16-1, T16-2, and T1611 yielded calibrated (2-sigma) ages of 6662 (+117,365



NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

Fault: N70 °E

Fig

ur

e5

c

a

c

b

Figure 5. (a) A fracture formed during the August 1999 earthquake. (b) Two different units are juxtaposed on both sides of the
North Anatolian fault in Trench T-12. (c) Close-up view of the fault on the western wall of the trench.

164) ybp, 6131 (+146,-139) ybp, and 5922 (+68,152) ybp, respectively. The ~6.6 ka-old T16-1 was
recovered from marine terrace deposits (Unit K). The
~6.1 ka-old T16-2A, however, was recovered from a
large anthropologic excavation (Unit L) cutting and
postdating units F, I, K, and J. These dates suggest
that the marine terrace deposits emerged above sea
level some time between ~6.6 and 6.1 ka years before
present. The units north of the fault zone are older
than the buried soil horizon (Unit D) south of the

fault zone, where Sample T16-11 was recovered.
366

These results suggest that units north of the fault zone
did not override the units south of the fault as a result
of reverse faulting until ~5.9 ka years before present.
The trench exposures provided direct
confirmation of the location of fault strands of the
NAF and demonstrated that the style of deformation
(right-lateral with a considerable north-side-up
reverse component) is consistent with the long-term
style of deformation produced from repeated surface
rupturing earthquakes reflected in the uplift and tilt
of Dedeler Hill.


Ö. KOZACI ET AL.

T-12a

S

N

root

B

?


F

?

carbonate
lining
contact

2

4

D

6

2

0

F
carbonate
lining
contact F

E

fissure N65ºW, sub-vertical

F


F

F

C
D

0m

A
A

FAULT ZONE
N70ºE, sub-vertical
8

10

12

A

very coarse shell hash; minor sand minor amount of recrystalized fibrous material, weakly cemented; localized alterations

14

B

medium coarse shell hash to shell rich zone; upper 20 cm of unit contains fewer shell fragments and greater clay content


C

medium coarse shell to shell rich zone; upper 30-40 cm of zone contains very few shells, fine sand to silty sand, weakly cemented

D

medium coarse shell hash and some sand, fining upwards, fine sand to silty sand matrix supported

E

thin lens of fine sand; no shell fragments

F

clay (bedrock) interbedded with sand, gravel, cobbles; clay is massive, mottled; sands range from fine to well sorted and well

16 m

Figure 6. Log of trench T-12 (western wall).

Geophysical Surveys
Seismic reflection and Very Low Frequency – Electro
Magnetometer (VLF-EM) surveys were performed
on the delta plain in order to locate the westward
continuation of the North Anatolian Fault (Figure 2).
The north–south-oriented, 650-m-long seismic
reflection profile is located ~600 m west of the lagoon
(see Figure 2). A sledge hammer was used as the energy
source. A 12-channel recording system was used with

five-metre geophone spacing. Interpretation of the
low-fold stacked profile indicates the presence of a
discontinuity 200 metres north of the southern end
of the seismic profile (Figure 9).
VLF-EM surveys, which have been successfully
used for non-mineralized shallow fault zone
investigations (e.g., Jeng et al. 2004), were focused
on the area of deformation in seismic reflection data
(Figure 2). Four parallel, 90-metre-long profiles were
performed five metres apart in order to confirm this
deformation both laterally and vertically. Data were
collected using an ENVI Scintrex VLF instrument
with 2 metre intervals. The in-phase (IP), outof-phase (OP), and TILT values were measured
simultaneously in three different frequencies between
15 kHz to 30 kHz (16.0, 23.4, and 26.8 kHz). All
measurements were stacked into three dimensional

plots and demonstrate a structural anomaly between
metres 50 and 70, in agreement with the observed
deformation on the seismic reflection profile (Figure
10).
Model
Combination of our palaeoseismic investigations on
Hersek Peninsula and offshore geophysical surveys
(Kuşçu et al. 2002 and Cormier et al. 2006) revealed
a left-stepping geometry for the North Anatolian
Fault (Figure 11). As a further test, we utilized finite
element modelling in half elastic space for comparing
the resultant deformation of this fault geometry
with the present day geomorphology (Figure 12). In

addition, a simple Coulomb model (Figure 13) was
employed to provide a plausible physical explanation
on how this restraining stepover might have affected
the 1999 rupture propagation.
Finite Element Modelling in Half Elastic Space
We tested the fault geometry documented during
our field studies by using finite element modelling in
half-elastic space (Figure 12). Coulomb 2.0 (King et
al. 1994 and Toda et al. 1998) was used to correlate
the modelled deformation patterns of various fault
367


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

C

B

a

A1

A2
C

0

2


4

D

F

N

14-T14/14

F

H

H

F

F

G

8

6

C

A2


E

D

14-T14/9

12

10

A1 Ahorizon, similar toA2 but includes some silt

14

16

18

2

C

14-T14/6

0 m

Trench T-14
S

20


22 m

b

A2 clay with sand and gravel, organic rich
B sandy clay to clayey sand with gravel, many gravel

clasts with diameters up to 3 cm; few tile fragments,
weakly disseminated carbonate concentrated along roots
and pores

C similar to unit B but no carbonate concentration; fewer

and smaller tile fragments; amount of sand increases
towards the bottom of the unit

D terrace deposits composed of gravelly sand to locally
clayey sand; upper contact is formed by well-rounded
cobbles with diameters up to 8 cm; common shell
fragments

E palaeo-soil; sandy gravel with rounded clasts up to 1 cm in

diameter, common shell fragments, weakly disseminated
carbonate along the roots and pores

F marine terrace deposits composed of interbedded medium
to very coarse sand and fine gravel lenses; common to
many shell fragments concentrated along beds


G clay, gravely clay, gravely sand and clay interbedding
H palaeo-trenches by human activity
charcoal samples C14-T14/6 C

14-T14/9

C

14-T14/14

Figure 7. (a) Photo showing two different units (white and black arrow heads) juxtaposing both sides of the fault (red arrow). (b) Log
of trench T-14 (western wall).

geometries with the current morphology of the
Hersek Peninsula. We ran different models with
various plausible fault geometries (such as right
stepping, left stepping, overlapping, no overlap)
determined by onshore and offshore studies (see
online data repository for results). In all models the
368

same fault parameters were applied: 1 m of dextral
and 0.3 m vertical slip for the segments to the east of
the peninsula and on the peninsula. These values are
both compatible with the InSAR inversions (please see
discussions for details) and a potential segmentation
boundary-type deformation. Assuming that the fault



B

0

B

2

D

A

6

H

0E

12

F

14

J

16

I1


18

I2

F

K

K

20

J

22

L

K

24

A

C

26 m

14-T16/1


N

charcoal samples C

14-T16/1

C14-T16/2 C14-T16/11

shell fragments

tile fragments

sandy clay with few-many shells, common tile fragments, dense and stiff, highly variable in clast and shell content
south end derived from shells in F, grades diffusely upward into modern A horizon, carbonate nodules near base,

interbedded silty fine sand with large shell fragments, moderately indurated with loose friable shell fragments

dense/stiff clay with few pockets of sand and sandy clay, massive

silty fine sand with few small shell fragments

I2

J
K
L

fine to medium sand with fine rounded gravels, poorly sorted common to variable few to common shell fragments

well sorted fine sand, friable, well bedded


poorly sorted fine to coarse sand with few gravels and common shell fragments

very coarse, very poorly sorted shell hash, pockets of sand (fine-coarse), mostly oyster shells and some gastropods

E- very coarse, very poorly sorted shell debris, fragment size varies from medium-coarse sand size
1- very friable, same organics, >90 shell fragments
2- more indurated, matrix supported, more dissemenated carbonate than E1
3- more dissemenated carbonate than E2

sandy silt-silty sand, contains few shell fragments and more commonly charcoal fragments

silty fine sand, well sorted

silty sand with gravel sized shell fragments

Ahorizon; modern soil

10

Fault: N65

8

G

F

A


A

14-T16/2

I1

F
G
H

E3

E2

E1

A
B
C
D

Fault Zone

E2

T-15

4

E3


E1

14-T16/11

A

C

Figure 8. (a) Log of trench T-16 (western wall). (b) A photo showing trenches T-15 and T-16. White dashed bold line shows the trend of the North Anatolian fault.

b

a

C

A

C

Trench T-16
0m
2

S

Ö. KOZACI ET AL.

369



NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

Figure 9. Seismic reflection profile and interpretation (see Figure 2 for location).

steps or overlaps, both segments are considered to
be dipping north at 84°. The depth of seismogenic
zone is taken to be 15 km. Of these models one
fault geometry provided a good match with fault
topography at Dedeler Hill and a selected offshore
profile (see Figure 12a, b, respectively).
Cross-section locations on the deformation
models are targeted for optimal correlation with
real topography (Figure 12). The NW–SE-oriented
western profile on the Hersek Peninsula is normal to
the NE–SW orientation of Dedeler Hill. The northwestern flank of the Dedeler Hill is a gentle slope
whereas its southeast slope is steep and abruptly
abuts the lagoon along the fault scarp (Figure 12a).
However, the approximately N–S-oriented eastern
profile corresponds to an offshore seismic profile
location (from Kuşçu et al. 2002). In this profile
bedding north of the fault is folded asymmetrically
370

with the steeper slope to the south adjacent to
the fault. South of the fault, however, basin fill
stratigraphy can be observed on that subsided side
(Figure 12b).
The best fit fault geometry model, with leftstepping faults that do not overlap, has the highest

correlation between both the onshore topography
and the offshore seismic profile (Figure 12, see
supplementary data for other fault models). In this
model the eastern segment (offshore) does not
extend to the peninsula. This model does not favour
an overlap or right-stepping geometry between these
two fault segments. The deformation obtained in this
model successfully correlates with the pressure ridge
located north of the delta and the depression area of
the Hersek Lagoon (Figure12a, c, d). Correlation of
these geomorphic features is not only limited to their
locations, but the amount of vertical deformation


%Hs/%Hp

%Hs/%Hp

approx. depth 10- 15 m

approx. depth 5-10 m

approx. depth 0-5 m

-4.0

-2.0

0.0


2.0

4.0

6.0

8.0

10.0

-4.0

-2.0

0.0

2.0

4.0

6.0

8.0

-9.0

-7.0

-5.0


-3.0

-1.0

1.0

3.0

5.0

approx. depth 10- 15 m

approx. depth 5-10 m

approx. depth 0-5 m

% OP 3-D (16.0 kHz - 23.4 kHz - 26.8 kHz)

-1.5

-1.0

-0.5

0.0

0.5

1.0


1.5

2.0

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-3.0

-2.5

-2.0


-1.5

-1.0

-0.5

0.0

0.5

1.0

approx. depth 10- 15 m

approx. depth 5-10 m

approx. depth 0-5 m

TILT 3-D (16.0 kHz - 23.4 kHz - 26.8 kHz)

-2.5

-1.5

-0.5

0.5

1.5


2.5

3.5

4.5

5.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

4.5

-5.0

-4.0

-3.0


-2.0

-1.0

0.0

1.0

2.0

3.0

Figure 10. VLF-EM measurement results are shown (see Figure 2 for location). The four profile results are combined and evaluated as a block diagram.
3-D %IP (In Phase), %OP (Out of Phase) and TILT values are plotted (left to right) for 16 kHz, 23.4 kHz and 26.8 kHz frequencies representing
approximately 0–5, 5–10 and 10–15 metre depth intervals (top to bottom) respectively. The x-axis of the 3-D diagram is along the profile line,
where the y-axis shows the width of the four parallel profiles. Note that in these diagrams a significant change in the electrical conductivity can be
observed approximately in the middle of the profiles, which are on the same trend as the anomaly on the seismic reflection profile. Black arrows
indicate fault location.

%Hs/%Hp

%Hs/%Hp

%Hs/%Hp

%Hs/%Hp

%Hs/%Hp

%Hs/%Hp


%Hs/%Hp

% IP 3-D (16.0 kHz - 23.4 kHz - 26.8 kHz)

Ö. KOZACI ET AL.

371


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

29º30´E

29º40´E

29º50´E

N

W

strike-slip fault

HEREKE

E

normal fault


İZMİT

Gulf of İzmit

DERİNCE

GÖLCÜK

HERSEK PENINSULA

0

2

4 km

40°42´N

DEĞİRMENDERE

40°42´N

40º45´N

40°45´N

S
DARICA

KARAMÜRSEL


Figure 11. Interpretation of fault geometries (from Kozacı 2002) based on detailed bathymetry data by Kuşçu et al. (2002).
There is a 2-km-wide stepover west of Gölcük. Note that there are two ~1-km-wide, rhomboidal releasing stepovers
between Değirmendere and the Hersek Peninsula. The North Anatolian fault makes a restraining stepover just east
of the Hersek Peninsula and continues westwards with a trend of N70°E.

ratios also shows similarities. Furthermore, the
observed folding geometry on the seismic profiles,
run in the east of the Hersek peninsula by Kuşçu et
al. (2002), can be correlated very accurately with the
modelled deformation pattern (Figures 12b, f).

Hersek onshore segment (Figure 13). The modelled
stress shadow caused by a rupture on the NAF east
of the Hersek Peninsula reaches –0.2 bars and creates
an unfavourable Coulomb failure condition for the
receiver fault on the Hersek Peninsula.

Coulomb Model

Results and Discussion

Stein et al. (1997) demonstrated that calculation of
static stress changes resulting from large earthquakes
can help identify how earthquakes on adjacent fault
segments interact. Their study of the 20th century
earthquakes along the NAF showed that nine out
of ten epicentres struck within the area of increased
stress (2–4 bars) caused by the preceding earthquake.
Most segments within decreased stress changes (–0.1

to –0.6 bars), however, did not experience rupture.

As presented above, the Hersek Delta is a flat plain
~2–3 m a.s.l. and the NE–SW-oriented, oval-shaped
Dedeler Hill is a prominent topographic high (28
m a.s.l.) at the tip of the peninsula (Figure 2). Thus,
it is necessary to discuss its presence because the
following observations suggest that Dedeler Hill was
raised tectonically. (1) The NE–SW-trending Dedeler
Hill is an asymmetric high; its NW flank is gentle
while its SE flank is steep (Figure 2); (2) Detailed
geomorphologic mapping revealed marine terraces
nestled around the hill at different elevations above
sea level (Figure 3); (3) Trenching on the south-facing
scarp exposed tilted (Figure 6) and folded units along
a major fault (Figure 8), and (4) the presence of the
Hersek Lagoon is evidence of subsidence south of
Dedeler Hill (Figure 2). Based on these observations,
it can be concluded that the Dedeler Hill has been
actively uplifting in this part of the Hersek Delta and
its existence provides key evidence for the style of
tectonic deformation in the study area.

Coulomb stress change calculations depend on
fault geometry, slip, and the coefficient of friction of a
source fault, and on the fault orientation of a receiver
fault. We used the best fit fault model parameters
(location, geometry, and physical fault parameters)
from a finite element model to calculate a simple
Coulomb static stress change. The coefficient of

friction value was set at 0.4, as suggested by Stein et
al. (1997). A model rupture with a 1 m dextral and
0.3 m vertical slip on a source fault corresponding to
the East–West-oriented offshore segment east of the
peninsula generates a stress shadow area in the Hersek
Peninsula area for faults oriented ~N70°E, like the
372

Offshore bathymetry and seismic data showed that
the NAF trends nearly east–west east of the Hersek


Ö. KOZACI ET AL.

Figure 12. Modelling of deformation in the vicinity of the Hersek Peninsula using finite elements in elastic half-space. The two dextral
faults (left-stepping faults with no overlap) used for this model are located according to the findings of onshore (Receiver
Fault - RF) and offshore (Source Fault – SF) studies. (a) Topography of Dedeler Hill on the peninsula is correlated with
the modelled deformation. Plan view of the grid model showing the fault geometry and the NW–SE (A–A’) cross-section
is compared to the morphology of the Hersek Peninsula. The NW–SE-oriented cross-section (A–A’) across Dedeler Hill
presents a NW facing gentle slope and a SE facing scarp. (b) An offshore seismic profile (Kuşçu et al. 2002) east of the
peninsula is correlated with the modelled deformation. The N–S seismic profile (B–B’) displays folded sediments with a
sudden dip towards the fault (south). Plan view of the grid model showing the fault geometry and the N–S (B–B’) crosssection is correlated with the offshore seismic profile east of the peninsula. Note that many geometries were run but only the
displayed geometry provides an acceptable fit to the observed morphology.

373


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

The Western Extent of the 1999 İzmit Surface Rupture

Geodetic measurements and models suggest that the
rupture of the 1999 İzmit earthquake propagated
10–30 km west of the Hersek Peninsula, with
displacements of up to 2 metres at depth. Feigl
(2002) correlated the geodetic and seismic moment
estimates and gave a detailed list of potential causes
for the discrepancies between field and geophysical
observations. A lengthy discussion of these causes
was provided by Feigl et al. (2002) specifically for the
İzmit earthquake.

SF

RF

bars
-0.2

-0.1

-0.02 0.02

0.1

0.2

Figure 13. Coulomb stress change model for the faults in the
vicinity of the Hersek Peninsula. A source fault (SF),
corresponding to the offshore fault in the east of the
Hersek Peninsula with an east–west trend, and a

receiver fault (RF– the fault on which the Coulomb
failure is calculated) in the west corresponding to
the N70°E-trending onshore segment, were placed
according to the field observations and best-fit
deformation model. The source fault was divided
into patches and the slip on this fault was assigned
to be 2 m in the middle and decreasing towards the
ends to 1 m. In addition, a 0.3 m vertical slip was put
in as a fault parameter. Note that the receiver fault
in the west that represents the fault on the Hersek
Peninsula falls in the stress shadow area.

Peninsula (Figures 11 & 12). Our palaeoseismic
trenches on the south-eastern flank of Dedeler Hill
provide evidence for major strike-slip faulting with
a north-side up reverse component (Figures 5–8).
Although other trenches on the delta plain did
not provide any evidence for faulting, geophysical
surveys confirm the westward extension of this fault
at depth (Figures 9 & 10). Palaeoseismic trenches, in
combination with the geophysical survey, indicate
that the NAF trends N70°E in the study area (Figures
3 & 4). Both field observations and existing data
suggest that Dedeler Hill has been rising as a result of
a restraining bend on this part of the North Anatolian
Fault (Figures 11 & 12).
374

We would like to emphasize that the discrepancy
between the geodetic and geologic techniques may

very well be within the uncertainties of geodetic
measurement techniques and modelling parameters.
The discrepancy between the geodetic studies and our
observations may be the product of a few reasons: (1)
methodological uncertainties, (2) some artefact of
geodynamic models used to model deformation with
geodetic data, (3) comparison of observations from
different depths, and (4) the length of observation
period. The first reason for the apparent discrepancy
between the field observations and the geodetic
models is demonstrated by Feigl et al. (2002) who
report that the uncertainties of inferred slip from
geodetic models for the 1999 İzmit rupture could be
as high as 1 metre. Also, using smooth versus stepping
fault geometry and, more importantly, using the most
accurate fault geometry, are some of the important
parameters used in geodynamic models with a direct
effect on the modelling results (Feigl et al. 2002). In
addition, Hearn & Bürgmann (2005) demonstrated
that using depth-dependent versus uniform
geodynamic models may affect the seismic moment
calculations up to a factor of three. Thirdly, our field
observations are limited to only very shallow depths
(< 40 m), in contrast to the geodetic measurements.
And lastly, the extent of an earthquake rupture may
continue to evolve after days, weeks or even years
following the main shock. Feigl et al. (2002) pointed
out that the GPS data and interferograms record
75 and 30 days of deformation and may contribute
to the uncertainties up to 10%. Hence, some of the

deformation inferred from geodetic measurements
could be the result of post-seismic deformation
beyond rupture termination that was included within
the measurement over an extended interval.


Ö. KOZACI ET AL.

Our field observations agree with Barka et
al. (2000) that the Hersek Peninsula did not
experience any surface rupture during the 1999
İzmit earthquake. It is possible that the saturated and
unconsolidated delta sediments may have masked
minor slip hence making surface rupture recognition
difficult. Alternatively, the surface rupture may have
‘skipped’ the Hersek Peninsula. However, we find
these alternatives highly unlikely, based on our field
observations. In palaeoseismic trench exposures
north of the lagoon, it is evident that the NAF has
ruptured to the surface on the Hersek Peninsula
during the late to middle Holocene. Therefore, there
is no mechanical reason why the rupture should bypass only the on-land location between the off-shore
basins that are suggested to have evidence for 1999
surface rupture. Although submarine investigations
documented surface deformation west of the Hersek
Peninsula (Uçarkuş et al. 2008), there are no piercing
features that would suggest consistent dextral
displacement. We suggest that the observed ‘fresh
looking’ surface deformation on the Yalova fault
segment to the west of Hersek Peninsula, most likely

represents secondary sympathetic deformation.
During our field observations following the 1999
İzmit earthquake we observed similar secondary
deformation on the Taşköprü Delta to the west.
Although this deformation was parallel to the
general strike of the North Anatolian fault in this
area, the associated lateral displacements at the
surface were in the order of a few centimetres only.
This kind of secondary soft sediment deformation
can be explained by strong ground shaking induced
slope failure or lateral spreading, depending on the
morphologic location.
As a result, our studies on the Hersek Peninsula
suggest that the surface rupture of the 1999 İzmit
earthquake did not extend west of the Hersek
Peninsula. It is likely that the ‘required’ slip at depth
to the west of the peninsula is the result of triggered
aftershocks similar to the Düzce earthquake
(Reilinger et al. 2000; Langridge et al. 2002; Cormier et
al. 2006) and may potentially indicate the nucleation
point of the next earthquake or simply post-seismic
deformation. This section may also re-rupture during
the expected Marmara earthquake similar to the
M7.2 1999 Düzce earthquake.

What Stopped the 1999 Surface Rupture at Hersek
Peninsula?
Our field observations (the geomorphology of
Dedeler Hill, uplifted marine terraces, depression
of Hersek Lagoon, multiple exposures of the NAF

within trenches on the south facing scarp of Dedeler
Hill, and presence of a deformation zone within
geophysical profiles) and field evidence-based simple
models demonstrate that the stepover of the NAF on
the Hersek Peninsula creates a restraining bend. Our
investigations suggest that this was efficient enough to
terminate the 1999 rupture propagation. Contrary to
the geodetic models, the absence of a surface rupture
beyond this stepover makes a compelling argument
against extended rupture. The effects of geometrical
fault discontinuities are discussed in various studies
as a candidate mechanism for stopping earthquake
rupture propagation (e.g., Sibson 1985; KadinskyCade & Barka 1989; Harris & Day 1999; Harris et al.
2002; Lettis et al. 2002). Many factors may affect this
process: (1) the type of step (releasing or restraining);
(2) the width of this step; (3) the presence of transfer
faults within the basin (Harris & Day 1993; Oglesby
2005); (4) the amount of remaining energy for the
continuation of the rupture propagation; (5) the
amount of accumulated slip on the neighbouring
segment in the rupture direction, and (6) the
direction of the source directivity.
Kozacı (2002) re-interpreted the fault geometry
between Gölcük and the Hersek Peninsula, based on
the very detailed bathymetry study results published
by Kuşçu et al. (2002). Unlike previous studies that
had suggested a ~5-km-wide releasing Karamürsel
stepover (Barka 1999; Lettis et al. 2000) or a single
east–west-trending Karamürsel segment (Harris
et al. 2002) based on previous bathymetry data, we

propose that there are two relatively narrow (~1
km wide) releasing stepovers between the Hersek
Peninsula and Değirmendere (Figure 11). As a result,
a significant amount of energy should have been
dissipated within this stretch of the fault. The location
of these geometrical discontinuities coincides with
the sudden decrease in the slip amount anticipated
by the models of Feigl et al. (2002) and Çakır et al.
(2003). However, perhaps these releasing stepover
basins are not wide enough to completely arrest the
rupture. Moreover, although the restraining step on
the Hersek Peninsula is less than 1 km wide, the fault

375


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

segment on the peninsula remains within the stress
shadow area of the adjacent fault rupture to the east
(Figure 13). Our two-dimensional coulomb model
may be used to explain why restraining stepovers, are
equally, if not more, likely to arrest rupture than a
wider releasing stepover (Figure 13).
Another cause for the rupture propagation to
run out of energy might be the 1894 earthquake,
which occurred between the Hersek Peninsula and
the Çınarcık Basin (Eginitis 1895; Ambraseys 2001;
Harris et al. 2002). Alternately, this geographical
limitation itself, as suggested by Cormier et al. (2006),

suggests a structural discontinuity during a historic
earthquake at the same location.
Lastly, the North Anatolian fault begins to
bifurcate into two branches (Princes Islands segment
in the north and Çınarcık segment in the south)
at the Hersek Peninsula. This structural junction
on its own could be considered as a significant
segmentation location capable of rupture arrest
(Kame et al. 2003). The Yalova segment exposed
within our palaeoseismic trenches along the scarp
north of the lagoon strikes ~N70°E and possibly
is the continuation of the Çınarcık segment. The
structural connection between the Princes Islands
segment and Karamürsel segment, however, is not
well developed. Cormier et al. (2006) bathymetry
data showed a ~250-m-wide, 5-km-long en-échelon
style deformation zone between the Hersek Peninsula
and where the Princes Islands segment becomes well
defined further west. In addition, two potential buried
faults were observed on the northern extent of our
seismic reflection profile west of Dedeler Hill. These
buried fault splays are potentially the continuation of
the en-échelon fault structure observed by Cormier
et al. (2006) using bathymetry west of the Hersek
Peninsula. Based on the orientation and the degree of
geomorphic expressions we suggest that a westwardpropagating rupture on the Karamürsel segment
would preferentially propagate on to the southern
(Yalova and then to Çınarcık) segments.

Conclusions

Our study demonstrates that the pressure ridge
(Dedeler Hill) located in the middle of the İzmit
Bay is a product of a restraining stepover at this
location. In addition, it implies that the 1999 surface
rupture did not extend west of the Hersek Peninsula.
We suggest that this conclusion corresponds to the
location where the North Anatolian Fault begins to
bifurcate into the Yalova and Çınarcık segments to
the southwest and the Princes Islands segment to the
northwest.
Although, the geodetic models suggest 2 m of
slip beneath the Hersek Peninsula at depth (i.e. 10–
20 km) diminishing within 10–30 km to the west
(Reilinger et al. 2000; Wright et al. 2001; Bürgmann
et al. 2002; Feigl et al. 2002; Çakır et al. 2003) the
lack of surface rupture implies that the 1999 rupture
did not extend beyond Hersek Peninsula to the west.
As a consequence we speculate that the next large
earthquake in this area with a surface rupture will
probably break the segment crossing the Hersek
Peninsula, as well as the faults to the west with
displacements similar to the 1999 earthquakes (3–5
m) at or near the surface. We therefore propose that
the restraining step over at the Hersek Peninsula
presents an efficient structural barrier for earthquake
rupture propagation at shallow crustal levels.
Acknowledgments
We would like to thank PG&E and Lloyd Cluff for
their support that made this study possible. We also
thank AK Kağıt A.S. for their generous hospitality

at their facilities in Yalova. Emre Evren and Uğur
Meray provided much appreciated help in the field
and trenches. Çağlar Yalçıner performed the VLF
measurements and processing. Ziyadin Çakır and
Matt McMackin provided much appreciated input
during discussions. We would like to further thank
reviewers Helen Cormier, Aurelia Hubert-Ferrari,
and two anonymous reviewers for their constructive
reviews.

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Ö. KOZACI ET AL.

SUPPLEMENTARY DATA
A- Archeoseismology

Figure 1. Mapshowing historical towns, cities and locations. Red dashed box indicates the study site of the Hersek
Peninsula.

See next page for Table

I


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

Table 1. Table showing the historical earthquakes affecting Hersek Peninsula and its vicinity.
DATE
M.Ö. 19
24.11.29
33
02.01.69
120
121
128
170
268
269

?.10.350
24.08.358
?.11.359
02.12.362
26.01.446
08.12.447
448
467
25.9.478
488
500
551/554
15.08.553
16.8.554
26.10.740
25.10.989
23.09.1064
14.09.1509
01.10.1567
25.05.1672
25.05.1672
25.05.1719
02.09.1754
13.01.1871
23.11.1875
19.04.1878
10.05.1878
10.07.1894
20.06.1943
26.05.1957

18.09.1963
22.07.1967

INTENSITY
VIII
IX
VIII
VII
VIII

VIII
VIII
VIII
IX, VI
VIII
VIII, VI
VIII, VI
IX, VIII
VIII
VI
VII
VIII
VIII
X
VIII
VIII
IX
VII
VIII
IX

IX, VII
VI
VI
VIII
VIII, IX
IX
M= 6.4
M= 7.0
M= 6.4, 6.3
M= 7.1

LOCATION
İznik, İzmit
İznik, İzmit
İznik, Kocaeli, Bursa and surroundings
İznik, İzmit
İznik, İzmit
İzmit
İzmit
İzmit and surroundings
İzmit and surroundings
İzmit-Gebze
İzmit, İznik
Kocaeli, İznik, İstanbul
İzmit
İznik, İzmit, İstanbul
İzmit Körfezi, İstanbul, İzmit
İzmit Körfezi, İstanbul, İznik
İzmit, Karamürsel
İzmit

Karamürsel (Helenopolis), İzmit
İzmit-Yalova
İzmit
İzmit and surroundings
İzmit, Kocaeli
İzmit
İstanbul, İzmit, İznik
Doğu Marmara
İstanbul-İzmit
İstanbul, Edirne, İzmit, Bolu, Bursa
Sapanca
İzmit
İzmit, İstanbul
İstanbul, İzmit, Karamürsel
İzmit Körfezi, İstanbul, İzmit
İzmit, Erdek
İstanbul
İzmit, İstanbul, Bursa, Sapanca
İzmit, İstanbul, Bursa
İstanbul, İznik, Karamürsel, Tekirdağ, Lapseki
Adapazarı, Hendek, Akyazı, Arifiye
Abant
Yalova, Princes Islands
Mudurnu

1. Yüksel 1995; 2. Ambraseys & Finkel 1991; 3. Ergin et al. 1967

II

RESOURCE

1, 2
1
1
1, 2
1
2
2
1
1
2
1
1
1, 3
1, 2, 3
1, 2, 3
1, 3
1
1, 3
2
3
1
3
1
2
1, 2
2
2, 3
3
2
3

1, 2
1, 2
1, 2, 3
3
3
1, 2, 3
1, 2, 3
3
2
2
2, 3
2


Ö. KOZACI ET AL.

.

Figure 2. Some of the historical remnant locations shown on a 1/10000 scale aerial photo (a), and their
photos (b–e) (photos by Kozacı, 2000). B– Roman aqueduct tower, C– Cistern, D– Public
bath, E– Hersekzade Ahmet Paşa Mosque.

III


NORTH ANATOLIAN FAULT ON THE HERSEK PENINSULA

SUPPLEMENTARY DATA
B- MODELS
N

N
A
A

A’

a

A’

b

A

A’

c
B

B’

N
B

B’
d
e
B

f

Figure 3. Left-stepping model with gap or potential restraining bend. Best-fit model.

IV

B’


Ö. KOZACI ET AL.

N

N
A

A

A’
a

b

A’

A

A’

c

B


B’

N
B

B’
d

e
B

B’

f

Figure 4. Right-stepping model. Note that this fault geometry does not create a model that is
comparable to the real geomorphology.

V


×