of Istanbul, Institute of Marine Sciences and Management, Vefa,
34470, Istanbul, Turkey
East Technical University, Dept of Civil Engineering, 06531,
Ankara, Turkey and University of South California, Dept of Civil
Engineering, 90089-2531, U.S.A.
In the present study,
coastal field observations, detailed bathynetric data and analyses
of single-channel, high resolution seismic reflection data are
used to characterize the tsunami generated during the Koaceli
Earthquake (August 17th, 1999) in the Izmit Bay.
Tsunami generation, Izmit Bay, Marmara Sea, seismic
The Izmit Bay is a
E-W trending (53 km long and 2-10 km wide) tectonically active
basin. The sea-floor relief and coastal zone physiography lie
in E-W direction. The Izmit Bay is formed by three small tectonic
basins; western, central and eastern. These basins are separated
from each other by shallow and narrow ridges. The water passage
between the western and central basins (2.7 km wide with an average
depth of 55 m) is separated by the restriction produced by the
growth of the Hersek Delta.
The stratigraphy of
the Izmit Bay starts with 25-30 m thick recent sediments unconformably
overlying the basement lithologies. The small tectonic basins
of the Izmit Bay are covered mainly by fine-grained continental
siliclastic material resulting from fluvial and littoral processes.
The western basin is also subjected to accumulation of silt-sized
sediments (Algan, et al, 1999). The average sedimentation rate
was calculated as 20 cm Per 1000 year with a maximum of 150 cm
Per 1000 year for deepest parts (Ergin and Yörük, 1990).
The effect of active
tectonic setting onshore the Izmit Bay has been described by
Akartuna (1968) and Altðnlð (1970). The tectonic basins
in the Izmit Bay were created by the EW compressional and NS
tensional forces resulted as a response to the kinematical block
displacements at active zones (Barka and Kadinsky-Cade 1988;
Kurtuluþ, 1990; Barka, 1992).
The North Anatolian
Fault Zone (NAFZ) has been the source of numerous large earthquakes
throughout the history. It splits into three strands at the eastern
part of the Marmara Sea. The northern strand passes through Izmit
Bay, traverses Marmara Sea and reaches to the Saros Gulf (Barka
and Kadinsky-Cade, 1988). The transpressional and transecstensional
regimes of the NAFZ, which has a dextral displacement about 1500
km, affected the Izmit Bay during the neotectonic period (Crampin
and Evans 1986). Active normal and lateral faults also affect
the actual basin-fill deposits in the Izmit Bay (Özhan et
al., 1985; Sakðnç and Bargu, 1989; Koral and Öncel,
1995; Seymen, 1995).
According to Barka
and Kuþçu (1996), the best structural model for
the Izmit Bay is a pull-apart model in which strike-slip fault
segments (laterally descending towards right) create the tectonic
basins of the Izmit Bay.
August 1999 Earthquake and its damages
The Kocaeli earthquake
(00:01:39.80 UTC, August 17 th 1999) of magnitude Mw=7.4 occurred
on the northern strand of the North Anatolian Fault Zone with
a macroseismic epicenter near the town of Gölcük (40.702
N, 29.987 E). The earthquake originated at a depth of 17 km and
caused right-lateral strike-slip movement on the fault. The field
observations indicate that the earthquake produced at least 125
km of surface rupture and right-lateral offsets as large as 4.2
m with an average of 2.7 m.
Almost all the industrial
facilities are located along the coastal area of the Izmit Bay.
Damages which are concentrated within 20 km of Gölcük
and ranging from small displacements to complete collapses have
been reported to the coastal structures such as ports, jetties,
cranes and the piping systems. Subsidence, coastal landslides
and the sea water inundation were occurred at Kavaklð (Gölcük),
De¤irmendere and Karamürsel.
The aim of this paper
is to describe the tsunami generated by the Kocaeli Earthquake
based on coastal observations, bathymetry and offshore shallow
seismic data. The surface ruptures of the Kocaeli Earthquake
was investigated onshore around the Bay and offshore in the Karamürsel
and Izmit basins. The seismic data gathered in this study have
led us to propose a new tectonic model with which the source
of the tsunami event can be explained.
the Kocaeli Earthquake, more than 15 field expeditions have been
arranged along the coastal area of the Izmit Bay. Tsunami events
have been investigated at 35 localities along the coasts of Izmit
Bay and more than 70 eyewitnesses have been interviewed. Some
tsunami findings and onland geological observations have been
tried to relate with the interpretation of the single-channel
high-resolution digital (º ms) sparker
(1.25 kJ) seismic reflection profiles with which the sedimentary
deposits were cleared up to 150 m below the seabed with a positional
accuracy of ±20 m. Available literature on the bathymetry
and neotectonic studies have also been re-evaluated.
reveal that more than 90 tsunamis had occurred along the Turkish
coasts between the period covering 1410±100 BC and 1999
AD. Following the Kocaeli Earthquake and knowing that many of
the historical tsunamis were clustered around the Izmit Bay,
for example in 325, 24/08/358, 08/11/447, 26/09/488, 15/08/553,
15-16/08/555, 14/12/557, 715, 740, 19/04/1878, 10/05/1878 and
18/09/1963 (Soysal, 1985; Kuran and Yalçðner, 1993;
Altðnok and Ersoy, 1996-1997, 1998), the coastal line from
Tuzla on the northern part to Çðnarcðk on the
southern part (Figure 1) has been investigated for tsunami events.
Because of the coastal subsidence which occurred between Seymen
and Kavaklð (the localities 17 and 19 in Figure 1), the determination
of the tsunami evidence could not be accomplished. These findings
were getting lost through Yalova (the locality 33 in Figure 1).
The findings that
help to detect the tsunami can be generally defined as retreat
and inundation of the sea, maximum and minimum sea level elevations
and runup heights (Table 1). Some findings of this survey are
and inundation of the sea
Along the north coast,
at Tavþancðl (at the locality 5 in Figure 1), all water
in the local port withdrew during the earthquake. In a very short
period of time, the sea came back and flooded up to 25 m inland
invading the first floor of the houses. At Þirinyalð
(at the locality 7 in Figure 1), the first floors which are 5
m close to the sea were flooded. The wave carried the seabed
living mussels into the houses damaging their doors and windows.
At the Yarðmca
Yachting Club (at the locality 9 in Figure 1), the sea was at
first receded 15-20 m and when it came back, uplifted the motor
yacht 25 m and moved it 50 m. The second wave inundated 30 m
on the shore.
Table 1. Tsunami observations in the Izmit Bay. The
signs (-, --, + and ++) preceding the values have different meanings;
receding distance, minimum elevation, + inundation distance and,
maximum elevation, respectively.
- receding distance (m)
-- Minimum Elevation (m)
inundation distance (m)
++ Maximum Elevation (m)
|| + 4
|| > 1
|| + 15
|| > 1
|| -- 3
|| ++ 2, 2.5
|| + 25, 30
|| + 30
|| - 15, 20
|| + > 60
|| + 100
|| - - ?
|| ++ ?
|| 2 - 2.5
|| - 80
|| + 60
|| Izmit, Marina
|| - 40
|| - 2 ?
|| + 50
|| + 300 ?
|| - 150 ?
|| + 35 ?,
|| - 15, - -
|| > 5
|| - 10,15
|| + 4
|| + 15 ?
|| + ? 30
|| 2 ?
|| - - 30?
|| ++ 30 ?
In the Izmit Marina
(at the locality 14 in Figure 1), the sea receded about 40 m
and passing down the seaport, caused the coast become wet. Between
the eastern part of the bay, where the fault rupture enters into
the sea, and Seymen (at the locality 17 in Figure 1) at southern
part, small disturbances, coming from northwest (Yalçðner
et al., 1999), was observed.
At Degirmendere (locality
21 in Figure 1), the sea receded about 150 m away in a very short
period of time (possibly less than 2 minutes) just before the
earthquake and when it came back, it flooded up to 35 m inland
since some mussel and dead fishes were seen in this inundation
area. There was a subsidence along the coastline 250 m along
the shore and 70 m width with two piers, a hotel, restaurant,
cafe and 14 trees at Çðnarlðk Park. Bubbles were
seen over the sea just after the earthquake.
At Halidere (locality
22 in Figure 1), the sea receded 10-15 m and then flooded up
to 50 m inland where moss and jelly fishes have been observed.
At Ulaþlð (locality 23 in Figure 1), the sea first
receded and inundated more than 5 m. The wave dragged 7 people
near the seaside and only 2 of them have been survived. The building
of Ulaþlð Municipality and the restaurants along the
coast sank into the sea together with cars, construction equipment
boats taken away by sea.
At Güzelyal (locality
24 in Figure 1), at the onset of the earthquake, outside the
breakwater, the sea rose up and then withdrew in the local port
and boats stranded. When the sea came back, the inundation distance
was about 5 m. Also at Karamürsel (locality 26 in Figure
1), the sea receded first and then inundated the shore. There
was a coastal subsidence (20 m) along 800 m coastline. At Topçular
(locality 30 in Figure 1), as usual, the sea receded first. Moss
and dead fishes were found along the 70-100 m coastal band at
the Aksa factory (KðlðC Delta, west of locality 30 in
Figure 1), showing inundation.
were belong to the captains or the seamen on the boats during
Along the northern
coasts of Izmit Bay, at Dilovasð, Körfez, Derince and
Izmit, (localities 4, 10, 12, 14 in Figure 1), the captains had
experienced the motion of the wave. At the onset of the earthquake,
at Dilovas Port (at the locality 4 in Figure 1), 1998 gross ton
tanker "Nazan" with a draft of 4.5 m, along with the
other ships (Greek Empros and Turkish Bora Mete) first fell down
and then uplifted (within the range of ~ 3 m).
At the port of Derince
(locality 12 in Figure 1), where the main cranes went off the
rails due to horizontal and vertical movement of the caisson
of up to 40 cm, two tugboats (1501 and 1503), boarding alongside
a ship which was moored to the port, first dived on their bows
as result of receding and then uplifted 2-2.5 m. The boat "Körfez-1"
was mooring a fisherman wharf at Körfez (locality 10 in
Figure 1) at around 3:00 a.m. at that night. The captain had
experienced that the boat bottom touched the sea floor and boat
drifted back to the sea. In less than half a minute, the boat
rose with the rising water and drifted to the fisherman wharf.
The captain rescued the boat by giving a maximum engine power
back. In Izmit Marina (locality 14 in Figure 1) the moored boats
fell down 2 m, as well.
Along the northern
coasts of Izmit Bay, at Degirmendere, Halidere, and Ulaþl
(localities 21-23 in Figure 1), the captains had experienced
the motion of the wave. The passenger ship "Atatürk"
(375 gross ton and 50 m in length) had been moored to the Degirmendere
Pier and the fishing boat "Kðrcðllðo¤lu-4"
(300 gross ton and 36 m in length) was boarding alongside "Atatürk".
Both were drifted with the receding of the sea. The captain of
the fishing boat "Abonoz" which was near "Atatürk"
and "Kðrcðllðo¤lu-4" reported that
"Kðrcðllðo¤lu-4" was uplifted as
high as a plane tree (more than 10 m) with the sea rise. The
fishing boat "Kðrcðllðo¤lu-4" uplifted
two times above the "Atatürk" ship and then sank.
At the Halidere Pier
(locality 22 in Figure 1), "Tatlðsu Ship" (349
gross ton and with a drift of 4 m) fell down more than 1 m below
the pier, hit the bottom, her shaft and propeller were damaged
and robes were broken off.
At the Ulaþl
local port (locality 23 in Figure 1), the ship "Kðrat"
broke her ropes and fell down below the pier and then uplifted
above its previous level. Meanwhile the ferryboat "Okmeydanð"
was sailing with 10-knots speed from Topçular to Eskihisar
(localities 30 and 3 in Figure 1), 2.6 miles far from Topçular,
at the locality 35 (Figure 1) where the water depth was 90 m.
The ferry fell down with the sea and the captain suddenly came
across with a wave having 30-40 m height about 100 m away from
bow. He then observed that the wave wall progressed towards Eskihisar
(offshore Topçular in Table 1).
According to the eyewitness
reports, the run-up and inundation measurements, the period of
the tsunami is less than a minute. The arrival time is a few
minutes to the northern coasts and a minute or so to the southern
coasts (see also Yalçiner et al., 1999).
The isopach map of
Güneysu (1999) is the most detailed bathymetric map of the
Izmit Bay drawn before the Kocaeli Earthquake. It provides a
useful tool to recognise the physiographic elements and the main
morphosedimentary features. The northern margins are steep and
the basins are asymmetric in geometry.
With the Kocaeli Earthquake,
some depth changes should have been occurred. In our interviews,
some depth changes have been reported from Ulaþli and Degirmendere.
A coastal slumping at Degirmendere caused about 20 m deepening.
On the other hand, in front of the building of the Ulaþli
Municipality, the sea deepened from 3 m to about 17 m. Such findings
punctuate the importance of micro topographic surveys using swath
Seismic data show
two main stratigraphic sequences (Figures 2a, b, c). The upper
stratigraphic units are generally unconformable on the lower
units. The upper units are less deformed and bear occasional
slumps, probably triggered by active faulting. The lower units
are deformed by faulting and folding and most probably noticing
the opening of the bay.
Seismic profiles show
that the 17th August fracture zone was located as two segments
offshore of southern margins of the Izmit and Karamürsel
basins. The western segment between De¤irmendere and Hersek
Point lies parallel to the shoreline (Figure 3). The eastern
segment strikes E-W in the south of the Izmit Basin and continues
eastward onland. The study of the onland fractures clearly demonstrates
the strike-slip nature of this segment. Small pull-apart basins
were developed between right step en echeleon faults.
The rupture at Kavaklð
(Gölcük) (Figure 4a) is 3.2 km (personal communication
with Mr. Erdal Herece) with N60W orientation. It is an oblique
normal fault. The north block of the faulting blocks has been
downthrown by about 2 m with maximum of 2.5 m. These downthrown
regions are now under the sea. Its strike-slip component is about
0.5 m with maximum of 1 m.
The faulting in the
TÜPRAS Refinery area, in the north of the Bay (west of Derince)
has been first documented by the authors. This fault strikes
N80W and is located near the shore (Figure 4b). It is a normal
fault with strike-slip component. Since both ends of this fault
enter into the sea, its length is at least 200 m. The fractures
developed are 30 cm to 1 m wide. Some of the small blocks between
these open fractures were downthrown.
The south block of
the faulting blocks has been downthrown by about 8 cm. Its strike-slip
component is about 10 cm. The faulting caused a serious fire
in the refinery. Gas plumes on Line B17 (Figure 2c) indicate
possible sediment compression in that area which is close to
the TÜPRAS fault.
Izmit Bay is a tectonically
active depositional area. The basins in the bay area are asymmetric
in geometry where the northern margins are steep. Seismic profiles
show that this asymmetric geometry is a result of half graben
formation. The seismic sequences reveal intervening hydrodynamic
and tectonic conditions during late Quaternary. Sediments in
the basin are thickest in the deepest part of the graben and
gradually thin southward. The less deformed upper seismic units,
which are unconformable on the lower units, bear occasional slumps.
These may be new generated slumps triggered by the active faulting.
This matter deserves further studying.
The subsidence of
coastal zones and the wave motions caused deaths along the southern
coasts (Altðnok, 1999). Furthermore, sank or broken boats,
lost persons and dragged objects show that the Kocaeli Earthquake
generated tsunami with an average runup of 2.5 m. The most prominent
evidence of the tsunami is the sea receding during the earthquake
at both sides of the bay. However, De¤irmendere case is
an exception, where sea receding took place a very short period
before the earthquake.
Since the period of
the tsunami is less than a minute and the tsunami arrived to
the northern coasts a few minutes later than to the southern
coasts, the centre line of the tsunami source is lying along
the central basin of the Izmit Bay closer to the southern coast.
It is highly possible that this line follows the deepest parts
of the basins.
The subsidence and
slumpings at some localities along the southern coast such as
Seymen-Kavaklð, De¤irmendere, Ulaþlð and
Karamürsel are not due to tsunami but they are probably
the result of the tectonic deformation (flower structure) of
the NAFZ. The normal faulting of the Kavaklð and TÜPRAÞ
faults are the result of this tectonic deformation, indicating
a NNE-SSW orientedextension (Figure 3).
As a consequence,
the tsunami events occurred in the bay are mainly caused by the
E-W trending tectonic deformation along the basin closer to the
southern coast. The waves possibly became more complicated by
local subsidence in coastal areas and underwater slumping.
kðyðlarð boyunca yapðlan tsunami gözlemleri,
jeolojik incelenmeler ve yüksek çözünürlü
sð¤ su sismik çalðþmalarðnðn
ðþð¤ðnda 17 A¤ustos Kocaeli Depremi
ile ortaya çðkan tsunaminin oluþum yeri ve
This study was partly
supported by the University of Istanbul, Research Fund (No 1268/050599).
The authors wish to thank to Prof. Dr. C. Synolakis from University
of South California, Prof. Dr. S. Tinti from Bologna University,
Italy, Assoc. Prof. Dr. F. Imamura from Tohoku University, Japan
and Mr. U¤ur Kuran from the General Directorate of Disaster
Affairs, Earthquake Research Department, Ankara. The authors
wish also to express their sincere thanks to Prof. Dr. E. Do¤an,
the director of the Marine Sciences and Management Institute,
Istanbul University, for his financial support, and also to the
officers and crew of the research vessel R/V Arar for their assistance
in data acquisition.
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