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COASTAL DEFORMATION OCCURRED DURING THE AUGUST 17, 1999 İZMİT
EARTHQUAKE
A. BARKA1, W. LETTIS 2, E. ALTUNEL 3
1)
Deceased, Formerly ITU, Eurasian Earth Science Institute,İstanbul, Turkey
William Lettis &Association, Walnut Creek, CA, USA
3)
Osmangazi University, Engineering Faculty, Department of Geology,
Eskişehir, Turkey
2)
Abstract
Sudden elastic motions, deformation of the continental slopes such as large mass movements,
and landslides are major reasons for the tsunamis. The types of nearshore deformations,
resulted from the August 17, 1999 İzmit Earthquake are investigated and described under the
basic headings of faulting, lateral spreading, and slumping in this study. Analysis of near shore
deformation can help to prevent the future losses of both lifes and properties in similar areas.
1. Introduction
Sudden elastic motion and deformation of the continental slopes such as large mass movements
are major reasons for the tsunamis. In this paper, types of near shore deformation resulted from
the August 17, 1999 İzmit Earthquake are described. Basically, three main types of coastal
deformation are observed in the Gulf of İzmit and Sapanca Lake; faulting, lateral spreading and
slumping (Fig. 1).
2. Faulting
Coastal deformation was characterized by two main types of faulting during the August 17,
1999 İzmit earthquake; normal and strike-slip faulting or their combination. Strike-slip faulting
in some cases was responsible for local slumping such as in Değirmendere. In Değirmendere,
about 150 m by 100 m portion of the delta submerged about 35 m under the sea due to unstable
slope cut by the reactivation of the Gölcük-Karamürsel strike-slip segment. The Gölcük delta
also submerged about 2.3 m due to normal faulting along the 2 km long secondary oblique fault
connecting the Gölcük-Karamürsel and Sapanca segments of the rupture zone (Fig. 1). As a
result of this submerge, the sea advanced into the land more than 1 km in places (Fig. 2).
A. C. Yalçıner, E. Pelinovsky, E. Okal, C. E. Synolakis (eds.),
Submarine Landslides and Tsunamis 171-174.
@2003 Kluwer Academic Publishers. Printed in Netherlands
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3. Lateral spreading
Lateral spreadings were most common in the recent depositional environments such as deltas
and beaches along the coast of Sapanca Lake and Gulf of İzmit. Lateral spreading caused
extensive damages both in the north and south sides of Sapanca Lake (Fig. 1). The Sapanca
Hotel, located in the south side of the lake (Fig. 3a), was tilted towards north as a result of
lateral spreading (Fig. 3b). In the Gulf of İzmit, Gölcük delta, Halıdere, Değirmendere and the
Derince regions were effected by lateral spreadings (Fig. 4).
Figure 1. Location of surface rupture, lateral speareding (dimonds), slumping and
liquefactions (squares).
Figure 1. Coastal deformations observed in the Gulf of İzmit and Sapanca Lake
Kavaklı fayı
(a)
(b)
Figure 2. (a) Normal fault on the Gölcük delta,(b) pre and post earthquake shoreline on the
delta.
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(a)
(b)
Figure 3. Sapanca Hotel (a) before the August earthquake, (b) after the earthquake.
(a)
(b)
Figure 4. Two lateral spreading examples,in north of Sapanca Lake (a) and Gölcük delta (b)
4. Slumping
As mentioned above, the major slumping occurred in Değirmendere during the August 17,
1999 İzmit earthquake. Değirmendere is located on a delta in the south coast of İzmit Gulf
(Fig. 1). Foot of the unstable delta was cut by the reactivation of the Gölcük-Karamürsel
segment and a major part of the delta submerged into the see (Fig. 5). Except for
Değirmendere, there are some evidence indicate that some submarine slumping might have
occurred in north of Aksa and Yalova in the south coast of the Gulf.
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(a)
(b)
Figure 5. Slumping in Değirmendere. Arrows show the slumping direction .(a) A general view.
Dashed red line shows approximate delta border before slumping. (b) Close-up view.
5. Conclusion
The lesson learned from the August 17, 1999 İzmit Earthquake is applicable both to the
historical and future earthquakes. After examining the coastal deformation of the August 17,
1999 İzmit earthquake, it is possible to predict the future sites of similar submarine and near
coast deformation and to prevent the future losses of both lifes and properties. This information
is also valuable for analysing tsunami potentials in certain regions. This experience can also
help to enlarge our understanding of near shore deformation which occurred during the large
historical earthquakes.