Last update on April 2, 2000

Field Report on the

Geological Study of the Kocaeli (August 17,1999) Earthquake

Sponsored by

Science and Technology Agency, Government of Japan (STA)
Geological Survey of Japan
and
General Directorate of Mineral Research and Exploration of Trukey (MTA)

PARTICIPANTS

Yasuo Awata (Geological Survey of Japan)
Makoto Okamura and Hiromi Matsuoka (Kochi University)
Toshihiko Sugai, Shinji Toda, and Taichi Furuhashi (Tokyo University)
Koji Okumura (Hiroshima University)
Tsuyoshi Haraguchi (Fukken Co. Ltd.)
Omer Emre, Tamer Y. Duman, Ismail Kuscu, Ahmet Dogan, Selim Ozalp
Sahin Karagoz, Ertan Toker, Rezzan Baysungur and Bahtisen Gokergil
(MTA Geological Research Department)

Introduction

Japanese and Turkish researchers on the geology of earthquake are now condcting a joint research on the Kocaeli (or Izmit) earthquake of August 17, 1999. The mission is based on the urgent needs to understand the earthquake itself as well as the past earthquakes in and around the Marmara Sea.

This field report introduces the outline of the ongoing research in order to help better coordination and communication among the international community of seismologists and geologists devoted for earthquake hazard mitigation. Koji Okumura is preparing this page and is responsible for the contents, which are very provisional and are not always based on the concensus of the all participants. Further information on the results will be published later on various occasion.

The ongoing research consists marine geological survey of the North Anatolian fault in Izmit bay and paleoseismological study of the fault on shore.

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The North Anatolian fault around Marmara Sea

The North Anatolian fault in Izmit Bay

The marine survey aims to profile the fault under the sea using high-resolution sono-probe techniques developed in Japan by Okamura and others. As of March 10th, we are getting clear image of the fault under the sea. We try to map the fault as extensive as possible in Izmit Bay in hope of defining the western termination of the August 1999 ruptures.

[IMAGE]

High-resolution profile of a submaine fault

[IMAGE]

Marine survey team appeared on newspaper, from left to right; Hiromi Matsuoka, Makoto Okamura, and Ismail Kuscu.

Paleoseismological study on shore

Paleoseismological studies are being carried out in two sites. One is near Sarimese, south of Kosekoy, east of Izmit [40d 43m 22.7s N --30d 01m 43.1s E] and another is near Kadikoy, east of Adapazar [40d 42m 02.9s N --30d 28m 56.3s E].

Sarimese site

Sarimese site is situated in a distinct right-stepping jog of 60 meter wide and 150 meter long. This jog comprises a small pull apart basin bounded by the faults with about 1 meter dip-slip during the August earthquake. The attempt to excavate the evidence of repeated basin subsidence was not successful. Instead, we succeeded to identify a couple of events in 3 trenches just west of the jog. 2 or 3 events during past 300 to 500 years including the 1999 event are recognized in the trenches.

[IMAGE]

Norther Strand of the fault at Sarimese site

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EDM-GMT map of the Northern Strand above, 20m grid

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Subsidiary ruptures further north

[IMAGE]

Master rupture zone on trench wall

Kadikoy site

At Kadikoy site, the 1999 ruptures show almost pure strike slip with a rectilinear strands. On each trench wall, the rupture is represented by single shear plane. However, there are several trancated fault planes within 1 to 2 meters from the 1999 rupture. Those trancated fault planes may indicate ealier faulting events. At this site, we applied the GeoSlicer technique. A series of 1.4 meter wide and 1.5 meter tall slices clearly showed the 1999 rupture and earlier deformation. Now we try to slice the sediments from the bottom of 1.5 meter deep trench to get more information on past earthquakes.

[IMAGE]

Trenchs at Kadikyo site

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GeoSlicer brings out the fault.

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Do you see the deformation?

The research team is located below until March 23rd. We welcome you visit and discussion.

Hotel Ardahan in Hendek
Phone and Fax: +90-264-614-6822
Cellular phone: +90-535-223-6231

E-mail: kojiok@ipc.hiroshima-u.ac.jp

11 March 2000