Novensia: Studia i Materiały (14.2003)

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Fig. 2. The geological structure of the island of Marmara [after Asgari
1978]: 1 — marble; 2 — gneiss; 3 — shale

The Sea of Marmara fills a tectonic collapse sink which developed in the late
Tertiary and early Quaternary. As recently as at the end of the Tertiary Period,
the north-western part of Anatolia, bordering on the sea, still communicated with
the mountains in Thrace and the Rhodopes. Due to the breaking of the Earth’s
crust, a tectonic collapse sink developed, which tumed a former river bed into
the straits of the Bosporus and the Dardanelles. However, the two straits differ
considerably. The Dardanelles, the straits which joins the Sea of Marmara with
the Aegean Sea, is app. 120 km long and 1.3-27 km wide. It is relatively shal-
low, its maximum depth amounting to 153 m, and minimum, to 29 m. Its cuts
through a layer of Tertiary limestone, marł and sandstone. Its shores are fiat and
treeless. The strait of Bosporus is a meandering channel app. 31 km long and
0.7-3.8 km wide. Its shores are steep and abound in inlets (fig. 1). The strait cuts
through old Paleozoic structures of shale and sandstone, and old volcanic rock.
Both straits allow exchange of water between the seas, the outflow of water from
the Black Sea being much larger than from the Aegean Sea.
Earthąuakes are freąuent in the basin of the Sea of Marmara. The one that
took place on July 17, 1999, in the region of Izmit (the ancient Nicomedia) was
particularly disastrous, taking many lives and causing enormous damage. The
earthąuake occurred 15 km under the ground, east of Gólciik on the North Ana-
tolian Fault (fig. 1). The Fault, 1600 km long, extends from the east of Turkey to
Greece, and basically consists of a series of smaller faults, constituting the bound-
ary between the Eurasian and the considerably smaller Anatolian plates of the
lithosphere [Misar 1987, 219-255; Zuchiewicz 2000, 971-990]. Although the two