The Sea of Marmara lies between the Aegean Sea and the Black Sea (Fig.1 and 3) and it connects to these basins trough the Dardanelles and Bosforus Straits. It forms an active system of strike-slip basins developed along the submerged portion of the NAF system. The NAF extends east-west for over 1600 km across Turkey representing a major continental transform plate boundary between Anatolia and Eurasia (Fig.2). Earthquake epicenters and focal mechanism solutions in western Anatolia show a clustering on or near the major faults. A sequence of eight M7+ earthquakes has ruptured this boundary progressively from east to west during the last century. The most recent and westernmost events in this sequence, the M7.4 Kocaeli and M7.1 Düzce mainshocks in 1999 [Celebi et al.(2005),USGS(2000),Reilinger et al.(2000)], located in the eastern Marmara Sea region, were particularly destructive. Together they ruptured about 160 km of this fault system including its submarine portion in the Gulf of Izmit. Except for the 1912 M7.3 earthquake in the west of the Sea of Marmara and the Ganos region however, relatively little strain is thought to have been released by earthquakes along 150km long part of the transform fault in the Marmara Sea and since the mid 1700's. This portion of the transform is, therefore, identified as a seismic gap where accumulated elastic strain is about as much as it was released by slip in the 1999 earthquake sequence.
After the 1999 earthquakes the international community is collecting geological and geophysical data to study the fault distribution, dynamics and kinematics in the Sea of Marmara, focusing in particular on the seismic risk assessment in the region close to Istanbul [Le Pichon et al.(2001),Imren et al.(2001),Armijo et al(2002),Le Pichon et al.(2003),Flerit et al.(2003),Kurt et al.(2000),Polonia et al.(2002),Polonia et al.(2004)].
There are two reasons for the strong interest in this region. First, this area is high seismic risk, including the city of Istanbulwith its 15 million inhabitants. Second, there is no consensus on the geometry of the faults strands underwater, the likely mechanism of strain partitioning along the main fault strand, and on the components of shortening and extension within the dominantly transcurrent regime [Okay et al.(2000),Le Pichon etc al.(1999),Parke et al.(1999),Aksu et al.(2000),Armijo et al(2002),Armijo et al.(2005)]. These uncertainties prevent a reliable evaluation of hazards in this region.
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Two geological/geophysical expeditions were carried out in the Sea of Marmara by ISMAR-CNR , in the frame of an international collaboration between the Istanbul Technical University (ITU), TÜBITAK and L-DEO (Columbia University).
The first cruise [Bortoluzzi et al.(2001,a)] (MARM2000) with R/V Odin Finder started in late October 2000 and produced detailed multibeam, chirp and SSS profiles and some cores in the areas of Izmit and on the shelf SW of Istanbul. The second cruise [Bortoluzzi et al.(2001,b)] (MARM2001) took place in spring 2001 with R/V CNR Urania. High and very high resolution geophysical data were acquired during this expedition (Multibeam morphobathymetry, side-scan sonar, chirp sonar, MCS, magnetometry), together with 166 m of gravity and piston cores. The main aim was to identify the seismogenic strands of the NAF and to define their kinematics in the studied area. The principal results of these two cruises were published in [Polonia et al.(2002),Polonia et al.(2004),Cagatay et al.(2003),Seeber et al.(2004),Cormier et al.(2005,in press)].
Since then, an additional project collaboration was signed between Turkish ITU-EMCOL and Italian ISMAR-CNR. University of Trieste (DISGAM) and University La Sapienza from the Italian side, and MTA, IBB and SHOD from the Turkish side were also partners of the project.
The ISMAR-CNR presented a proposal for R/V Urania ship time.
The main objectives may be listed as folllows:
Starting from the work already done, we planned to acquire a new set of geophysical data and to map at various vertical scales (from a few cm to a few m of resolution and from few tens of m to 1 to 2 km of penetration) the active strands of the NAF in two key areas at the eastern and western ends of the Marmara basin. The work planned is mainly located in shallow water to understand the transition from the subaerial to the submerged portion of the NAF system close to the epicenter of 1999(Izmit) and 1912 (Ganos) eartquakes. To further investigate the geology of the Marmara region we focused on other areas, such as (a) the Saros Gulf, as the continuation of the northern strand of NAF in the Aegean Sea and (b) the Gemlik Gulf, interested by the Central strand of NAF. Other work was also planned in order to find active faults in the Northern shelf of the Sea of Marmara, from Gaziköy to Siliviri and Büyükçekmece, but principally on the shelf around the Prince Islands, from the Marmara junction of the Bosphorus in the west to the Tuzla Gulf in the east.
A ship period of 26 days, including 5 days of transit was assigned to the project by CNR and scheduled for late summer 2005. This paper reports the shipboard activities during the cruise MARM05 with R/V Urania of CNR.
We focused on multibeam swath bathymetry, CHIRP-SBP, MCS, coring, core-logging and description, to study five areas of the continental shelf and slope in the Sea of Marmara and of the Northern Aeagean Sea(Fig. 3):
The cruise started in Rhodes 2005-09-08 and ended in Bari 2005-10-05. Weather conditions were generally good to very good, except for one day in the Aegean Sea during the transit to Italy.
Hereafter, a description of the ship, equipment and their usage is given, along with details of the general settings, performances and some scientific and technical results.
