INTRODUCTION

The Sea of Marmara lies between the Aegean Sea and the Black Sea (Fig.1 and 2). It forms an active system of pull-apart basins developed along the NAF system, that extends east-west for over 1600 km across Turkey and is one of the world's major continental transforms. 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 Duzce mainshocks in 1999, were particularly destructive [1]. Together they ruptured about 160 km of this fault system including the submarine portion of the fault in the Gulf of Izmit , eastern Marmara Sea. Relatively little strain, however, is thought to have been released by earthquakes along 150km of the transform through the Marmara Sea 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 sequence.

After the 1999 earthquakes the international community is attempting to study the fault distribution in the Sea of Marmara. Moreover, a thorough study of the seismogenic behaviour of the fault system in the Sea of Marmara has not been attempted yet.

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Figure 1: Geographical area setting. Topographic and bathymetric data by Sandwell and Smith [3].

To tackle these objectives an international collaboration between LDEO,TÜBITAK , and IGM-CNR was set up and resulted with an integrated research project in the area. A first cruise [2] (MARM2000) was done with R/V Odin Finder 29-oct-2000 to 4-nov-2000, that produced detailed multibeam, chirp and SSS profiles and some cores in the areas of Izmit and on the shelf SW of Istanbul .

We believe that an integrated approach involving the acquisition and analysis of geophysical (multibeam, side-scan-sonar, chirp), geological (cores) and seismological data would represent an innovative strategy in the emerging field of "submarine earthquake geology" to assess the seismic hazard in the Marmara region. The project involves geological/geophysical surveys combining Multibeam, side-scan sonar maps and chirp sub-bottom profiles, reflection seismic and magnetometry with carefully positioned core samples to resolve the shallow geometry and kinematics of the fault system in the northeastern Marmara Sea.

We expect to resolve fault geometry and kinematics and to date their most recent ruptures at the same scale as typical paleoseismic studies on land. We will be guided by previous and ongoing projects studying larger scale and deeper characteristics of the fault system in the Sea of Marmara.

The principal objectives are:

• the identification of the main faults accounting strike-slip motion through Marmara;
• determination of offset on features and structures by these faults;
• dating of their most recent ruptures at the same scale as typical paleoseismic studies on land;
• the dating of the slip on the faults using C14 to calibrate sub-bottom reflectors and determine the displacements of the faults trough time for the past 25000 years.

This paper reports the shipboard activities during the cruise MARM2001, which took place 24-May-2001 to 21-Jun-2001 with R/V Urania of CNR.

During this 19-days cruise in the area we focused on multibeam bathymetry, CHIRP-SBP, Multichannel seismic, coring, core-logging and description, and ROV, to study six areas of the Continental shelf and slope in the Sea of Marmara (Fig. 2):

AREA a

the Gulf of Izmit 

1. the approach to the Gulf, Yalova to Tuzla,
2. the western portion, Darica to Hersek,
3. the central portion, Hersek to Körfez ,
4. the eastern portion, Golcuk and Izmit 

AREA b

the area between the Imrali I. and the Armutlu Peninsula

AREA c

the area SW of Tuzla to the Çinarcik Basin

AREA d

the area offshore Büyükçekmece on the continental slope and shelf SW of Istanbul 

AREA e

the shelf areas in proximity of the Prince Islands, SE of Istanbul 

AREA f

the area offshore Gaziköy to the Tekirdag Basin.

The accurate bathymetric DTMs, DGPS positioning and ship's capabilities to keep position on station were used also to recover cores strategically positioned along the CHIRP-SBP profiles that crossed the faults. Some cores were also taken for stratigraphic control. A particular focus was put on areas A and F, which lie directly on the NAF.

The cruise started in Ravenna 24-may-2001 and ended in Ravenna 21-jun-2001. Weather conditions were generally good to very good (6 hours stand-by meteo were reported).

Hereafter, a description of the ship, equipment and their usage and is given, along with details of the general settings, performances and some results.

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Figure 2: Geographical area setting. The capital letters point to the areas surveyed during the present cruise. The red point is the epicenter of the M7.4 17-aug-1999 Kocaeli earthquake (after www.eeri.org). Heavy and dotted black lines are the NAF locations in its North, Central and South strands (digitized by the MTA map found at www.ifjf.uib.no). Bathymetric data regridded with the digital data of IBCM [6] [5].