Imaging the basin and fault geometry from the multichannel seismic reflection data in the Tekirdağ Basin, Marmara Sea, Turkey

Abstract

S U M M A R YDetermination of the fault geometry in the Marmara Sea has been a major problem for the researchers after the occurrence of the 1999 August 17 Golcuk (M = 7.4) earthquake. To shed a light to the problem we applied the pre-stack Kirchhoff depth migration technique to the multichannel seismic reflection data of three profiles to investigate the basin and fault geometry in the Tekirdag Basin in the western Marmara Sea. The boundary of the basin and its sediments were revealed in N-S and NE-SW directions in depth sections. We identify major fault types involving these structures at different locations in Tekirdag Basin showing that the basin is developed under their movement. The North Anatolian Fault is imaged and interpreted as transtensional character at the centre of the Tekirdag Basin that is symmetrically divided with a large distributed zone. The fault plane is imaged through the depth of 2 km dipping to the north with 90 • in the upper 350 m and 82 • in the lower part. The basin thickness reaches about 2.5 km at that point. Syn-transform sediments of the basin are disturbed by some normal faults dipping to the north. These faults are represented by notable displacements of the reflections which prompted us to consider them as a potential tsunami source if they move during a large earthquake along the major fault. Another major fault is identified at the westernmost of the basin. Because it shows the same character as Ganos fault, it might be submarine part of it. It has reverse component with the dip angle of 65 • to the north and trending along the western flank of the basin. A reverse fault is identified appearing in low angle (∼20 • ) surrounding the edge of the submarine slide at southwest of the basin. From its geometry it is interpreted as a local fault formed between two main faults. From the sketch of the basin and the fault geometry obtained from the images we suggest that the basin should be formed by a pull-apart system.

Interpretation of ambiguous reflection data by imaging processes: An example profile crossing steep submarine valley at the sea bottom

“…Later, studies (Okay et al, 2004;Seeber et al, 2004;Kanbur et al, 2007) have shown that this interpretation is inconsistent with the land data requiring north-dipping reverse fault, indicating an obvious misinterpretation of the seismic profile by Okay et al (1999). At that point, the main question is why and how this misinterpretation is possible.…”

“…The results of Kanbur et al (2007) have clearly shown the importance of the advanced stacking process in interpreting the multichannel reflection data profile across the complex structure of the Northern strand under the western Marmara Sea. The main objective in this study is to clarify the inconsistency between the interpretations of the seismic reflection profile (profile 3 in Fig.…”

“…The main objective in this study is to clarify the inconsistency between the interpretations of the seismic reflection profile (profile 3 in Fig. 1c) performed by Okay et al (1999) and those by Kanbur et al (2007) and the reasons behind the inconsistencies.…”

“…Therefore, some other advanced methods, such as prestack Kirchhoff depth migration, is also used to process the data in the multi-offset form of seismic experiment; in addition to stacking, post-stack migration is used to overcome the problem and to provide additional information. Several studies have shown that pre-stack Kirchhoff depth migration technique may image the steeply dipping structures and give significant contribution to the conventional stacking process technique in tectonically complex areas (Louie et al, 1988;Louie and Qin, 1991;Honjas, 1995;Kanbur et al, 2000;Kanbur, 2006;Kanbur et al, 2007).…”

“…This section is presently one of the most known and hazardous seismic gap on the earth because it lies in close vicinity to the densely populated and industrial center of Turkey. Therefore, extensive scientific studies have been implemented to reveal geometry and structure of the Northern strand since the 1999 _ Izmit earthquake (Okay et al, 2000;Imren et al, 2001;Le Pichon et al, 2001;Armijo et al, 2002;Parke et al, 2002;Okay et al, 2004;Seeber et al, 2004;Armijo et al, 2005;Kanbur et al, 2007).…”