Segmentation along the North Anatolian Fault between the Central Marmara Basin and the Gulf of Saros and Behaviour of the Segments during the Large Earthquakes in the 20th Century

TUR H., GÖKAŞAN E., USTAÖMER T., GÖRÜM T., Emre Ö.

63RD Geological Congress of Turkey, Ankara, Turkey, 5 - 09 September 2010, pp.1-2, (Summary Text)

  • Publication Type: Conference Paper / Summary Text
  • City: Ankara
  • Country: Turkey
  • Page Numbers: pp.1-2
  • Istanbul University Affiliated: Yes

Abstract

In this study, geometric features and segmentation of the 190 km-long part of North Anatolian Fault
(NAF) between the Central Marmara Trough and the west of the Gulf of Saros are studied and the
surface ruptures formed during the major earthquakes in 20th Century are discussed.
The NAF between the Central Marmara Trough and the Gulf of Saros is composed of three fault
segments; the Tekirdağ, Ganos and Saros segments. The Tekirdağ fault segment, trending N85°E on
the floor of the Marmara Sea has a 35 km-length. Strikes of the Tekirdağ and Ganos segments
intersect at ~15° angle. These two segments are connected by a bend of 7 km long and 3 km wide.
The 90 km-long transpressional Ganos fault, trending N68-70°E, is made up of four sub-geometric
segments. The Ganos and Saros segments, on the other hand, are separated from each other by a 0,
4 km wide releasing step-over. N75°E trending, 42 km-long transtensional Saros fault probably
creates the Saros inner basin. The northern margin of the basin is bounded by the principle fault
whereas the southern margin is delimited by secondary faults having dominantly normal offsets.
The principle fault is divided into two geometric sections, the eastern segment (30 km-long) and the
western segment (13 km-long).
Major earthquakes with magnitudes greater than 5.0 (1912/Mw: 7.4; 1975/Mw 6.7, 2003/Mw 5.7)
have occurred in this portion of the NAF during the 20th Century. The 1975 and 2003 earthquakes
originated from the Saros fault. The 1912 earthquake produced a 140 km-long multi-segment
surface faulting along Ganos and Tekirdağ fault segments. This rupture displays geometrical
similarities to those that formed during the 1999 İzmit and Düzce earthquakes. In 1912, there were
two main shocks, the first one occurring on 9th of August, 1912 (Mw 7,4) and the second one on
13th of September, 1912 (Ms:6,9). The previous studies proposed that the second event was thought
to have occurred on the Ganos fault. There is, however, no identifiable barrier to stop fault rupture
propagation during the first main-shock on the Ganos fault. We speculate that the first main event
occurred on the Ganos fault during the 1912 earthquake, whereas the second event (M 6.9) was