IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS004 Oral Presentation 1895
Active fault geometry and kinematics of NW Anatolia, new insights from
revision of active fault map of Turkey
Mr. Cengiz Yildirim
Geology MTA IASPEI
The revision of the Active Fault Map of Turkey has been caried out by the MTA and this study presents
the preliminary results of the project in NW Anatolia. NW Anatolia is a transition zone between the
Aegean extensional tectonic regime and the North Anatolian transform fault system (NAFS). The NAFS
turns into a broad deformation zone and bifurcates into two strands as the northern and the southern in
the Marmara region. Lateral motion of the Anatolian block is essentialy accommodated by the northern
strand in the Sea of Marmara. However, the southern strand is included in the NW Anatolian transition
zone as a major splay bifurcating from the master strand of the NAFS. The transition zone (NATZ) is
structurally delimited by the S nd rg -Sincanl fault and the Bergama-Zeytindag fault zones from the
Aegean graben system in the south. However, the eastern boundary of the zone is connected to the
Eskisehir and the Tuzgolu fault zones delimiting the eastern boundary of the Aegean extensional
regime. In this study, about forty active faults were mapped in detail and the active faults were
classifed into four sub-classes as earthquake rupture, active fault, potentially active fault and
neotectonic fault or lineament. The new data reveal that the active faults were localized along four
major bend systems concave to the south in the region, namely the Band rma-Biga, Manyas-Gonen,
Bursa and Bal kesir bends. The Band rma-Biga bend is connected to the westernmost tip of the southern
strand or splay of the NAFS. However, in the east the Bursa bend is connected to the Eskisehir fault
zone via the Dodurga fault. Both the eastern and the western flanks of the bends are controlled by right
lateral strike slip faults. However, the faults trending NE-SW are transpressional and those trending E-W
and NW-SE are transtensional just at the apex of the bends. This structural pattern accommodates a
counter-clockwise rotation of the sub-blocks delimited by the active faults. The Manyas-Gonen bend and
the Bursa bend are the best examples of the bend kinematics of the region. The Bursa fault of E-W and
NW-SE trends at the apex of the bend display normal dip-slip characteristics, however, the Uluabat fault
which is located immediately to the west of the bend is a reverse oblique right lateral strike slip fault.
The findings from this study are consistent with the seismologic and the GPS data. The overall geometry
of the bends are parallel to the Gediz graben and to the large bend of the NAFS in the Sea of Marmara.
Our data imply that bend geometry due to block rotations dominates the kinematics of active faults in
NW Anatolia. The active faults in the southern Marmara and the Biga peninsula are the Yenice-Gonen,
Manyas, Orhaneli, Ulubat and Bursa faults forming the Manyas-Gonen and the Bursa bends that can not
be directly connected with the NAFS. These two bends connect to inner west Anatolia instead of to the
NAFS. The geometry of the bends is controlled by the paleotectonic structures and the granitic plutons
as in the Bursa and Manyas-Gonen bends. The 1855 historical earthquakes originated on the reverse
strike slip Ulubat fault and then the normal dip-slip Bursa fault on the Bursa bend. In the 20th century,
a similar earthquake sequence occurred on the ManyasGonen bend during the 1953 Yenice- Gonen
(M:7.2) and the 1964 Manyas earthquakes. The Yenice-Gonen earthquake nucleated on the restraining
flank of the Manyas-Gonen bend, whereas the 1964 Manyas earthquake (M: 6.9) nucleated on the
releasing flank of the bend and occurred on a dip-slip oblique normal fault. Hence we suggest that the
earthquake sequences in the region primarily initiate on the restraining flanks and then propagate
toward the releasing flanks of the bends. Submission Information 1-JSS004 2- Non-instrumental
seismometry - Quantification of past and future earthquakes: balancing the geological, historical and
contemporary strain records 3-Active tectonic, Kinematic, NW-Anatolia 4-Cengiz YILDIRIM, MTA