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    Kinematics of the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), eastern Turkey
    (Springer, 2006) Yilmaz, Huseyin; Over, Semir; Ozden, Suha
    In this study we determined the stress regime acting along the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), from the Neocene to present-day, based on the inversion of striations measured on faults and on the focal mechanisms of earthquakes having magnitudes greater than 5.0. The inversions yield a strike-slip stress regime with a reverse component (i.e., transpression) operative in the Neocene to present with a consistent N-to NW-trending or, axis 156 +/- 11 degrees and an E- to NE-trending sigma(3) axis, sigma(7) 9 degrees sigma(3), producing left-lateral motion along the East Anatolian Fault Zone. The inversions of focal mechanisms yield a strike-slip stress deviator characterized by an approximately N-S (N1 degrees W)-trending sigma(1), and an approximately E-W (N89 degrees E)-trending sigma(3) axis. Both the kinematic analysis and structural observations indicate that the stress regime operating in the study area has had a transpressional character, giving rise to the Mio-Pliocene compressive structures (reverse faults, thrusts and folds) observed in the study area. Field observations allow estimation of a Pliocene age for the strike-slip East Anatolian Fault Zone.
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    Late cenozoic stress field in the Cameli Basin, SW Turkey
    (Elsevier, 2010) Over, Semir; Pinar, Ali; Ozden, Suha; Yilmaz, Huseyin; Unlugenc, Ulvi Can; Kamaci, Zuheyr
    A history of deformation has been determined for the Cameli Basin located in the western part of the major Fethiye-Burdur Fault Zone, interpreted as the on-land continuation of Pliny-Strabo fault system (e.g., eastern boundary of the Hellenic Arc). Inversion of fault slip vectors affecting Mio-Pliocene to Quaternary formations in the Cameli Basin, in the southwestern segment of the transtensional Fethiye-Burdur Fault Zone, yields two different normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes; a NW-SE (N129 +/- 19 degrees E) sigma(3) axis and a NE-SW (N50 +/- 16 degrees E) sigma(3) axis. The orientation of fault sets is predominantly around the NE-SW direction in the major Fethiye-Burdur Fault Zone, making the extension NW-SE. The mean R values are 0.74 and 0.69 for both extensions indicating a triaxial stress state, which is clearly different from radial extension and from transitional to strike-slip stress state. The NW-SE extension is probably responsible for the formation of the Cameli Basin during Mio-Pliocene time. In contrast, the inversion of focal mechanism solutions of shallow earthquakes occurring within the Cameli basin identifies a present-day, predominantly extensional stress regime, characterized by an approximately N-S (N184 degrees E) sigma(3) axis, which has an R value of 0.637 indicating a triaxial stress state. The nearly orthogonal extensional stress regimes seem to have been acting contemporaneously with each other at different intensities from the Mio-Pliocene onwards in SW Turkey. This may be attributed to the geodynamic effects related to the subduction of the African plate beneath Anatolia, diffusing along Hellenic and Cyprus arcs and in the west-southwestward extrusion of Anatolia. Our hypothesis is that the cause of the early NW-SE extension is the slab-pull force due to the subduction process along the Cyprus arc, considered to be dominant up to Plio-Quaternary. The later NE-SW to present-day similar to N-S extension, dominant since the Plio-Quaternary, is related to the combined forces of the Anatolian extrusion and the subduction process along the Hellenic arc. (C) 2010 Elsevier B.V. All rights reserved.
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    Late Cenozoic stress states around the Bolu Basin along the North Anatolian Fault, NW Turkey
    (Pergamon-Elsevier Science Ltd, 2008) Ozden, Suha; Over, Semir; Kavak, Kaan Sevki; Inal, Serife Sevinc
    This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional trainstensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively. The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trencling sigma(Hmax) (sigma(1)) and sigma(Hmin) (sigma(3)) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending sigma(3) axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trencling sigma(1) and sigma(3) axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block. (C) 2008 Elsevier Ltd. All rights reserved.
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    Plio-Quaternary stress regime in Esen Cay Basin, SW Turkey
    (Geological Soc Publishing House, 2013) Over, Semir; Ozden, Suha; Yilmaz, Huseyin; Pinar, Ali; Unlugenc, Ulvi Can; Kamaci, Zuheyr
    The Plio-Quaternary Esen Cay Basin is situated at the junction of Hellenic and Cyprus arcs in southwestern Turkey. The basin is important for understanding the tectonic evolution of the region in relation to the Hellenic and Cyprus arcs. Fault data from unconsolidated Pliocene and Quaternary deposits, as well as from pre-Pliocene lithologies, are analysed in order to reconstruct the evolution of the stress field evolution from Pliocene onwards. Inversion of measured fault slip vector data identifies two main stress states: extensional and strike-slip. Both states are characterized by a NE-SW-trending minimum horizontal stress axis (sigma(Hmin) = sigma(3)). The mean R value is 0.67, indicating a triaxial state of stress. The inversion also indicates the existence of extensional and strike-slip faulting characterized by a NW-SE-trending sigma(3) axis. This indicates a change in the direction of the minimum horizontal stress axis (sigma(3)) from a NW-SE-trending sigma(3) that dominated prior to Quaternary to a NE-SW-trending sigma(3) that dominated during Quaternary up to actual time.
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    Plio-Quaternary Stress State in the Burdur Basin, SW-Turkey
    (Elsevier, 2013) Over, Semir; Yilmaz, Huseyin; Pinar, Ali; Ozden, Suha; Unlugenc, Ulvi Can; Kamaci, Zuheyr
    This study defines the Plio-Quaternary to present day stress regime in the Burdur Basin, located at the northeastern end of the Fethiye-Burdur Fault Zone in SW Turkey. This fault length, which is considered the landward continuation of the Pliny-Strabo trench, is an important feature in SW Turkey. The inversion slip vectors measured on fault planes indicate a consistent normal faulting stress regime during Plio-Quaternary time, continuing into recent times as indicated by earthquake focal mechanism inversions. Both states have consistent NW-SE trending horizontal minimum stress axes (sigma(3)). The orientation of fault sets is predominantly around the NE-SW direction in the major Fethiye-Burdur Fault Zone, making the extension NW-SE. The mean stress ratio is 0.74 indicating a triaxial stress state, which is clearly different from radial extension. The NW-SE extension is probably responsible for the formation of the Burdur Basin during Plio-Quaternary time. This extension, which is probably caused by slab-pull force due to the subduction process along the Cyprus arc, produces a dominant normal motion along the FBFZ. (C) 2013 Elsevier B.V. All rights reserved.