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    An active extensional deformation example: 19 May 2011 Simav earthquake (Mw=5.8), Western Anatolia, Turkey
    (Oxford Univ Press, 2015) Demirci, Alper; Özden, Süha; Bekler, Tolga; Kalafat, Dogan; Pinar, Ali
    The Simav Earthquake that occurred on 19 May 2011 in western Turkey was investigated on the basis of seismological data and geological observations. Approximately WNW-ESE trending surface ruptures were observed on the Simav Fault. The focal mechanism parameters of the earthquake (Mw = 5.8) and its aftershocks (Mw > 3.5) were estimated using time-domain moment tensor inversion. A total of 2245 events were located with Geiger's conventional absolute location method then relocated using the double difference (DD) algorithm. The calculated locations at a depths between 2 and 16 km were found to be consistent with Coulomb stress variation in the area. Average variance reduction (VR) of the solutions was calculated as similar to 70%. The focal parameters of strike dip and slip of the main shock, occurring at a depth of 11 km dipping towards the NNE, were estimated at 277, 62 and -92, respectively. The most striking indication of the study is that the area is dominated by normal faults with mainly WNW-ESE trends. It is also concluded that earthquakes in the region are caused by an active and regional NNE-SSW (N 12 degrees E) trending (sigma(3) axis) extension regime. The mean stress ratio is 0.80, indicating a triaxial stress state. This extension is probably associated with a slab-pull force and /or roll-back due to the complex subduction process of the African Plate beneath Anatolian block along both the Hellenic and Cyprus arcs in the eastern Mediterranean region.
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    Late cenozoic stress field in the Cameli Basin, SW Turkey
    (Elsevier, 2010) Over, Semir; Pinar, Ali; Özden, Süha; 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 state distributions at the intersection of the Hellenic and Cyprus Arcs, SW Turkey
    (Pergamon-Elsevier Science Ltd, 2016) Over, Semir; Özden, Süha; Pinar, Ali; Yilmaz, Huseyin; Kamaci, Zuheyr; Unlugenc, Ulvi Can
    The history of the Late Cenozoic stress regime was determined for an area between the gulfs of Fethiye and Antalya. Fault kinematic analysis and inversion of focal mechanisms of shallow earthquakes reveal significant evolution of the regional stress regime in SW Anatolia, i.e., the area of interaction between the Hellenic and Cyprus arcs, from the Mio-Pliocene to the present time. Fault kinematic analysis yields two different normal faulting stress regimes along the southwestern part of Fethiye-Burdur Fault zone, e.g., in and around cameli Basin (Zone Al) and two different strike-slip to normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes between Fethiye and Demre (Zone B) with an older NW-SE al axis for Mio-Pliocene and a younger NE-SW sigma 3 axis for Plio-Quaternary time. Inversion of focal mechanisms of the earthquakes occurring in Zone Al provideS an extensional stress. state with approximately N- sigma 3 axis. Inversion of those occurring in Zone B, south of Zone Al, yields a dominantly strike-slip stress state with a NE-SW sigma 3 axis and a NW-SE A1 axis respectively. The inversion slip vectors from fault planes yield a consistent normal faulting stress regime in Burdur Basin and its surroundings (i.e., along the northeastern part of Fethiye-Burdur Fault Zone, (Zone A2)) during Plio-Quaternary, continuing into recent time as indicated by earthquake focal mechanism inversions. Both states-have a consistent NW-SE cs3 axis. Fault kinematic analysis indicates NW-SE extension acting in Zone C (subarea between Demre and Antalya), south of Zone A2, during Mio-Pliocene time. The inversion of focal mechanisms yields normal faulting also characterized by a consistent NW-SE sigma 3 axis. The nearly orthogonal extensional stress regimes (NW-SE and NE-SW) obtained by inversion of both measured and seismic faults 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 the Hellenic and Cyprus arcs and in the west-southwestward extrusion of Anatolia. 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 dotninant until the Plio-Quaternary in the western part of the study area in zones A1 and B. The dominant status of the Cyprus arc continues today in the eastern part of study area in zones A2 and C. The later NE-SW to present day approximately 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) 2016 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; Özden, Süha; 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; Özden, Süha; 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.
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    Tectonic implications of the 2017 Ayvacik (Canakkale) earthquakes, Biga Peninsula, NW Turkey
    (Pergamon-Elsevier Science Ltd, 2018) Özden, Süha; Over, Semir; Poyraz, Selda Altuncu; Gunes, Yavuz; Pinar, Ali
    The west to southwestward motion of the Anatolian block results from the relative motions between the Eurasian, Arabian and African plates along the right-lateral North Anatolian Fault Zone in the north and left lateral East Anatolian Fault Zone in the east. The Biga Peninsula is tectonically influenced by the Anatolian motion originating along the North Anatolian Fault Zone which splits into two main (northern and southern) branches in the east of Marmara region: the southern branch extends towards the Biga Peninsula which is characterized by strike-slip to oblique normal faulting stress regime in the central to northern part. The southernmost part of peninsula is characterized by a normal to oblique faulting stress regime. The analysis of both seismological and structural field data confirms the change of stress regime from strike-slip character in the center and north to normal faulting character in the south of peninsula where the earthquake swarm recently occurred. The earthquakes began on 14 January 2017 (Mw: 4.4) on Tuzla Fault and migrated southward along the Kocakoy and Babakale's stepped-normal faults of over three months. The inversion of focal mechanisms yields a normal faulting stress regime with an approximately N-S (N4 degrees E) sigma 3 axis. The inversion of earthquakes occurring in central and northern Biga Peninsula and the north Aegean region gives a strike-slip stress regime with approximately WNW-ESE (N85 degrees W) sigma 1 and NNE-SSW (N17 degrees E) sigma 3 axis. The strike-slip stress regime is attributed to westward Anatolian motion, while the normal faulting stress regime is attributed to both the extrusion of Anatolian block and the slab-pull force of the subducting African plate along the Hellenic arc.
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    Upper crust response to geodynamic processes beneath Isparta Angle, SW Turkey: Revealed by CMT solutions of earthquakes
    (Elsevier, 2016) Over, Semir; Özden, Süha; Kamaci, Zuheyr; Yilmaz, Huseyin; Unlugenc, Ulvi Can; Pinar, Ali
    The Isparta Angle is an important area of SW Anatolia where extensions in all directions (N-S, NE-SW, NW-SE and E-W) meet These extensions were determined by normal faulting structures as well as by shallow earthquakes. All extensions, except the E-W one, were attributed to the deviatoric stresses in relation to slab forces and/or extrusion of Anatolia. The moment tensor inversion of 40 shallow earthquakes which occurred in the inner part of the Isparta Angle give focal mechanisms mostly indicating normal faulting. Inversion of all focal mechanisms of the earthquakes obtained from the moment tensor inversion yields normal faulting characterized by an approximately E-W (N268 degrees E) sigma(3) axis. The calculated stress ratio R is 0.6944 indicating a triaxial stress state. Commonly accepted geodynamic models for the eastern Mediterranean region do not include plate boundary forces acting in the east or west direction. Our hypothesis is that the cause of the E-W extension is the combined forces of Gravitational Potential Energy and the hot asthenosphere upwelling through a tear fault in the subducted African plate between the Hellenic and Cyprus arcs beneath the Isparta Angle. (C) 2016 Elsevier B.V. All rights reserved.