Late Cenozoic stress state distributions at the intersection of the Hellenic and Cyprus Arcs, SW Turkey

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 Çameli Basin (Zone A1) 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 ?3 axis for Mio-Pliocene and a younger NE–SW ?3 axis for Plio-Quaternary time. Inversion of focal mechanisms of the earthquakes occurring in Zone A1 provides an extensional stress state with approximately N-S ?3 axis. Inversion of those occurring in Zone B, south of Zone A1, yields a dominantly strike-slip stress state with a NE-SW ?3 axis and a NW-SE ?1 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 ?3 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 ?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 dominant 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. © 2016 Elsevier Ltd107Y321This work was financially supported by TUBİTAK-ÇAYDAG (Project no: 107Y321 ). The authors would like to thank Catherine Yiğit for assistance with English that improved a recent version of the text. The authors are also grateful to the two anonymous reviewers for their valuable comments and suggestions that greatly improved the quality of the manuscript

Upper crust response to geodynamic processes beneath Isparta Angle, SW Turkey: Revealed by CMT solutions of earthquakes

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°E) ?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. © 2016 Elsevier B.V.107Y321This work was financially supported by TUBİTAK-ÇAYDAG (Project no: 107Y321 ). The authors would like to thank Catherine Yiğit for assistance with English that improved a recent version of the text. The authors are also grateful to the anonymous reviewers for their valuable comments and suggestions that greatly improved the quality of the manuscript