An active extensional deformation example: 19 May 2011 Simav earthquake ( Mw = 5.8), Western Anatolia, Turkey

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 ~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° E) trending (σ3 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.