Focal mechanisms of small-moderate earthquakes in Denizli Graben (SW Turkey)

Abstract

The present study seeks to determine the fault mechanisms of small-moderate earthquakes in Denizli Graben in Turkey and to define the relation of the fault mechanism with the regional tectonics. For this purpose, 20 earthquakes, which occurred in the time period 2004-2009, were analyzed. Focal mechanisms were determined using the focmec algorithm and time domain regional waveform inversion techniques. The analyzed earthquakes were characterized by a normal faulting mechanism with a large dip angle and a small amount of strike-slip components. The depths of the earthquakes were located in the range of 6-8 km. The stress inversion of the studied earthquake focal mechanism data show that the present-day stress field is characterized by a pure extensional regime (R = 0.74) and a horizontal direction of extension at N9°E, close to N-S. The orientations of the principal stress axes are vertical for σ1 and horizontal for σ2 and σ3. Axis orientations are found as 62°/277°, 28°/100°, and 1°/9° (dip/azimuth direction) for σ1, σ2 and σ3, respectively. According to the direction of the principal stress axes, Denizli Graben is opening in the direction of NE-SW. The extension rate is calculated as 0.41 mm/year for the whole of Denizli Graben, using the seismic moment values. Focal mechanism solutions and the directions of the horizontal stresses, SHmax and Shmin, inferred from the analysis of the focal mechanisms, show good agreement with the general features for Denizli Graben.