Figure 1 . a ) Seismotectonics of the study area. Star shows the mainshock hypocenter location and the related focal mechanism as reported by IRSC. Faults are shown with solid and dashed lines. Dotted lines marked N-R and Ka are related to the North-Ray and Kahrizak scarps, respectively, that are uncertain whether created by faulting or are old shorelines (after Nazari et al., 2010). Vectors are geodetic surface deformation rates by Djamour et al., (2010), with respect to a fixed central Iran block. Triangles are the used station data of the Broadband national Iranian Network (BIN) for moment tensor inversion (section 2). Hexagons are historical earthquakes (Ambraseys and Melvile, 1982; Berberian and Yeats, 1999; Nazari et al., 2009). Circles are instrumental earthquakes by Engdahl et al. (2006). Dashed ellipses show affected regions by historical earthquakes. Fault names are: Ga: Garmsar; So: Sorkhe; Ey: Eyvanakey; Fi: Firuzkuh; Pi: Pishva; N-T: North Tehran; Ba: Baijan; Rk: Robat Karim; NR: North Rey. Tehran area is in Green. MSH in red solid line. b ) Circles: Seismicity recorded by the IRSC network from 2006 until just before the M 5.1 mainshock. Colors represent hypocentral depths. Faults are the same as (a). Focal mechanisms with label G are from the GCMT catalog. The ones without labels and those labeled 1, 2, and 3 are from small to moderate magnitude earthquakes (3.6<M<4.8) that occurred from 2006 to 2012 in the region and obtained by inverting local broadband seismic data for their moment tensors (Momeni, 2012). Triangles are the Strong motion stations locations of the Iranian Strong Motion Network (ISMN) that we used their data for extended rupture inversion (section 3).