Analysis of the 2010 Damghan earthquake in Central Alborz (Mw 5.7) and faultplane identification by H.C method

The works done in the study area indicate the potential of the existing fault systems in the region to cause large earthquakes, i.e. magnitude close to 7. In addition, an exact understanding of source parameters gives rise to the recognition of the physical process that occurs as a result of an earthquake. This concept is one of the most important parameters that ultimately leads to the identification of both main and auxiliary planes. The purpose of this study is to determine the mechanism of the Mw  5.7 earthquake occurred in the southeastern region of Damghan at 19:23:48 UTC (23:53:48 local time) on 27 August 2010 (as the biggest event of the last few decades in this region) and its largest aftershock. In this work, nodal planes were first obtained by using timedomain moment tensor inversion method; then, the main fault plane was determined using the geometrical method of HC which can be implemented by obtaining a centroid moment tensor solution and earthquake focal parameters. Furthermore, the stability of the solution was checked by condition number and jackknifing test. According to the results of this research, a branch of the Toroud fault zone with leftlateral strikeslip motion and northeastsouthwest strike was the causative fault of this event. Moreover, the strike, dip and rake of these two events were determined 215, 78, 8 and 222, 66, 11 degrees, respectively. Due to the fact that this area has not been significantly active before, careful monitoring and further studies in such areas is necessary to prevent serious damages.