Proposed modification on velocity attenuation relationships in West of with special respect to Dorood fault

As a routine procedure, the estimation of source parameters such as focal mechanism and magnitude is known for moderate to great earthquakes, however some of them such as directivity effect and filing step are rarely taking into account. According to the radiation pattern, directivity effect is a source parameter, which causes significant spatial variations in near field strong ground motion. Its significant variations could be obtained on strike normal component of velocity in forward and backward directions. This study has an attempt on estimation of a modification factor, which can define the effect of directivity in empirical attenuation relationships in Dorood fault. In order to model unilateral and bilateral rupturing Finite Elements Method (FEM) is applied to achieve reliable functions.The authors used Somervill et al. (1997) directivity model parameter with some changes as variable parameter. To obtain modified ground motion parameters, these models were applied for earthquakes which Dorood fault caused them. These parameters consist of fault normal component to fault parallel component of velocity ratio ( Vn/Vp ) and fault normal component to average horizontal velocity ratio) Vn/V (.It shows Vn/V is controlled by directivity angle, distance between the site, epicenter and rupture length. This ratio has the same trend in studied region earthquakes velocity data.