Variation of Anisotropy Parameters and Seismic Velocity before the 5 April 2017 (M=6) Sefidsang Earthquake, Iran

One of the common methods for achieving the aim of earthquake stress-forecast is to investigate the precursors. Precursors are the changes that happen before occurring an earthquake. In this research, two classes of precursors have been studied based on foreshocks preceding the 5 April 2017 M=6, SefidSang (Fariman) earthquake, Khorasan Razavi province, Iran. These two observations are: 1- anisotropy parameters (azimuth of the fast wave polarization direction, cp, and the delay time between fast and slow polarized shear waves, ōt) 2- the ratio between compressional wave and shear-wave velocity (Vp/Vs). The results indicate that both observables experience fluctuations before occurrence of the main shock. According to the research, if there is a dense three-component seismic network, which continuously monitors the variations of anisotropy parameters or velocity ratio -with the existence of a foreshock sequence- investigating the stress fluctuations before an impeding earthquake is possible.